Table of Contents

I. SDL Guide

Preface

About SDL

About SDLdoc

Credits

1. The Basics

Introduction

Initializing SDL

2. Graphics and Video

Introduction to SDL Video

Using OpenGL With SDL

3. Input handling

Handling Joysticks

Handling the Keyboard

4. Examples

Introduction

Event Examples

Audio Examples

CDROM Examples

Time Examples

II. SDL Reference

5. General

SDL_Init — Initializes SDL

SDL_InitSubSystem — Initialize subsystems

SDL_QuitSubSystem — Shut down a subsystem

SDL_Quit — Shut down SDL

SDL_WasInit — Check which subsystems are initialized

SDL_GetError — Get SDL error string

6. Video

SDL_GetVideoSurface — returns a pointer to the current display surface

SDL_GetVideoInfo — returns a pointer to information about the video hardware

SDL_VideoDriverName — Obtain the name of the video driver

SDL_ListModes — Returns a pointer to an array of available screen dimensions for the given format and video flags

SDL_VideoModeOK — Check to see if a particular video mode is supported.

SDL_SetVideoMode — Set up a video mode with the specified width, height and bits-per-pixel.

SDL_UpdateRect — Makes sure the given area is updated on the given screen.

SDL_UpdateRects — Makes sure the given list of rectangles is updated on the given screen.

SDL_Flip — Swaps screen buffers

SDL_SetColors — Sets a portion of the colormap for the given 8-bit surface.

SDL_SetPalette — Sets the colors in the palette of an 8-bit surface.

SDL_SetGamma — Sets the color gamma function for the display

SDL_GetGammaRamp — Gets the color gamma lookup tables for the display

SDL_SetGammaRamp — Sets the color gamma lookup tables for the display

SDL_MapRGB — Map a RGB color value to a pixel format.

SDL_MapRGBA — Map a RGBA color value to a pixel format.

SDL_GetRGB — Get RGB values from a pixel in the specified pixel format.

SDL_GetRGBA — Get RGBA values from a pixel in the specified pixel format.

SDL_CreateRGBSurface — Create an empty SDL_Surface

SDL_CreateRGBSurfaceFrom — Create an SDL_Surface from pixel data

SDL_FreeSurface — Frees (deletes) a SDL_Surface

SDL_LockSurface — Lock a surface for directly access.

SDL_UnlockSurface — Unlocks a previously locked surface.

SDL_LoadBMP — Load a Windows BMP file into an SDL_Surface.

SDL_SaveBMP — Save an SDL_Surface as a Windows BMP file.

SDL_SetColorKey — Sets the color key (transparent pixel) in a blittable surface and RLE acceleration.

SDL_SetAlpha — Adjust the alpha properties of a surface

SDL_SetClipRect — Sets the clipping rectangle for a surface.

SDL_GetClipRect — Gets the clipping rectangle for a surface.

SDL_ConvertSurface — Converts a surface to the same format as another surface.

SDL_BlitSurface — This performs a fast blit from the source surface to the destination surface.

SDL_FillRect — This function performs a fast fill of the given rectangle with some color

SDL_DisplayFormat — Convert a surface to the display format

SDL_DisplayFormatAlpha — Convert a surface to the display format

SDL_WarpMouse — Set the position of the mouse cursor.

SDL_CreateCursor — Creates a new mouse cursor.

SDL_FreeCursor — Frees a cursor created with SDL_CreateCursor.

SDL_SetCursor — Set the currently active mouse cursor.

SDL_GetCursor — Get the currently active mouse cursor.

SDL_ShowCursor — Toggle whether or not the cursor is shown on the screen.

SDL_GL_LoadLibrary — Specify an OpenGL library

SDL_GL_GetProcAddress — Get the address of a GL function

SDL_GL_GetAttribute — Get the value of a special SDL/OpenGL attribute

SDL_GL_SetAttribute — Set a special SDL/OpenGL attribute

SDL_GL_SwapBuffers — Swap OpenGL framebuffers/Update Display

SDL_CreateYUVOverlay — Create a YUV video overlay

SDL_LockYUVOverlay — Lock an overlay

SDL_UnlockYUVOverlay — Unlock an overlay

SDL_DisplayYUVOverlay — Blit the overlay to the display

SDL_FreeYUVOverlay — Free a YUV video overlay

SDL_GLattr — SDL GL Attributes

SDL_Rect — Defines a rectangular area

SDL_Color — Format independent color description

SDL_Palette — Color palette for 8-bit pixel formats

SDL_PixelFormat — Stores surface format information

SDL_Surface — Graphical Surface Structure

SDL_VideoInfo — Video Target information

SDL_Overlay — YUV video overlay

7. Window Management

SDL_WM_SetCaption — Sets the window tile and icon name.

SDL_WM_GetCaption — Gets the window title and icon name.

SDL_WM_SetIcon — Sets the icon for the display window.

SDL_WM_IconifyWindow — Iconify/Minimise the window

SDL_WM_ToggleFullScreen — Toggles fullscreen mode

SDL_WM_GrabInput — Grabs mouse and keyboard input.

8. Events

Introduction

SDL Event Structures.

Event Functions.

9. Joystick

SDL_NumJoysticks — Count available joysticks.

SDL_JoystickName — Get joystick name.

SDL_JoystickOpen — Opens a joystick for use.

SDL_JoystickOpened — Determine if a joystick has been opened

SDL_JoystickIndex — Get the index of an SDL_Joystick.

SDL_JoystickNumAxes — Get the number of joystick axes

SDL_JoystickNumBalls — Get the number of joystick trackballs

SDL_JoystickNumHats — Get the number of joystick hats

SDL_JoystickNumButtons — Get the number of joysitck buttons

SDL_JoystickUpdate — Updates the state of all joysticks

SDL_JoystickGetAxis — Get the current state of an axis

SDL_JoystickGetHat — Get the current state of a joystick hat

SDL_JoystickGetButton — Get the current state of a given button on a given joystick

SDL_JoystickGetBall — Get relative trackball motion

SDL_JoystickClose — Closes a previously opened joystick

10. Audio

SDL_AudioSpec — Audio Specification Structure

SDL_OpenAudio — Opens the audio device with the desired parameters.

SDL_PauseAudio — Pauses and unpauses the audio callback processing

SDL_GetAudioStatus — Get the current audio state

SDL_LoadWAV — Load a WAVE file

SDL_FreeWAV — Frees previously opened WAV data

SDL_AudioCVT — Audio Conversion Structure

SDL_BuildAudioCVT — Initializes a SDL_AudioCVT structure for conversion

SDL_ConvertAudio — Convert audio data to a desired audio format.

SDL_MixAudio — Mix audio data

SDL_LockAudio — Lock out the callback function

SDL_UnlockAudio — Unlock the callback function

SDL_CloseAudio — Shuts down audio processing and closes the audio device.

11. CD-ROM

SDL_CDNumDrives — Returns the number of CD-ROM drives on the system.

SDL_CDName — Returns a human-readable, system-dependent identifier for the CD-ROM.

SDL_CDOpen — Opens a CD-ROM drive for access.

SDL_CDStatus — Returns the current status of the given drive.

SDL_CDPlay — Play a CD

SDL_CDPlayTracks — Play the given CD track(s)

SDL_CDPause — Pauses a CDROM

SDL_CDResume — Resumes a CDROM

SDL_CDStop — Stops a CDROM

SDL_CDEject — Ejects a CDROM

SDL_CDClose — Closes a SDL_CD handle

SDL_CD — CDROM Drive Information

SDL_CDtrack — CD Track Information Structure

12. Multi-threaded Programming

SDL_CreateThread — Creates a new thread of execution that shares its parent's properties.

SDL_ThreadID — Get the 32-bit thread identifier for the current thread.

SDL_GetThreadID — Get the SDL thread ID of a SDL_Thread

SDL_WaitThread — Wait for a thread to finish.

SDL_KillThread — Gracelessly terminates the thread.

SDL_CreateMutex — Create a mutex

SDL_DestroyMutex — Destroy a mutex

SDL_mutexP — Lock a mutex

SDL_mutexV — Unlock a mutex

SDL_CreateSemaphore — Creates a new semaphore and assigns an initial value to it.

SDL_DestroySemaphore — Destroys a semaphore that was created by SDL_CreateSemaphore.

SDL_SemWait — Lock a semaphore and suspend the thread if the semaphore value is zero.

SDL_SemTryWait — Attempt to lock a semaphore but don't suspend the thread.

SDL_SemWaitTimeout — Lock a semaphore, but only wait up to a specified maximum time.

SDL_SemPost — Unlock a semaphore.

SDL_SemValue — Return the current value of a semaphore.

SDL_CreateCond — Create a condition variable

SDL_DestroyCond — Destroy a condition variable

SDL_CondSignal — Restart a thread wait on a condition variable

SDL_CondBroadcast — Restart all threads waiting on a condition variable

SDL_CondWait — Wait on a condition variable

SDL_CondWaitTimeout — Wait on a condition variable, with timeout

13. Time

SDL_GetTicks — Get the number of milliseconds since the SDL library initialization.

SDL_Delay — Wait a specified number of milliseconds before returning.

SDL_AddTimer — Add a timer which will call a callback after the specified number of milliseconds has elapsed.

SDL_RemoveTimer — Remove a timer which was added with SDL_AddTimer.

SDL_SetTimer — Set a callback to run after the specified number of milliseconds has elapsed.

List of Tables

8-1. SDL Keysym definitions

8-2. SDL modifier definitions

List of Examples

1-1. Initializing SDL

2-1. Initializing the Video Display

2-2. Initializing the Best Video Mode

2-3. Loading and Displaying a BMP File

2-4. getpixel()

2-5. putpixel()

2-6. Using putpixel()

2-7. Initializing SDL with OpenGL

2-8. SDL and OpenGL

3-1. Initializing SDL with Joystick Support

3-2. Querying the Number of Available Joysticks

3-3. Opening a Joystick

3-4. Joystick Axis Events

3-5. More Joystick Axis Events

3-6. Joystick Button Events

3-7. Joystick Ball Events

3-8. Joystick Hat Events

3-9. Querying Joystick Characteristics

3-10. Reading Keyboard Events

3-11. Interpreting Key Event Information

3-12. Proper Game Movement

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Table of Contents

About SDL

About SDLdoc

Credits

About SDL

The SDL library is designed to make it easy to write games that run on Linux, *BSD, MacOS, Win32 and BeOS using the various native high-performance media interfaces, (for video, audio, etc) and presenting a single source-code level API to your application. SDL is a fairly low level API, but using it, completely portable applications can be written with a great deal of flexibility.

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About SDLdoc

SDLdoc (The SDL Documentation Project) was formed to completely rewrite the SDL documentation and to keep it continually up to date. The team consists completely of volunteers ranging from people working with SDL in their spare time to people who use SDL in their everyday working lives.

The latest version of this documentation can always be found here: http://sdldoc.csn.ul.ie Downloadable PS, man pages and html tarballs are available at http://sdldoc.csn.ul.ie/pub/

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Credits

Sam Lantinga, slouken@libsdl.org

Martin Donlon, akawaka@skynet.ie

Mattias Engdegård

Julian Peterson

Ken Jordan

Maxim Sobolev

Wesley Poole

Michael Vance

Andreas Umbach

Andreas Hofmeister

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Initializing SDL

Introduction

The SDL Guide section is pretty incomplete. If you feel you have anything to add mail akawaka@skynet.ie or visit http://akawaka.csn.ul.ie/tne/.

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Initializing SDL

SDL is composed of eight subsystems - Audio, CDROM, Event Handling, File I/O, Joystick Handling, Threading, Timers and Video. Before you can use any of these subsystems they must be initialized by calling SDL_Init (or SDL_InitSubSystem). SDL_Init must be called before any other SDL function. It automatically initializes the Event Handling, File I/O and Threading subsystems and it takes a parameter specifying which other subsystems to initialize. So, to initialize the default subsystems and the Video subsystems you would call:

    SDL_Init ( SDL_INIT_VIDEO );

To initialize the default subsystems, the Video subsystem and the Timers subsystem you would call:

    SDL_Init ( SDL_INIT_VIDEO | SDL_INIT_TIMER );

SDL_Init is complemented by SDL_Quit (and SDL_QuitSubSystem). SDL_Quit shuts down all subsystems, including the default ones. It should always be called before a SDL application exits.

With SDL_Init and SDL_Quit firmly embedded in your programmers toolkit you can write your first and most basic SDL application. However, we must be prepare to handle errors. Many SDL functions return a value and indicates whether the function has succeeded or failed, SDL_Init, for instance, returns -1 if it could not initialize a subsystem. SDL provides a useful facility that allows you to determine exactly what the problem was, every time an error occurs within SDL an error message is stored which can be retrieved using SDL_GetError. Use this often, you can never know too much about an error.

Example 1-1. Initializing SDL

#include "SDL.h"   /* All SDL App's need this */
#include <stdio.h>

int main() {

    printf("Initializing SDL.\n");

    /* Initialize defaults, Video and Audio */
    if((SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO)==-1)) {
        printf("Could not initialize SDL: %s.\n", SDL_GetError());
        exit(-1);
    }

    printf("SDL initialized.\n");

    printf("Quiting SDL.\n");

    /* Shutdown all subsystems */
    SDL_Quit();

    printf("Quiting....\n");

    exit(0);
}

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Chapter 2. Graphics and Video

Table of Contents

Introduction to SDL Video

Using OpenGL With SDL

Introduction to SDL Video

Video is probably the most common thing that SDL is used for, and so it has the most complete subsystem. Here are a few examples to demonstrate the basics.

Initializing the Video Display

This is what almost all SDL programs have to do in one way or another.

Example 2-1. Initializing the Video Display

    SDL_Surface *screen;

    /* Initialize the SDL library */
    if( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
        fprintf(stderr,
                "Couldn't initialize SDL: %s\n", SDL_GetError());
        exit(1);
    }

    /* Clean up on exit */
    atexit(SDL_Quit);

    /*
     * Initialize the display in a 640x480 8-bit palettized mode,
     * requesting a software surface
     */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }

Initializing the Best Video Mode

If you have a preference for a certain pixel depth but will accept any other, use SDL_SetVideoMode with SDL_ANYFORMAT as below. You can also use SDL_VideoModeOK() to find the native video mode that is closest to the mode you request.

Example 2-2. Initializing the Best Video Mode

    /* Have a preference for 8-bit, but accept any depth */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_ANYFORMAT);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }
    printf("Set 640x480 at %d bits-per-pixel mode\n",
           screen->format->BitsPerPixel);

Loading and Displaying a BMP File

The following function loads and displays a BMP file given as argument, once SDL is initialised and a video mode has been set.

Example 2-3. Loading and Displaying a BMP File

void display_bmp(char *file_name)
{
    SDL_Surface *image;

    /* Load the BMP file into a surface */
    image = SDL_LoadBMP(file_name);
    if (image == NULL) {
        fprintf(stderr, "Couldn't load %s: %s\n", file_name, SDL_GetError());
        return;
    }

    /*
     * Palettized screen modes will have a default palette (a standard
     * 8*8*4 colour cube), but if the image is palettized as well we can
     * use that palette for a nicer colour matching
     */
    if (image->format->palette && screen->format->palette) {
    SDL_SetColors(screen, image->format->palette->colors, 0,
                  image->format->palette->ncolors);
    }

    /* Blit onto the screen surface */
    if(SDL_BlitSurface(image, NULL, screen, NULL) < 0)
        fprintf(stderr, "BlitSurface error: %s\n", SDL_GetError());

    SDL_UpdateRect(screen, 0, 0, image->w, image->h);

    /* Free the allocated BMP surface */
    SDL_FreeSurface(image);
}

Drawing Directly to the Display

The following two functions can be used to get and set single pixels of a surface. They are carefully written to work with any depth currently supported by SDL. Remember to lock the surface before calling them, and to unlock it before calling any other SDL functions.

To convert between pixel values and their red, green, blue components, use SDL_GetRGB() and SDL_MapRGB().

Example 2-4. getpixel()

/*
 * Return the pixel value at (x, y)
 * NOTE: The surface must be locked before calling this!
 */
Uint32 getpixel(SDL_Surface *surface, int x, int y)
{
    int bpp = surface->format->BytesPerPixel;
    /* Here p is the address to the pixel we want to retrieve */
    Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;

    switch(bpp) {
    case 1:
        return *p;

    case 2:
        return *(Uint16 *)p;

    case 3:
        if(SDL_BYTEORDER == SDL_BIG_ENDIAN)
            return p[0] << 16 | p[1] << 8 | p[2];
        else
            return p[0] | p[1] << 8 | p[2] << 16;

    case 4:
        return *(Uint32 *)p;

    default:
        return 0;       /* shouldn't happen, but avoids warnings */
    }
}

Example 2-5. putpixel()

/*
 * Set the pixel at (x, y) to the given value
 * NOTE: The surface must be locked before calling this!
 */
void putpixel(SDL_Surface *surface, int x, int y, Uint32 pixel)
{
    int bpp = surface->format->BytesPerPixel;
    /* Here p is the address to the pixel we want to set */
    Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;

    switch(bpp) {
    case 1:
        *p = pixel;
        break;

    case 2:
        *(Uint16 *)p = pixel;
        break;

    case 3:
        if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {
            p[0] = (pixel >> 16) & 0xff;
            p[1] = (pixel >> 8) & 0xff;
            p[2] = pixel & 0xff;
        } else {
            p[0] = pixel & 0xff;
            p[1] = (pixel >> 8) & 0xff;
            p[2] = (pixel >> 16) & 0xff;
        }
        break;

    case 4:
        *(Uint32 *)p = pixel;
        break;
    }
}

The following code uses the putpixel() function above to set a yellow pixel in the middle of the screen.

Example 2-6. Using putpixel()

    /* Code to set a yellow pixel at the center of the screen */

    int x, y;
    Uint32 yellow;

    /* Map the color yellow to this display (R=0xff, G=0xFF, B=0x00)
       Note:  If the display is palettized, you must set the palette first.
    */
    yellow = SDL_MapRGB(screen->format, 0xff, 0xff, 0x00);

    x = screen->w / 2;
    y = screen->h / 2;

    /* Lock the screen for direct access to the pixels */
    if ( SDL_MUSTLOCK(screen) ) {
        if ( SDL_LockSurface(screen) < 0 ) {
            fprintf(stderr, "Can't lock screen: %s\n", SDL_GetError());
            return;
        }
    }

    putpixel(screen, x, y, yellow);

    if ( SDL_MUSTLOCK(screen) ) {
        SDL_UnlockSurface(screen);
    }
    /* Update just the part of the display that we've changed */
    SDL_UpdateRect(screen, x, y, 1, 1);

    return;

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Using OpenGL With SDL

SDL has the ability to create and use OpenGL contexts on several platforms(Linux/X11, Win32, BeOS, MacOS Classic/Toolbox, MacOS X, FreeBSD/X11 and Solaris/X11). This allows you to use SDL's audio, event handling, threads and times in your OpenGL applications (a function often performed by GLUT).

Initialisation

Initialising SDL to use OpenGL is not very different to initialising SDL normally. There are three differences; you must pass SDL_OPENGL to SDL_SetVideoMode, you must specify several GL attributes (depth buffer size, framebuffer sizes) using SDL_GL_SetAttribute and finally, if you wish to use double buffering you must specify it as a GL attribute, not by passing the SDL_DOUBLEBUF flag to SDL_SetVideoMode.

Example 2-7. Initializing SDL with OpenGL

    /* Information about the current video settings. */
    const SDL_VideoInfo* info = NULL;
    /* Dimensions of our window. */
    int width = 0;
    int height = 0;
    /* Color depth in bits of our window. */
    int bpp = 0;
    /* Flags we will pass into SDL_SetVideoMode. */
    int flags = 0;

    /* First, initialize SDL's video subsystem. */
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
        /* Failed, exit. */
        fprintf( stderr, "Video initialization failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }

    /* Let's get some video information. */
    info = SDL_GetVideoInfo( );

    if( !info ) {
        /* This should probably never happen. */
        fprintf( stderr, "Video query failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }

    /*
     * Set our width/height to 640/480 (you would
     * of course let the user decide this in a normal
     * app). We get the bpp we will request from
     * the display. On X11, VidMode can't change
     * resolution, so this is probably being overly
     * safe. Under Win32, ChangeDisplaySettings
     * can change the bpp.
     */
    width = 640;
    height = 480;
    bpp = info->vfmt->BitsPerPixel;

    /*
     * Now, we want to setup our requested
     * window attributes for our OpenGL window.
     * We want *at least* 5 bits of red, green
     * and blue. We also want at least a 16-bit
     * depth buffer.
     *
     * The last thing we do is request a double
     * buffered window. '1' turns on double
     * buffering, '0' turns it off.
     *
     * Note that we do not use SDL_DOUBLEBUF in
     * the flags to SDL_SetVideoMode. That does
     * not affect the GL attribute state, only
     * the standard 2D blitting setup.
     */
    SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
    SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );

    /*
     * We want to request that SDL provide us
     * with an OpenGL window, in a fullscreen
     * video mode.
     *
     * EXERCISE:
     * Make starting windowed an option, and
     * handle the resize events properly with
     * glViewport.
     */
    flags = SDL_OPENGL | SDL_FULLSCREEN;

    /*
     * Set the video mode
     */
    if( SDL_SetVideoMode( width, height, bpp, flags ) == 0 ) {
        /*
         * This could happen for a variety of reasons,
         * including DISPLAY not being set, the specified
         * resolution not being available, etc.
         */
        fprintf( stderr, "Video mode set failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }

Drawing

Apart from initialisation, using OpenGL within SDL is the same as using OpenGL with any other API, e.g. GLUT. You still use all the same function calls and data types. However if you are using a double-buffered display, then you must use SDL_GL_SwapBuffers() to swap the buffers and update the display. To request double-buffering with OpenGL, use SDL_GL_SetAttribute with SDL_GL_DOUBLEBUFFER, and use SDL_GL_GetAttribute to see if you actually got it.

A full example code listing is now presented below.

Example 2-8. SDL and OpenGL

/*
 * SDL OpenGL Tutorial.
 * (c) Michael Vance, 2000
 * briareos@lokigames.com
 *
 * Distributed under terms of the LGPL.
 */

#include <SDL/SDL.h>
#include <GL/gl.h>
#include <GL/glu.h>

#include <stdio.h>
#include <stdlib.h>

static GLboolean should_rotate = GL_TRUE;

static void quit_tutorial( int code )
{
    /*
     * Quit SDL so we can release the fullscreen
     * mode and restore the previous video settings,
     * etc.
     */
    SDL_Quit( );

    /* Exit program. */
    exit( code );
}

static void handle_key_down( SDL_keysym* keysym )
{

    /*
     * We're only interested if 'Esc' has
     * been presssed.
     *
     * EXERCISE:
     * Handle the arrow keys and have that change the
     * viewing position/angle.
     */
    switch( keysym->sym ) {
    case SDLK_ESCAPE:
        quit_tutorial( 0 );
        break;
    case SDLK_SPACE:
        should_rotate = !should_rotate;
        break;
    default:
        break;
    }

}

static void process_events( void )
{
    /* Our SDL event placeholder. */
    SDL_Event event;

    /* Grab all the events off the queue. */
    while( SDL_PollEvent( &event ) ) {

        switch( event.type ) {
        case SDL_KEYDOWN:
            /* Handle key presses. */
            handle_key_down( &event.key.keysym );
            break;
        case SDL_QUIT:
            /* Handle quit requests (like Ctrl-c). */
            quit_tutorial( 0 );
            break;
        }

    }

}

static void draw_screen( void )
{
    /* Our angle of rotation. */
    static float angle = 0.0f;

    /*
     * EXERCISE:
     * Replace this awful mess with vertex
     * arrays and a call to glDrawElements.
     *
     * EXERCISE:
     * After completing the above, change
     * it to use compiled vertex arrays.
     *
     * EXERCISE:
     * Verify my windings are correct here ;).
     */
    static GLfloat v0[] = { -1.0f, -1.0f,  1.0f };
    static GLfloat v1[] = {  1.0f, -1.0f,  1.0f };
    static GLfloat v2[] = {  1.0f,  1.0f,  1.0f };
    static GLfloat v3[] = { -1.0f,  1.0f,  1.0f };
    static GLfloat v4[] = { -1.0f, -1.0f, -1.0f };
    static GLfloat v5[] = {  1.0f, -1.0f, -1.0f };
    static GLfloat v6[] = {  1.0f,  1.0f, -1.0f };
    static GLfloat v7[] = { -1.0f,  1.0f, -1.0f };
    static GLubyte red[]    = { 255,   0,   0, 255 };
    static GLubyte green[]  = {   0, 255,   0, 255 };
    static GLubyte blue[]   = {   0,   0, 255, 255 };
    static GLubyte white[]  = { 255, 255, 255, 255 };
    static GLubyte yellow[] = {   0, 255, 255, 255 };
    static GLubyte black[]  = {   0,   0,   0, 255 };
    static GLubyte orange[] = { 255, 255,   0, 255 };
    static GLubyte purple[] = { 255,   0, 255,   0 };

    /* Clear the color and depth buffers. */
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    /* We don't want to modify the projection matrix. */
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity( );

    /* Move down the z-axis. */
    glTranslatef( 0.0, 0.0, -5.0 );

    /* Rotate. */
    glRotatef( angle, 0.0, 1.0, 0.0 );

    if( should_rotate ) {

        if( ++angle > 360.0f ) {
            angle = 0.0f;
        }

    }

    /* Send our triangle data to the pipeline. */
    glBegin( GL_TRIANGLES );

    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( blue );
    glVertex3fv( v2 );

    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( blue );
    glVertex3fv( v2 );
    glColor4ubv( white );
    glVertex3fv( v3 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( black );
    glVertex3fv( v5 );
    glColor4ubv( orange );
    glVertex3fv( v6 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( orange );
    glVertex3fv( v6 );
    glColor4ubv( blue );
    glVertex3fv( v2 );

    glColor4ubv( black );
    glVertex3fv( v5 );
    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( purple );
    glVertex3fv( v7 );

    glColor4ubv( black );
    glVertex3fv( v5 );
    glColor4ubv( purple );
    glVertex3fv( v7 );
    glColor4ubv( orange );
    glVertex3fv( v6 );

    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( white );
    glVertex3fv( v3 );

    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( white );
    glVertex3fv( v3 );
    glColor4ubv( purple );
    glVertex3fv( v7 );

    glColor4ubv( white );
    glVertex3fv( v3 );
    glColor4ubv( blue );
    glVertex3fv( v2 );
    glColor4ubv( orange );
    glVertex3fv( v6 );

    glColor4ubv( white );
    glVertex3fv( v3 );
    glColor4ubv( orange );
    glVertex3fv( v6 );
    glColor4ubv( purple );
    glVertex3fv( v7 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( yellow );
    glVertex3fv( v4 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( black );
    glVertex3fv( v5 );

    glEnd( );

    /*
     * EXERCISE:
     * Draw text telling the user that 'Spc'
     * pauses the rotation and 'Esc' quits.
     * Do it using vetors and textured quads.
     */

    /*
     * Swap the buffers. This this tells the driver to
     * render the next frame from the contents of the
     * back-buffer, and to set all rendering operations
     * to occur on what was the front-buffer.
     *
     * Double buffering prevents nasty visual tearing
     * from the application drawing on areas of the
     * screen that are being updated at the same time.
     */
    SDL_GL_SwapBuffers( );
}

static void setup_opengl( int width, int height )
{
    float ratio = (float) width / (float) height;

    /* Our shading model--Gouraud (smooth). */
    glShadeModel( GL_SMOOTH );

    /* Culling. */
    glCullFace( GL_BACK );
    glFrontFace( GL_CCW );
    glEnable( GL_CULL_FACE );

    /* Set the clear color. */
    glClearColor( 0, 0, 0, 0 );

    /* Setup our viewport. */
    glViewport( 0, 0, width, height );

    /*
     * Change to the projection matrix and set
     * our viewing volume.
     */
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity( );
    /*
     * EXERCISE:
     * Replace this with a call to glFrustum.
     */
    gluPerspective( 60.0, ratio, 1.0, 1024.0 );
}

int main( int argc, char* argv[] )
{
    /* Information about the current video settings. */
    const SDL_VideoInfo* info = NULL;
    /* Dimensions of our window. */
    int width = 0;
    int height = 0;
    /* Color depth in bits of our window. */
    int bpp = 0;
    /* Flags we will pass into SDL_SetVideoMode. */
    int flags = 0;

    /* First, initialize SDL's video subsystem. */
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
        /* Failed, exit. */
        fprintf( stderr, "Video initialization failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }

    /* Let's get some video information. */
    info = SDL_GetVideoInfo( );

    if( !info ) {
        /* This should probably never happen. */
        fprintf( stderr, "Video query failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }

    /*
     * Set our width/height to 640/480 (you would
     * of course let the user decide this in a normal
     * app). We get the bpp we will request from
     * the display. On X11, VidMode can't change
     * resolution, so this is probably being overly
     * safe. Under Win32, ChangeDisplaySettings
     * can change the bpp.
     */
    width = 640;
    height = 480;
    bpp = info->vfmt->BitsPerPixel;

    /*
     * Now, we want to setup our requested
     * window attributes for our OpenGL window.
     * We want *at least* 5 bits of red, green
     * and blue. We also want at least a 16-bit
     * depth buffer.
     *
     * The last thing we do is request a double
     * buffered window. '1' turns on double
     * buffering, '0' turns it off.
     *
     * Note that we do not use SDL_DOUBLEBUF in
     * the flags to SDL_SetVideoMode. That does
     * not affect the GL attribute state, only
     * the standard 2D blitting setup.
     */
    SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
    SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );

    /*
     * We want to request that SDL provide us
     * with an OpenGL window, in a fullscreen
     * video mode.
     *
     * EXERCISE:
     * Make starting windowed an option, and
     * handle the resize events properly with
     * glViewport.
     */
    flags = SDL_OPENGL | SDL_FULLSCREEN;

    /*
     * Set the video mode
     */
    if( SDL_SetVideoMode( width, height, bpp, flags ) == 0 ) {
        /*
         * This could happen for a variety of reasons,
         * including DISPLAY not being set, the specified
         * resolution not being available, etc.
         */
        fprintf( stderr, "Video mode set failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }

    /*
     * At this point, we should have a properly setup
     * double-buffered window for use with OpenGL.
     */
    setup_opengl( width, height );

    /*
     * Now we want to begin our normal app process--
     * an event loop with a lot of redrawing.
     */
    while( 1 ) {
        /* Process incoming events. */
        process_events( );
        /* Draw the screen. */
        draw_screen( );
    }

    /*
     * EXERCISE:
     * Record timings using SDL_GetTicks() and
     * and print out frames per second at program
     * end.
     */

    /* Never reached. */
    return 0;
}

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Chapter 3. Input handling

Table of Contents

Handling Joysticks

Handling the Keyboard

Handling Joysticks

Initialization

The first step in using a joystick in a SDL program is to initialize the Joystick subsystems of SDL. This done by passing the SDL_INIT_JOYSTICK flag to SDL_Init. The joystick flag will usually be used in conjunction with other flags (like the video flag) because the joystick is usually used to control something.

Example 3-1. Initializing SDL with Joystick Support

    if (SDL_Init( SDL_INIT_VIDEO | SDL_INIT_JOYSTICK ) < 0)
    {
        fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
        exit(1);
    }

This will attempt to start SDL with both the video and the joystick subsystems activated.

Querying

If we have reached this point then we can safely assume that the SDL library has been initialized and that the Joystick subsystem is active. We can now call some video and/or sound functions to get things going before we need the joystick. Eventually we have to make sure that there is actually a joystick to work with. It's wise to always check even if you know a joystick will be present on the system because it can also help detect when the joystick is unplugged. The function used to check for joysticks is SDL_NumJoysticks.

This function simply returns the number of joysticks available on the system. If it is at least one then we are in good shape. The next step is to determine which joystick the user wants to use. If the number of joysticks available is only one then it is safe to assume that one joystick is the one the user wants to use. SDL has a function to get the name of the joysticks as assigned by the operations system and that function is SDL_JoystickName. The joystick is specified by an index where 0 is the first joystick and the last joystick is the number returned by SDL_NumJoysticks - 1. In the demonstration a list of all available joysticks is printed to stdout.

Example 3-2. Querying the Number of Available Joysticks

    printf("%i joysticks were found.\n\n", SDL_NumJoysticks() );
    printf("The names of the joysticks are:\n");

    for( i=0; i < SDL_NumJoysticks(); i++ )
    {
        printf("    %s\n", SDL_JoystickName(i));
    }

Opening a Joystick and Receiving Joystick Events

SDL's event driven architecture makes working with joysticks a snap. Joysticks can trigger 4 different types of events:

SDL_JoyAxisEvent | Occurs when an axis changes
SDL_JoyBallEvent | Occurs when a joystick trackball's position changes
SDL_JoyHatEvent | Occurs when a hat's position changes
SDL_JoyButtonEvent | Occurs when a button is pressed or released

Events are received from all joysticks opened. The first thing that needs to be done in order to receive joystick events is to call SDL_JoystickEventState with the SDL_ENABLE flag. Next you must open the joysticks that you want to receive envents from. This is done with the SDL_JoystickOpen function. For the example we are only interested in events from the first joystick on the system, regardless of what it may be. To receive events from it we would do this:

Example 3-3. Opening a Joystick

    SDL_Joystick *joystick;

    SDL_JoystickEventState(SDL_ENABLE);
    joystick = SDL_JoystickOpen(0);

If we wanted to receive events for other joysticks we would open them with calls to SDL_JoystickOpen just like we opened joystick 0, except we would store the SDL_Joystick structure they return in a different pointer. We only need the joystick pointer when we are querying the joysticks or when we are closing the joystick.

Up to this point all the code we have is used just to initialize the joysticks in order to read values at run time. All we need now is an event loop, which is something that all SDL programs should have anyway to receive the systems quit events. We must now add code to check the event loop for at least some of the above mentioned events. Let's assume our event loop looks like this:

    SDL_Event event;
    /* Other initializtion code goes here */

    /* Start main game loop here */

    while(SDL_PollEvent(&event))
    {
        switch(event.type)
        {
            case SDL_KEYDOWN:
            /* handle keyboard stuff here */
            break;

            case SDL_QUIT:
            /* Set whatever flags are necessary to */
            /* end the main game loop here */
            break;
        }
    }

    /* End loop here */

To handle Joystick events we merely add cases for them, first we'll add axis handling code. Axis checks can get kinda of tricky because alot of the joystick events received are junk. Joystick axis have a tendency to vary just a little between polling due to the way they are designed. To compensate for this you have to set a threshold for changes and ignore the events that have'nt exceeded the threshold. 10% is usually a good threshold value. This sounds a lot more complicated than it is. Here is the Axis event handler:

Example 3-4. Joystick Axis Events

    case SDL_JOYAXISMOTION:  /* Handle Joystick Motion */
    if ( ( event.jaxis.value < -3200 ) || (event.jaxis.value > 3200 ) )
    {
      /* code goes here */
    }
    break;

Another trick with axis events is that up-down and left-right movement are two different sets of axes. The most important axis is axis 0 (left-right) and axis 1 (up-down). To handle them seperatly in the code we do the following:

Example 3-5. More Joystick Axis Events

    case SDL_JOYAXISMOTION:  /* Handle Joystick Motion */
    if ( ( event.jaxis.value < -3200 ) || (event.jaxis.value > 3200 ) )
    {
        if( event.jaxis.axis == 0)
        {
            /* Left-right movement code goes here */
        }

        if( event.jaxis.axis == 1)
        {
            /* Up-Down movement code goes here */
        }
    }
    break;

Ideally the code here should use event.jaxis.value to scale something. For example lets assume you are using the joystick to control the movement of a spaceship. If the user is using an analog joystick and they push the stick a little bit they expect to move less than if they pushed it a lot. Designing your code for this situation is preferred because it makes the experience for users of analog controls better and remains the same for users of digital controls.

If your joystick has any additional axis then they may be used for other sticks or throttle controls and those axis return values too just with different event.jaxis.axis values.

Button handling is simple compared to the axis checking.

Example 3-6. Joystick Button Events

    case SDL_JOYBUTTONDOWN:  /* Handle Joystick Button Presses */
    if ( event.jbutton.button == 0 )
    {
        /* code goes here */
    }
    break;

Button checks are simpler than axis checks because a button can only be pressed or not pressed. The SDL_JOYBUTTONDOWN event is triggered when a button is pressed and the SDL_JOYBUTTONUP event is fired when a button is released. We do have to know what button was pressed though, that is done by reading the event.jbutton.button field.

Lastly when we are through using our joysticks we should close them with a call to SDL_JoystickClose. To close our opened joystick 0 we would do this at the end of our program:

    SDL_JoystickClose(joystick);

Advanced Joystick Functions

That takes care of the controls that you can count on being on every joystick under the sun, but there are a few extra things that SDL can support. Joyballs are next on our list, they are alot like axis with a few minor differences. Joyballs store relative changes unlike the the absolute postion stored in a axis event. Also one trackball event contains both the change in x and they change in y. Our case for it is as follows:

Example 3-7. Joystick Ball Events

    case SDL_JOYBALLMOTION:  /* Handle Joyball Motion */
    if( event.jball.ball == 0 )
    {
      /* ball handling */
    }
    break;

The above checks the first joyball on the joystick. The change in position will be stored in event.jball.xrel and event.jball.yrel.

Finally we have the hat event. Hats report only the direction they are pushed in. We check hat's position with the bitmasks:

SDL_HAT_CENTERED

SDL_HAT_UP

SDL_HAT_RIGHT

SDL_HAT_DOWN

SDL_HAT_LEFT

Also there are some predefined combinations of the above:

SDL_HAT_RIGHTUP

SDL_HAT_RIGHTDOWN

SDL_HAT_LEFTUP

SDL_HAT_LEFTDOWN

Our case for the hat may resemble the following:

Example 3-8. Joystick Hat Events

    case SDL_JOYHATMOTION:  /* Handle Hat Motion */
    if ( event.jhat.hat & SDL_HAT_UP )
    {
        /* Do up stuff here */
    }

    if ( event.jhat.hat & SDL_HAT_LEFT )
    {
        /* Do left stuff here */
    }

    if ( event.jhat.hat & SDL_HAT_RIGHTDOWN )
    {
        /* Do right and down together stuff here */
    }
    break;

In addition to the queries for number of joysticks on the system and their names there are additional functions to query the capabilities of attached joysticks:

SDL_JoystickNumAxes | Returns the number of joysitck axes
SDL_JoystickNumButtons | Returns the number of joysitck buttons
SDL_JoystickNumBalls | Returns the number of joysitck balls
SDL_JoystickNumHats | Returns the number of joysitck hats

To use these functions we just have to pass in the joystick structure we got when we opened the joystick. For Example:

Example 3-9. Querying Joystick Characteristics

    int number_of_buttons;
    SDL_Joystick *joystick;

    joystick = SDL_JoystickOpen(0);
    number_of_buttons = SDL_JoystickNumButtons(joystick);

This block of code would get the number of buttons on the first joystick in the system.

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Next

Handling the Keyboard

Keyboard Related Structures

It should make it a lot easier to understand this tutorial is you are familiar with the data types involved in keyboard access, so I'll explain them first.

SDLKey

SDLKey is an enumerated type defined in SDL/include/SDL_keysym.h and detailed here. Each SDLKey symbol represents a key, SDLK_a corresponds to the 'a' key on a keyboard, SDLK_SPACE corresponds to the space bar, and so on.

SDLMod

SDLMod is an enumerated type, similar to SDLKey, however it enumerates keyboard modifiers (Control, Alt, Shift). The full list of modifier symbols is here. SDLMod values can be AND'd together to represent several modifiers.

SDL_keysym

typedef struct{
  Uint8 scancode;
  SDLKey sym;
  SDLMod mod;
  Uint16 unicode;
} SDL_keysym;

The SDL_keysym structure describes a key press or a key release. The scancode field is hardware specific and should be ignored unless you know what your doing. The sym field is the SDLKey value of the key being pressed or released. The mod field describes the state of the keyboard modifiers at the time the key press or release occurred. So a value of KMOD_NUM | KMOD_CAPS | KMOD_LSHIFT would mean that Numlock, Capslock and the left shift key were all press (or enabled in the case of the lock keys). Finally, the unicode field stores the 16-bit unicode value of the key.

Note: It should be noted and understood that this field is only valid when the SDL_keysym is describing a key press, not a key release. Unicode values only make sense on a key press because the unicode value describes an international character and only key presses produce characters. More information on Unicode can be found at www.unicode.org

Note: Unicode translation must be enabled using the SDL_EnableUNICODE function.

SDL_KeyboardEvent

typedef struct{
  Uint8 type;
  Uint8 state;
  SDL_keysym keysym;
} SDL_KeyboardEvent;

The SDL_KeyboardEvent describes a keyboard event (obviously). The key member of the SDL_Event union is a SDL_KeyboardEvent structure. The type field specifies whether the event is a key release (SDL_KEYUP) or a key press (SDL_KEYDOWN) event. The state is largely redundant, it reports the same information as the type field but uses different values (SDL_RELEASED and SDL_PRESSED). The keysym contains information of the key press or release that this event represents (see above).

Reading Keyboard Events

Reading keybaord events from the event queue is quite simple (the event queue and using it is described here). We read events using SDL_PollEvent in a while() loop and check for SDL_KEYUP and SDL_KEYDOWN events using a switch statement, like so:

Example 3-10. Reading Keyboard Events

  SDL_Event event;
  .
  .
  /* Poll for events. SDL_PollEvent() returns 0 when there are no  */
  /* more events on the event queue, our while loop will exit when */
  /* that occurs.                                                  */
  while( SDL_PollEvent( &event ) ){
    /* We are only worried about SDL_KEYDOWN and SDL_KEYUP events */
    switch( event.type ){
      case SDL_KEYDOWN:
        printf( "Key press detected\n" );
        break;

      case SDL_KEYUP:
        printf( "Key release detected\n" );
        break;

      default:
        break;
    }
  }
  .
  .

This is a very basic example. No information about the key press or release is interpreted. We will explore the other extreme out our first full example below - reporting all available information about a keyboard event.

A More Detailed Look

Before we can read events SDL must be initialised with SDL_Init and a video mode must be set using SDL_SetVideoMode. There are, however, two other functions we must use to obtain all the information required. We must enable unicode translation by calling SDL_EnableUNICODE(1) and we must convert SDLKey values into something printable, using SDL_GetKeyName

Note: It is useful to note that unicode values < 0x80 translate directly a characters ASCII value. THis is used in the example below

Example 3-11. Interpreting Key Event Information

    #include "SDL.h"

    /* Function Prototypes */
    void PrintKeyInfo( SDL_KeyboardEvent *key );
    void PrintModifiers( SDLMod mod );

    /* main */
    int main( int argc, char *argv[] ){

        SDL_Event event;
        int quit = 0;

        /* Initialise SDL */
        if( SDL_Init( SDL_INIT_VIDEO ) < 0){
            fprintf( stderr, "Could not initialise SDL: %s\n", SDL_GetError() );
            exit( -1 );
        }

        /* Set a video mode */
        if( !SDL_SetVideoMode( 320, 200, 0, 0 ) ){
            fprintf( stderr, "Could not set video mode: %s\n", SDL_GetError() );
            SDL_Quit();
            exit( -1 );
        }

        /* Enable Unicode translation */
        SDL_EnableUNICODE( 1 );

        /* Loop until an SDL_QUIT event is found */
        while( !quit ){

            /* Poll for events */
            while( SDL_PollEvent( &event ) ){

                switch( event.type ){
                    /* Keyboard event */
                    /* Pass the event data onto PrintKeyInfo() */
                    case SDL_KEYDOWN:
                    case SDL_KEYUP:
                        PrintKeyInfo( &event.key );
                        break;

                    /* SDL_QUIT event (window close) */
                    case SDL_QUIT:
                        quit = 1;
                        break;

                    default:
                        break;
                }

            }

        }

        /* Clean up */
        SDL_Quit();
        exit( 0 );
    }

    /* Print all information about a key event */
    void PrintKeyInfo( SDL_KeyboardEvent *key ){
        /* Is it a release or a press? */
        if( key->type == SDL_KEYUP )
            printf( "Release:- " );
        else
            printf( "Press:- " );

        /* Print the hardware scancode first */
        printf( "Scancode: 0x%02X", key->keysym.scancode );
        /* Print the name of the key */
        printf( ", Name: %s", SDL_GetKeyName( key->keysym.sym ) );
        /* We want to print the unicode info, but we need to make */
        /* sure its a press event first (remember, release events */
        /* don't have unicode info                                */
        if( key->type == SDL_KEYDOWN ){
            /* If the Unicode value is less than 0x80 then the    */
            /* unicode value can be used to get a printable       */
            /* representation of the key, using (char)unicode.    */
            printf(", Unicode: " );
            if( key->keysym.unicode < 0x80 && key->keysym.unicode > 0 ){
                printf( "%c (0x%04X)", (char)key->keysym.unicode,
                        key->keysym.unicode );
            }
            else{
                printf( "? (0x%04X)", key->keysym.unicode );
            }
        }
        printf( "\n" );
        /* Print modifier info */
        PrintModifiers( key->keysym.mod );
    }

    /* Print modifier info */
    void PrintModifiers( SDLMod mod ){
        printf( "Modifers: " );

        /* If there are none then say so and return */
        if( mod == KMOD_NONE ){
            printf( "None\n" );
            return;
        }

        /* Check for the presence of each SDLMod value */
        /* This looks messy, but there really isn't    */
        /* a clearer way.                              */
        if( mod & KMOD_NUM ) printf( "NUMLOCK " );
        if( mod & KMOD_CAPS ) printf( "CAPSLOCK " );
        if( mod & KMOD_LCTRL ) printf( "LCTRL " );
        if( mod & KMOD_RCTRL ) printf( "RCTRL " );
        if( mod & KMOD_RSHIFT ) printf( "RSHIFT " );
        if( mod & KMOD_LSHIFT ) printf( "LSHIFT " );
        if( mod & KMOD_RALT ) printf( "RALT " );
        if( mod & KMOD_LALT ) printf( "LALT " );
        if( mod & KMOD_CTRL ) printf( "CTRL " );
        if( mod & KMOD_SHIFT ) printf( "SHIFT " );
        if( mod & KMOD_ALT ) printf( "ALT " );
        printf( "\n" );
    }

Game-type Input

I have found that people using keyboard events for games and other interactive applications don't always understand one fundemental point.

Keyboard events only take place when a keys state changes from being unpressed to pressed, and vice versa.

Imagine you have an image of an alien that you wish to move around using the cursor keys - when you pressed the left arrow key you want him to slide over to the left, when you press the down key you want him to slide down the screen. Examine the following code, it highlights and error that many people have made.

    /* Alien screen coordinates */
    int alien_x=0, alien_y=0;
    .
    .
    /* Initialise SDL and video modes and all that */
    .
    /* Main game loop */
    /* Check for events */
    while( SDL_PollEvent( &event ) ){
        switch( event.type ){
            /* Look for a keypress */
            case SDL_KEYDOWN:
                /* Check the SDLKey values and move change the coords */
                switch( event.key.keysym.sym ){
                    case SDLK_LEFT:
                        alien_x -= 1;
                        break;
                    case SDLK_RIGHT:
                        alien_x += 1;
                        break;
                    case SDLK_UP:
                        alien_y -= 1;
                        break;
                    case SDLK_DOWN:
                        alien_y += 1;
                        break;
                    default:
                        break;
                }
            }
        }
    }
    .
    .

At first glance you may think this is a perfectly reasonable piece of code for the task, but it isn't. Like I said keyboard events only occur when a key changes state, so the user would have to press and release the left cursor key 100 times to move the alien 100 pixels to the left.

To get around this problem we must not use the events to change the position of the alien, we use the events to set flags which are then used in a seperate section of code to move the alien. Something like this:

Example 3-12. Proper Game Movement

    /* Alien screen coordinates */
    int alien_x=0, alien_y=0;
    int alien_xvel=0, alien_yvel=0;
    .
    .
    /* Initialise SDL and video modes and all that */
    .
    /* Main game loop */
    /* Check for events */
    while( SDL_PollEvent( &event ) ){
        switch( event.type ){
            /* Look for a keypress */
            case SDL_KEYDOWN:
                /* Check the SDLKey values and move change the coords */
                switch( event.key.keysym.sym ){
                    case SDLK_LEFT:
                        alien_xvel = -1;
                        break;
                    case SDLK_RIGHT:
                        alien_xvel =  1;
                        break;
                    case SDLK_UP:
                        alien_yvel = -1;
                        break;
                    case SDLK_DOWN:
                        alien_yvel =  1;
                        break;
                    default:
                        break;
                }
                break;
            /* We must also use the SDL_KEYUP events to zero the x */
            /* and y velocity variables. But we must also be       */
            /* careful not to zero the velocities when we shouldn't*/
            case SDL_KEYUP:
                switch( event.key.keysym.sym ){
                    case SDLK_LEFT:
                        /* We check to make sure the alien is moving */
                        /* to the left. If it is then we zero the    */
                        /* velocity. If the alien is moving to the   */
                        /* right then the right key is still press   */
                        /* so we don't tocuh the velocity            */
                        if( alien_xvel < 0 )
                            alien_xvel = 0;
                        break;
                    case SDLK_RIGHT:
                        if( alien_xvel > 0 )
                            alien_xvel = 0;
                        break;
                    case SDLK_UP:
                        if( alien_yvel < 0 )
                            alien_yvel = 0;
                        break;
                    case SDLK_DOWN:
                        if( alien_yvel > 0 )
                            alien_yvel = 0;
                        break;
                    default:
                        break;
                }
                break;

            default:
                break;
        }
    }
    .
    .
    /* Update the alien position */
    alien_x += alien_xvel;
    alien_y += alien_yvel;

As can be seen, we use two extra variables, alien_xvel and alien_yvel, which represent the motion of the ship, it is these variables that we update when we detect keypresses and releases.

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Chapter 4. Examples

Table of Contents

Introduction

Event Examples

Audio Examples

CDROM Examples

Time Examples

Introduction

For the moment these examples are taken directly from the old SDL documentation. By the 1.2 release these examples should hopefully deal with most common SDL programming problems.

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Event Examples

Filtering and Handling Events

#include <stdio.h>
#include <stdlib.h>

#include "SDL.h"

/* This function may run in a separate event thread */
int FilterEvents(const SDL_Event *event) {
    static int boycott = 1;

    /* This quit event signals the closing of the window */
    if ( (event->type == SDL_QUIT) && boycott ) {
        printf("Quit event filtered out -- try again.\n");
        boycott = 0;
        return(0);
    }
    if ( event->type == SDL_MOUSEMOTION ) {
        printf("Mouse moved to (%d,%d)\n",
                event->motion.x, event->motion.y);
        return(0);    /* Drop it, we've handled it */
    }
    return(1);
}

int main(int argc, char *argv[])
{
    SDL_Event event;

    /* Initialize the SDL library (starts the event loop) */
    if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
        fprintf(stderr,
                "Couldn't initialize SDL: %s\n", SDL_GetError());
        exit(1);
    }

    /* Clean up on exit, exit on window close and interrupt */
    atexit(SDL_Quit);

    /* Ignore key events */
    SDL_EventState(SDL_KEYDOWN, SDL_IGNORE);
    SDL_EventState(SDL_KEYUP, SDL_IGNORE);

    /* Filter quit and mouse motion events */
    SDL_SetEventFilter(FilterEvents);

    /* The mouse isn't much use unless we have a display for reference */
    if ( SDL_SetVideoMode(640, 480, 8, 0) == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }

    /* Loop waiting for ESC+Mouse_Button */
    while ( SDL_WaitEvent(&event) >= 0 ) {
        switch (event.type) {
            case SDL_ACTIVEEVENT: {
                if ( event.active.state & SDL_APPACTIVE ) {
                    if ( event.active.gain ) {
                        printf("App activated\n");
                    } else {
                        printf("App iconified\n");
                    }
                }
            }
            break;

            case SDL_MOUSEBUTTONDOWN: {
                Uint8 *keys;

                keys = SDL_GetKeyState(NULL);
                if ( keys[SDLK_ESCAPE] == SDL_PRESSED ) {
                    printf("Bye bye...\n");
                    exit(0);
                }
                printf("Mouse button pressed\n");
            }
            break;

            case SDL_QUIT: {
                printf("Quit requested, quitting.\n");
                exit(0);
            }
            break;
        }
    }
    /* This should never happen */
    printf("SDL_WaitEvent error: %s\n", SDL_GetError());
    exit(1);
}

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Audio Examples

Opening the audio device

    SDL_AudioSpec wanted;
    extern void fill_audio(void *udata, Uint8 *stream, int len);

    /* Set the audio format */
    wanted.freq = 22050;
    wanted.format = AUDIO_S16;
    wanted.channels = 2;    /* 1 = mono, 2 = stereo */
    wanted.samples = 1024;  /* Good low-latency value for callback */
    wanted.callback = fill_audio;
    wanted.userdata = NULL;

    /* Open the audio device, forcing the desired format */
    if ( SDL_OpenAudio(&wanted, NULL) < 0 ) {
        fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
        return(-1);
    }
    return(0);

Playing audio

    static Uint8 *audio_chunk;
    static Uint32 audio_len;
    static Uint8 *audio_pos;

    /* The audio function callback takes the following parameters:
       stream:  A pointer to the audio buffer to be filled
       len:     The length (in bytes) of the audio buffer
    */
    void fill_audio(void *udata, Uint8 *stream, int len)
    {
        /* Only play if we have data left */
        if ( audio_len == 0 )
            return;

        /* Mix as much data as possible */
        len = ( len > audio_len ? audio_len : len );
        SDL_MixAudio(stream, audio_pos, len, SDL_MIX_MAXVOLUME);
        audio_pos += len;
        audio_len -= len;
    }

    /* Load the audio data ... */

    ;;;;;

    audio_pos = audio_chunk;

    /* Let the callback function play the audio chunk */
    SDL_PauseAudio(0);

    /* Do some processing */

    ;;;;;

    /* Wait for sound to complete */
    while ( audio_len > 0 ) {
        SDL_Delay(100);         /* Sleep 1/10 second */
    }
    SDL_CloseAudio();

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CDROM Examples

Listing CD-ROM drives

    #include "SDL.h"

    /* Initialize SDL first */
    if ( SDL_Init(SDL_INIT_CDROM) < 0 ) {
        fprintf(stderr, "Couldn't initialize SDL: %s\n",SDL_GetError());
        exit(1);
    }
    atexit(SDL_Quit);

    /* Find out how many CD-ROM drives are connected to the system */
    printf("Drives available: %d\n", SDL_CDNumDrives());
    for ( i=0; i<SDL_CDNumDrives(); ++i ) {
        printf("Drive %d:  \"%s\"\n", i, SDL_CDName(i));
    }

Opening the default drive

    SDL_CD *cdrom;
    CDstatus status;
    char *status_str;

    cdrom = SDL_CDOpen(0);
    if ( cdrom == NULL ) {
        fprintf(stderr, "Couldn't open default CD-ROM drive: %s\n",
                        SDL_GetError());
        exit(2);
    }

    status = SDL_CDStatus(cdrom);
    switch (status) {
        case CD_TRAYEMPTY:
            status_str = "tray empty";
            break;
        case CD_STOPPED:
            status_str = "stopped";
            break;
        case CD_PLAYING:
            status_str = "playing";
            break;
        case CD_PAUSED:
            status_str = "paused";
            break;
        case CD_ERROR:
            status_str = "error state";
            break;
    }
    printf("Drive status: %s\n", status_str);
    if ( status >= CD_PLAYING ) {
        int m, s, f;
        FRAMES_TO_MSF(cdrom->cur_frame, &m, &s, &f);
        printf("Currently playing track %d, %d:%2.2d\n",
        cdrom->track[cdrom->cur_track].id, m, s);
    }

Listing the tracks on a CD

    SDL_CD *cdrom;          /* Assuming this has already been set.. */
    int i;
    int m, s, f;

    SDL_CDStatus(cdrom);
    printf("Drive tracks: %d\n", cdrom->numtracks);
    for ( i=0; i<cdrom->numtracks; ++i ) {
        FRAMES_TO_MSF(cdrom->track[i].length, &m, &s, &f);
        if ( f > 0 )
            ++s;
        printf("\tTrack (index %d) %d: %d:%2.2d\n", i,
        cdrom->track[i].id, m, s);
    }

Play an entire CD

    SDL_CD *cdrom;          /* Assuming this has already been set.. */

    // Play entire CD:
    if ( CD_INDRIVE(SDL_CDStatus(cdrom)) )
        SDL_CDPlayTracks(cdrom, 0, 0, 0, 0);

        // Play last track:
        if ( CD_INDRIVE(SDL_CDStatus(cdrom)) ) {
            SDL_CDPlayTracks(cdrom, cdrom->numtracks-1, 0, 0, 0);
        }

        // Play first and second track and 10 seconds of third track:
        if ( CD_INDRIVE(SDL_CDStatus(cdrom)) )
            SDL_CDPlayTracks(cdrom, 0, 0, 2, CD_FPS * 10);

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Time Examples

Time based game loop

#define TICK_INTERVAL    30

static Uint32 next_time;

Uint32 time_left(void)
{
    Uint32 now;

    now = SDL_GetTicks();
    if(next_time <= now)
        return 0;
    else
        return next_time - now;
}

/* main game loop */

    next_time = SDL_GetTicks() + TICK_INTERVAL;
    while ( game_running ) {
        update_game_state();
        SDL_Delay(time_left());
        next_time += TICK_INTERVAL;
    }

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Video Examples

Initializing the video display

    SDL_Surface *screen;

    /* Initialize the SDL library */
    if( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
        fprintf(stderr,
                "Couldn't initialize SDL: %s\n", SDL_GetError());
        exit(1);
    }

    /* Clean up on exit */
    atexit(SDL_Quit);

    /* Initialize the display in a 640x480 8-bit palettized mode */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }

Initializing the best video mode

    /* Have a preference for 8-bit, but accept any depth */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_ANYFORMAT);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }
    printf("Set 640x480 at %d bits-per-pixel mode\n",
           screen->format->BitsPerPixel);

Loading and displaying a BMP file

    SDL_Surface *image;
    SDL_Rect dest;
    int ncolors, i;
    SDL_Color *colors;

    /* Load the BMP file into a surface */
    image = SDL_LoadBMP("sample.bmp");
    if ( image == NULL ) {
        fprintf(stderr, "Couldn't load sample.bmp: %s\n",
                        SDL_GetError());
        return;
    }

    /* Set the display colors -- SDL_SetColors() only does something on
       palettized displays, but it doesn't hurt anything on HiColor or
       TrueColor displays.
       If the display colors have already been set, this step can be
       skipped, and the library will automatically map the image to
       the current display colors.
    */
    if ( image->format->palette ) {
        ncolors = image->format->palette->ncolors;
        colors  = (SDL_Color *)malloc(ncolors*sizeof(SDL_Color));
        memcpy(colors, image->format->palette->colors, ncolors);
    }
    else {
        int r, g, b;

        /* Allocate 256 color palette */
        ncolors = 256;
        colors  = (SDL_Color *)malloc(ncolors*sizeof(SDL_Color));

        /* Set a 3,3,2 color cube */
        for ( r=0; r<8; ++r ) {
            for ( g=0; g<8; ++g ) {
                for ( b=0; b<4; ++b ) {
                    i = ((r<<5)|(g<<2)|b);
                    colors[i].r = r<<5;
                    colors[i].g = g<<5;
                    colors[i].b = b<<6;
                }
            }
        }
        /* Note: A better way of allocating the palette might be
           to calculate the frequency of colors in the image
           and create a palette based on that information.
        */
    }
    /* Set colormap, try for all the colors, but don't worry about it */
    SDL_SetColors(screen, colors, 0, ncolors);
    free(colors);

    /* Blit onto the screen surface */
    dest.x = 0;
    dest.y = 0;
    dest.w = image->w;
    dest.h = image->h;
    SDL_BlitSurface(image, NULL, screen, &dest);

    SDL_UpdateRects(screen, 1, &dest);

    /* Free the allocated BMP surface */
    SDL_FreeSurface(image);
    return;

Drawing directly to the display

    /* Code to set a yellow pixel at the center of the screen */

    Sint32   X, Y;
    Uint32   pixel;
    Uint8   *bits, bpp;

    /* Map the color yellow to this display (R=0xFF, G=0xFF, B=0x00)
       Note:  If the display is palettized, you must set the palette first.
    */
    pixel = SDL_MapRGB(screen->format, 0xFF, 0xFF, 0x00);

    /* Calculate the framebuffer offset of the center of the screen */
    if ( SDL_MUSTLOCK(screen) ) {
        if ( SDL_LockSurface(screen) < 0 )
            return;
    }
    bpp = screen->format->BytesPerPixel;
    X = screen->w/2;
    Y = screen->h/2;
    bits = ((Uint8 *)screen->pixels)+Y*screen->pitch+X*bpp;

    /* Set the pixel */
    switch(bpp) {
        case 1:
            *((Uint8 *)(bits)) = (Uint8)pixel;
            break;
        case 2:
            *((Uint16 *)(bits)) = (Uint16)pixel;
            break;
        case 3: { /* Format/endian independent */
            Uint8 r, g, b;

            r = (pixel>>screen->format->Rshift)&0xFF;
            g = (pixel>>screen->format->Gshift)&0xFF;
            b = (pixel>>screen->format->Bshift)&0xFF;
            *((bits)+screen->format->Rshift/8) = r;
            *((bits)+screen->format->Gshift/8) = g;
            *((bits)+screen->format->Bshift/8) = b;
            }
            break;
        case 4:
            *((Uint32 *)(bits)) = (Uint32)pixel;
            break;
    }

    /* Update the display */
    if ( SDL_MUSTLOCK(screen) ) {
        SDL_UnlockSurface(screen);
    }
    SDL_UpdateRect(screen, X, Y, 1, 1);

    return;

Fastest possible surface blit

There are three different ways you can draw an image to the screen:

1.Create a surface and use SDL_BlitSurface to blit it to the screen

2.Create the video surface in system memory and call SDL_UpdateRect

3.Create the video surface in video memory and call SDL_LockSurface

The best way to do this is to combine methods:

#include <stdio.h>
#include <stdlib.h>
#include "SDL.h"
#include "SDL_timer.h"

void ComplainAndExit(void)
{
    fprintf(stderr, "Problem: %s\n", SDL_GetError());
    exit(1);
}

int main(int argc, char *argv[])
{
    SDL_PixelFormat fmt;
    SDL_Surface *screen, *locked;
    SDL_Surface *imagebmp, *image;
    SDL_Rect dstrect;
    int i;
    Uint8 *buffer;

    /* Initialize SDL */
    if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
        ComplainAndExit();
    }
    atexit(SDL_Quit);

    /* Load a BMP image into a surface */
    imagebmp = SDL_LoadBMP("image.bmp");
    if ( imagebmp == NULL ) {
        ComplainAndExit();
    }

    /* Set the video mode (640x480 at native depth) */
    screen = SDL_SetVideoMode(640, 480, 0, SDL_HWSURFACE|SDL_FULLSCREEN);
    if ( screen == NULL ) {
        ComplainAndExit();
    }

    /* Set the video colormap */
    if ( imagebmp->format->palette != NULL ) {
        SDL_SetColors(screen,
                      imagebmp->format->palette->colors, 0,
                      imagebmp->format->palette->ncolors);
    }

    /* Convert the image to the video format (maps colors) */
    image = SDL_DisplayFormat(imagebmp);
    SDL_FreeSurface(imagebmp);
    if ( image == NULL ) {
        ComplainAndExit();
    }

    /* Draw bands of color on the raw surface */
    if ( SDL_MUSTLOCK(screen) ) {
        if ( SDL_LockSurface(screen) < 0 )
            ComplainAndExit();
    }
    buffer=(Uint8 *)screen->pixels;
    for ( i=0; i<screen->h; ++i ) {
        memset(buffer,(i*255)/screen->h,
               screen->w*screen->format->BytesPerPixel);
               buffer += screen->pitch;
    }
    if ( SDL_MUSTLOCK(screen) ) {
        SDL_UnlockSurface(screen);
    }

    /* Blit the image to the center of the screen */
    dstrect.x = (screen->w-image->w)/2;
    dstrect.y = (screen->h-image->h)/2;
    dstrect.w = image->w;
    dstrect.h = image->h;
    if ( SDL_BlitSurface(image, NULL, screen, &dstrect) < 0 ) {
        SDL_FreeSurface(image);
        ComplainAndExit();
    }
    SDL_FreeSurface(image);

    /* Update the screen */
    SDL_UpdateRects(screen, 1, &dstrect);

    SDL_Delay(5000);        /* Wait 5 seconds */
    exit(0);
}

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II. SDL Reference

Table of Contents

5. General

6. Video

7. Window Management

8. Events

9. Joystick

10. Audio

11. CD-ROM

12. Multi-threaded Programming

13. Time

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SDL Library Documentation

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Chapter 5. General

Table of Contents

SDL_Init — Initializes SDL

SDL_InitSubSystem — Initialize subsystems

SDL_QuitSubSystem — Shut down a subsystem

SDL_Quit — Shut down SDL

SDL_WasInit — Check which subsystems are initialized

SDL_GetError — Get SDL error string

Before SDL can be used in a program it must be initialized with SDL_Init. SDL_Init initializes all the subsystems that the user requests (video, audio, joystick, timers and/or cdrom). Once SDL is initialized with SDL_Init subsystems can be shut down and initialized as needed using SDL_InitSubSystem and SDL_QuitSubSystem.

SDL must also be shut down before the program exits to make sure it cleans up correctly. Calling SDL_Quit shuts down all subsystems and frees any resources allocated to SDL.

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SDL_Init

Name

SDL_Init -- Initializes SDL

Synopsis

#include "SDL.h"

int SDL_Init(Uint32 flags);

Description

Initializes SDL. This should be called before all other SDL functions. The flags parameter specifies what part(s) of SDL to initialize.

SDL_INIT_TIMER | Initializes the timer subsystem.
SDL_INIT_AUDIO | Initializes the audio subsystem.
SDL_INIT_VIDEO | Initializes the video subsystem.
SDL_INIT_CDROM | Initializes the cdrom subsystem.
SDL_INIT_JOYSTICK | Initializes the joystick subsystem.
SDL_INIT_EVERYTHING | Initialize all of the above.
SDL_INIT_NOPARACHUTE | Prevents SDL from catching fatal signals.
SDL_INIT_EVENTTHREAD |

Return Value

Returns -1 on an error or 0 on success.

See Also

SDL_Quit, SDL_InitSubSystem

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SDL_InitSubSystem

Name

SDL_InitSubSystem -- Initialize subsystems

Synopsis

#include "SDL.h"

int SDL_InitSubSystem(Uint32 flags);

Description

After SDL has been initialized with SDL_Init you may initialize uninitialized subsystems with SDL_InitSubSystem. The flags parameter is the same as that used in SDL_Init.

Examples

/* Seperating Joystick and Video initialization. */
SDL_Init(SDL_INIT_VIDEO);
.
.
SDL_SetVideoMode(640, 480, 16, SDL_DOUBLEBUF|SDL_FULLSCREEN);
.
/* Do Some Video stuff */
.
.
/* Initialize the joystick subsystem */
SDL_InitSubSystem(SDL_INIT_JOYSTICK);

/* Do some stuff with video and joystick */
.
.
.
/* Shut them both down */
SDL_Quit();

Return Value

Returns -1 on an error or 0 on success.

See Also

SDL_Init, SDL_Quit, SDL_QuitSubSystem

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SDL Library Documentation

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SDL_QuitSubSystem

Name

SDL_QuitSubSystem -- Shut down a subsystem

Synopsis

#include "SDL.h"

void SDL_QuitSubSystem(Uint32 flags);

Description

SDL_QuitSubSystem allows you to shut down a subsystem that has been previously initialized by SDL_Init or SDL_InitSubSystem. The flags tells SDL_QuitSubSystem which subsystems to shut down, it uses the same values that are passed to SDL_Init.

See Also

SDL_Quit, SDL_Init, SDL_InitSubSystem

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SDL Library Documentation

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SDL_Quit

Name

SDL_Quit -- Shut down SDL

Synopsis

#include "SDL.h"

void SDL_Quit(void);

Description

SDL_Quit shuts down all SDL subsystems and frees the resources allocated to them. This should always be called before you exit. For the sake of simplicity you can set SDL_Quit as your atexit call, like:

SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO);
atexit(SDL_Quit);
.
.

Note: While using atexit maybe be fine for small programs, more advanced users should shut down SDL in their own cleanup code. Plus, using atexit in a library is a sure way to crash dynamically loaded code

See Also

SDL_QuitSubsystem, SDL_Init

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SDL Library Documentation

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SDL_WasInit

Name

SDL_WasInit -- Check which subsystems are initialized

Synopsis

#include "SDL.h"

Uint32 SDL_WasInit(Uint32 flags);

Description

SDL_WasInit allows you to see which SDL subsytems have been initialized. flags is a bitwise OR'd combination of the subsystems you wish to check (see SDL_Init for a list of subsystem flags).

Return Value

SDL_WasInit returns a bitwised OR'd combination of the initialized subsystems.

Examples

/* Here are several ways you can use SDL_WasInit() */

/* Get init data on all the subsystems */
Uint32 subsystem_init;

subsystem_init=SDL_WasInit(SDL_INIT_EVERYTHING);

if(subsystem_init&SDL_INIT_VIDEO)
  printf("Video is initialized.\n");
else
  printf("Video is not initialized.\n");

/* Just check for one specfic subsystem */

if(SDL_WasInit(SDL_INIT_VIDEO)!=0)
  printf("Video is initialized.\n");
else
  printf("Video is not initialized.\n");

/* Check for two subsystems */

Uint32 subsystem_mask=SDL_INIT_VIDEO|SDL_INIT_AUDIO;

if(SDL_WasInit(subsystem_mask)==subsystem_mask)
  printf("Video and Audio initialized.\n");
else
  printf("Video and Audio not initialized.\n");

See Also

SDL_Init, SDL_Subsystem

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SDL Library Documentation

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SDL_GetError

Name

SDL_GetError -- Get SDL error string

Synopsis

#include "SDL/SDL.h"

char *SDL_GetError(void);

Description

SDL_GetError returns a NULL terminated string containing information about the last internal SDL error.

Return Value

SDL_GetError returns a string containing the last error.

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SDL Library Documentation

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Chapter 6. Video

Table of Contents

SDL_GetVideoSurface — returns a pointer to the current display surface

SDL_GetVideoInfo — returns a pointer to information about the video hardware

SDL_VideoDriverName — Obtain the name of the video driver

SDL_ListModes — Returns a pointer to an array of available screen dimensions for the given format and video flags

SDL_VideoModeOK — Check to see if a particular video mode is supported.

SDL_SetVideoMode — Set up a video mode with the specified width, height and bits-per-pixel.

SDL_UpdateRect — Makes sure the given area is updated on the given screen.

SDL_UpdateRects — Makes sure the given list of rectangles is updated on the given screen.

SDL_Flip — Swaps screen buffers

SDL_SetColors — Sets a portion of the colormap for the given 8-bit surface.

SDL_SetPalette — Sets the colors in the palette of an 8-bit surface.

SDL_SetGamma — Sets the color gamma function for the display

SDL_GetGammaRamp — Gets the color gamma lookup tables for the display

SDL_SetGammaRamp — Sets the color gamma lookup tables for the display

SDL_MapRGB — Map a RGB color value to a pixel format.

SDL_MapRGBA — Map a RGBA color value to a pixel format.

SDL_GetRGB — Get RGB values from a pixel in the specified pixel format.

SDL_GetRGBA — Get RGBA values from a pixel in the specified pixel format.

SDL_CreateRGBSurface — Create an empty SDL_Surface

SDL_CreateRGBSurfaceFrom — Create an SDL_Surface from pixel data

SDL_FreeSurface — Frees (deletes) a SDL_Surface

SDL_LockSurface — Lock a surface for directly access.

SDL_UnlockSurface — Unlocks a previously locked surface.

SDL_LoadBMP — Load a Windows BMP file into an SDL_Surface.

SDL_SaveBMP — Save an SDL_Surface as a Windows BMP file.

SDL_SetColorKey — Sets the color key (transparent pixel) in a blittable surface and RLE acceleration.

SDL_SetAlpha — Adjust the alpha properties of a surface

SDL_SetClipRect — Sets the clipping rectangle for a surface.

SDL_GetClipRect — Gets the clipping rectangle for a surface.

SDL_ConvertSurface — Converts a surface to the same format as another surface.

SDL_BlitSurface — This performs a fast blit from the source surface to the destination surface.

SDL_FillRect — This function performs a fast fill of the given rectangle with some color

SDL_DisplayFormat — Convert a surface to the display format

SDL_DisplayFormatAlpha — Convert a surface to the display format

SDL_WarpMouse — Set the position of the mouse cursor.

SDL_CreateCursor — Creates a new mouse cursor.

SDL_FreeCursor — Frees a cursor created with SDL_CreateCursor.

SDL_SetCursor — Set the currently active mouse cursor.

SDL_GetCursor — Get the currently active mouse cursor.

SDL_ShowCursor — Toggle whether or not the cursor is shown on the screen.

SDL_GL_LoadLibrary — Specify an OpenGL library

SDL_GL_GetProcAddress — Get the address of a GL function

SDL_GL_GetAttribute — Get the value of a special SDL/OpenGL attribute

SDL_GL_SetAttribute — Set a special SDL/OpenGL attribute

SDL_GL_SwapBuffers — Swap OpenGL framebuffers/Update Display

SDL_CreateYUVOverlay — Create a YUV video overlay

SDL_LockYUVOverlay — Lock an overlay

SDL_UnlockYUVOverlay — Unlock an overlay

SDL_DisplayYUVOverlay — Blit the overlay to the display

SDL_FreeYUVOverlay — Free a YUV video overlay

SDL_GLattr — SDL GL Attributes

SDL_Rect — Defines a rectangular area

SDL_Color — Format independent color description

SDL_Palette — Color palette for 8-bit pixel formats

SDL_PixelFormat — Stores surface format information

SDL_Surface — Graphical Surface Structure

SDL_VideoInfo — Video Target information

SDL_Overlay — YUV video overlay

SDL presents a very simple interface to the display framebuffer. The framebuffer is represented as an offscreen surface to which you can write directly. If you want the screen to show what you have written, call the update function which will guarantee that the desired portion of the screen is updated.

Before you call any of the SDL video functions, you must first call SDL_Init(SDL_INIT_VIDEO), which initializes the video and events in the SDL library. Check the return code, which should be 0, to see if there were any errors in starting up.

If you use both sound and video in your application, you need to call SDL_Init(SDL_INIT_AUDIO | SDL_INIT_VIDEO) before opening the sound device, otherwise under Win32 DirectX, you won't be able to set full-screen display modes.

After you have initialized the library, you can start up the video display in a number of ways. The easiest way is to pick a common screen resolution and depth and just initialize the video, checking for errors. You will probably get what you want, but SDL may be emulating your requested mode and converting the display on update. The best way is to query, for the best video mode closest to the desired one, and then convert your images to that pixel format.

SDL currently supports any bit depth >= 8 bits per pixel. 8 bpp formats are considered 8-bit palettized modes, while 12, 15, 16, 24, and 32 bits per pixel are considered "packed pixel" modes, meaning each pixel contains the RGB color components packed in the bits of the pixel.

After you have initialized your video mode, you can take the surface that was returned, and write to it like any other framebuffer, calling the update routine as you go.

When you have finished your video access and are ready to quit your application, you should call "SDL_Quit()" to shutdown the video and events.

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SDL_GetError | Up | SDL_GetVideoSurface

SDL Library Documentation

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SDL_GetVideoSurface

Name

SDL_GetVideoSurface -- returns a pointer to the current display surface

Synopsis

#include "SDL.h"

SDL_Surface *SDL_GetVideoSurface(void);

Description

This function returns a pointer to the current display surface. If SDL is doing format conversion on the display surface, this function returns the publicly visible surface, not the real video surface.

See Also

SDL_Surface

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Video | Up | SDL_GetVideoInfo

SDL Library Documentation

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SDL_GetVideoInfo

Name

SDL_GetVideoInfo -- returns a pointer to information about the video hardware

Synopsis

#include "SDL.h"

SDL_VideoInfo *SDL_GetVideoInfo(void);

Description

This function returns a read-only pointer to information about the video hardware. If this is called before SDL_SetVideoMode, the vfmt member of the returned structure will contain the pixel format of the "best" video mode.

See Also

SDL_SetVideoMode, SDL_VideoInfo

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SDL_GetVideoSurface | Up | SDL_VideoDriverName

SDL Library Documentation

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SDL_VideoDriverName

Name

SDL_VideoDriverName -- Obtain the name of the video driver

Synopsis

#include "SDL.h"

char *SDL_VideoDriverName(char *namebuf, int maxlen);

Description

The buffer pointed to by namebuf is filled up to a maximum of maxlen characters (include the NULL terminator) with the name of the initialised video driver. The driver name is a simple one word identifier like "x11" or "windib".

Return Value

Returns NULL if video has not been initialised with SDL_Init or a pointer to namebuf otherwise.

See Also

SDL_Init SDL_InitSubSystem

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SDL_GetVideoInfo | Up | SDL_ListModes

SDL Library Documentation

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SDL_ListModes

Name

SDL_ListModes -- Returns a pointer to an array of available screen dimensions for the given format and video flags

Synopsis

#include "SDL.h"

SDL_Rect **SDL_ListModes(SDL_PixelFormat *format, Uint32 flags);

Description

Return a pointer to an array of available screen dimensions for the given format and video flags, sorted largest to smallest. Returns NULL if there are no dimensions available for a particular format, or -1 if any dimension is okay for the given format.

If format is NULL, the mode list will be for the format returned by SDL_GetVideoInfo()->vfmt. The flag parameter is an OR'd combination of surface flags. The flags are the same as those used SDL_SetVideoMode and they play a strong role in deciding what modes are valid. For instance, if you pass SDL_HWSURFACE as a flag only modes that support hardware video surfaces will be returned.

Example

SDL_Rect **modes;
int i;
.
.
.

/* Get available fullscreen/hardware modes */
modes=SDL_ListModes(NULL, SDL_FULLSCREEN|SDL_HWSURFACE);

/* Check is there are any modes available */
if(modes == (SDL_Rect **)0){
  printf("No modes available!\n");
  exit(-1);
}

/* Check if or resolution is restricted */
if(modes == (SDL_Rect **)-1){
  printf("All resolutions available.\n");
}
else{
  /* Print valid modes */
  printf("Available Modes\n");
  for(i=0;modes[i];++i)
    printf("  %d x %d\n", modes[i]->w, modes[i]->h);
}
.
.

See Also

SDL_SetVideoMode, SDL_GetVideoInfo, SDL_Rect, SDL_PixelFormat

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SDL_VideoDriverName | Up | SDL_VideoModeOK

SDL Library Documentation

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SDL_VideoModeOK

Name

SDL_VideoModeOK -- Check to see if a particular video mode is supported.

Synopsis

#include "SDL.h"

int SDL_VideoModeOK(int width, int height, int bpp, Uint32 flags);

Description

SDL_VideoModeOK returns 0 if the requested mode is not supported under any bit depth, or returns the bits-per-pixel of the closest available mode with the given width, height and requested surface flags (see SDL_SetVideoMode).

The bits-per-pixel value returned is only a suggested mode. You can usually request and bpp you want when setting the video mode and SDL will emulate that color depth with a shadow video surface.

The arguments to SDL_VideoModeOK are the same ones you would pass to SDL_SetVideoMode

Example

SDL_Surface *screen;
Uint32 bpp;
.
.
.
printf("Checking mode 640x480@16bpp.\n");
bpp=SDL_VideoModeOK(640, 480, 16, SDL_HWSURFACE);

if(!bpp){
  printf("Mode not available.\n");
  exit(-1);
}

printf("SDL Recommends 640x480@%dbpp.\n", bpp);
screen=SDL_SetVideoMode(640, 480, bpp, SDL_HWSURFACE);
.
.

See Also

SDL_SetVideoMode, SDL_GetVideoInfo

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SDL_ListModes | Up | SDL_SetVideoMode

SDL Library Documentation

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SDL_SetVideoMode

Name

SDL_SetVideoMode -- Set up a video mode with the specified width, height and bits-per-pixel.

Synopsis

#include "SDL.h"

SDL_Surface *SDL_SetVideoMode(int width, int height, int bpp, Uint32 flags);

Description

Set up a video mode with the specified width, height and bits-per-pixel.

If bpp is 0, it is treated as the current display bits per pixel.

The flags parameter is the same as the flags field of the SDL_Surface structure. OR'd combinations of the following values are valid.

SDL_SWSURFACE
Create the video surface in system memory

SDL_HWSURFACE
Create the video surface in video memory

SDL_ASYNCBLIT
Enables the use of asynchronous updates of the display surface. This will usually slow down blitting on single CPU machines, but may provide a speed increase on SMP systems.

SDL_ANYFORMAT
Normally, if a video surface of the requested bits-per-pixel (bpp) is not available, SDL will emulate one with a shadow surface. Passing SDL_ANYFORMAT prevents this and causes SDL to use the video surface, regardless of its pixel depth.

SDL_HWPALETTE
Give SDL exclusive palette access. Without this flag you may not always get the the colors you request with SDL_SetColors or SDL_SetPalette.

SDL_DOUBLEBUF
Enable hardware double buffering; only valid with SDL_HWSURFACE. Calling SDL_Flip will flip the buffers and update the screen. All drawing will take place on the surface that is not displayed at the moment. If double buffering could not be enabled then SDL_Flip will just perform a SDL_UpdateRect on the entire screen.

SDL_FULLSCREEN
SDL will attempt to use a fullscreen mode. If a hardware resolution change is not possible (for whatever reason), the next higher resolution will be used and the display window centered on a black background.

SDL_OPENGL
Create an OpenGL rendering context. You should have previously set OpenGL video attributes with SDL_GL_SetAttribute.

SDL_OPENGLBLIT
Create an OpenGL rendering context, like above, but allow normal blitting operations. The screen (2D) surface may have an alpha channel, and SDL_UpdateRects must be used for updating changes to the screen surface.

SDL_RESIZABLE
Create a resizable window. When the window is resized by the user a SDL_VIDEORESIZE event is generated and SDL_SetVideoMode can be called again with the new size.

SDL_NOFRAME
If possible, SDL_NOFRAME causes SDL to create a window with no title bar or frame decoration. Fullscreen modes automatically have this flag set.

Note: Whatever flags SDL_SetVideoMode could satisfy are set in the flags member of the returned surface.

Note: The bpp parameter is the number of bits per pixel, so a bpp of 24 uses the packed representation of 3 bytes/pixel. For the more common 4 bytes/pixel mode, use a bpp of 32. Somewhat oddly, both 15 and 16 will request a 2 bytes/pixel mode, but different pixel formats.

Return Value

The framebuffer surface, or NULL if it fails. The surface returned is freed by SDL_Quit() and should nt be freed by the caller.

See Also

SDL_LockSurface, SDL_SetColors, SDL_Flip, SDL_Surface

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SDL_VideoModeOK | Up | SDL_UpdateRect

SDL Library Documentation

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SDL_UpdateRect

Name

SDL_UpdateRect -- Makes sure the given area is updated on the given screen.

Synopsis

#include "SDL.h"

void SDL_UpdateRect(SDL_Surface *screen, Sint32 x, Sint32 y, Sint32 w, Sint32 h);

Description

Makes sure the given area is updated on the given screen. The rectangle must be confined within the screen boundaries (no clipping is done).

If 'x', 'y', 'w' and 'h' are all 0, SDL_UpdateRect will update the entire screen.

This function should not be called while 'screen' is locked.

See Also

SDL_UpdateRects, SDL_Rect, SDL_Surface, SDL_LockSurface

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SDL_SetVideoMode | Up | SDL_UpdateRects

SDL Library Documentation

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SDL_UpdateRects

Name

SDL_UpdateRects -- Makes sure the given list of rectangles is updated on the given screen.

Synopsis

#include "SDL.h"

void SDL_UpdateRects(SDL_Surface *screen, int numrects, SDL_Rect *rects);

Description

Makes sure the given list of rectangles is updated on the given screen. The rectangles must all be confined within the screen boundaries (no clipping is done).

This function should not be called while screen is locked.

Note: It is adviced to call this function only once per frame, since each call has some processing overhead. This is no restriction since you can pass any number of rectangles each time.

The rectangles are not automatically merged or checked for overlap. In general, the programmer can use his knowledge about his particular rectangles to merge them in an efficient way, to avoid overdraw.

See Also

SDL_UpdateRect, SDL_Rect, SDL_Surface, SDL_LockSurface

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SDL_UpdateRect | Up | SDL_Flip

SDL Library Documentation

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SDL_Flip

Name

SDL_Flip -- Swaps screen buffers

Synopsis

#include "SDL.h"

int SDL_Flip(SDL_Surface *screen);

Description

On hardware that supports double-buffering, this function sets up a flip and returns. The hardware will wait for vertical retrace, and then swap video buffers before the next video surface blit or lock will return. On hardware that doesn't support double-buffering, this is equivalent to calling SDL_UpdateRect(screen, 0, 0, 0, 0)

The SDL_DOUBLEBUF flag must have been passed to SDL_SetVideoMode, when setting the video mode for this function to perform hardware flipping.

Return Value

This function returns 0 if successful, or -1 if there was an error.

See Also

SDL_SetVideoMode, SDL_UpdateRect, SDL_Surface

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SDL_UpdateRects | Up | SDL_SetColors

SDL Library Documentation

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SDL_SetColors

Name

SDL_SetColors -- Sets a portion of the colormap for the given 8-bit surface.

Synopsis

#include "SDL.h"

int SDL_SetColors(SDL_Surface *surface, SDL_Color *colors, int firstcolor, int ncolors);

Description

Sets a portion of the colormap for the given 8-bit surface.

When surface is the surface associated with the current display, the display colormap will be updated with the requested colors. If SDL_HWPALETTE was set in SDL_SetVideoMode flags, SDL_SetColors will always return 1, and the palette is guaranteed to be set the way you desire, even if the window colormap has to be warped or run under emulation.

The color components of a SDL_Color structure are 8-bits in size, giving you a total of 256³ =16777216 colors.

Palettized (8-bit) screen surfaces with the SDL_HWPALETTE flag have two palettes, a logical palette that is used for mapping blits to/from the surface and a physical palette (that determines how the hardware will map the colors to the display). SDL_SetColors modifies both palettes (if present), and is equivalent to calling SDL_SetPalette with the flags set to (SDL_LOGPAL | SDL_PHYSPAL).

Return Value

If surface is not a palettized surface, this function does nothing, returning 0. If all of the colors were set as passed to SDL_SetColors, it will return 1. If not all the color entries were set exactly as given, it will return 0, and you should look at the surface palette to determine the actual color palette.

Example

/* Create a display surface with a grayscale palette */
SDL_Surface *screen;
SDL_Color colors[256];
int i;
.
.
.
/* Fill colors with color information */
for(i=0;i<256;i++){
  colors[i].r=i;
  colors[i].g=i;
  colors[i].b=i;
}

/* Create display */
screen=SDL_SetVideoMode(640, 480, 8, SDL_HWPALETTE);
if(!screen){
  printf("Couldn't set video mode: %s\n", SDL_GetError());
  exit(-1);
}

/* Set palette */
SDL_SetColors(screen, colors, 0, 256);
.
.
.
.

See Also

SDL_Color SDL_Surface, SDL_SetPalette, SDL_SetVideoMode

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SDL_Flip | Up | SDL_SetPalette

SDL Library Documentation

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SDL_SetPalette

Name

SDL_SetPalette -- Sets the colors in the palette of an 8-bit surface.

Synopsis

#include "SDL.h"

int SDL_SetPalette(SDL_Surface *surface, int flags, SDL_Color *colors, int firstcolor, int ncolors);

Description

Sets a portion of the palette for the given 8-bit surface.

Palettized (8-bit) screen surfaces with the SDL_HWPALETTE flag have two palettes, a logical palette that is used for mapping blits to/from the surface and a physical palette (that determines how the hardware will map the colors to the display). SDL_BlitSurface always uses the logical palette when blitting surfaces (if it has to convert between surface pixel formats). Because of this, it is often useful to modify only one or the other palette to achieve various special color effects (e.g., screen fading, color flashes, screen dimming).

This function can modify either the logical or physical palette by specifing SDL_LOGPAL or SDL_PHYSPALthe in the flags parameter.

When surface is the surface associated with the current display, the display colormap will be updated with the requested colors. If SDL_HWPALETTE was set in SDL_SetVideoMode flags, SDL_SetPalette will always return 1, and the palette is guaranteed to be set the way you desire, even if the window colormap has to be warped or run under emulation.

The color components of a SDL_Color structure are 8-bits in size, giving you a total of 256³=16777216 colors.

Return Value

If surface is not a palettized surface, this function does nothing, returning 0. If all of the colors were set as passed to SDL_SetPalette, it will return 1. If not all the color entries were set exactly as given, it will return 0, and you should look at the surface palette to determine the actual color palette.

Example

        /* Create a display surface with a grayscale palette */
        SDL_Surface *screen;
        SDL_Color colors[256];
        int i;
        .
        .
        .
        /* Fill colors with color information */
        for(i=0;i<256;i++){
          colors[i].r=i;
          colors[i].g=i;
          colors[i].b=i;
        }

        /* Create display */
        screen=SDL_SetVideoMode(640, 480, 8, SDL_HWPALETTE);
        if(!screen){
          printf("Couldn't set video mode: %s\n", SDL_GetError());
          exit(-1);
        }

        /* Set palette */
        SDL_SetPalette(screen, SDL_LOGPAL|SDL_PHYSPAL, colors, 0, 256);
        .
        .
        .
        .

See Also

SDL_SetColors, SDL_SetVideoMode, SDL_Surface, SDL_Color

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SDL_SetColors | Up | SDL_SetGamma

SDL Library Documentation

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SDL_SetGamma

Name

SDL_SetGamma -- Sets the color gamma function for the display

Synopsis

#include "SDL.h"

int SDL_SetGamma(float redgamma, float greengamma, float bluegamma);

Description

Sets the "gamma function" for the display of each color component. Gamma controls the brightness/contrast of colors displayed on the screen. A gamma value of 1.0 is identity (i.e., no adjustment is made).

This function adjusts the gamma based on the "gamma function" parameter, you can directly specify lookup tables for gamma adjustment with SDL_SetGammaRamp.

Not all display hardware is able to change gamma.

Return Value

Returns -1 on error (or if gamma adjustment is not supported).

See Also

SDL_GetGammaRamp SDL_SetGammaRamp

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SDL_SetPalette | Up | SDL_GetGammaRamp

SDL Library Documentation

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SDL_GetGammaRamp

Name

SDL_GetGammaRamp -- Gets the color gamma lookup tables for the display

Synopsis

#include "SDL.h"

int SDL_GetGammaRamp(Uint16 *redtable, Uint16 *greentable, Uint16 *bluetable);

Description

Gets the gamma translation lookup tables currently used by the display. Each table is an array of 256 Uint16 values.

Not all display hardware is able to change gamma.

Return Value

Returns -1 on error.

See Also

SDL_SetGamma SDL_SetGammaRamp

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SDL_SetGamma | Up | SDL_SetGammaRamp

SDL Library Documentation

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SDL_SetGammaRamp

Name

SDL_SetGammaRamp -- Sets the color gamma lookup tables for the display

Synopsis

#include "SDL.h"

int SDL_SetGammaRamp(Uint16 *redtable, Uint16 *greentable, Uint16 *bluetable);

Description

Sets the gamma lookup tables for the display for each color component. Each table is an array of 256 Uint16 values, representing a mapping between the input and output for that channel. The input is the index into the array, and the output is the 16-bit gamma value at that index, scaled to the output color precision. You may pass NULL to any of the channels to leave them unchanged.

This function adjusts the gamma based on lookup tables, you can also have the gamma calculated based on a "gamma function" parameter with SDL_SetGamma.

Not all display hardware is able to change gamma.

Return Value

Returns -1 on error (or if gamma adjustment is not supported).

See Also

SDL_SetGamma SDL_GetGammaRamp

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SDL_GetGammaRamp | Up | SDL_MapRGB

SDL Library Documentation

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SDL_MapRGB

Name

SDL_MapRGB -- Map a RGB color value to a pixel format.

Synopsis

#include "SDL.h"

Uint32 SDL_MapRGB(SDL_PixelFormat *fmt, Uint8 r, Uint8 g, Uint8 b);

Description

Maps the RGB color value to the specified pixel format and returns the pixel value as a 32-bit int.

If the format has a palette (8-bit) the index of the closest matching color in the palette will be returned.

If the specified pixel format has an alpha component it will be returned as all 1 bits (fully opaque).

Return Value

A pixel value best approximating the given RGB color value for a given pixel format. If the pixel format bpp (color depth) is less than 32-bpp then the unused upper bits of the return value can safely be ignored (e.g., with a 16-bpp format the return value can be assigned to a Uint16, and similarly a Uint8 for an 8-bpp format).

See Also

SDL_GetRGB, SDL_GetRGBA, SDL_MapRGBA, SDL_PixelFormat

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SDL_SetGammaRamp | Up | SDL_MapRGBA

SDL Library Documentation

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SDL_MapRGBA

Name

SDL_MapRGBA -- Map a RGBA color value to a pixel format.

Synopsis

#include "SDL.h"

Uint32 SDL_MapRGBA(SDL_PixelFormat *fmt, Uint8 r, Uint8 g, Uint8 b, Uint8 a);

Description

Maps the RGBA color value to the specified pixel format and returns the pixel value as a 32-bit int.

If the format has a palette (8-bit) the index of the closest matching color in the palette will be returned.

If the specified pixel format has no alpha component the alpha value will be ignored (as it will be in formats with a palette).

Return Value

A pixel value best approximating the given RGBA color value for a given pixel format. If the pixel format bpp (color depth) is less than 32-bpp then the unused upper bits of the return value can safely be ignored (e.g., with a 16-bpp format the return value can be assigned to a Uint16, and similarly a Uint8 for an 8-bpp format).

See Also

SDL_GetRGB, SDL_GetRGBA, SDL_MapRGB, SDL_PixelFormat

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SDL_MapRGB | Up | SDL_GetRGB

SDL Library Documentation

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SDL_GetRGB

Name

SDL_GetRGB -- Get RGB values from a pixel in the specified pixel format.

Synopsis

#include "SDL.h"

void SDL_GetRGB(Uint32 pixel, SDL_PixelFormat *fmt, Uint8 *r, Uint8 *g, Uint8 *b);

Description

Get RGB component values from a pixel stored in the specified pixel format.

This function uses the entire 8-bit [0..255] range when converting color components from pixel formats with less than 8-bits per RGB component (e.g., a completely white pixel in 16-bit RGB565 format would return [0xff, 0xff, 0xff] not [0xf8, 0xfc, 0xf8]).

See Also

SDL_GetRGBA, SDL_MapRGB, SDL_MapRGBA, SDL_PixelFormat

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SDL_MapRGBA | Up | SDL_GetRGBA

SDL Library Documentation

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SDL_GetRGBA

Name

SDL_GetRGBA -- Get RGBA values from a pixel in the specified pixel format.

Synopsis

#include "SDL.h"

void SDL_GetRGBA(Uint32 pixel, SDL_PixelFormat *fmt, Uint8 *r, Uint8 *g, Uint8 *b, Uint8 *a);

Description

Get RGBA component values from a pixel stored in the specified pixel format.

This function uses the entire 8-bit [0..255] range when converting color components from pixel formats with less than 8-bits per RGB component (e.g., a completely white pixel in 16-bit RGB565 format would return [0xff, 0xff, 0xff] not [0xf8, 0xfc, 0xf8]).

If the surface has no alpha component, the alpha will be returned as 0xff (100% opaque).

See Also

SDL_GetRGB, SDL_MapRGB, SDL_MapRGBA, SDL_PixelFormat

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SDL_GetRGB | Up | SDL_CreateRGBSurface

SDL Library Documentation

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SDL_CreateRGBSurface

Name

SDL_CreateRGBSurface -- Create an empty SDL_Surface

Synopsis

#include "SDL.h"

SDL_Surface *SDL_CreateRGBSurface(Uint32 flags, int width, int height, int depth, Uint32 Rmask, Uint32 Gmask, Uint32 Bmask, Uint32 Amask);

Description

Allocate an empty surface (must be called after SDL_SetVideoMode)

If depth is 8 bits an empty palette is allocated for the surface, otherwise a 'packed-pixel' SDL_PixelFormat is created using the [RGBA]mask's provided (see SDL_PixelFormat). The flags specifies the type of surface that should be created, it is an OR'd combination of the following possible values.

SDL_SWSURFACE | SDL will create the surface in system memory. This improves the performance of pixel level access, however you may not be able to take advantage of some types of hardware blitting.
SDL_HWSURFACE | SDL will attempt to create the surface in video memory. This will allow SDL to take advantage of Video->Video blits (which are often accelerated).
SDL_SRCCOLORKEY | This flag turns on colourkeying for blits from this surface. If SDL_HWSURFACE is also specified and colourkeyed blits are hardware-accelerated, then SDL will attempt to place the surface in video memory. Use SDL_SetColorKey to set or clear this flag after surface creation.
SDL_SRCALPHA | This flag turns on alpha-blending for blits from this surface. If SDL_HWSURFACE is also specified and alpha-blending blits are hardware-accelerated, then the surface will be placed in video memory if possible. Use SDL_SetAlpha to set or clear this flag after surface creation.

Note: If an alpha-channel is specified (that is, if Amask is nonzero), then the SDL_SRCALPHA flag is automatically set. You may remove this flag by calling SDL_SetAlpha after surface creation.

Return Value

Returns the created surface, or NULL upon error.

Example

    /* Create a 32-bit surface with the bytes of each pixel in R,G,B,A order,
       as expected by OpenGL for textures */
    SDL_Surface *surface;
    Uint32 rmask, gmask, bmask, amask;

    /* SDL interprets each pixel as a 32-bit number, so our masks must depend
       on the endianness (byte order) of the machine */
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
    rmask = 0xff000000;
    gmask = 0x00ff0000;
    bmask = 0x0000ff00;
    amask = 0x000000ff;
#else
    rmask = 0x000000ff;
    gmask = 0x0000ff00;
    bmask = 0x00ff0000;
    amask = 0xff000000;
#endif

    surface = SDL_CreateRGBSurface(SDL_SWSURFACE, width, height, 32,
                                   rmask, gmask, bmask, amask);
    if(surface == NULL) {
        fprintf(stderr, "CreateRGBSurface failed: %s\n", SDL_GetError());
        exit(1);
    }

See Also

SDL_CreateRGBSurfaceFrom, SDL_FreeSurface, SDL_SetVideoMode, SDL_LockSurface, SDL_PixelFormat, SDL_Surface SDL_SetAlpha SDL_SetColorKey

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SDL_GetRGBA | Up | SDL_CreateRGBSurfaceFrom

SDL Library Documentation

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SDL_CreateRGBSurfaceFrom

Name

SDL_CreateRGBSurfaceFrom -- Create an SDL_Surface from pixel data

Synopsis

#include "SDL.h"

SDL_Surface *SDL_CreateRGBSurfaceFrom(void *pixels, int width, int height, int depth, int pitch, Uint32 Rmask, Uint32 Gmask, Uint32 Bmask, Uint32 Amask);

Description

Creates an SDL_Surface from the provided pixel data.

The data stored in pixels is assumed to be of the depth specified in the parameter list. The pixel data is not copied into the SDL_Surface structure so it should not be freed until the surface has been freed with a called to SDL_FreeSurface. pitch is the length of each scanline in bytes.

See SDL_CreateRGBSurface for a more detailed description of the other parameters.

Return Value

Returns the created surface, or NULL upon error.

See Also

SDL_CreateRGBSurface, SDL_FreeSurface

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SDL_CreateRGBSurface | Up | SDL_FreeSurface

SDL Library Documentation

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SDL_FreeSurface

Name

SDL_FreeSurface -- Frees (deletes) a SDL_Surface

Synopsis

#include "SDL.h"

void SDL_FreeSurface(SDL_Surface *surface);

Description

Frees the resources used by a previously created SDL_Surface. If the surface was created using SDL_CreateRGBSurfaceFrom then the pixel data is not freed.

See Also

SDL_CreateRGBSurface SDL_CreateRGBSurfaceFrom

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SDL_CreateRGBSurfaceFrom | Up | SDL_LockSurface

SDL Library Documentation

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SDL_LockSurface

Name

SDL_LockSurface -- Lock a surface for directly access.

Synopsis

#include "SDL.h"

int SDL_LockSurface(SDL_Surface *surface);

Description

SDL_LockSurface sets up a surface for directly accessing the pixels. Between calls to SDL_LockSurface and SDL_UnlockSurface, you can write to and read from surface->pixels, using the pixel format stored in surface->format. Once you are done accessing the surface, you should use SDL_UnlockSurface to release it.

Not all surfaces require locking. If SDL_MUSTLOCK(surface) evaluates to 0, then you can read and write to the surface at any time, and the pixel format of the surface will not change.

No operating system or library calls should be made between lock/unlock pairs, as critical system locks may be held during this time.

It should be noted, that since SDL 1.1.8 surface locks are recursive. This means that you can lock a surface multiple times, but each lock must have a match unlock.

    .
    .
    SDL_LockSurface( surface );
    .
    /* Surface is locked */
    /* Direct pixel access on surface here */
    .
    SDL_LockSurface( surface );
    .
    /* More direct pixel access on surface */
    .
    SDL_UnlockSurface( surface );
    /* Surface is still locked */
    /* Note: Is versions < 1.1.8, the surface would have been */
    /* no longer locked at this stage                         */
    .
    SDL_UnlockSurface( surface );
    /* Surface is now unlocked */
    .
    .

Return Value

SDL_LockSurface returns 0, or -1 if the surface couldn't be locked.

See Also

SDL_UnlockSurface

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SDL_FreeSurface | Up | SDL_UnlockSurface

SDL Library Documentation

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SDL_UnlockSurface

Name

SDL_UnlockSurface -- Unlocks a previously locked surface.

Synopsis

#include "SDL.h"

void SDL_UnlockSurface(SDL_Surface *surface);

Description

Surfaces that were previously locked using SDL_LockSurface must be unlocked with SDL_UnlockSurface. Surfaces should be unlocked as soon as possible.

It should be noted that since 1.1.8, surface locks are recursive. See SDL_LockSurface.

See Also

SDL_LockSurface

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SDL_LockSurface | Up | SDL_LoadBMP

SDL Library Documentation

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SDL_LoadBMP

Name

SDL_LoadBMP -- Load a Windows BMP file into an SDL_Surface.

Synopsis

#include "SDL.h"

SDL_Surface *SDL_LoadBMP(const char *file);

Description

Loads a surface from a named Windows BMP file.

Return Value

Returns the new surface, or NULL if there was an error.

See Also

SDL_SaveBMP

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SDL_UnlockSurface | Up | SDL_SaveBMP

SDL Library Documentation

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SDL_SaveBMP

Name

SDL_SaveBMP -- Save an SDL_Surface as a Windows BMP file.

Synopsis

#include "SDL.h"

int SDL_SaveBMP(SDL_Surface *surface, const char *file);

Description

Saves the SDL_Surface surface as a Windows BMP file named file.

Return Value

Returns 0 if successful or -1 if there was an error.

See Also

SDL_LoadBMP

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SDL_LoadBMP | Up | SDL_SetColorKey

SDL Library Documentation

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SDL_SetColorKey

Name

SDL_SetColorKey -- Sets the color key (transparent pixel) in a blittable surface and RLE acceleration.

Synopsis

#include "SDL.h"

int SDL_SetColorKey(SDL_Surface *surface, Uint32 flag, Uint32 key);

Description

Sets the color key (transparent pixel) in a blittable surface and enables or disables RLE blit acceleration.

RLE acceleration can substantially speed up blitting of images with large horizontal runs of transparent pixels (i.e., pixels that match the key value). The key must be of the same pixel format as the surface, SDL_MapRGB is often useful for obtaining an acceptable value.

If flag is SDL_SRCCOLORKEY then key is the transparent pixel value in the source image of a blit.

If flag is OR'd with SDL_RLEACCEL then the surface will be draw using RLE acceleration when drawn with SDL_BlitSurface. The surface will actually be encoded for RLE acceleration the first time SDL_BlitSurface or SDL_DisplayFormat is called on the surface.

If flag is 0, this function clears any current color key.

Return Value

This function returns 0, or -1 if there was an error.

See Also

SDL_BlitSurface, SDL_DisplayFormat, SDL_MapRGB, SDL_SetAlpha

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SDL_SaveBMP | Up | SDL_SetAlpha

SDL Library Documentation

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SDL_SetAlpha

Name

SDL_SetAlpha -- Adjust the alpha properties of a surface

Synopsis

#include "SDL.h"

int SDL_SetAlpha(SDL_Surface *surface, Uint32 flag, Uint8 alpha);

Description

Note: This function and the semantics of SDL alpha blending have changed since version 1.1.4. Up until version 1.1.5, an alpha value of 0 was considered opaque and a value of 255 was considered transparent. This has now been inverted: 0 (SDL_ALPHA_TRANSPARENT) is now considered transparent and 255 (SDL_ALPHA_OPAQUE) is now considered opaque.

SDL_SetAlpha is used for setting the per-surface alpha value and/or enabling and disabling alpha blending.

Thesurface parameter specifies which surface whose alpha attributes you wish to adjust. flags is used to specify whether alpha blending should be used (SDL_SRCALPHA) and whether the surface should use RLE acceleration for blitting (SDL_RLEACCEL). flags can be an OR'd combination of these two options, one of these options or 0. If SDL_SRCALPHA is not passed as a flag then all alpha information is ignored when blitting the surface. The alpha parameter is the per-surface alpha value; a surface need not have an alpha channel to use per-surface alpha and blitting can still be accelerated with SDL_RLEACCEL.

Note: The per-surface alpha value of 128 is considered a special case and is optimised, so it's much faster than other per-surface values.

Alpha effects surface blitting in the following ways:

RGBA->RGB with SDL_SRCALPHA

The source is alpha-blended with the destination, using the alpha channel. SDL_SRCCOLORKEY and the per-surface alpha are ignored.

RGBA->RGB without SDL_SRCALPHA

The RGB data is copied from the source. The source alpha channel and the per-surface alpha value are ignored.

RGB->RGBA with SDL_SRCALPHA

The source is alpha-blended with the destination using the per-surface alpha value. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied. The alpha channel of the copied pixels is set to opaque.

RGB->RGBA without SDL_SRCALPHA

The RGB data is copied from the source and the alpha value of the copied pixels is set to opaque. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied.

RGBA->RGBA with SDL_SRCALPHA

The source is alpha-blended with the destination using the source alpha channel. The alpha channel in the destination surface is left untouched. SDL_SRCCOLORKEY is ignored.

RGBA->RGBA without SDL_SRCALPHA

The RGBA data is copied to the destination surface. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied.

RGB->RGB with SDL_SRCALPHA

The source is alpha-blended with the destination using the per-surface alpha value. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied.

RGB->RGB without SDL_SRCALPHA

The RGB data is copied from the source. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied.

Note: Note that RGBA->RGBA blits (with SDL_SRCALPHA set) keep the alpha of the destination surface. This means that you cannot compose two arbitrary RGBA surfaces this way and get the result you would expect from "overlaying" them; the destination alpha will work as a mask.

Also note that per-pixel and per-surface alpha cannot be combined; the per-pixel alpha is always used if available

Return Value

This function returns 0, or -1 if there was an error.

See Also

SDL_MapRGBA, SDL_GetRGBA, SDL_DisplayFormatAlpha, SDL_BlitSurface

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SDL_SetColorKey | Up | SDL_SetClipRect

SDL Library Documentation

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SDL_SetClipRect

Name

SDL_SetClipRect -- Sets the clipping rectangle for a surface.

Synopsis

#include "SDL.h"

void SDL_SetClipRect(SDL_Surface *surface, SDL_Rect *rect);

Description

Sets the clipping rectangle for a surface. When this surface is the destination of a blit, only the area within the clip rectangle will be drawn into.

The rectangle pointed to by rect will be clipped to the edges of the surface so that the clip rectangle for a surface can never fall outside the edges of the surface.

If rect is NULL the clipping rectangle will be set to the full size of the surface.

See Also

SDL_GetClipRect, SDL_BlitSurface, SDL_Surface

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SDL_SetAlpha | Up | SDL_GetClipRect

SDL Library Documentation

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SDL_GetClipRect

Name

SDL_GetClipRect -- Gets the clipping rectangle for a surface.

Synopsis

#include "SDL.h"

void SDL_GetClipRect(SDL_Surface *surface, SDL_Rect *rect);

Description

Gets the clipping rectangle for a surface. When this surface is the destination of a blit, only the area within the clip rectangle is drawn into.

The rectangle pointed to by rect will be filled with the clipping rectangle of the surface.

See Also

SDL_SetClipRect, SDL_BlitSurface, SDL_Surface

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SDL_SetClipRect | Up | SDL_ConvertSurface

SDL Library Documentation

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SDL_ConvertSurface

Name

SDL_ConvertSurface -- Converts a surface to the same format as another surface.

Synopsis

#include "SDL/SDL.h"

SDL_Surface *SDL_ConvertSurface(SDL_Surface *src, SDL_PixelFormat *fmt, Uint32 flags);

Description

Creates a new surface of the specified format, and then copies and maps the given surface to it. If this function fails, it returns NULL.

The flags parameter is passed to SDL_CreateRGBSurface and has those semantics.

This function is used internally by SDL_DisplayFormat.

This function can only be called after SDL_Init.

Return Value

Returns either a pointer to the new surface, or NULL on error.

See Also

SDL_CreateRGBSurface, SDL_DisplayFormat, SDL_PixelFormat, SDL_Surface

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SDL_GetClipRect | Up | SDL_BlitSurface

SDL Library Documentation

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SDL_BlitSurface

Name

SDL_BlitSurface -- This performs a fast blit from the source surface to the destination surface.

Synopsis

#include "SDL.h"

int SDL_BlitSurface(SDL_Surface *src, SDL_Rect *srcrect, SDL_Surface *dst, SDL_Rect *dstrect);

Description

This performs a fast blit from the source surface to the destination surface.

Only the position is used in the dstrect (the width and height are ignored).

If either srcrect or dstrect are NULL, the entire surface (src or dst) is copied.

The final blit rectangle is saved in dstrect after all clipping is performed (srcrect is not modified).

The blit function should not be called on a locked surface.

The results of blitting operations vary greatly depending on whether SDL_SRCAPLHA is set or not. See SDL_SetAlpha for an explaination of how this affects your results. Colorkeying and alpha attributes also interact with surface blitting, as the following pseudo-code should hopefully explain.

if (source surface has SDL_SRCALPHA set) {
    if (source surface has alpha channel (that is, format->Amask != 0))
        blit using per-pixel alpha, ignoring any colour key
    else {
        if (source surface has SDL_SRCCOLORKEY set)
            blit using the colour key AND the per-surface alpha value
        else
            blit using the per-surface alpha value
    }
} else {
    if (source surface has SDL_SRCCOLORKEY set)
        blit using the colour key
    else
        ordinary opaque rectangular blit
}

Return Value

If the blit is successful, it returns 0, otherwise it returns -1.

If either of the surfaces were in video memory, and the blit returns -2, the video memory was lost, so it should be reloaded with artwork and re-blitted:

        while ( SDL_BlitSurface(image, imgrect, screen, dstrect) == -2 ) {
                while ( SDL_LockSurface(image)) < 0 )
                        Sleep(10);
                -- Write image pixels to image->pixels --
                SDL_UnlockSurface(image);
        }

This happens under DirectX 5.0 when the system switches away from your fullscreen application. Locking the surface will also fail until you have access to the video memory again.

See Also

SDL_LockSurface, SDL_FillRect, SDL_Surface, SDL_Rect

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SDL_ConvertSurface | Up | SDL_FillRect

SDL Library Documentation

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SDL_FillRect

Name

SDL_FillRect -- This function performs a fast fill of the given rectangle with some color

Synopsis

#include "SDL.h"

int SDL_FillRect(SDL_Surface *dst, SDL_Rect *dstrect, Uint32 color);

Description

This function performs a fast fill of the given rectangle with color. If dstrect is NULL, the whole surface will be filled with color.

The color should be a pixel of the format used by the surface, and can be generated by the SDL_MapRGB or SDL_MapRGBA functions. If the color value contains an alpha value then the destination is simply "filled" with that alpha information, no blending takes place.

If there is a clip rectangle set on the destination (set via SDL_SetClipRect) then this function will clip based on the intersection of the clip rectangle and the dstrect rectangle and the dstrect rectangle will be modified to represent the area actually filled.

Return Value

This function returns 0 on success, or -1 on error.

See Also

SDL_MapRGB, SDL_MapRGBA, SDL_BlitSurface, SDL_Rect

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SDL_BlitSurface | Up | SDL_DisplayFormat

SDL Library Documentation

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SDL_DisplayFormat

Name

SDL_DisplayFormat -- Convert a surface to the display format

Synopsis

#include "SDL.h"

SDL_Surface *SDL_DisplayFormat(SDL_Surface *surface);

Description

This function takes a surface and copies it to a new surface of the pixel format and colors of the video framebuffer, suitable for fast blitting onto the display surface. It calls SDL_ConvertSurface

If you want to take advantage of hardware colorkey or alpha blit acceleration, you should set the colorkey and alpha value before calling this function.

If you want an alpha channel, see SDL_DisplayFormatAlpha.

Return Value

If the conversion fails or runs out of memory, it returns NULL

See Also

SDL_ConvertSurface, SDL_DisplayFormatAlpha SDL_SetAlpha, SDL_SetColorKey, SDL_Surface

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SDL_FillRect | Up | SDL_DisplayFormatAlpha

SDL Library Documentation

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SDL_DisplayFormatAlpha

Name

SDL_DisplayFormatAlpha -- Convert a surface to the display format

Synopsis

#include "SDL.h"

SDL_Surface *SDL_DisplayFormatAlpha(SDL_Surface *surface);

Description

This function takes a surface and copies it to a new surface of the pixel format and colors of the video framebuffer plus an alpha channel, suitable for fast blitting onto the display surface. It calls SDL_ConvertSurface

If you want to take advantage of hardware colorkey or alpha blit acceleration, you should set the colorkey and alpha value before calling this function.

This function can be used to convert a colourkey to an alpha channel, if the SDL_SRCCOLORKEY flag is set on the surface. The generated surface will then be transparent (alpha=0) where the pixels match the colourkey, and opaque (alpha=255) elsewhere.

Return Value

If the conversion fails or runs out of memory, it returns NULL

See Also

SDL_ConvertSurface, SDL_SetAlpha, SDL_SetColorKey, SDL_DisplayFormat, SDL_Surface

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SDL_DisplayFormat | Up | SDL_WarpMouse

SDL Library Documentation

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SDL_WarpMouse

Name

SDL_WarpMouse -- Set the position of the mouse cursor.

Synopsis

#include "SDL.h"

void SDL_WarpMouse(Uint16 x, Uint16 y);

Description

Set the position of the mouse cursor (generates a mouse motion event).

See Also

SDL_MouseMotionEvent

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SDL_DisplayFormatAlpha | Up | SDL_CreateCursor

SDL Library Documentation

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SDL_CreateCursor

Name

SDL_CreateCursor -- Creates a new mouse cursor.

Synopsis

#include "SDL.h"

SDL_Cursor *SDL_CreateCursor(Uint8 *data, Uint8 *mask, int w, int h, int hot_x, int hot_y);

Description

Create a cursor using the specified data and mask (in MSB format). The cursor width must be a multiple of 8 bits.

The cursor is created in black and white according to the following:

Data / Mask | Resulting pixel on screen
0 / 1 | White
1 / 1 | Black
0 / 0 | Transparent
1 / 0 | Inverted color if possible, black if not.

Cursors created with this function must be freed with SDL_FreeCursor.

Example

/* Stolen from the mailing list */
/* Creates a new mouse cursor from an XPM */

/* XPM */
static const char *arrow[] = {
  /* width height num_colors chars_per_pixel */
  "    32    32        3            1",
  /* colors */
  "X c #000000",
  ". c #ffffff",
  "  c None",
  /* pixels */
  "X                               ",
  "XX                              ",
  "X.X                             ",
  "X..X                            ",
  "X...X                           ",
  "X....X                          ",
  "X.....X                         ",
  "X......X                        ",
  "X.......X                       ",
  "X........X                      ",
  "X.....XXXXX                     ",
  "X..X..X                         ",
  "X.X X..X                        ",
  "XX  X..X                        ",
  "X    X..X                       ",
  "     X..X                       ",
  "      X..X                      ",
  "      X..X                      ",
  "       XX                       ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "                                ",
  "0,0"
};

static SDL_Cursor *init_system_cursor(const char *image[])
{
  int i, row, col;
  Uint8 data[4*32];
  Uint8 mask[4*32];
  int hot_x, hot_y;

  i = -1;
  for ( row=0; row<32; ++row ) {
    for ( col=0; col<32; ++col ) {
      if ( col % 8 ) {
        data[i] <<= 1;
        mask[i] <<= 1;
      } else {
        ++i;
        data[i] = mask[i] = 0;
      }
      switch (image[4+row][col]) {
        case 'X':
          data[i] |= 0x01;
          k[i] |= 0x01;
          break;
        case '.':
          mask[i] |= 0x01;
          break;
        case ' ':
          break;
      }
    }
  }
  sscanf(image[4+row], "%d,%d", &hot_x, &hot_y);
  return SDL_CreateCursor(data, mask, 32, 32, hot_x, hot_y);
}

See Also

SDL_FreeCursor, SDL_SetCursor, SDL_ShowCursor

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SDL_WarpMouse | Up | SDL_FreeCursor

SDL Library Documentation

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SDL_FreeCursor

Name

SDL_FreeCursor -- Frees a cursor created with SDL_CreateCursor.

Synopsis

#include "SDL.h"

void SDL_FreeCursor(SDL_Cursor *cursor);

Description

Frees a SDL_Cursor that was created using SDL_CreateCursor.

See Also

SDL_CreateCursor

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SDL_CreateCursor | Up | SDL_SetCursor

SDL Library Documentation

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SDL_SetCursor

Name

SDL_SetCursor -- Set the currently active mouse cursor.

Synopsis

#include "SDL.h"

void *SDL_SetCursor(SDL_Cursor *cursor);

Description

Sets the currently active cursor to the specified one. If the cursor is currently visible, the change will be immediately represented on the display.

See Also

SDL_GetCursor, SDL_CreateCursor, SDL_ShowCursor

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SDL_FreeCursor | Up | SDL_GetCursor

SDL Library Documentation

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SDL_GetCursor

Name

SDL_GetCursor -- Get the currently active mouse cursor.

Synopsis

#include "SDL.h"

SDL_Cursor *SDL_GetCursor(void);

Description

Returns the currently active mouse cursor.

See Also

SDL_SetCursor, SDL_CreateCursor, SDL_ShowCursor

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SDL_SetCursor | Up | SDL_ShowCursor

SDL Library Documentation

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SDL_ShowCursor

Name

SDL_ShowCursor -- Toggle whether or not the cursor is shown on the screen.

Synopsis

#include "SDL.h"

int SDL_ShowCursor(int toggle);

Description

Toggle whether or not the cursor is shown on the screen. Passing SDL_ENABLE displays the cursor and passing SDL_DISABLE hides it. The current state of the mouse cursor can be queried by passing SDL_QUERY, either SDL_DISABLE or SDL_ENABLE will be returned.

The cursor starts off displayed, but can be turned off.

Return Value

Returns the current state of the cursor.

See Also

SDL_CreateCursor, SDL_SetCursor

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SDL_GetCursor | Up | SDL_GL_LoadLibrary

SDL Library Documentation

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SDL_GL_LoadLibrary

Name

SDL_GL_LoadLibrary -- Specify an OpenGL library

Synopsis

#include "SDL.h"

int SDL_GL_LoadLibrary(const char *path);

Description

If you wish, you may load the OpenGL library at runtime, this must be done before SDL_SetVideoMode is called. The path of the GL library is passed to SDL_GL_LoadLibrary and it returns 0 on success, or -1 on an error. You must then use SDL_GL_GetProcAddress to retrieve function pointers to GL functions.

See Also

SDL_GL_GetProcAddress

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SDL_ShowCursor | Up | SDL_GL_GetProcAddress

SDL Library Documentation

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SDL_GL_GetProcAddress

Name

SDL_GL_GetProcAddress -- Get the address of a GL function

Synopsis

#include "SDL.h"

void *SDL_GL_GetProcAddress(const char* proc);

Description

Returns the address of the GL function proc, or NULL if the function is not found. If the GL library is loaded at runtime, with SDL_GL_LoadLibrary, then all GL functions must be retrieved this way. Usually this is used to retrieve function pointers to OpenGL extensions.

Example

typedef void (*GL_ActiveTextureARB_Func)(unsigned int);
GL_ActiveTextureARB_Func glActiveTextureARB_ptr = 0;
int has_multitexture=1;
.
.
.
/* Get function pointer */
glActiveTextureARB_ptr=(GL_ActiveTextureARB_Func) SDL_GL_GetProcAddress("glActiveTextureARB");

/* Check for a valid function ptr */
if(!glActiveTextureARB_ptr){
  fprintf(stderr, "Multitexture Extensions not present.\n");
  has_multitexture=0;
}
.
.
.
.
if(has_multitexture){
  glActiveTextureARB_ptr(GL_TEXTURE0_ARB);
  .
  .
}
else{
  .
  .
}

See Also

SDL_GL_LoadLibrary

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SDL_GL_LoadLibrary | Up | SDL_GL_GetAttribute

SDL Library Documentation

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SDL_GL_GetAttribute

Name

SDL_GL_GetAttribute -- Get the value of a special SDL/OpenGL attribute

Synopsis

#include "SDL.h"

int SDL_GL_GetAttribute(SDLGLattr attr, int *value);

Description

Places the value of the SDL/OpenGL attribute attr into value. This is useful after a call to SDL_SetVideoMode to check whether your attributes have been set as you expected.

Return Value

Returns 0 on success, or -1 on an error.

See Also

SDL_GL_SetAttribute, GL Attributes

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SDL_GL_GetProcAddress | Up | SDL_GL_SetAttribute

SDL Library Documentation

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SDL_GL_SetAttribute

Name

SDL_GL_SetAttribute -- Set a special SDL/OpenGL attribute

Synopsis

#include "SDL.h"

int SDL_GL_SetAttribute(SDL_GLattr attr, int value);

Description

Sets the OpenGL attribute attr to value. The attributes you set don't take effect until after a call to SDL_SetVideoMode. You should use SDL_GL_GetAttribute to check the values after a SDL_SetVideoMode call.

Return Value

Returns 0 on success, or -1 on error.

Example

SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
if ( (screen=SDL_SetVideoMode( 640, 480, 16, SDL_OPENGL )) == NULL ) {
  fprintf(stderr, "Couldn't set GL mode: %s\n", SDL_GetError());
  SDL_Quit();
  return;
}

Note: The SDL_DOUBLEBUF flag is not required to enable double buffering when setting an OpenGL video mode. Double buffering is enabled or disabled using the SDL_GL_DOUBLEBUFFER attribute.

See Also

SDL_GL_GetAttribute, GL Attributes

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SDL_GL_GetAttribute | Up | SDL_GL_SwapBuffers

SDL Library Documentation

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SDL_GL_SwapBuffers

Name

SDL_GL_SwapBuffers -- Swap OpenGL framebuffers/Update Display

Synopsis

#include "SDL.h"

void SDL_GL_SwapBuffers(void );

Description

Swap the OpenGL buffers, if double-buffering is supported.

See Also

SDL_SetVideoMode, SDL_GL_SetAttribute

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SDL_GL_SetAttribute | Up | SDL_CreateYUVOverlay

SDL Library Documentation

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SDL_CreateYUVOverlay

Name

SDL_CreateYUVOverlay -- Create a YUV video overlay

Synopsis

#include "SDL.h"

SDL_Overlay *SDL_CreateYUVOverlay(int width, int height, Uint32 format, SDL_Surface *display);

Description

SDL_CreateYUVOverlay creates a YUV overlay of the specified width, height and format (see SDL_Overlay for a list of available formats), for the provided display. A SDL_Overlay structure is returned.

The term 'overlay' is a misnomer since, unless the overlay is created in hardware, the contents for the display surface underneath the area where the overlay is shown will be overwritten when the overlay is displayed.

See Also

SDL_Overlay, SDL_DisplayYUVOverlay, SDL_FreeYUVOverlay

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SDL_GL_SwapBuffers | Up | SDL_LockYUVOverlay

SDL Library Documentation

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SDL_LockYUVOverlay

Name

SDL_LockYUVOverlay -- Lock an overlay

Synopsis

#include "SDL.h"

int SDL_LockYUVOverlay(SDL_Overlay *overlay);

Description

Much the same as SDL_LockSurface, SDL_LockYUVOverlay locks the overlay for direct access to pixel data.

Return Value

Returns 0 on success, or -1 on an error.

See Also

SDL_UnlockYUVOverlay, SDL_CreateYUVOverlay, SDL_Overlay

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SDL_CreateYUVOverlay | Up | SDL_UnlockYUVOverlay

SDL Library Documentation

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SDL_UnlockYUVOverlay

Name

SDL_UnlockYUVOverlay -- Unlock an overlay

Synopsis

#include "SDL.h"

void SDL_UnlockYUVOverlay(SDL_Overlay *overlay);

Description

The opposite to SDL_LockYUVOverlay. Unlocks a previously locked overlay. An overlay must be unlocked before it can be displayed.

See Also

SDL_UnlockYUVOverlay, SDL_CreateYUVOverlay, SDL_Overlay

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SDL_LockYUVOverlay | Up | SDL_DisplayYUVOverlay

SDL Library Documentation

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SDL_DisplayYUVOverlay

Name

SDL_DisplayYUVOverlay -- Blit the overlay to the display

Synopsis

#include "SDL.h"

int SDL_DisplayYUVOverlay(SDL_Overlay *overlay, SDL_Rect *dstrect);

Description

Blit the overlay to the surface specified when it was created. The SDL_Rect structure, dstrect, specifies the position and size of the destination. If the dstrect is a larger or smaller than the overlay then the overlay will be scaled, this is optimized for 2x scaling.

Return Values

Returns 0 on success

See Also

SDL_Overlay, SDL_CreateYUVOverlay

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SDL_UnlockYUVOverlay | Up | SDL_FreeYUVOverlay

SDL Library Documentation

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SDL_FreeYUVOverlay

Name

SDL_FreeYUVOverlay -- Free a YUV video overlay

Synopsis

#include "SDL.h"

void SDL_FreeYUVOverlay(SDL_Overlay *overlay);

Description

Frees and overlay created by SDL_CreateYUVOverlay.

See Also

SDL_Overlay, SDL_DisplayYUVOverlay, SDL_FreeYUVOverlay

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SDL_DisplayYUVOverlay | Up | SDL_GLattr

SDL Library Documentation

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SDL_GLattr

Name

SDL_GLattr -- SDL GL Attributes

Attributes

SDL_GL_RED_SIZE | Size of the framebuffer red component, in bits
SDL_GL_GREEN_SIZE | Size of the framebuffer green component, in bits
SDL_GL_BLUE_SIZE | Size of the framebuffer blue component, in bits
SDL_GL_ALPHA_SIZE | Size of the framebuffer alpha component, in bits
SDL_GL_DOUBLEBUFFER | 0 or 1, enable or disable double buffering
SDL_GL_BUFFER_SIZE | Size of the framebuffer, in bits
SDL_GL_DEPTH_SIZE | Size of the depth buffer, in bits
SDL_GL_STENCIL_SIZE | Size of the stencil buffer, in bits
SDL_GL_ACCUM_RED_SIZE | Size of the accumulation buffer red component, in bits
SDL_GL_ACCUM_GREEN_SIZE | Size of the accumulation buffer green component, in bits
SDL_GL_ACCUM_BLUE_SIZE | Size of the accumulation buffer blue component, in bits
SDL_GL_ACCUM_ALPHA_SIZE | Size of the accumulation buffer alpha component, in bits

Description

While you can set most OpenGL attributes normally, the attributes list above must be known before SDL sets the video mode. These attributes a set and read with SDL_GL_SetAttribute and SDL_GL_GetAttribute.

See Also

SDL_GL_SetAttribute, SDL_GL_GetAttribute

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SDL_FreeYUVOverlay | Up | SDL_Rect

SDL Library Documentation

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SDL_Rect

Name

SDL_Rect -- Defines a rectangular area

Structure Definition

typedef struct{
  Sint16 x, y;
  Uint16 w, h;
} SDL_Rect;

Structure Data

x, y | Position of the upper-left corner of the rectangle
w, h | The width and height of the rectangle

Description

A SDL_Rect defines a rectangular area of pixels. It is used by SDL_BlitSurface to define blitting regions and by several other video functions.

See Also

SDL_BlitSurface, SDL_UpdateRect

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SDL_GLattr | Up | SDL_Color

SDL Library Documentation

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SDL_Color

Name

SDL_Color -- Format independent color description

Structure Definition

typedef struct{
  Uint8 r;
  Uint8 g;
  Uint8 b;
  Uint8 unused;
} SDL_Color;

Structure Data

r | Red intensity
g | Green intensity
b | Blue intensity
unused | Unused

Description

SDL_Color describes a color in a format independent way. You can convert a SDL_Color to a pixel value for a certain pixel format using SDL_MapRGB.

See Also

SDL_PixelFormat, SDL_SetColors, SDL_Palette

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SDL_Rect | Up | SDL_Palette

SDL Library Documentation

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SDL_Palette

Name

SDL_Palette -- Color palette for 8-bit pixel formats

Structure Definition

typedef struct{
  int ncolors;
  SDL_Color *colors;
} SDL_Palette;

Structure Data

ncolors | Number of colors used in this palette
colors | Pointer to SDL_Color structures that make up the palette.

Description

Each pixel in an 8-bit surface is an index into the colors field of the SDL_Palette structure store in SDL_PixelFormat. A SDL_Palette should never need to be created manually. It is automatically created when SDL allocates a SDL_PixelFormat for a surface. The colors values of a SDL_Surfaces palette can be set with the SDL_SetColors.

See Also

SDL_Color, SDL_Surface, SDL_SetColors SDL_SetPalette

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SDL_Color | Up | SDL_PixelFormat

SDL Library Documentation

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SDL_PixelFormat

Name

SDL_PixelFormat -- Stores surface format information

Structure Definition

typedef struct{
  SDL_Palette *palette;
  Uint8  BitsPerPixel;
  Uint8  BytesPerPixel;
  Uint32 Rmask, Gmask, Bmask, Amask;
  Uint8  Rshift, Gshift, Bshift, Ashift;
  Uint8  Rloss, Gloss, Bloss, Aloss;
  Uint32 colorkey;
  Uint8  alpha;
} SDL_PixelFormat;

Structure Data

palette | Pointer to the palette, or NULL if the BitsPerPixel>8
BitsPerPixel | The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32.
BytesPerPixel | The number of bytes used to represent each pixel in a surface. Usually one to four.
[RGBA]mask | Binary mask used to retrieve individual color values
[RGBA]loss | Precision loss of each color component (2[RGBA]loss)
[RGBA]shift | Binary left shift of each color component in the pixel value
colorkey | Pixel value of transparent pixels
alpha | Overall surface alpha value

Description

A SDL_PixelFormat describes the format of the pixel data stored at the pixels field of a SDL_Surface. Every surface stores a SDL_PixelFormat in the format field.

If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential.

8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 BitsPerPixel and 1 BytesPerPixel. Since BytesPerPixel is 1, all pixels are represented by a Uint8 which contains an index into palette->colors. So, to determine the color of a pixel in a 8-bit surface: we read the color index from surface->pixels and we use that index to read the SDL_Color structure from surface->format->palette->colors. Like so:

SDL_Surface *surface;
SDL_PixelFormat *fmt;
SDL_Color *color;
Uint8 index;

.
.

/* Create surface */
.
.
fmt=surface->format;

/* Check the bitdepth of the surface */
if(fmt->BitsPerPixel!=8){
  fprintf(stderr, "Not an 8-bit surface.\n");
  return(-1);
}

/* Lock the surface */
SDL_LockSurface(surface);

/* Get the topleft pixel */
index=*(Uint8 *)surface->pixels;
color=fmt->palette->colors[index];

/* Unlock the surface */
SDL_UnlockSurface(surface);
printf("Pixel Color-> Red: %d, Green: %d, Blue: %d. Index: %d\n",
          color->r, color->g, color->b, index);
.
.

Pixel formats above 8-bit are an entirely different experience. They are considered to be "TrueColor" formats and the color information is stored in the pixels themselves, not in a palette. The mask, shift and loss fields tell us how the color information is encoded. The mask fields allow us to isolate each color component, the shift fields tell us the number of bits to the right of each component in the pixel value and the loss fields tell us the number of bits lost from each component when packing 8-bit color component in a pixel.

/* Extracting color components from a 32-bit color value */
SDL_PixelFormat *fmt;
SDL_Surface *surface;
Uint32 temp, pixel;
Uint8 red, green, blue, alpha;
.
.
.
fmt=surface->format;
SDL_LockSurface(surface);
pixel=*((Uint32*)surface->pixels);
SDL_UnlockSurface(surface);

/* Get Red component */
temp=pixel&fmt->Rmask; /* Isolate red component */
temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */
temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */
red=(Uint8)temp;

/* Get Green component */
temp=pixel&fmt->Gmask; /* Isolate green component */
temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */
temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */
green=(Uint8)temp;

/* Get Blue component */
temp=pixel&fmt->Bmask; /* Isolate blue component */
temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */
temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */
blue=(Uint8)temp;

/* Get Alpha component */
temp=pixel&fmt->Amask; /* Isolate alpha component */
temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */
temp=temp<<fmt->Aloss; /* Expand to a full 8-bit number */
alpha=(Uint8)temp;

printf("Pixel Color -> R: %d,  G: %d,  B: %d,  A: %d\n", red, green, blue, alpha);
.
.
.

See Also

SDL_Surface, SDL_MapRGB

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SDL_Palette | Up | SDL_Surface

SDL Library Documentation

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SDL_Surface

Name

SDL_Surface -- Graphical Surface Structure

Structure Definition

typedef struct SDL_Surface {
        Uint32 flags;                           /* Read-only */
        SDL_PixelFormat *format;                /* Read-only */
        int w, h;                               /* Read-only */
        Uint16 pitch;                           /* Read-only */
        void *pixels;                           /* Read-write */

        /* clipping information */
        SDL_Rect clip_rect;                     /* Read-only */

        /* Reference count -- used when freeing surface */
        int refcount;                           /* Read-mostly */

	/* This structure also contains private fields not shown here */
} SDL_Surface;

Structure Data

flags | Surface flags
format | Pixel format
w, h | Width and height of the surface
pitch | Length of a surface scanline in bytes
pixels | Pointer to the actual pixel data
clip_rect | surface clip rectangle

Description

SDL_Surface's represent areas of "graphical" memory, memory that can be drawn to. The video framebuffer is returned as a SDL_Surface by SDL_SetVideoMode and SDL_GetVideoSurface. Most of the fields should be pretty obvious. w and h are the width and height of the surface in pixels. pixels is a pointer to the actual pixel data, the surface should be locked before accessing this field. The clip_rect field is the clipping rectangle as set by SDL_SetClipRect.

The following are supported in the flags field.

SDL_SWSURFACE | Surface is stored in system memory
SDL_HWSURFACE | Surface is stored in video memory
SDL_ASYNCBLIT | Surface uses asynchronous blits if possible
SDL_ANYFORMAT | Allows any pixel-format (Display surface)
SDL_HWPALETTE | Surface has exclusive palette
SDL_DOUBLEBUF | Surface is double buffered (Display surface)
SDL_FULLSCREEN | Surface is full screen (Display Surface)
SDL_OPENGL | Surface has an OpenGL context (Display Surface)
SDL_OPENGLBLIT | Surface supports OpenGL blitting (Display Surface)
SDL_RESIZABLE | Surface is resizable (Display Surface)
SDL_HWACCEL | Surface blit uses hardware acceleration
SDL_SRCCOLORKEY | Surface use colorkey blitting
SDL_RLEACCEL | Colorkey blitting is accelerated with RLE
SDL_SRCALPHA | Surface blit uses alpha blending
SDL_PREALLOC | Surface uses preallocated memory

See Also

SDL_PixelFormat

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SDL_PixelFormat | Up | SDL_VideoInfo

SDL Library Documentation

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SDL_VideoInfo

Name

SDL_VideoInfo -- Video Target information

Structure Definition

typedef struct{
  Uint32 hw_available:1;
  Uint32 wm_available:1;
  Uint32 blit_hw:1;
  Uint32 blit_hw_CC:1;
  Uint32 blit_hw_A:1;
  Uint32 blit_sw:1;
  Uint32 blit_sw_CC:1;
  Uint32 blit_sw_A:1;
  Uint32 blit_fill;
  Uint32 video_mem;
  SDL_PixelFormat *vfmt;
} SDL_VideoInfo;

Structure Data

hw_available | Is it possible to create hardware surfaces?
wm_available | Is there a window manager available
blit_hw | Are hardware to hardware blits accelerated?
blit_hw_CC | Are hardware to hardware colorkey blits accelerated?
blit_hw_A | Are hardware to hardware alpha blits accelerated?
blit_sw | Are software to hardware blits accelerated?
blit_sw_CC | Are software to hardware colorkey blits accelerated?
blit_sw_A | Are software to hardware alpha blits accelerated?
blit_fill | Are color fills accelerated?
video_mem | Total amount of video memory in Kilobytes
vfmt | Pixel format of the video device

Description

This (read-only) structure is returned by SDL_GetVideoInfo. It contains information on either the 'best' available mode (if called before SDL_SetVideoMode) or the current video mode.

See Also

SDL_PixelFormat, SDL_GetVideoInfo

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SDL_Surface | Up | SDL_Overlay

SDL Library Documentation

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SDL_Overlay

Name

SDL_Overlay -- YUV video overlay

Structure Definition

typedef struct{
  Uint32 format;
  int w, h;
  int planes;
  Uint16 *pitches;
  Uint8 **pixels;
  Uint32 hw_overlay:1;
} SDL_Overlay;

Structure Data

format | Overlay format (see below)
w, h | Width and height of overlay
planes | Number of planes in the overlay. Usually either 1 or 3
pitches | An array of pitches, one for each plane. Pitch is the length of a row in bytes.
pixels | An array of pointers to teh data of each plane. The overlay should be locked before these pointers are used.
hw_overlay | This will be set to 1 if the overlay is hardware accelerated.

Description

A SDL_Overlay is similar to a SDL_Surface except it stores a YUV overlay. All the fields are read only, except for pixels which should be locked before use. The format field stores the format of the overlay which is one of the following:

#define SDL_YV12_OVERLAY  0x32315659  /* Planar mode: Y + V + U */
#define SDL_IYUV_OVERLAY  0x56555949  /* Planar mode: Y + U + V */
#define SDL_YUY2_OVERLAY  0x32595559  /* Packed mode: Y0+U0+Y1+V0 */
#define SDL_UYVY_OVERLAY  0x59565955  /* Packed mode: U0+Y0+V0+Y1 */
#define SDL_YVYU_OVERLAY  0x55595659  /* Packed mode: Y0+V0+Y1+U0 */

More information on YUV formats can be found at http://www.webartz.com/fourcc/indexyuv.htm.

See Also

SDL_CreateYUVOverlay, SDL_LockYUVOverlay, SDL_UnlockYUVOverlay, SDL_FreeYUVOverlay

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SDL_VideoInfo | Up | Window Management

SDL Library Documentation

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Chapter 7. Window Management

Table of Contents

SDL_WM_SetCaption — Sets the window tile and icon name.

SDL_WM_GetCaption — Gets the window title and icon name.

SDL_WM_SetIcon — Sets the icon for the display window.

SDL_WM_IconifyWindow — Iconify/Minimise the window

SDL_WM_ToggleFullScreen — Toggles fullscreen mode

SDL_WM_GrabInput — Grabs mouse and keyboard input.

SDL provides a small set of window management functions which allow applications to change their title and toggle from windowed mode to fullscreen (if available)

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SDL_Overlay | Up | SDL_WM_SetCaption

SDL Library Documentation

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SDL_WM_GetCaption

Name

SDL_WM_GetCaption -- Gets the window title and icon name.

Synopsis

#include "SDL.h"

void SDL_WM_GetCaption(char **title, char **icon);

Description

Set pointers to the window title and icon name.

See Also

SDL_WM_SetCaption, SDL_WM_SetIcon

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SDL_WM_SetCaption | Up | SDL_WM_SetIcon

SDL Library Documentation

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SDL_WM_SetCaption

Name

SDL_WM_SetCaption -- Sets the window tile and icon name.

Synopsis

#include "SDL.h"

void SDL_WM_SetCaption(const char *title, const char *icon);

Description

Sets the title-bar and icon name of the display window.

See Also

SDL_WM_GetCaption, SDL_WM_SetIcon

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Window Management | Up | SDL_WM_GetCaption

SDL Library Documentation

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SDL_WM_SetIcon

Name

SDL_WM_SetIcon -- Sets the icon for the display window.

Synopsis

#include "SDL.h"

void SDL_WM_SetIcon(SDL_Surface *icon, Uint8 *mask);

Description

Sets the icon for the display window. Win32 icons must be 32x32.

This function must be called before the first call to SDL_SetVideoMode.

It takes an icon surface, and a mask in MSB format.

If mask is NULL, the entire icon surface will be used as the icon.

Example

SDL_WM_SetIcon(SDL_LoadBMP("icon.bmp"), NULL);

See Also

SDL_SetVideoMode, SDL_WM_SetCaption

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SDL_WM_GetCaption | Up | SDL_WM_IconifyWindow

SDL Library Documentation

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SDL_WM_IconifyWindow

Name

SDL_WM_IconifyWindow -- Iconify/Minimise the window

Synopsis

#include "SDL.h"

int SDL_WM_IconifyWindow(void);

Description

If the application is running in a window managed environment SDL attempts to iconify/minimise it. If SDL_WM_IconifyWindow is successful, the application will receive a SDL_APPACTIVE loss event.

Return Value

Returns non-zero on success or 0 if iconification is not support or was refused by the window manager.

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SDL_WM_SetIcon | Up | SDL_WM_ToggleFullScreen

SDL Library Documentation

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SDL_WM_ToggleFullScreen

Name

SDL_WM_ToggleFullScreen -- Toggles fullscreen mode

Synopsis

#include "SDL.h"

int SDL_WM_ToggleFullScreen(SDL_Surface *surface);

Description

Toggles the application between windowed and fullscreen mode, if supported. (X11 is the only target currently supported, BeOS support is experimental).

Return Value

Returns 0 on failure or 1 on success.

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SDL_WM_IconifyWindow | Up | SDL_WM_GrabInput

SDL Library Documentation

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SDL_WM_GrabInput

Name

SDL_WM_GrabInput -- Grabs mouse and keyboard input.

Synopsis

#include "SDL.h"

SDL_GrabMode SDL_WM_GrabInput(SDL_GrabMode mode);

Description

Grabbing means that the mouse is confined to the application window, and nearly all keyboard input is passed directly to the application, and not interpreted by a window manager, if any.

When mode is SDL_GRAB_QUERY the grab mode is not changed, but the current grab mode is returned.

typedef enum {
  SDL_GRAB_QUERY,
  SDL_GRAB_OFF,
  SDL_GRAB_ON
} SDL_GrabMode;

Return Value

The current/new SDL_GrabMode.

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SDL_WM_ToggleFullScreen | Up | Events

SDL Library Documentation

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Chapter 8. Events

Table of Contents

Introduction

SDL Event Structures.

Event Functions.

Introduction

Event handling allows your application to receive input from the user. Event handling is initalised (along with video) with a call to:

SDL_Init(SDL_INIT_VIDEO);

Internally, SDL stores all the events waiting to be handled in an event queue. Using functions like SDL_PollEvent and SDL_PeepEvents you can observe and handle waiting input events.

The key to event handling in SDL is the SDL_Event union. The event queue itself is composed of a series of SDL_Event unions, one for each waiting event. SDL_Event unions are read from the queue with the SDL_PollEvent function and it is then up to the application to process the information stored with them.

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SDL_WM_GrabInput | Up | SDL Event Structures.

SDL Library Documentation

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Chapter 8. Events
Next

SDL Event Structures.

Table of Contents

SDL_Event — General event structure

SDL_ActiveEvent — Application visibility event structure

SDL_KeyboardEvent — Keyboard event structure

SDL_MouseMotionEvent — Mouse motion event structure

SDL_MouseButtonEvent — Mouse button event structure

SDL_JoyAxisEvent — Joystick axis motion event structure

SDL_JoyButtonEvent — Joystick button event structure

SDL_JoyHatEvent — Joystick hat position change event structure

SDL_JoyBallEvent — Joystick trackball motion event structure

SDL_ResizeEvent — Window resize event structure

SDL_ExposeEvent — Quit requested event

SDL_SysWMEvent — Platform-dependent window manager event.

SDL_UserEvent — A user-defined event type

SDL_QuitEvent — Quit requested event

SDL_keysym — Keysym structure

SDLKey — Keysym definitions.

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Events | Up | SDL_Event

SDL Library Documentation

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SDL_Event

Name

SDL_Event -- General event structure

Structure Definition

typedef union{
  Uint8 type;
  SDL_ActiveEvent active;
  SDL_KeyboardEvent key;
  SDL_MouseMotionEvent motion;
  SDL_MouseButtonEvent button;
  SDL_JoyAxisEvent jaxis;
  SDL_JoyBallEvent jball;
  SDL_JoyHatEvent jhat;
  SDL_JoyButtonEvent jbutton;
  SDL_ResizeEvent resize;
  SDL_ExposeEvent expose;
  SDL_QuitEvent quit;
  SDL_UserEvent user;
  SDL_SywWMEvent syswm;
} SDL_Event;

Structure Data

type | The type of event
active | Activation event
key | Keyboard event
motion | Mouse motion event
button | Mouse button event
jaxis | Joystick axis motion event
jball | Joystick trackball motion event
jhat | Joystick hat motion event
jbutton | Joystick button event
resize | Application window resize event
expose | Application window expose event
quit | Application quit request event
user | User defined event
syswm | Undefined window manager event

Description

The SDL_Event union is the core to all event handling is SDL, its probably the most important structure after SDL_Surface. SDL_Event is a union of all event structures used in SDL, using it is a simple matter of knowing which union member relates to which event type.

Event type | Event Structure
SDL_ACTIVEEVENT | SDL_ActiveEvent
SDL_KEYDOWN/UP | SDL_KeyboardEvent
SDL_MOUSEMOTION | SDL_MouseMotionEvent
SDL_MOUSEBUTTONDOWN/UP | SDL_MouseButtonEvent
SDL_JOYAXISMOTION | SDL_JoyAxisEvent
SDL_JOYBALLMOTION | SDL_JoyBallEvent
SDL_JOYHATMOTION | SDL_JoyHatEvent
SDL_JOYBUTTONDOWN/UP | SDL_JoyButtonEvent
SDL_QUIT | SDL_QuitEvent
SDL_SYSWMEVENT | SDL_SysWMEvent
SDL_VIDEORESIZE | SDL_ResizeEvent
SDL_VIDEOEXPOSE | SDL_ExposeEvent
SDL_USEREVENT | SDL_UserEvent

Use

The SDL_Event structure has two uses

Reading events on the event queue

Placing events on the event queue

Reading events from the event queue is done with either SDL_PollEvent or SDL_PeepEvents. We'll use SDL_PollEvent and step through an example.

First off, we create an empty SDL_Event structure.

SDL_Event test_event;

SDL_PollEvent removes the next event from the event queue, if there are no events on the queue it returns 0 otherwise it returns 1. We use a while loop to process each event in turn.

while(SDL_PollEvent(&test_event)) {

The SDL_PollEvent function take a pointer to an SDL_Event structure that is to be filled with event information. We know that if SDL_PollEvent removes an event from the queue then the event information will be placed in our test_event structure, but we also know that the type of event will be placed in the type member of test_event. So to handle each event type seperately we use a switch statement.

  switch(test_event.type) {

We need to know what kind of events we're looking for and the event type's of those events. So lets assume we want to detect where the user is moving the mouse pointer within our application. We look through our event types and notice that SDL_MOUSEMOTION is, more than likely, the event we're looking for. A little more research tells use that SDL_MOUSEMOTION events are handled within the SDL_MouseMotionEvent structure which is the motion member of SDL_Event. We can check for the SDL_MOUSEMOTION event type within our switch statement like so:

    case SDL_MOUSEMOTION:

All we need do now is read the information out of the motion member of test_event.

      printf("We got a motion event.\n");
      printf("Current mouse position is: (%d, %d)\n", test_event.motion.x, test_event.motion.y);
      break;
    default:
      printf("Unhandled Event!\n");
      break;
  }
}
printf("Event queue empty.\n");

It is also possible to push events onto the event queue and so use it as a two-way communication path. Both SDL_PushEvent and SDL_PeepEvents allow you to place events onto the event queue. This is usually used to place a SDL_USEREVENT on the event queue, however you could use it to post fake input events if you wished. Creating your own events is a simple matter of choosing the event type you want, setting the type member and filling the appropriate member structure with information.

SDL_Event user_event;

user_event.type=SDL_USEREVENT;
user_event.user.code=2;
user_event.user.data1=NULL;
user_event.user.data2=NULL;
SDL_PushEvent(&user_event);

See Also

SDL_PollEvent, SDL_PushEvent, SDL_PeepEvents

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SDL Event Structures. | Up | SDL_ActiveEvent

SDL Library Documentation

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SDL_ActiveEvent

Name

SDL_ActiveEvent -- Application visibility event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 gain;
  Uint8 state;
} SDL_ActiveEvent;

Structure Data

type | SDL_ACTIVEEVENT.
gain | 0 if the event is a loss or 1 if it is a gain.
state | SDL_APPMOUSEFOCUS if mouse focus was gained or lost, SDL_APPINPUTFOCUS if input focus was gained or lost, or SDL_APPACTIVE if the application was iconified (gain=0) or restored(gain=1).

Description

SDL_ActiveEvent is a member of the SDL_Event union and is used when an event of type SDL_ACTIVEEVENT is reported.

When the mouse leaves or enters the window area a SDL_APPMOUSEFOCUS type activation event occurs, if the mouse entered the window then gain will be 1, otherwise gain will be 0. A SDL_APPINPUTFOCUS type activation event occurs when the application loses or gains keyboard focus. This usually occurs when another application is made active. Finally, a SDL_APPACTIVE type event occurs when the application is either minimised/iconified (gain=0) or restored.

Note: This event does not occur when an application window is first created.

See Also

SDL_Event, SDL_GetAppState

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SDL_Event | Up | SDL_KeyboardEvent

SDL Library Documentation

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SDL_KeyboardEvent

Name

SDL_KeyboardEvent -- Keyboard event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 state;
  SDL_keysym keysym;
} SDL_KeyboardEvent;

Structure Data

type | SDL_KEYDOWN or SDL_KEYUP
state | SDL_PRESSED or SDL_RELEASED
keysym | Contains key press information

Description

SDL_KeyboardEvent is a member of the SDL_Event union and is used when an event of type SDL_KEYDOWN or SDL_KEYUP is reported.

The type and state actually report the same information, they just use different values to do it! A keyboard event occurs when a key is released (type=SDK_KEYUP or state=SDL_RELEASED) and when a key is pressed (type=SDL_KEYDOWN or state=SDL_PRESSED). The information on what key was pressed or released is in the keysym structure.

Note: Repeating SDL_KEYDOWN events will occur if key repeat is enabled (see SDL_EnableKeyRepeat).

See Also

SDL_Event, SDL_keysym, SDL_EnableKeyRepeat, SDL_EnableUNICODE

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SDL_ActiveEvent | Up | SDL_MouseMotionEvent

SDL Library Documentation

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SDL_MouseMotionEvent

Name

SDL_MouseMotionEvent -- Mouse motion event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 state;
  Uint16 x, y;
  Sint16 xrel, yrel;
} SDL_MouseMotionEvent;

Structure Data

type | SDL_MOUSEMOTION
state | The current button state
x, y | The X/Y coordinates of the mouse
xrel, yrel | Relative motion in the X/Y direction

Description

SDL_MouseMotionEvent is a member of the SDL_Event union and is used when an event of type SDL_MOUSEMOTION is reported.

Simply put, a SDL_MOUSEMOTION type event occurs when a user moves the mouse within the application window or when SDL_WarpMouse is called. Both the absolute (x and y) and relative (xrel and yrel) coordinates are reported along with the current button states (state). The button state can be interpreted using the SDL_BUTTON macro (see SDL_GetMouseState).

If the cursor is hidden (SDL_ShowCursor(0)) and the input is grabbed (SDL_WM_GrabInput(SDL_GRAB_ON)), then the mouse will give relative motion events even when the cursor reaches the edge fo the screen. This is currently only implemented on Windows and Linux/Unix-a-likes.

See Also

SDL_Event, SDL_MouseButtonEvent

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SDL_KeyboardEvent | Up | SDL_MouseButtonEvent

SDL Library Documentation

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SDL_MouseButtonEvent

Name

SDL_MouseButtonEvent -- Mouse button event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 button;
  Uint8 state;
  Uint16 x, y;
} SDL_MouseButtonEvent;

Structure Data

type | SDL_MOUSEBUTTONDOWN or SDL_MOUSEBUTTONUP
button | The mouse button index (SDL_BUTTON_LEFT, SDL_BUTTON_MIDDLE, SDL_BUTTON_RIGHT)
state | SDL_PRESSED or SDL_RELEASED
x, y | The X/Y coordinates of the mouse at press/release time

Description

SDL_MouseButtonEvent is a member of the SDL_Event union and is used when an event of type SDL_MOUSEBUTTONDOWN or SDL_MOUSEBUTTONUP is reported.

When a mouse button press or release is detected then number of the button pressed (from 1 to 255, with 1 usually being the left button and 2 the right) is placed into button, the position of the mouse when this event occured is stored in the x and the y fields. Like SDL_KeyboardEvent, information on whether the event was a press or a release event is stored in both the type and state fields, but this should be obvious.

See Also

SDL_Event, SDL_MouseMotionEvent

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SDL_MouseMotionEvent | Up | SDL_JoyAxisEvent

SDL Library Documentation

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SDL_JoyAxisEvent

Name

SDL_JoyAxisEvent -- Joystick axis motion event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 which;
  Uint8 axis;
  Sint16 value;
} SDL_JoyAxisEvent;

Structure Data

type | SDL_JOYAXISMOTION
which | Joystick device index
axis | Joystick axis index
value | Axis value (range: -32768 to 32767)

Description

SDL_JoyAxisEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYAXISMOTION is reported.

A SDL_JOYAXISMOTION event occurs when ever a user moves an axis on the joystick. The field which is the index of the joystick that reported the event and axis is the index of the axis (for a more detailed explaination see the Joystick section). value is the current position of the axis.

See Also

SDL_Event, Joystick Functions, SDL_JoystickEventState, SDL_JoystickGetAxis

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SDL_MouseButtonEvent | Up | SDL_JoyButtonEvent

SDL Library Documentation

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SDL_JoyButtonEvent

Name

SDL_JoyButtonEvent -- Joystick button event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 which;
  Uint8 button;
  Uint8 state;
} SDL_JoyButtonEvent;

Structure Data

type | SDL_JOYBUTTONDOWN or SDL_JOYBUTTONUP
which | Joystick device index
button | Joystick button index
state | SDL_PRESSED or SDL_RELEASED

Description

SDL_JoyButtonEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYBUTTONDOWN or SDL_JOYBUTTONUP is reported.

A SDL_JOYBUTTONDOWN or SDL_JOYBUTTONUP event occurs when ever a user presses or releases a button on a joystick. The field which is the index of the joystick that reported the event and button is the index of the button (for a more detailed explaination see the Joystick section). state is the current state or the button which is either SDL_PRESSED or SDL_RELEASED.

See Also

SDL_Event, Joystick Functions, SDL_JoystickEventState, SDL_JoystickGetButton

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SDL_JoyAxisEvent | Up | SDL_JoyHatEvent

SDL Library Documentation

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SDL_JoyHatEvent

Name

SDL_JoyHatEvent -- Joystick hat position change event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 which;
  Uint8 hat;
  Uint8 value;
} SDL_JoyHatEvent;

Structure Data

type | SDL_JOY
which | Joystick device index
hat | Joystick hat index
value | Hat position

Description

SDL_JoyHatEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYHATMOTION is reported.

A SDL_JOYHATMOTION event occurs when ever a user moves a hat on the joystick. The field which is the index of the joystick that reported the event and hat is the index of the hat (for a more detailed exlaination see the Joystick section). value is the current position of the hat. It is a logically OR'd combination of the following values (whose meanings should be pretty obvious:) :

SDL_HAT_CENTERED

SDL_HAT_UP

SDL_HAT_RIGHT

SDL_HAT_DOWN

SDL_HAT_LEFT

The following defines are also provided:

SDL_HAT_RIGHTUP

SDL_HAT_RIGHTDOWN

SDL_HAT_LEFTUP

SDL_HAT_LEFTDOWN

See Also

SDL_Event, Joystick Functions, SDL_JoystickEventState, SDL_JoystickGetHat

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SDL_JoyButtonEvent | Up | SDL_JoyBallEvent

SDL Library Documentation

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SDL_JoyBallEvent

Name

SDL_JoyBallEvent -- Joystick trackball motion event structure

Structure Definition

typedef struct{
  Uint8 type;
  Uint8 which;
  Uint8 ball;
  Sint16 xrel, yrel;
} SDL_JoyBallEvent;

Structure Data

type | SDL_JOYBALLMOTION
which | Joystick device index
ball | Joystick trackball index
xrel, yrel | The relative motion in the X/Y direction

Description

SDL_JoyBallEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYBALLMOTION is reported.

A SDL_JOYBALLMOTION event occurs when a user moves a trackball on the joystick. The field which is the index of the joystick that reported the event and ball is the index of the trackball (for a more detailed explaination see the Joystick section). Trackballs only return relative motion, this is the change in position on the ball since it was last polled (last cycle of the event loop) and it is stored in xrel and yrel.

See Also

SDL_Event, Joystick Functions, SDL_JoystickEventState, SDL_JoystickGetBall

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SDL_JoyHatEvent | Up | SDL_ResizeEvent

SDL Library Documentation

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SDL_ResizeEvent

Name

SDL_ResizeEvent -- Window resize event structure

Structure Definition

typedef struct{
  Uint8 type;
  int w, h;
} SDL_ResizeEvent;

Structure Data

type | SDL_VIDEORESIZE
w, h | New width and height of the window

Description

SDL_ResizeEvent is a member of the SDL_Event union and is used when an event of type SDL_VIDEORESIZE is reported.

When SDL_RESIZABLE is passed as a flag to SDL_SetVideoMode the user is allowed to resize the applications window. When the window is resized an SDL_VIDEORESIZE is report, with the new window width and height values stored in w and h, respectively. When an SDL_VIDEORESIZE is recieved the window should be resized to the new dimensions using SDL_SetVideoMode.

See Also

SDL_Event, SDL_SetVideoMode

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SDL_JoyBallEvent | Up | SDL_ExposeEvent

SDL Library Documentation

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SDL_ExposeEvent

Name

SDL_ExposeEvent -- Quit requested event

Structure Definition

typedef struct{
  Uint8 type
} SDL_ExposeEvent;

Structure Data

type
SDL_QUIT

Description

SDL_ExposeEvent is a member of the SDL_Event union and is used whan an event of type SDL_VIDEOEXPOSE is reported.

A VIDEOEXPOSE event is triggered when the screen has been modified outside of the application, usually by the window manager and needs to be redrawn.

See Also

SDL_Event, SDL_SetEventFilter

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SDL_ResizeEvent | Up | SDL_SysWMEvent

SDL Library Documentation

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SDL_SysWMEvent

Name

SDL_SysWMEvent -- Platform-dependent window manager event.

Description

The system window manager event contains a pointer to system-specific information about unknown window manager events. If you enable this event using SDL_EventState(), it will be generated whenever unhandled events are received from the window manager. This can be used, for example, to implement cut-and-paste in your application.

typedef struct {
         Uint8 type;   /* Always SDL_SysWM */
 } SDL_SysWMEvent;

If you want to obtain system-specific information about the window manager, you can fill the version member of a SDL_SysWMinfo structure (details can be found in SDL_syswm.h, which must be included) using the SDL_VERSION() macro found in SDL_version.h, and pass it to the function:

int SDL_GetWMInfo(SDL_SysWMinfo *info);

See Also

SDL_EventState

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SDL_ExposeEvent | Up | SDL_UserEvent

SDL Library Documentation

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SDL_UserEvent

Name

SDL_UserEvent -- A user-defined event type

Structure Definition

typedef struct{
  Uint8 type;
  int code;
  void *data1;
  void *data2;
} SDL_UserEvent;

Structure Data

type | SDL_USEREVENT through to SDL_NUMEVENTS-1
code | User defined event code
data1 | User defined data pointer
data2 | User defined data pointer

Description

SDL_UserEvent is in the user member of the structure SDL_Event. This event is unique, it is never created by SDL but only by the user. The event can be pushed onto the event queue using SDL_PushEvent. The contents of the structure members or completely up to the programmer, the only requirement is that type is a value from SDL_USEREVENT to SDL_NUMEVENTS-1 (inclusive).

Examples

SDL_Event event;

event.type = SDL_USEREVENT;
event.user.code = my_event_code;
event.user.data1 = significant_data;
event.user.data2 = 0;
SDL_PushEvent(&event);

See Also

SDL_Event, SDL_PushEvent

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SDL_SysWMEvent | Up | SDL_QuitEvent

SDL Library Documentation

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SDL_QuitEvent

Name

SDL_QuitEvent -- Quit requested event

Structure Definition

typedef struct{
  Uint8 type
} SDL_QuitEvent;

Structure Data

type
SDL_QUIT

Description

SDL_QuitEvent is a member of the SDL_Event union and is used whan an event of type SDL_QUIT is reported.

As can be seen, the SDL_QuitEvent structure serves no useful purpose. The event itself, on the other hand, is very important. If you filter out or ignore a quit event then it is impossible for the user to close the window. On the other hand, if you do accept a quit event then the application window will be closed, and screen updates will still report success event though the application will no longer be visible.

Note: The macro SDL_QuitRequested will return non-zero if a quit event is pending

See Also

SDL_Event, SDL_SetEventFilter

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SDL_UserEvent | Up | SDL_keysym

SDL Library Documentation

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SDL_keysym

Name

SDL_keysym -- Keysym structure

Structure Definition

typedef struct{
  Uint8 scancode;
  SDLKey sym;
  SDLMod mod;
  Uint16 unicode;
} SDL_keysym;

Structure Data

scancode | Hardware specific scancode
sym | SDL virtual keysym
mod | Current key modifiers
unicode | Translated character

Description

The SDL_keysym structure is used by reporting key presses and releases since it is a part of the SDL_KeyboardEvent.

The scancode field should generally be left alone, it is the hardware dependent scancode returned by the keyboard. The sym field is extremely useful. It is the SDL-defined value of the key (see SDL Key Syms. This field is very useful when you are checking for certain key presses, like so:

.
.
while(SDL_PollEvent(&event)){
  switch(event.type){
    case SDL_KEYDOWN:
      if(event.key.keysym.sym==SDLK_LEFT)
        move_left();
      break;
    .
    .
    .
  }
}
.
.

mod stores the current state of the keyboard modifiers as explained in SDL_GetModState. The unicode is only used when UNICODE translation is enabled with SDL_EnableUNICODE. If unicode is non-zero then this a the UNICODE character corresponding to the keypress. If the high 9 bits of the character are 0, then this maps to the equivalent ASCII character:

char ch;
if ( (keysym.unicode & 0xFF80) == 0 ) {
  ch = keysym.unicode & 0x7F;
}
else {
  printf("An International Character.\n");
}

UNICODE translation does have a slight overhead so don't enable it unless its needed.

See Also

SDLKey

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SDL_QuitEvent | Up | SDLKey

SDL Library Documentation

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SDLKey

Name

SDLKey -- Keysym definitions.

Description

Table 8-1. SDL Keysym definitions

SDLKey | ASCII value | Common name
SDLK_BACKSPACE | '\b' | backspace
SDLK_TAB | '\t' | tab
SDLK_CLEAR |  | clear
SDLK_RETURN | '\r' | return
SDLK_PAUSE |  | pause
SDLK_ESCAPE | '^[' | escape
SDLK_SPACE | ' ' | space
SDLK_EXCLAIM | '!' | exclaim
SDLK_QUOTEDBL | '"' | quotedbl
SDLK_HASH | '#' | hash
SDLK_DOLLAR | '$' | dollar
SDLK_AMPERSAND | '&' | ampersand
SDLK_QUOTE | ''' | quote
SDLK_LEFTPAREN | '(' | left parenthesis
SDLK_RIGHTPAREN | ')' | right parenthesis
SDLK_ASTERISK | '*' | asterisk
SDLK_PLUS | '+' | plus sign
SDLK_COMMA | ',' | comma
SDLK_MINUS | '-' | minus sign
SDLK_PERIOD | '.' | period
SDLK_SLASH | '/' | forward slash
SDLK_0 | '0' | 0
SDLK_1 | '1' | 1
SDLK_2 | '2' | 2
SDLK_3 | '3' | 3
SDLK_4 | '4' | 4
SDLK_5 | '5' | 5
SDLK_6 | '6' | 6
SDLK_7 | '7' | 7
SDLK_8 | '8' | 8
SDLK_9 | '9' | 9
SDLK_COLON | ':' | colon
SDLK_SEMICOLON | ';' | semicolon
SDLK_LESS | '<' | less-than sign
SDLK_EQUALS | '=' | equals sign
SDLK_GREATER | '>' | greater-than sign
SDLK_QUESTION | '?' | question mark
SDLK_AT | '@' | at
SDLK_LEFTBRACKET | '[' | left bracket
SDLK_BACKSLASH | '\' | backslash
SDLK_RIGHTBRACKET | ']' | right bracket
SDLK_CARET | '^' | caret
SDLK_UNDERSCORE | '_' | underscore
SDLK_BACKQUOTE | '`' | grave
SDLK_a | 'a' | a
SDLK_b | 'b' | b
SDLK_c | 'c' | c
SDLK_d | 'd' | d
SDLK_e | 'e' | e
SDLK_f | 'f' | f
SDLK_g | 'g' | g
SDLK_h | 'h' | h
SDLK_i | 'i' | i
SDLK_j | 'j' | j
SDLK_k | 'k' | k
SDLK_l | 'l' | l
SDLK_m | 'm' | m
SDLK_n | 'n' | n
SDLK_o | 'o' | o
SDLK_p | 'p' | p
SDLK_q | 'q' | q
SDLK_r | 'r' | r
SDLK_s | 's' | s
SDLK_t | 't' | t
SDLK_u | 'u' | u
SDLK_v | 'v' | v
SDLK_w | 'w' | w
SDLK_x | 'x' | x
SDLK_y | 'y' | y
SDLK_z | 'z' | z
SDLK_DELETE | '^?' | delete
SDLK_KP0 |  | keypad 0
SDLK_KP1 |  | keypad 1
SDLK_KP2 |  | keypad 2
SDLK_KP3 |  | keypad 3
SDLK_KP4 |  | keypad 4
SDLK_KP5 |  | keypad 5
SDLK_KP6 |  | keypad 6
SDLK_KP7 |  | keypad 7
SDLK_KP8 |  | keypad 8
SDLK_KP9 |  | keypad 9
SDLK_KP_PERIOD | '.' | keypad period
SDLK_KP_DIVIDE | '/' | keypad divide
SDLK_KP_MULTIPLY | '*' | keypad multiply
SDLK_KP_MINUS | '-' | keypad minus
SDLK_KP_PLUS | '+' | keypad plus
SDLK_KP_ENTER | '\r' | keypad enter
SDLK_KP_EQUALS | '=' | keypad equals
SDLK_UP |  | up arrow
SDLK_DOWN |  | down arrow
SDLK_RIGHT |  | right arrow
SDLK_LEFT |  | left arrow
SDLK_INSERT |  | insert
SDLK_HOME |  | home
SDLK_END |  | end
SDLK_PAGEUP |  | page up
SDLK_PAGEDOWN |  | page down
SDLK_F1 |  | F1
SDLK_F2 |  | F2
SDLK_F3 |  | F3
SDLK_F4 |  | F4
SDLK_F5 |  | F5
SDLK_F6 |  | F6
SDLK_F7 |  | F7
SDLK_F8 |  | F8
SDLK_F9 |  | F9
SDLK_F10 |  | F10
SDLK_F11 |  | F11
SDLK_F12 |  | F12
SDLK_F13 |  | F13
SDLK_F14 |  | F14
SDLK_F15 |  | F15
SDLK_NUMLOCK |  | numlock
SDLK_CAPSLOCK |  | capslock
SDLK_SCROLLOCK |  | scrollock
SDLK_RSHIFT |  | right shift
SDLK_LSHIFT |  | left shift
SDLK_RCTRL |  | right ctrl
SDLK_LCTRL |  | left ctrl
SDLK_RALT |  | right alt
SDLK_LALT |  | left alt
SDLK_RMETA |  | right meta
SDLK_LMETA |  | left meta
SDLK_LSUPER |  | left windows key
SDLK_RSUPER |  | right windows key
SDLK_MODE |  | mode shift
SDLK_HELP |  | help
SDLK_PRINT |  | print-screen
SDLK_SYSREQ |  | SysRq
SDLK_BREAK |  | break
SDLK_MENU |  | menu
SDLK_POWER |  | power
SDLK_EURO |  | euro

Table 8-2. SDL modifier definitions

SDL Modifier | Meaning
KMOD_NONE | No modifiers applicable
KMOD_NUM | Numlock is down
KMOD_CAPS | Capslock is down
KMOD_LCTRL | Left Control is down
KMOD_RCTRL | Right Control is down
KMOD_RSHIFT | Right Shift is down
KMOD_LSHIFT | Left Shift is down
KMOD_RALT | Right Alt is down
KMOD_LALT | Left Alt is down
KMOD_CTRL | A Control key is down
KMOD_SHIFT | A Shift key is down
KMOD_ALT | An Alt key is down

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SDL_keysym | Up | Event Functions.

SDL Library Documentation

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Chapter 8. Events
Next

Event Functions.

Table of Contents

SDL_PumpEvents — Pumps the event loop, gathering events from the input devices.

SDL_PeepEvents — Checks the event queue for messages and optionally returns them.

SDL_PollEvent — Polls for currently pending events.

SDL_WaitEvent — Waits indefinitely for the next available event.

SDL_PushEvent — Pushes an event onto the event queue

SDL_SetEventFilter — Sets up a filter to process all events before they are posted to the event queue.

SDL_GetEventFilter — Retrieves a pointer to he event filter

SDL_EventState — This function allows you to set the state of processing certain events.

SDL_GetKeyState — Get a snapshot of the current keyboard state

SDL_GetModState — Get the state of modifier keys.

SDL_SetModState — Set the current key modifier state

SDL_GetKeyName — Get the name of an SDL virtual keysym

SDL_EnableUNICODE — Enable UNICODE translation

SDL_EnableKeyRepeat — Set keyboard repeat rate.

SDL_GetMouseState — Retrieve the current state of the mouse

SDL_GetRelativeMouseState — Retrieve the current state of the mouse

SDL_GetAppState — Get the state of the application

SDL_JoystickEventState — Enable/disable joystick event polling

SDL_PumpEvents | Pumps the event loop, gathering events from the input devices
SDL_PeepEvents | Checks the event queue for messages and optionally returns them
SDL_PollEvent | Polls for currently pending events
SDL_WaitEvent | Waits indefinitely for the next available event
SDL_PushEvent | Pushes an event onto the event queue
SDL_SetEventFilter | Sets up a filter to process all events
SDL_EventState | Allows you to set the state of processing certain events
SDL_GetKeyState | Get a snapshot of the current keyboard state
SDL_GetModState | Get the state of modifier keys
SDL_SetModState | Set the state of modifier keys
SDL_GetKeyName | Get the name of an SDL virtual keysym
SDL_EnableUNICODE | Enable UNICODE translation
SDL_EnableKeyRepeat | Set keyboard repeat rate
SDL_GetMouseState | Retrieve the current state of the mouse
SDL_GetRelativeMouseState | Retrieve the current state of the mouse
SDL_GetAppState | Get the state of the application
SDL_JoystickEventState | Enable/disable joystick event polling

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SDLKey | Up | SDL_PumpEvents

SDL Library Documentation

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SDL_PumpEvents

Name

SDL_PumpEvents -- Pumps the event loop, gathering events from the input devices.

Synopsis

#include "SDL.h"

void SDL_PumpEvents(void);

Description

Pumps the event loop, gathering events from the input devices.

SDL_PumpEvents gathers all the pending input information from devices and places it on the event queue. Without calls to SDL_PumpEvents no events would ever be placed on the queue. Often calls the need for SDL_PumpEvents is hidden from the user since SDL_PollEvent and SDL_WaitEvent implicitly call SDL_PumpEvents. However, if you are not polling or waiting for events (e.g. your filtering them), then you must call SDL_PumpEvents to force an event queue update.

Note: You can only call this function in the thread that set the video mode.

See Also

SDL_PollEvent

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Event Functions. | Up | SDL_PeepEvents

SDL Library Documentation

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SDL_WaitEvent

Name

SDL_WaitEvent -- Waits indefinitely for the next available event.

Synopsis

#include "SDL.h"

int SDL_WaitEvent(SDL_Event *event);

Description

Waits indefinitely for the next available event, returning 1, or 0 if there was an error while waiting for events.

If event is not NULL, the next event is removed from the queue and stored in that area.

See Also

SDL_Event, SDL_PollEvent

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SDL_PollEvent | Up | SDL_PushEvent

SDL Library Documentation

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SDL_PeepEvents

Name

SDL_PeepEvents -- Checks the event queue for messages and optionally returns them.

Synopsis

#include "SDL.h"

int SDL_PeepEvents(SDL_Event *events, int numevents, SDL_eventaction action, Uint32 mask);

Description

Checks the event queue for messages and optionally returns them.

If action is SDL_ADDEVENT, up to numevents events will be added to the back of the event queue.

If action is SDL_PEEKEVENT, up to numevents events at the front of the event queue, matching mask, will be returned and will not be removed from the queue.

If action is SDL_GETEVENT, up to numevents events at the front of the event queue, matching mask, will be returned and will be removed from the queue.

This function is thread-safe.

Return Value

This function returns the number of events actually stored, or -1 if there was an error.

See Also

SDL_Event, SDL_PollEvent, SDL_PushEvent

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SDL_PumpEvents | Up | SDL_PollEvent

SDL Library Documentation

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SDL_PollEvent

Name

SDL_PollEvent -- Polls for currently pending events.

Synopsis

#include "SDL.h"

int SDL_PollEvent(SDL_Event *event);

Description

Polls for currently pending events, and returns 1 if there are any pending events, or 0 if there are none available.

If event is not NULL, the next event is removed from the queue and stored in that area.

Examples

SDL_Event event; /* Event structure */

.
.
.
/* Check for events */
while(SDL_PollEvent(&event)){  /* Loop until there are no events left on the queue */
  switch(event.type){  /* Process the appropiate event type */
    case SDL_KEYDOWN:  /* Handle a KEYDOWN event */
      printf("Oh! Key press\n");
      break;
    case SDL_MOUSEMOTION:
      .
      .
      .
    default: /* Report an unhandled event */
      printf("I don't know what this event is!\n");
  }
}

See Also

SDL_Event, SDL_WaitEvent, SDL_PeepEvents

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SDL_PeepEvents | Up | SDL_WaitEvent

SDL Library Documentation

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SDL_PushEvent

Name

SDL_PushEvent -- Pushes an event onto the event queue

Synopsis

#include "SDL.h"

int SDL_PushEvent(SDL_Event *event);

Description

The event queue can actually be used as a two way communication channel. Not only can events be read from the queue, but the user can also push their own events onto it. event is a pointer to the event structure you wish to push onto the queue.

Note: Pushing device input events onto the queue doesn't modify the state of the device within SDL.

Return Value

Returns 0 on success or -1 if the event couldn't be pushed.

Examples

See SDL_Event.

See Also

SDL_PollEvent, SDL_PeepEvents, SDL_Event

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SDL_WaitEvent | Up | SDL_SetEventFilter

SDL Library Documentation

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SDL_SetEventFilter

Name

SDL_SetEventFilter -- Sets up a filter to process all events before they are posted to the event queue.

Synopsis

#include "SDL.h"

void SDL_SetEventFilter(SDL_EventFilter filter);

Description

This function sets up a filter to process all events before they are posted to the event queue. This is a very powerful and flexible feature. The filter is prototyped as:

typedef int (*SDL_EventFilter)(const SDL_Event *event);

If the filter returns 1, then the event will be added to the internal queue. If it returns 0, then the event will be dropped from the queue. This allows selective filtering of dynamically.

There is one caveat when dealing with the SDL_QUITEVENT event type. The event filter is only called when the window manager desires to close the application window. If the event filter returns 1, then the window will be closed, otherwise the window will remain open if possible. If the quit event is generated by an interrupt signal, it will bypass the internal queue and be delivered to the application at the next event poll.

Note: Events pushed onto the queue with SDL_PushEvent or SDL_PeepEvents do not get passed through the event filter.

Note: Be Careful! The event filter function may run in a different thread so be careful what you do within it.

See Also

SDL_Event, SDL_GetEventFilter, SDL_PushEvent

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SDL_PushEvent | Up | SDL_GetEventFilter

SDL Library Documentation

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SDL_GetEventFilter

Name

SDL_GetEventFilter -- Retrieves a pointer to he event filter

Synopsis

#include "SDL.h"

SDL_EventFilter SDL_GetEventFilter(void);

Description

This function retrieces a pointer to the event filter that was previously set using SDL_SetEventFilter. An SDL_EventFilter function is defined as:

typedef int (*SDL_EventFilter)(const SDL_Event *event);

Return Value

Returns a pointer to the event filter or NULL if no filter has been set.

See Also

SDL_Event, SDL_SetEventFilter

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SDL_SetEventFilter | Up | SDL_EventState

SDL Library Documentation

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SDL_EventState

Name

SDL_EventState -- This function allows you to set the state of processing certain events.

Synopsis

#include "SDL.h"

Uint8 SDL_EventState(Uint8 type, int state);

Description

This function allows you to set the state of processing certain event type's.

If state is set to SDL_IGNORE, that event type will be automatically dropped from the event queue and will not be filtered.

If state is set to SDL_ENABLE, that event type will be processed normally.

If state is set to SDL_QUERY, SDL_EventState will return the current processing state of the specified event type.

A list of event type's can be found in the SDL_Event section.

See Also

SDL_Event

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SDL_GetEventFilter | Up | SDL_GetKeyState

SDL Library Documentation

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SDL_GetKeyState

Name

SDL_GetKeyState -- Get a snapshot of the current keyboard state

Synopsis

#include "SDL.h"

Uint8 *SDL_GetKeyState(int *numkeys);

Description

Gets a snapshot of the current keyboard state. The current state is return as a pointer to an array, the size of this array is stored in numkeys. The array is indexed by the SDLK_* symbols. A value of 1 means the key is pressed and a value of 0 means its not. The pointer returned is a pointer to an internal SDL array and should not be freed by the caller.

Note: Use SDL_PumpEvents to update the state array.

Example

Uint8 *keystate = SDL_GetKeyState(NULL);
if ( keystate[SDLK_RETURN] ) printf("Return Key Pressed.\n");

See Also

SDL Key Symbols, SDL_PumpEvents

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SDL_EventState | Up | SDL_GetModState

SDL Library Documentation

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SDL_GetModState

Name

SDL_GetModState -- Get the state of modifier keys.

Synopsis

#include "SDL.h"

SDLMod SDL_GetModState(void);

Description

Returns the current state of the modifier keys (CTRL, ALT, etc.).

Return Value

The return value can be an OR'd combination of the SDLMod enum.

SDLMod

typedef enum {
  KMOD_NONE  = 0x0000,
  KMOD_LSHIFT= 0x0001,
  KMOD_RSHIFT= 0x0002,
  KMOD_LCTRL = 0x0040,
  KMOD_RCTRL = 0x0080,
  KMOD_LALT  = 0x0100,
  KMOD_RALT  = 0x0200,
  KMOD_LMETA = 0x0400,
  KMOD_RMETA = 0x0800,
  KMOD_NUM   = 0x1000,
  KMOD_CAPS  = 0x2000,
  KMOD_MODE  = 0x4000,
} SDLMod;

SDL also defines the following symbols for convenience:

#define KMOD_CTRL (KMOD_LCTRL|KMOD_RCTRL)
#define KMOD_SHIFT  (KMOD_LSHIFT|KMOD_RSHIFT)
#define KMOD_ALT  (KMOD_LALT|KMOD_RALT)
#define KMOD_META (KMOD_LMETA|KMOD_RMETA)

See Also

SDL_GetKeyState

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SDL_GetKeyState | Up | SDL_SetModState

SDL Library Documentation

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SDL_SetModState

Name

SDL_SetModState -- Set the current key modifier state

Synopsis

#include "SDL.h"

void SDL_SetModState(SDLMod modstate);

Description

The inverse of SDL_GetModState, SDL_SetModState allows you to impose modifier key states on your application.

Simply pass your desired modifier states into modstate. This value my be a logical OR'd combination of the following:

typedef enum {
  KMOD_NONE  = 0x0000,
  KMOD_LSHIFT= 0x0001,
  KMOD_RSHIFT= 0x0002,
  KMOD_LCTRL = 0x0040,
  KMOD_RCTRL = 0x0080,
  KMOD_LALT  = 0x0100,
  KMOD_RALT  = 0x0200,
  KMOD_LMETA = 0x0400,
  KMOD_RMETA = 0x0800,
  KMOD_NUM   = 0x1000,
  KMOD_CAPS  = 0x2000,
  KMOD_MODE  = 0x4000,
} SDLMod;

See Also

SDL_GetModState

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SDL_GetModState | Up | SDL_GetKeyName

SDL Library Documentation

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SDL_GetKeyName

Name

SDL_GetKeyName -- Get the name of an SDL virtual keysym

Synopsis

#include "SDL.h"

char *SDL_GetKeyName(SDLKey key);

Description

Returns the SDL-defined name of the SDLKey key.

See Also

SDLKey

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SDL_SetModState | Up | SDL_EnableUNICODE

SDL Library Documentation

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SDL_EnableUNICODE

Name

SDL_EnableUNICODE -- Enable UNICODE translation

Synopsis

#include "SDL.h"

int SDL_EnableUNICODE(int enable);

Description

Enables/Disables Unicode keyboard translation.

To obtain the character codes corresponding to received keyboard events, Unicode translation must first be turned on using this function. The translation incurs a slight overhead for each keyboard event and is therefore disabled by default. For each subsequently received key down event, the unicode member of the SDL_keysym structure will then contain the corresponding character code, or zero for keysyms that do not correspond to any character code.

A value of 1 for enable enables Unicode translation; 0 disables it, and -1 leaves it unchanged (useful for querying the current translation mode).

Note that only key press events will be translated, not release events.

Return Value

Returns the previous translation mode (0 or 1).

See Also

SDL_keysym

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SDL_GetKeyName | Up | SDL_EnableKeyRepeat

SDL Library Documentation

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SDL_EnableKeyRepeat

Name

SDL_EnableKeyRepeat -- Set keyboard repeat rate.

Synopsis

#include "SDL.h"

int SDL_EnableKeyRepeat(int delay, int interval);

Description

Enables or disables the keyboard repeat rate. delay specifies how long the key must be pressed before it begins repeating, it then repeats at the speed specified by interval. Both delay and interval are expressed in milliseconds.

Setting delay to 0 disables key repeating completely. Good default values are SDL_DEFAULT_REPEAT_DELAY and SDL_DEFAULT_REPEAT_INTERVAL.

Return Value

Returns 0 on success and -1 on failure.

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SDL_EnableUNICODE | Up | SDL_GetMouseState

SDL Library Documentation

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SDL_GetMouseState

Name

SDL_GetMouseState -- Retrieve the current state of the mouse

Synopsis

#include "SDL.h"

Uint8 SDL_GetMouseState(int *x, int *y);

Description

The current button state is returned as a button bitmask, which can be tested using the SDL_BUTTON(X) macros, and x and y are set to the current mouse cursor position. You can pass NULL for either x or y.

Example

SDL_PumpEvents();
if(SDL_GetMouseState(NULL, NULL)&SDL_BUTTON(1))
  printf("Mouse Button 1(left) is pressed.\n");

See Also

SDL_GetRelativeMouseState, SDL_PumpEvents

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SDL_EnableKeyRepeat | Up | SDL_GetRelativeMouseState

SDL Library Documentation

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SDL_GetRelativeMouseState

Name

SDL_GetRelativeMouseState -- Retrieve the current state of the mouse

Synopsis

#include "SDL.h"

Uint8 SDL_GetRelativeMouseState(int *x, int *y);

Description

The current button state is returned as a button bitmask, which can be tested using the SDL_BUTTON(X) macros, and x and y are set to the change in the mouse position since the last call to SDL_GetRelativeMouseState or since event initialization. You can pass NULL for either x or y.

See Also

SDL_GetMouseState

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SDL_GetMouseState | Up | SDL_GetAppState

SDL Library Documentation

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SDL_GetAppState

Name

SDL_GetAppState -- Get the state of the application

Synopsis

#include "SDL.h"

Uint8 SDL_GetAppState(void);

Description

This function returns the current state of the application. The value returned is a bitwise combination of:

SDL_APPMOUSEFOCUS | The application has mouse focus.
SDL_APPINPUTFOCUS | The application has keyboard focus
SDL_APPACTIVE | The application is visible

See Also

SDL_ActiveEvent

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SDL_GetRelativeMouseState | Up | SDL_JoystickEventState

SDL Library Documentation

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SDL_JoystickEventState

Name

SDL_JoystickEventState -- Enable/disable joystick event polling

Synopsis

#include "SDL.h"

int SDL_JoystickEventState(int state);

Description

This function is used to enable or disable joystick event processing. With joystick event processing disabled you will have to update joystick states with SDL_JoystickUpdate and read the joystick information manually. state is either SDL_QUERY, SDL_ENABLE or SDL_IGNORE.

Note: Joystick event handling is prefered

Return Value

If state is SDL_QUERY then the current state is returned, otherwise the new processing state is returned.

See Also

SDL Joystick Functions, SDL_JoystickUpdate, SDL_JoyAxisEvent, SDL_JoyBallEvent, SDL_JoyButtonEvent, SDL_JoyHatEvent

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SDL_GetAppState | Up | Joystick

SDL Library Documentation

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Chapter 9. Joystick

Table of Contents

SDL_NumJoysticks — Count available joysticks.

SDL_JoystickName — Get joystick name.

SDL_JoystickOpen — Opens a joystick for use.

SDL_JoystickOpened — Determine if a joystick has been opened

SDL_JoystickIndex — Get the index of an SDL_Joystick.

SDL_JoystickNumAxes — Get the number of joystick axes

SDL_JoystickNumBalls — Get the number of joystick trackballs

SDL_JoystickNumHats — Get the number of joystick hats

SDL_JoystickNumButtons — Get the number of joysitck buttons

SDL_JoystickUpdate — Updates the state of all joysticks

SDL_JoystickGetAxis — Get the current state of an axis

SDL_JoystickGetHat — Get the current state of a joystick hat

SDL_JoystickGetButton — Get the current state of a given button on a given joystick

SDL_JoystickGetBall — Get relative trackball motion

SDL_JoystickClose — Closes a previously opened joystick

Joysticks, and other similar input devices, have a very strong role in game playing and SDL provides comprehensive support for them. Axes, Buttons, POV Hats and trackballs are all supported.

Joystick support is initialized by passed the SDL_INIT_JOYSTICK flag to SDL_Init. Once initilized joysticks must be opened using SDL_JoystickOpen.

While using the functions describe in this secton may seem like the best way to access and read from joysticks, in most cases they aren't. Ideally joysticks should be read using the event system. To enable this, you must set the joystick event processing state with SDL_JoystickEventState. Joysticks must be opened before they can be used of course.

Note: If you are not handling the joystick via the event queue then you must explicitly request a joystick update by calling SDL_JoystickUpdate.

Note: Force Feedback is not yet support. Sam (slouken@libsdl.org) is soliciting suggestions from people with force-feedback experience on the best wat to desgin the API.

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SDL_JoystickEventState | Up | SDL_NumJoysticks

SDL Library Documentation

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SDL_NumJoysticks

Name

SDL_NumJoysticks -- Count available joysticks.

Synopsis

#include "SDL.h"

int SDL_NumJoysticks(void);

Description

Counts the number of joysticks attached to the system.

Return Value

Returns the number of attached joysticks

See Also

SDL_JoystickName, SDL_JoystickOpen

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Joystick | Up | SDL_JoystickName

SDL Library Documentation

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SDL_JoystickName

Name

SDL_JoystickName -- Get joystick name.

Synopsis

#include "SDL.h"

const char *SDL_JoystickName(int index);

Description

Get the implementation dependent name of joystick. The index parameter refers to the N'th joystick on the system.

Return Value

Returns a char pointer to the joystick name.

Examples

/* Print the names of all attached joysticks */
int num_joy, i;
num_joy=SDL_NumJoysticks();
printf("%d joysticks found\n", num_joy);
for(i=0;i<num_joy;i++)
  printf("%s\n", SDL_JoystickName(i));

See Also

SDL_JoystickOpen

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SDL_NumJoysticks | Up | SDL_JoystickOpen

SDL Library Documentation

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SDL_JoystickOpen

Name

SDL_JoystickOpen -- Opens a joystick for use.

Synopsis

#include "SDL.h"

SDL_Joystick *SDL_JoystickOpen(int index);

Description

Opens a joystick for use within SDL. The index refers to the N'th joystick in the system. A joystick must be opened before it game be used.

Return Value

Returns a SDL_Joystick structure on success. NULL on failure.

Examples

SDL_Joystick *joy;
// Check for joystick
if(SDL_NumJoysticks()>0){
  // Open joystick
  joy=SDL_JoystickOpen(0);

  if(joy)
  {
    printf("Opened Joystick 0\n");
    printf("Name: %s\n", SDL_JoystickName(0));
    printf("Number of Axes: %d\n", SDL_JoystickNumAxes(joy));
    printf("Number of Buttons: %d\n", SDL_JoystickNumButtons(joy));
    printf("Number of Balls: %d\n", SDL_JoystickNumBalls(joy));
  }
  else
    printf("Couldn't open Joystick 0\n");

  // Close if opened
  if(SDL_JoystickOpened(0))
    SDL_JoystickClose(joy);
}

See Also

SDL_JoystickClose

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SDL_JoystickName | Up | SDL_JoystickOpened

SDL Library Documentation

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SDL_JoystickOpened

Name

SDL_JoystickOpened -- Determine if a joystick has been opened

Synopsis

#include "SDL.h"

int SDL_JoystickOpened(int index);

Description

Determines whether a joystick has already been opened within the application. index refers to the N'th joystick on the system.

Return Value

Returns 1 if the joystick has been opened, or 0 if it has not.

See Also

SDL_JoystickOpen, SDL_JoystickClose

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SDL_JoystickOpen | Up | SDL_JoystickIndex

SDL Library Documentation

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SDL_JoystickIndex

Name

SDL_JoystickIndex -- Get the index of an SDL_Joystick.

Synopsis

#include "SDL.h"

int SDL_JoystickIndex(SDL_Joystick *joystick);

Description

Returns the index of a given SDL_Joystick structure.

Return Value

Index number of the joystick.

See Also

SDL_JoystickOpen

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SDL_JoystickOpened | Up | SDL_JoystickNumAxes

SDL Library Documentation

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SDL_JoystickNumAxes

Name

SDL_JoystickNumAxes -- Get the number of joystick axes

Synopsis

#include "SDL.h"

int SDL_JoystickNumAxes(SDL_Joystick *joystick);

Description

Return the number of axes available from a previously opened SDL_Joystick.

Return Value

Number of axes.

See Also

SDL_JoystickGetAxis, SDL_JoystickOpen

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SDL_JoystickIndex | Up | SDL_JoystickNumBalls

SDL Library Documentation

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SDL_JoystickNumBalls

Name

SDL_JoystickNumBalls -- Get the number of joystick trackballs

Synopsis

#include "SDL.h"

int SDL_JoystickNumBalls(SDL_Joystick *joystick);

Description

Return the number of trackballs available from a previously opened SDL_Joystick.

Return Value

Number of trackballs.

See Also

SDL_JoystickGetBall, SDL_JoystickOpen

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SDL_JoystickNumAxes | Up | SDL_JoystickNumHats

SDL Library Documentation

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SDL_JoystickNumHats

Name

SDL_JoystickNumHats -- Get the number of joystick hats

Synopsis

#include "SDL.h"

int SDL_JoystickNumHats(SDL_Joystick *joystick);

Description

Return the number of hats available from a previously opened SDL_Joystick.

Return Value

Number of hats.

See Also

SDL_JoystickGetHat, SDL_JoystickOpen

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SDL_JoystickNumBalls | Up | SDL_JoystickNumButtons

SDL Library Documentation

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SDL_JoystickNumButtons

Name

SDL_JoystickNumButtons -- Get the number of joysitck buttons

Synopsis

#include "SDL.h"

int SDL_JoystickNumButtons(SDL_Joystick *joystick);

Description

Return the number of buttons available from a previously opened SDL_Joystick.

Return Value

Number of buttons.

See Also

SDL_JoystickGetButton, SDL_JoystickOpen

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SDL_JoystickNumHats | Up | SDL_JoystickUpdate

SDL Library Documentation

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SDL_JoystickUpdate

Name

SDL_JoystickUpdate -- Updates the state of all joysticks

Synopsis

#include "SDL.h"

void SDL_JoystickUpdate(void);

Description

Updates the state(position, buttons, etc.) of all open joysticks. If joystick events have been enabled with SDL_JoystickEventState then this is called automatically in the event loop.

See Also

SDL_JoystickEventState

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SDL_JoystickNumButtons | Up | SDL_JoystickGetAxis

SDL Library Documentation

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SDL_JoystickGetAxis

Name

SDL_JoystickGetAxis -- Get the current state of an axis

Synopsis

#include "SDL.h"

Sint16 SDL_JoystickGetAxis(SDL_Joystick *joystick, int axis);

Description

SDL_JoystickGetAxis returns the current state of the given axis on the given joystick.

On most modern joysticks the X axis is usually represented by axis 0 and the Y axis by axis 1. The value returned by SDL_JoystickGetAxis is a signed integer (-32768 to 32768) representing the current position of the axis, it maybe necessary to impose certain tolerances on these values to account for jitter. It is worth noting that some joysticks use axes 2 and 3 for extra buttons.

Return Value

Returns a 16-bit signed integer representing the current position of the axis.

Examples

Sint16 x_move, y_move;
SDL_Joystick *joy1;
.
.
x_move=SDL_JoystickGetAxis(joy1, 0);
y_move=SDL_JoystickGetAxis(joy1, 1);

See Also

SDL_JoystickNumAxes

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SDL_JoystickUpdate | Up | SDL_JoystickGetHat

SDL Library Documentation

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SDL_JoystickGetHat

Name

SDL_JoystickGetHat -- Get the current state of a joystick hat

Synopsis

#include "SDL.h"

Uint8 SDL_JoystickGetHat(SDL_Joystick *joystick, int hat);

Description

SDL_JoystickGetHat returns the current state of the given hat on the given joystick.

Return Value

The current state is returned as a Uint8 which is defined as an OR'd combination of one or more of the following

SDL_HAT_CENTERED

SDL_HAT_UP

SDL_HAT_RIGHT

SDL_HAT_DOWN

SDL_HAT_LEFT

SDL_HAT_RIGHTUP

SDL_HAT_RIGHTDOWN

SDL_HAT_LEFTUP

SDL_HAT_LEFTDOWN

See Also

SDL_JoystickNumHats

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SDL_JoystickGetAxis | Up | SDL_JoystickGetButton

SDL Library Documentation

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SDL_JoystickGetButton

Name

SDL_JoystickGetButton -- Get the current state of a given button on a given joystick

Synopsis

#include "SDL.h"

Uint8 SDL_JoystickGetButton(SDL_Joystick *joystick, int button);

Description

SDL_JoystickGetButton returns the current state of the given button on the given joystick.

Return Value

1 if the button is pressed. Otherwise, 0.

See Also

SDL_JoystickNumButtons

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SDL_JoystickGetHat | Up | SDL_JoystickGetBall

SDL Library Documentation

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SDL_JoystickGetBall

Name

SDL_JoystickGetBall -- Get relative trackball motion

Synopsis

#include "SDL.h"

int SDL_JoystickGetBall(SDL_Joystick *joystick, int ball, int *dx, int *dy);

Description

Get the ball axis change.

Trackballs can only return relative motion since the last call to SDL_JoystickGetBall, these motion deltas a placed into dx and dy.

Return Value

Returns 0 on success or -1 on failure

Examples

int delta_x, delta_y;
SDL_Joystick *joy;
.
.
.
SDL_JoystickUpdate();
if(SDL_JoystickGetBall(joy, 0, &delta_x, &delta_y)==-1)
  printf("TrackBall Read Error!\n");
printf("Trackball Delta- X:%d, Y:%d\n", delta_x, delta_y);

See Also

SDL_JoystickNumBalls

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SDL_JoystickGetButton | Up | SDL_JoystickClose

SDL Library Documentation

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SDL_JoystickClose

Name

SDL_JoystickClose -- Closes a previously opened joystick

Synopsis

#include "SDL.h"

void SDL_JoystickClose(SDL_Joystick *joystick);

Description

Close a joystick that was previously opened with SDL_JoystickOpen.

See Also

SDL_JoystickOpen, SDL_JoystickOpened

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SDL_JoystickGetBall | Up | Audio

SDL Library Documentation

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Chapter 10. Audio

Table of Contents

SDL_AudioSpec — Audio Specification Structure

SDL_OpenAudio — Opens the audio device with the desired parameters.

SDL_PauseAudio — Pauses and unpauses the audio callback processing

SDL_GetAudioStatus — Get the current audio state

SDL_LoadWAV — Load a WAVE file

SDL_FreeWAV — Frees previously opened WAV data

SDL_AudioCVT — Audio Conversion Structure

SDL_BuildAudioCVT — Initializes a SDL_AudioCVT structure for conversion

SDL_ConvertAudio — Convert audio data to a desired audio format.

SDL_MixAudio — Mix audio data

SDL_LockAudio — Lock out the callback function

SDL_UnlockAudio — Unlock the callback function

SDL_CloseAudio — Shuts down audio processing and closes the audio device.

Sound on the computer is translated from waves that you hear into a series of values, or samples, each representing the amplitude of the wave. When these samples are sent in a stream to a sound card, an approximation of the original wave can be recreated. The more bits used to represent the amplitude, and the greater frequency these samples are gathered, the closer the approximated sound is to the original, and the better the quality of sound.

This library supports both 8 and 16 bit signed and unsigned sound samples, at frequencies ranging from 11025 Hz to 44100 Hz, depending on the underlying hardware. If the hardware doesn't support the desired audio format or frequency, it can be emulated if desired (See SDL_OpenAudio())

A commonly supported audio format is 16 bits per sample at 22050 Hz.

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SDL_JoystickClose | Up | SDL_AudioSpec

SDL Library Documentation

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SDL_AudioSpec

Name

SDL_AudioSpec -- Audio Specification Structure

Structure Definition

typedef struct{
  int freq;
  Uint16 format;
  Uint8 channels;
  Uint8 silence;
  Uint16 samples;
  Uint32 size;
  void (*callback)(void *userdata, Uint8 *stream, int len);
  void *userdata;
} SDL_AudioSpec;

Structure Data

freq | Audio frequency in samples per second
format | Audio data format
channels | Number of channels: 1 mono, 2 stereo
silence | Audio buffer silence value (calculated)
samples | Audio buffer size in samples
size | Audio buffer size in bytes (calculated)
callback(..) | Callback function for filling the audio buffer
userdata | Pointer the user data which is passed to the callback function

Description

The SDL_AudioSpec structure is used to describe the format of some audio data. This structure is used by SDL_OpenAudio and SDL_LoadWAV. While all fields are used by SDL_OpenAudio only freq, format, samples and channels are used by SDL_LoadWAV. We will detail these common members here.

freq

The number of samples sent to the sound device every second. Common values are 11025, 22050 and 44100. The higher the better.

format

Specifies the size and type of each sample element

AUDIO_U8

Unsigned 8-bit samples

AUDIO_S8

Signed 8-bit samples

AUDIO_U16 or AUDIO_U16LSB

Unsigned 16-bit little-endian samples

AUDIO_S16 or AUDIO_S16LSB

Signed 16-bit little-endian samples

AUDIO_U16MSB

Unsigned 16-bit big-endian samples

AUDIO_S16MSB

Signed 16-bit big-endian samples

AUDIO_U16SYS

Either AUDIO_U16LSB or AUDIO_U16MSB depending on you systems endianness

AUDIO_S16SYS

Either AUDIO_S16LSB or AUDIO_S16MSB depending on you systems endianness

channels
The number of seperate sound channels. 1 is mono (single channel), 2 is stereo (dual channel).

samples
When used with SDL_OpenAudio this refers to the size of the audio buffer in samples. A sample a chunk of audio data of the size specified in format mulitplied by the number of channels. When the SDL_AudioSpec is used with SDL_LoadWAV samples is set to 4096.

See Also

SDL_OpenAudio, SDL_LoadWAV

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Audio | Up | SDL_OpenAudio

SDL Library Documentation

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SDL_OpenAudio

Name

SDL_OpenAudio -- Opens the audio device with the desired parameters.

Synopsis

#include "SDL.h"

int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained);

Description

This function opens the audio device with the desired parameters, and returns 0 if successful, placing the actual hardware parameters in the structure pointed to by obtained. If obtained is NULL, the audio data passed to the callback function will be guaranteed to be in the requested format, and will be automatically converted to the hardware audio format if necessary. This function returns -1 if it failed to open the audio device, or couldn't set up the audio thread.

To open the audio device a desired SDL_AudioSpec must be created.

SDL_AudioSpec *desired;
.
.
desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));

You must then fill this structure with your desired audio specifications.

desired->freq

The desired audio frequency in samples-per-second.

desired->format

The desired audio format (see SDL_AudioSpec)

desired->samples

The desired size of the audio buffer in samples. This number should be a power of two, and may be adjusted by the audio driver to a value more suitable for the hardware. Good values seem to range between 512 and 8192 inclusive, depending on the application and CPU speed. Smaller values yield faster response time, but can lead to underflow if the application is doing heavy processing and cannot fill the audio buffer in time. A stereo sample consists of both right and left channels in LR ordering. Note that the number of samples is directly related to time by the following formula: ms = (samples*1000)/freq

desired->callback

This should be set to a function that will be called when the audio device is ready for more data. It is passed a pointer to the audio buffer, and the length in bytes of the audio buffer. This function usually runs in a separate thread, and so you should protect data structures that it accesses by calling SDL_LockAudio and SDL_UnlockAudio in your code. The callback prototype is:

void callback(void *userdata, Uint8 *stream, int len);

userdata is the pointer stored in userdata field of the SDL_AudioSpec. stream is a pointer to the audio buffer you want to fill with information and len is the length of the audio buffer in bytes.

desired->userdata

This pointer is passed as the first parameter to the callback function.

SDL_OpenAudio reads these fields from the desired SDL_AudioSpec structure pass to the function and attempts to find an audio configuration matching your desired. As mentioned above, if the obtained parameter is NULL then SDL with convert from your desired audio settings to the hardware settings as it plays.

If obtained is NULL then the desired SDL_AudioSpec is your working specification, otherwise the obtained SDL_AudioSpec becomes the working specification and the desirec specification can be deleted. The data in the working specification is used when building SDL_AudioCVT's for converting loaded data to the hardware format.

SDL_OpenAudio calculates the size and silence fields for both the desired and obtained specifications. The size field stores the total size of the audio buffer in bytes, while the silence stores the value used to represent silence in the audio buffer

The audio device starts out playing silence when it's opened, and should be enabled for playing by calling SDL_PauseAudio(0) when you are ready for your audio callback function to be called. Since the audio driver may modify the requested size of the audio buffer, you should allocate any local mixing buffers after you open the audio device.

Examples

/* Prototype of our callback function */
void my_audio_callback(void *userdata, Uint8 *stream, int len);

/* Open the audio device */
SDL_AudioSpec *desired, *obtained;
SDL_AudioSpec *hardware_spec;

/* Allocate a desired SDL_AudioSpec */
desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));

/* Allocate space for the obtained SDL_AudioSpec */
obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));

/* 22050Hz - FM Radio quality */
desired->freq=22050;

/* 16-bit signed audio */
desired->format=AUDIO_S16LSB;

/* Mono */
desired->channels=0;

/* Large audio buffer reduces risk of dropouts but increases response time */
desired->samples=8192;

/* Our callback function */
desired->callback=my_audio_callback;

desired->userdata=NULL;

/* Open the audio device */
if ( SDL_OpenAudio(desired, obtained) < 0 ){
  fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
  exit(-1);
}
/* desired spec is no longer needed */
free(desired);
hardware_spec=obtained;
.
.
/* Prepare callback for playing */
.
.
.
/* Start playing */
SDL_PauseAudio(0);

See Also

SDL_AudioSpec, SDL_LockAudio, SDL_UnlockAudio, SDL_PauseAudio

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SDL_AudioSpec | Up | SDL_PauseAudio

SDL Library Documentation

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SDL_PauseAudio

Name

SDL_PauseAudio -- Pauses and unpauses the audio callback processing

Synopsis

#include "SDL.h"

void SDL_PauseAudio(int pause_on);

Description

This function pauses and unpauses the audio callback processing. It should be called with pause_on=0 after opening the audio device to start playing sound. This is so you can safely initialize data for your callback function after opening the audio device. Silence will be written to the audio device during the pause.

See Also

SDL_GetAudioStatus, SDL_OpenAudio

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SDL_OpenAudio | Up | SDL_GetAudioStatus

SDL Library Documentation

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SDL_GetAudioStatus

Name

SDL_GetAudioStatus -- Get the current audio state

Synopsis

#include "SDL.h"

SDL_audiostatusSDL_GetAudioStatus(void);

Description

typedef enum{
  SDL_AUDIO_STOPPED,
  SDL_AUDIO_PAUSED,
  SDL_AUDIO_PLAYING
} SDL_audiostatus;

Returns either SDL_AUDIO_STOPPED, SDL_AUDIO_PAUSED or SDL_AUDIO_PLAYING depending on the current audio state.

See Also

SDL_PauseAudio

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SDL_PauseAudio | Up | SDL_LoadWAV

SDL Library Documentation

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SDL_LoadWAV

Name

SDL_LoadWAV -- Load a WAVE file

Synopsis

#include "SDL.h"

SDL_AudioSpec *SDL_LoadWAV(const char *file, SDL_AudioSpec *spec, Uint8 **audio_buf, Uint32 *audio_len);

Description

SDL_LoadWAV This function loads a WAVE file into memory.

If this function succeeds, it returns the given SDL_AudioSpec, filled with the audio data format of the wave data, and sets audio_buf to a malloc'd buffer containing the audio data, and sets audio_len to the length of that audio buffer, in bytes. You need to free the audio buffer with SDL_FreeWAV when you are done with it.

This function returns NULL and sets the SDL error message if the wave file cannot be opened, uses an unknown data format, or is corrupt. Currently raw, MS-ADPCM and IMA-ADPCM WAVE files are supported.

Example

SDL_AudioSpec wav_spec;
Uint32 wav_length;
Uint8 *wav_buffer;

/* Load the WAV */
if( SDL_LoadWAV("test.wav", &wav_spec, &wav_buffer, &wav_length) == NULL ){
  fprintf(stderr, "Could not open test.wav: %s\n", SDL_GetError());
  exit(-1);
}
.
.
.
/* Do stuff with the WAV */
.
.
/* Free It */
SDL_FreeWAV(wav_buffer);

See Also

SDL_AudioSpec, SDL_OpenAudio, SDL_FreeWAV

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SDL_GetAudioStatus | Up | SDL_FreeWAV

SDL Library Documentation

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SDL_FreeWAV

Name

SDL_FreeWAV -- Frees previously opened WAV data

Synopsis

#include "SDL.h"

void SDL_FreeWAV(Uint8 *audio_buf);

Description

After a WAVE file has been opened with SDL_LoadWAV its data can eventually be freed with SDL_FreeWAV. audio_buf is a pointer to the buffer created by SDL_LoadWAV.

See Also

SDL_LoadWAV

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SDL_LoadWAV | Up | SDL_AudioCVT

SDL Library Documentation

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SDL_AudioCVT

Name

SDL_AudioCVT -- Audio Conversion Structure

Structure Definition

typedef struct{
  int needed;
  Uint16 src_format;
  Uint16 dest_format;
  double rate_incr;
  Uint8 *buf;
  int len;
  int len_cvt;
  int len_mult;
  double len_ratio;
  void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
  int filter_index;
} SDL_AudioCVT;

Structure Data

needed | Set to one if the conversion is possible
src_format | Audio format of the source
dest_format | Audio format of the destination
rate_incr | Rate conversion increment
buf | Audio buffer
len | Length of the original audio buffer in bytes
len_cvt | Length of converted audio buffer in bytes (calculated)
len_mult | buf must be len*len_mult bytes in size(calculated)
len_ratio | Final audio size is len*len_ratio
filters[10](..) | Pointers to functions needed for this conversion
filter_index | Current conversion function

Description

The SDL_AudioCVT is used to convert audio data between different formats. A SDL_AudioCVT structure is created with the SDL_BuildAudioCVT function, while the actual conversion is done by the SDL_ConvertAudio function.

Many of the fields in the SDL_AudioCVT structure should be considered private and their function will not be discussed here.

Uint8 *buf

This points to the audio data that will be used in the conversion. It is both the source and the destination, which means the converted audio data overwrites the original data. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure buf is large enough. See below.

int len

This is the length of the original audio data in bytes.

int len_mult

As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data. The length of buf should be len*len_mult.

double len_ratio

When you have finished converting your audio data, you need to know how much of your audio buffer is valid. len*len_ratio is the size of the converted audio data in bytes. This is very similar to len_mult, however when the convert audio data is shorter than the original len_mult would be 1. len_ratio, on the other hand, would be a fractional number between 0 and 1.

See Also

SDL_BuildAudioCVT, SDL_ConvertAudio, SDL_AudioSpec

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SDL_FreeWAV | Up | SDL_BuildAudioCVT

SDL Library Documentation

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SDL_BuildAudioCVT

Name

SDL_BuildAudioCVT -- Initializes a SDL_AudioCVT structure for conversion

Synopsis

#include "SDL.h"

int SDL_BuildAudioCVT(SDL_AudioCVT *cvt, Uint16 src_format, Uint8 src_channels, int src_rate, Uint16 dst_format, Uint8 dst_channels, int dst_rate);

Description

Before an SDL_AudioCVT structure can be used to convert audio data it must be initialized with source and destination information.

src_format and dst_format are the source and destination format of the conversion. (For information on audio formats see SDL_AudioSpec). src_channels and dst_channels are the number of channels in the source and destination formats. Finally, src_rate and dst_rate are the frequency or samples-per-second of the source and destination formats. Once again, see SDL_AudioSpec.

Return Values

Returns -1 if the filter could not be built or 1 if it could.

Examples

See SDL_ConvertAudio.

See Also

SDL_ConvertAudio, SDL_AudioCVT

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SDL_AudioCVT | Up | SDL_ConvertAudio

SDL Library Documentation

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SDL_ConvertAudio

Name

SDL_ConvertAudio -- Convert audio data to a desired audio format.

Synopsis

#include "SDL.h"

int SDL_ConvertAudio(SDL_AudioCVT *cvt);

Description

SDL_ConvertAudio takes one parameter, cvt, which was previously initilized. Initilizing a SDL_AudioCVT is a two step process. First of all, the structure must be passed to SDL_BuildAudioCVT along with source and destination format parameters. Secondly, the cvt->buf and cvt->len fields must be setup. cvt->buf should point to the audio data and cvt->len should be set to the length of the audio data in bytes. Remember, the length of the buffer pointed to by buf show be len*len_mult bytes in length.

Once the SDL_AudioCVTstructure is initilized then we can pass it to SDL_ConvertAudio, which will convert the audio data pointer to by cvt->buf. If SDL_ConvertAudio returned 0 then the conversion was completed successfully, otherwise -1 is returned.

If the conversion completed successfully then the converted audio data can be read from cvt->buf. The amount of valid, converted, audio data in the buffer is equal to cvt->len*cvt->len_ratio.

Examples

/* Converting some WAV data to hardware format */
void my_audio_callback(void *userdata, Uint8 *stream, int len);

SDL_AudioSpec *desired, *obtained;
SDL_AudioSpec wav_spec;
SDL_AudioCVT  wav_cvt;
Uint32 wav_len;
Uint8 *wav_buf;
int ret;

/* Allocated audio specs */
desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));

/* Set desired format */
desired->freq=22050;
desired->format=AUDIO_S16LSB;
desired->samples=8192;
desired->callback=my_audio_callback;
desired->userdata=NULL;

/* Open the audio device */
if ( SDL_OpenAudio(desired, obtained) < 0 ){
  fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
  exit(-1);
}

free(desired);

/* Load the test.wav */
if( SDL_LoadWAV("test.wav", &wav_spec, &wav_buf, &wav_len) == NULL ){
  fprintf(stderr, "Could not open test.wav: %s\n", SDL_GetError());
  SDL_CloseAudio();
  free(obtained);
  exit(-1);
}

/* Build AudioCVT */
ret = SDL_BuildAudioCVT(&wav_cvt,
                        wav_spec.format, wav_spec.channels, wav_spec.freq,
                        obtained->format, obtained->channels, obtained->freq);

/* Check that the convert was built */
if(ret==-1){
  fprintf(stderr, "Couldn't build converter!\n");
  SDL_CloseAudio();
  free(obtained);
  SDL_FreeWAV(wav_buf);
}

/* Setup for conversion */
wav_cvt.buf=(Uint8 *)malloc(wav_len*wav_cvt.len_mult);
wav_cvt.len=wav_len;
memcpy(wav_cvt.buf, wav_buf, wav_len);

/* We can delete to original WAV data now */
SDL_FreeWAV(wav_buf);

/* And now we're ready to convert */
SDL_ConvertAudio(&wav_cvt);

/* do whatever */
.
.
.
.

See Also

SDL_BuildAudioCVT, SDL_AudioCVT

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SDL_BuildAudioCVT | Up | SDL_MixAudio

SDL Library Documentation

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SDL_MixAudio

Name

SDL_MixAudio -- Mix audio data

Synopsis

#include "SDL.h"

void SDL_MixAudio(Uint8 *dst, Uint8 *src, Uint32 len, int volume);

Description

This function takes two audio buffers of len bytes each of the playing audio format and mixes them, performing addition, volume adjustment, and overflow clipping. The volume ranges from 0 to SDL_MIX_MAXVOLUME and should be set to the maximum value for full audio volume. Note this does not change hardware volume. This is provided for convenience -- you can mix your own audio data.

Note: Do not use this function for mixing together more than two streams of sample data. The output from repeated application of this function may be distorted by clipping, because there is no accumulator with greater range than the input (not to mention this being an inefficient way of doing it). Use mixing functions from SDL_mixer, OpenAL, or write your own mixer instead.

See Also

SDL_OpenAudio

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SDL_ConvertAudio | Up | SDL_LockAudio

SDL Library Documentation

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SDL_LockAudio

Name

SDL_LockAudio -- Lock out the callback function

Synopsis

#include "SDL.h"

void SDL_LockAudio(void);

Description

The lock manipulated by these functions protects the callback function. During a LockAudio period, you can be guaranteed that the callback function is not running. Do not call these from the callback function or you will cause deadlock.

See Also

SDL_OpenAudio

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SDL_MixAudio | Up | SDL_UnlockAudio

SDL Library Documentation

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SDL_UnlockAudio

Name

SDL_UnlockAudio -- Unlock the callback function

Synopsis

#include "SDL.h"

void SDL_UnlockAudio(void);

Description

Unlocks a previous SDL_LockAudio call.

See Also

SDL_OpenAudio

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SDL_LockAudio | Up | SDL_CloseAudio

SDL Library Documentation

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SDL_CloseAudio

Name

SDL_CloseAudio -- Shuts down audio processing and closes the audio device.

Synopsis

#include "SDL.h"

void SDL_CloseAudio(void);

Description

This function shuts down audio processing and closes the audio device.

See Also

SDL_OpenAudio

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SDL_UnlockAudio | Up | CD-ROM

SDL Library Documentation

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Chapter 11. CD-ROM

Table of Contents

SDL_CDNumDrives — Returns the number of CD-ROM drives on the system.

SDL_CDName — Returns a human-readable, system-dependent identifier for the CD-ROM.

SDL_CDOpen — Opens a CD-ROM drive for access.

SDL_CDStatus — Returns the current status of the given drive.

SDL_CDPlay — Play a CD

SDL_CDPlayTracks — Play the given CD track(s)

SDL_CDPause — Pauses a CDROM

SDL_CDResume — Resumes a CDROM

SDL_CDStop — Stops a CDROM

SDL_CDEject — Ejects a CDROM

SDL_CDClose — Closes a SDL_CD handle

SDL_CD — CDROM Drive Information

SDL_CDtrack — CD Track Information Structure

SDL supports audio control of up to 32 local CD-ROM drives at once.

You use this API to perform all the basic functions of a CD player, including listing the tracks, playing, stopping, and ejecting the CD-ROM. (Currently, multi-changer CD drives are not supported.)

Before you call any of the SDL CD-ROM functions, you must first call "SDL_Init(SDL_INIT_CDROM)", which scans the system for CD-ROM drives, and sets the program up for audio control. Check the return code, which should be 0, to see if there were any errors in starting up.

After you have initialized the library, you can find out how many drives are available using the SDL_CDNumDrives() function. The first drive listed is the system default CD-ROM drive. After you have chosen a drive, and have opened it with SDL_CDOpen(), you can check the status and start playing if there's a CD in the drive.

A CD-ROM is organized into one or more tracks, each consisting of a certain number of "frames". Each frame is ~2K in size, and at normal playing speed, a CD plays 75 frames per second. SDL works with the number of frames on a CD, but this can easily be converted to the more familiar minutes/seconds format by using the FRAMES_TO_MSF() macro.

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SDL_CloseAudio | Up | SDL_CDNumDrives

SDL Library Documentation

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SDL_CDNumDrives

Name

SDL_CDNumDrives -- Returns the number of CD-ROM drives on the system.

Synopsis

#include "SDL.h"

int SDL_CDNumDrives(void);

Description

Returns the number of CD-ROM drives on the system.

See Also

SDL_CDOpen

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CD-ROM | Up | SDL_CDName

SDL Library Documentation

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SDL_CDName

Name

SDL_CDName -- Returns a human-readable, system-dependent identifier for the CD-ROM.

Synopsis

#include "SDL.h"

const char *SDL_CDName(int drive);

Description

Returns a human-readable, system-dependent identifier for the CD-ROM. drive is the index of the drive. Drive indices start to 0 and end at SDL_CDNumDrives()-1.

Examples

"/dev/cdrom"

"E:"

"/dev/disk/ide/1/master"

See Also

SDL_CDNumDrives

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SDL_CDNumDrives | Up | SDL_CDOpen

SDL Library Documentation

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SDL_CDOpen

Name

SDL_CDOpen -- Opens a CD-ROM drive for access.

Synopsis

#include "SDL.h"

SDL_CD *SDL_CDOpen(int drive);

Description

Opens a CD-ROM drive for access. It returns a SDL_CD structure on success, or NULL if the drive was invalid or busy. This newly opened CD-ROM becomes the default CD used when other CD functions are passed a NULL CD-ROM handle.

Drives are numbered starting with 0. Drive 0 is the system default CD-ROM.

Examples

SDL_CD *cdrom;
int cur_track;
int min, sec, frame;
SDL_Init(SDL_INIT_CDROM);
atexit(SDL_Quit);

/* Check for CD drives */
if(!SDL_CDNumDrives()){
  /* None found */
  fprintf(stderr, "No CDROM devices available\n");
  exit(-1);
}

/* Open the default drive */
cdrom=SDL_CDOpen(0);

/* Did if open? Check if cdrom is NULL */
if(!cdrom){
  fprintf(stderr, "Couldn't open drive: %s\n", SDL_GetError());
  exit(-1);
}

/* Print Volume info */
printf("Name: %s\n", SDL_CDName(0));
printf("Tracks: %d\n", cdrom->numtracks);
for(cur_track=0;cur_track < cdrom->numtracks; cur_track++){
  FRAMES_TO_MSF(cdrom->track[cur_track].length, &min, &sec, &frame);
  printf("\tTrack %d: Length %d:%d\n", cur_track, min, sec);
}

SDL_CDClose(cdrom);

See Also

SDL_CD, SDL_CDtrack, SDL_CDClose

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SDL_CDName | Up | SDL_CDStatus

SDL Library Documentation

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SDL_CDStatus

Name

SDL_CDStatus -- Returns the current status of the given drive.

Synopsis

#include "SDL.h"

CDstatus SDL_CDStatus(SDL_CD *cdrom);

/* Given a status, returns true if there's a disk in the drive */
#define CD_INDRIVE(status)      ((int)status > 0)

Description

This function returns the current status of the given drive. Status is described like so:

typedef enum {
  CD_TRAYEMPTY,
  CD_STOPPED,
  CD_PLAYING,
  CD_PAUSED,
  CD_ERROR = -1
} CDstatus;

If the drive has a CD in it, the table of contents of the CD and current play position of the CD will be stored in the SDL_CD structure.

The macro CD_INDRIVE is provided for convenience, and given a status returns true if there's a disk in the drive.

Note: SDL_CDStatus also updates the SDL_CD structure passed to it.

Example

int playTrack(int track)
{
  int playing = 0;

  if ( CD_INDRIVE(SDL_CDStatus(cdrom)) ) {
  /* clamp to the actual number of tracks on the CD */
    if (track >= cdrom->numtracks) {
      track = cdrom->numtracks-1;
    }

    if ( SDL_CDPlayTracks(cdrom, track, 0, 1, 0) == 0 ) {
      playing = 1;
    }
  }
  return playing;
}

See Also

SDL_CD

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SDL_CDOpen | Up | SDL_CDPlay

SDL Library Documentation

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SDL_CDPlay

Name

SDL_CDPlay -- Play a CD

Synopsis

#include "SDL.h"

int SDL_CDPlay(SDL_CD *cdrom, int start, int length);

Description

Plays the given cdrom, starting a frame start for length frames.

Return Values

Returns 0 on success, or -1 on an error.

See Also

SDL_CDPlayTracks, SDL_CDStop

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SDL_CDStatus | Up | SDL_CDPlayTracks

SDL Library Documentation

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SDL_CDPlayTracks

Name

SDL_CDPlayTracks -- Play the given CD track(s)

Synopsis

#include "SDL.h"

int SDL_CDPlayTracks(SDL_CD *cdrom, int start_track, int start_frame, int ntracks, int nframes));

Description

SDL_CDPlayTracks plays the given CD starting at track start_track, for ntracks tracks.

start_frame is the frame offset, from the beginning of the start_track, at which to start. nframes is the frame offset, from the beginning of the last track (start_track+ntracks), at which to end playing.

SDL_CDPlayTracks should only be called after calling SDL_CDStatus to get track information about the CD.

Note: Data tracks are ignored.

Return Value

Returns 0, or -1 if there was an error.

Examples

/* assuming cdrom is a previously opened device */
/* Play the entire CD */
if(CD_INDRIVE(SDL_CDStatus(cdrom)))
  SDL_CDPlayTracks(cdrom, 0, 0, 0, 0);

/* Play the first track */
if(CD_INDRIVE(SDL_CDStatus(cdrom)))
  SDL_CDPlayTracks(cdrom, 0, 0, 1, 0);

/* Play first 15 seconds of the 2nd track */
if(CD_INDRIVE(SDL_CDStatus(cdrom)))
  SDL_CDPlayTracks(cdrom, 1, 0, 0, CD_FPS*15);

See Also

SDL_CDPlay, SDL_CDStatus, SDL_CD

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SDL_CDPlay | Up | SDL_CDPause

SDL Library Documentation

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SDL_CDPause

Name

SDL_CDPause -- Pauses a CDROM

Synopsis

#include "SDL.h"

int SDL_CDPause(SDL_CD *cdrom);

Description

Pauses play on the given cdrom.

Return Value

Returns 0 on success, or -1 on an error.

See Also

SDL_CDPlay, SDL_CDResume

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SDL_CDPlayTracks | Up | SDL_CDResume

SDL Library Documentation

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SDL_CDResume

Name

SDL_CDResume -- Resumes a CDROM

Synopsis

#include "SDL.h"

int SDL_CDResume(SDL_CD *cdrom);

Description

Resumes play on the given cdrom.

Return Value

Returns 0 on success, or -1 on an error.

See Also

SDL_CDPlay, SDL_CDPause

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SDL_CDPause | Up | SDL_CDStop

SDL Library Documentation

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SDL_CDStop

Name

SDL_CDStop -- Stops a CDROM

Synopsis

#include "SDL.h"

int SDL_CDStop(SDL_CD *cdrom);

Description

Stops play on the given cdrom.

Return Value

Returns 0 on success, or -1 on an error.

See Also

SDL_CDPlay,

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SDL_CDResume | Up | SDL_CDEject

SDL Library Documentation

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SDL_CDEject

Name

SDL_CDEject -- Ejects a CDROM

Synopsis

#include "SDL.h"

int SDL_CDEject(SDL_CD *cdrom);

Description

Ejects the given cdrom.

Return Value

Returns 0 on success, or -1 on an error.

See Also

SDL_CD

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SDL_CDStop | Up | SDL_CDClose

SDL Library Documentation

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SDL_CDClose

Name

SDL_CDClose -- Closes a SDL_CD handle

Synopsis

#include "SDL.h"

void SDL_CDClose(SDL_CD *cdrom);

Description

Closes the given cdrom handle.

See Also

SDL_CDOpen, SDL_CD

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SDL_CDEject | Up | SDL_CD

SDL Library Documentation

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SDL_CD

Name

SDL_CD -- CDROM Drive Information

Structure Definition

typedef struct{
  int id;
  CDstatus status;
  int numtracks;
  int cur_track;
  int cur_frame;
  SDL_CDtrack track[SDL_MAX_TRACKS+1];
} SDL_CD;

Structure Data

id | Private drive identifier
status | Drive status
numtracks | Number of tracks on the CD
cur_track | Current track
cur_frame | Current frame offset within the track
track[SDL_MAX_TRACKS+1] | Array of track descriptions. (see SDL_CDtrack)

Description

An SDL_CD structure is returned by SDL_CDOpen. It represents an opened CDROM device and stores information on the layout of the tracks on the disc.

A frame is the base data unit of a CD. CD_FPS frames is equal to 1 second of music. SDL provides two macros for converting between time and frames: FRAMES_TO_MSF(f, M,S,F) and MSF_TO_FRAMES.

Examples

int min, sec, frame;
int frame_offset;

FRAMES_TO_MSF(cdrom->cur_frame, &min, &sec, &frame);
printf("Current Position: %d minutes, %d seconds, %d frames\n", min, sec, frame);

frame_offset=MSF_TO_FRAMES(min, sec, frame);

See Also

SDL_CDOpen, SDL_CDtrack

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SDL_CDClose | Up | SDL_CDtrack

SDL Library Documentation

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SDL_CDtrack

Name

SDL_CDtrack -- CD Track Information Structure

Structure Definition

typedef struct{
  Uint8 id;
  Uint8 type;
  Uint32 length;
  Uint32 offset;
} SDL_CDtrack;

Structure Data

id | Track number (0-99)
type | SDL_AUDIO_TRACK or SDL_DATA_TRACK
length | Length, in frames, of this track
offset | Frame offset to the beginning of this track

Description

SDL_CDtrack stores data on each track on a CD, its fields should be pretty self explainatory. It is a member a the SDL_CD structure.

Note: Frames can be converted to standard timings. There are CD_FPS frames per second, so SDL_CDtrack.length/CD_FPS=length_in_seconds.

See Also

SDL_CD

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SDL_CD | Up | Multi-threaded Programming

SDL Library Documentation

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Chapter 12. Multi-threaded Programming

Table of Contents

SDL_CreateThread — Creates a new thread of execution that shares its parent's properties.

SDL_ThreadID — Get the 32-bit thread identifier for the current thread.

SDL_GetThreadID — Get the SDL thread ID of a SDL_Thread

SDL_WaitThread — Wait for a thread to finish.

SDL_KillThread — Gracelessly terminates the thread.

SDL_CreateMutex — Create a mutex

SDL_DestroyMutex — Destroy a mutex

SDL_mutexP — Lock a mutex

SDL_mutexV — Unlock a mutex

SDL_CreateSemaphore — Creates a new semaphore and assigns an initial value to it.

SDL_DestroySemaphore — Destroys a semaphore that was created by SDL_CreateSemaphore.

SDL_SemWait — Lock a semaphore and suspend the thread if the semaphore value is zero.

SDL_SemTryWait — Attempt to lock a semaphore but don't suspend the thread.

SDL_SemWaitTimeout — Lock a semaphore, but only wait up to a specified maximum time.

SDL_SemPost — Unlock a semaphore.

SDL_SemValue — Return the current value of a semaphore.

SDL_CreateCond — Create a condition variable

SDL_DestroyCond — Destroy a condition variable

SDL_CondSignal — Restart a thread wait on a condition variable

SDL_CondBroadcast — Restart all threads waiting on a condition variable

SDL_CondWait — Wait on a condition variable

SDL_CondWaitTimeout — Wait on a condition variable, with timeout

SDL provides functions for creating threads, mutexes, semphores and condition variables.

In general, you must be very aware of concurrency and data integrity issues when writing multi-threaded programs. Some good guidelines include:

Don't call SDL video/event functions from separate threads

Don't use any library functions in separate threads

Don't perform any memory management in separate threads

Lock global variables which may be accessed by multiple threads

Never terminate threads, always set a flag and wait for them to quit

Think very carefully about all possible ways your code may interact

Note: SDL's threading is not implemented on MacOS, due to that lack of preemptive thread support (MacOS X dos nt suffer from this problem)

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SDL_CDtrack | Up | SDL_CreateThread

SDL Library Documentation

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SDL_CreateThread

Name

SDL_CreateThread -- Creates a new thread of execution that shares its parent's properties.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

SDL_Thread *SDL_CreateThread(int (*fn)(void *), void *data);

Description

SDL_CreateThread creates a new thread of execution that shares all of its parent's global memory, signal handlers, file descriptors, etc, and runs the function fn passed the void pointer data The thread quits when this function returns.

See Also

SDL_KillThread

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Multi-threaded Programming | Up | SDL_ThreadID

SDL Library Documentation

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SDL_ThreadID

Name

SDL_ThreadID -- Get the 32-bit thread identifier for the current thread.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

Uint32 SDL_ThreadID(void);

Description

Get the 32-bit thread identifier for the current thread.

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SDL_CreateThread | Up | SDL_GetThreadID

SDL Library Documentation

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SDL_GetThreadID

Name

SDL_GetThreadID -- Get the SDL thread ID of a SDL_Thread

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

Uint32 SDL_GetThreadID(SDL_Thread *thread);

Description

Returns the ID of a SDL_Thread created by SDL_CreateThread.

See Also

SDL_CreateThread

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SDL_ThreadID | Up | SDL_WaitThread

SDL Library Documentation

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SDL_WaitThread

Name

SDL_WaitThread -- Wait for a thread to finish.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

void SDL_WaitThread(SDL_Thread *thread, int *status);

Description

Wait for a thread to finish (timeouts are not supported).

Return Value

The return code for the thread function is placed in the area pointed to by status, if status is not NULL.

See Also

SDL_CreateThread

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SDL_GetThreadID | Up | SDL_KillThread

SDL Library Documentation

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SDL_KillThread

Name

SDL_KillThread -- Gracelessly terminates the thread.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

void SDL_KillThread(SDL_Thread *thread);

Description

SDL_KillThread gracelessly terminates the thread associated with thread. If possible, you should use some other form of IPC to signal the thread to quit.

See Also

SDL_CreateThread, SDL_WaitThread

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SDL_WaitThread | Up | SDL_CreateMutex

SDL Library Documentation

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SDL_CreateMutex

Name

SDL_CreateMutex -- Create a mutex

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

SDL_mutex *SDL_CreateMutex(void);

Description

Create a new, unlocked mutex.

Examples

SDL_mutex *mut;

mut=SDL_CreateMutex();
.
.
if(SDL_mutexP(mut)==-1){
  fprintf(stderr, "Couldn't lock mutex\n");
  exit(-1);
}
.
/* Do stuff while mutex is locked */
.
.
if(SDL_mutexV(mut)==-1){
  fprintf(stderr, "Couldn't unlock mutex\n");
  exit(-1);
}

SDL_DestroyMutex(mut);

See Also

SDL_mutexP, SDL_mutexV, SDL_DestroyMutex

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SDL_KillThread | Up | SDL_DestroyMutex

SDL Library Documentation

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SDL_DestroyMutex

Name

SDL_DestroyMutex -- Destroy a mutex

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

void SDL_DestroyMutex(SDL_mutex *mutex);

Description

Destroy a previously created mutex.

See Also

SDL_CreateMutex

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SDL_CreateMutex | Up | SDL_mutexP

SDL Library Documentation

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SDL_mutexP

Name

SDL_mutexP -- Lock a mutex

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_mutexP(SDL_mutex *mutex);

Description

Locks the mutex, which was previously created with SDL_CreateMutex. If the mutex is already locked then SDL_mutexP will not return until it is unlocked. Returns 0 on success, or -1 on an error.

SDL also defines a macro #define SDL_LockMutex(m) SDL_mutexP(m).

See Also

SDL_CreateMutex, SDL_mutexV

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SDL_DestroyMutex | Up | SDL_mutexV

SDL Library Documentation

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SDL_mutexV

Name

SDL_mutexV -- Unlock a mutex

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_mutexV(SDL_mutex *mutex);

Description

Unlocks the mutex, which was previously created with SDL_CreateMutex. Returns 0 on success, or -1 on an error.

SDL also defines a macro #define SDL_UnlockMutex(m) SDL_mutexV(m).

See Also

SDL_CreateMutex, SDL_mutexP

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SDL_mutexP | Up | SDL_CreateSemaphore

SDL Library Documentation

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SDL_CreateSemaphore

Name

SDL_CreateSemaphore -- Creates a new semaphore and assigns an initial value to it.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

SDL_sem *SDL_CreateSemaphore(Uint32 initial_value);

Description

SDL_CreateSemaphore() creates a new semaphore and initializes it with the value initial_value. Each locking operation on the semaphore by SDL_SemWait, SDL_SemTryWait or SDL_SemWaitTimeout will atomically decrement the semaphore value. The locking operation will be blocked if the semaphore value is not positive (greater than zero). Each unlock operation by SDL_SemPost will atomically increment the semaphore value.

Return Value

Returns a pointer to an initialized semaphore or NULL if there was an error.

Examples

SDL_sem *my_sem;

my_sem = SDL_CreateSemaphore(INITIAL_SEM_VALUE);

if (my_sem == NULL) {
        return CREATE_SEM_FAILED;
}

See Also

SDL_DestroySemaphore, SDL_SemWait, SDL_SemTryWait, SDL_SemWaitTimeout, SDL_SemPost, SDL_SemValue

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SDL_mutexV | Up | SDL_DestroySemaphore

SDL Library Documentation

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SDL_DestroySemaphore

Name

SDL_DestroySemaphore -- Destroys a semaphore that was created by SDL_CreateSemaphore.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

void SDL_DestroySemaphore(SDL_sem *sem);

Description

SDL_DestroySemaphore destroys the semaphore pointed to by sem that was created by SDL_CreateSemaphore. It is not safe to destroy a semaphore if there are threads currently blocked waiting on it.

Examples

if (my_sem != NULL) {
        SDL_DestroySemaphore(my_sem);
        my_sem = NULL;
}

See Also

SDL_CreateSemaphore, SDL_SemWait, SDL_SemTryWait, SDL_SemWaitTimeout, SDL_SemPost, SDL_SemValue

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SDL_CreateSemaphore | Up | SDL_SemWait

SDL Library Documentation

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SDL_SemWait

Name

SDL_SemWait -- Lock a semaphore and suspend the thread if the semaphore value is zero.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_SemWait(SDL_sem *sem);

Description

SDL_SemWait() suspends the calling thread until either the semaphore pointed to by sem has a positive value, the call is interrupted by a signal or error. If the call is successful it will atomically decrement the semaphore value.

After SDL_SemWait() is successful, the semaphore can be released and its count atomically incremented by a successful call to SDL_SemPost.

Return Value

Returns 0 if successful or -1 if there was an error (leaving the semaphore unchanged).

Examples

if (SDL_SemWait(my_sem) == -1) {
        return WAIT_FAILED;
}

...

SDL_SemPost(my_sem);

See Also

SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemTryWait, SDL_SemWaitTimeout, SDL_SemPost, SDL_SemValue

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SDL_DestroySemaphore | Up | SDL_SemTryWait

SDL Library Documentation

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SDL_SemTryWait

Name

SDL_SemTryWait -- Attempt to lock a semaphore but don't suspend the thread.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_SemTryWait(SDL_sem *sem);

Description

SDL_SemTryWait is a non-blocking varient of SDL_SemWait. If the value of the semaphore pointed to by sem is positive it will atomically decrement the semaphore value and return 0, otherwise it will return SDL_MUTEX_TIMEOUT instead of suspending the thread.

After SDL_SemTryWait is successful, the semaphore can be released and its count atomically incremented by a successful call to SDL_SemPost.

Return Value

Returns 0 if the semaphore was successfully locked or either SDL_MUTEX_TIMEOUT or -1 if the thread would have suspended or there was an error, respectivly.

If the semaphore was not successfully locked, the semaphore will be unchanged.

Examples

res = SDL_SemTryWait(my_sem);

if (res == SDL_MUTEX_TIMEOUT) {
        return TRY_AGAIN;
}
if (res == -1) {
        return WAIT_ERROR;
}

...

SDL_SemPost(my_sem);

See Also

SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemWait, SDL_SemWaitTimeout, SDL_SemPost, SDL_SemValue

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SDL_SemWait | Up | SDL_SemWaitTimeout

SDL Library Documentation

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SDL_SemWaitTimeout

Name

SDL_SemWaitTimeout -- Lock a semaphore, but only wait up to a specified maximum time.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout);

Description

SDL_SemWaitTimeout() is a varient of SDL_SemWait with a maximum timeout value. If the value of the semaphore pointed to by sem is positive (greater than zero) it will atomically decrement the semaphore value and return 0, otherwise it will wait up to timeout milliseconds trying to lock the semaphore. This function is to be avoided if possible since on some platforms it is implemented by polling the semaphore every millisecond in a busy loop.

After SDL_SemWaitTimeout() is successful, the semaphore can be released and its count atomically incremented by a successful call to SDL_SemPost.

Return Value

Returns 0 if the semaphore was successfully locked or either SDL_MUTEX_TIMEOUT or -1 if the timeout period was exceeded or there was an error, respectivly.

If the semaphore was not successfully locked, the semaphore will be unchanged.

Examples

res = SDL_SemWaitTimeout(my_sem, WAIT_TIMEOUT_MILLISEC);

if (res == SDL_MUTEX_TIMEOUT) {
        return TRY_AGAIN;
}
if (res == -1) {
        return WAIT_ERROR;
}

...

SDL_SemPost(my_sem);

See Also

SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemWait, SDL_SemTryWait, SDL_SemPost, SDL_SemValue

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SDL_SemTryWait | Up | SDL_SemPost

SDL Library Documentation

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SDL_SemPost

Name

SDL_SemPost -- Unlock a semaphore.

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_SemPost(SDL_sem *sem);

Description

SDL_SemPost unlocks the semaphore pointed to by sem and atomically increments the semaphores value. Threads that were blocking on the semaphore may be scheduled after this call succeeds.

SDL_SemPost should be called after a semaphore is locked by a successful call to SDL_SemWait, SDL_SemTryWait or SDL_SemWaitTimeout.

Return Value

Returns 0 if successful or -1 if there was an error (leaving the semaphore unchanged).

Examples

SDL_SemPost(my_sem);

See Also

SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemWait, SDL_SemTryWait, SDL_SemWaitTimeout, SDL_SemValue

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SDL_SemWaitTimeout | Up | SDL_SemValue

SDL Library Documentation

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SDL_SemValue

Name

SDL_SemValue -- Return the current value of a semaphore.

Synopsis

#include "SDL.h"
#include "SDL/SDL_thread.h"

Uint32 SDL_SemValue(SDL_sem *sem);

Description

SDL_SemValue() returns the current semaphore value from the semaphore pointed to by sem.

Return Value

Returns current value of the semaphore.

Examples

  sem_value = SDL_SemValue(my_sem);

See Also

SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemWait, SDL_SemTryWait, SDL_SemWaitTimeout, SDL_SemPost

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SDL_SemPost | Up | SDL_CreateCond

SDL Library Documentation

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SDL_CreateCond

Name

SDL_CreateCond -- Create a condition variable

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

SDL_cond *SDL_CreateCond(void);

Description

Creates a condition variable.

Examples

SDL_cond *cond;

cond=SDL_CreateCond();
.
.
/* Do stuff */

.
.
SDL_DestroyCond(cond);

See Also

SDL_DestroyCond, SDL_CondWait, SDL_CondSignal

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SDL_SemValue | Up | SDL_DestroyCond

SDL Library Documentation

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SDL_DestroyCond

Name

SDL_DestroyCond -- Destroy a condition variable

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

void SDL_DestroyCond(SDL_cond *cond);

Description

Destroys a condition variable.

See Also

SDL_CreateCond

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SDL_CreateCond | Up | SDL_CondSignal

SDL Library Documentation

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SDL_CondSignal

Name

SDL_CondSignal -- Restart a thread wait on a condition variable

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_CondSignal(SDL_cond *cond);

Description

Restart one of the threads that are waiting on the condition variable, cond. Returns 0 on success of -1 on an error.

See Also

SDL_CondWait, SDL_CondBroadcast

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SDL_DestroyCond | Up | SDL_CondBroadcast

SDL Library Documentation

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SDL_CondBroadcast

Name

SDL_CondBroadcast -- Restart all threads waiting on a condition variable

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_CondBroadcast(SDL_cond *cond);

Description

Restarts all threads that are waiting on the condition variable, cond. Returns 0 on success, or -1 on an error.

See Also

SDL_CondSignal, SDL_CondWait

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SDL_CondSignal | Up | SDL_CondWait

SDL Library Documentation

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SDL_CondWait

Name

SDL_CondWait -- Wait on a condition variable

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_CondWait(SDL_cond *cond, SDL_mutex *mut);

Description

Wait on the condition variable cond and unlock the provided mutex. The mutex must the locked before entering this function. Returns 0 when it is signalled, or -1 on an error.

See Also

SDL_CondWaitTimeout, SDL_CondSignal, SDL_mutexP

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SDL_CondBroadcast | Up | SDL_CondWaitTimeout

SDL Library Documentation

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SDL_CondWaitTimeout

Name

SDL_CondWaitTimeout -- Wait on a condition variable, with timeout

Synopsis

#include "SDL.h"
#include "SDL_thread.h"

int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms);

Description

Wait on the condition variable cond for, at most, ms milliseconds. mut is unlocked so it must be locked when the function is called. Returns SDL_MUTEX_TIMEDOUT if the condition is not signalled in the allotted time, 0 if it was signalled or -1 on an error.

See Also

SDL_CondWait

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SDL_CondWait | Up | Time

SDL Library Documentation

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Chapter 13. Time

Table of Contents

SDL_GetTicks — Get the number of milliseconds since the SDL library initialization.

SDL_Delay — Wait a specified number of milliseconds before returning.

SDL_AddTimer — Add a timer which will call a callback after the specified number of milliseconds has elapsed.

SDL_RemoveTimer — Remove a timer which was added with SDL_AddTimer.

SDL_SetTimer — Set a callback to run after the specified number of milliseconds has elapsed.

SDL provides several cross-platform functions for dealing with time. It provides a way to get the current time, a way to wait a little while, and a simple timer mechanism. These functions give you two ways of moving an object every x milliseconds:

Use a timer callback function. This may have the bad effect that it runs in a seperate thread or uses alarm signals, but it's easier to implement.

Or you can get the number of milliseconds passed, and move the object if, for example, 30 ms passed.

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SDL_CondWaitTimeout | Up | SDL_GetTicks

SDL Library Documentation

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SDL_GetTicks

Name

SDL_GetTicks -- Get the number of milliseconds since the SDL library initialization.

Synopsis

#include "SDL.h"

Uint32 SDL_GetTicks(void);

Description

Get the number of milliseconds since the SDL library initialization. Note that this value wraps if the program runs for more than ~49 days.

See Also

SDL_Delay

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Time | Up | SDL_Delay

SDL Library Documentation

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SDL_Delay

Name

SDL_Delay -- Wait a specified number of milliseconds before returning.

Synopsis

#include "SDL.h"

void SDL_Delay(Uint32 ms);

Description

Wait a specified number of milliseconds before returning. SDL_Delay will wait at least the specified time, but possible longer due to OS scheduling.

Note: Count on a delay granularity of at least 10 ms. Some platforms have shorter clock ticks but this is the most common.

See Also

SDL_AddTimer

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SDL_GetTicks | Up | SDL_AddTimer

SDL Library Documentation

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SDL_AddTimer

Name

SDL_AddTimer -- Add a timer which will call a callback after the specified number of milliseconds has elapsed.

Synopsis

#include "SDL.h"

SDL_TimerID SDL_AddTimer(Uint32 interval, SDL_NewTimerCallback callback, void *param);

Callback

/* type definition for the "new" timer callback function */
typedef Uint32 (*SDL_NewTimerCallback)(Uint32 interval, void *param);

Description

Adds a callback function to be run after the specified number of milliseconds has elapsed. The callback function is passed the current timer interval and the user supplied parameter from the SDL_AddTimer call and returns the next timer interval. If the returned value from the callback is the same as the one passed in, the periodic alarm continues, otherwise a new alarm is scheduled.

To cancel a currently running timer call SDL_RemoveTimer with the timer ID returned from SDL_AddTimer.

The timer callback function may run in a different thread than your main program, and so shouldn't call any functions from within itself. You may always call SDL_PushEvent, however.

The granularity of the timer is platform-dependent, but you should count on it being at least 10 ms as this is the most common number. This means that if you request a 16 ms timer, your callback will run approximately 20 ms later on an unloaded system. If you wanted to set a flag signaling a frame update at 30 frames per second (every 33 ms), you might set a timer for 30 ms (see example below). If you use this function, you need to pass SDL_INIT_TIMER to SDL_Init.

Return Value

Returns an ID value for the added timer or NULL if there was an error.

Examples

my_timer_id = SDL_AddTimer((33/10)*10, my_callbackfunc, my_callback_param);

See Also

SDL_RemoveTimer, SDL_PushEvent

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SDL_Delay | Up | SDL_RemoveTimer

SDL Library Documentation

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SDL_RemoveTimer

Name

SDL_RemoveTimer -- Remove a timer which was added with SDL_AddTimer.

Synopsis

#include "SDL.h"

SDL_bool SDL_RemoveTimer(SDL_TimerID id);

Description

Removes a timer callback previously added with SDL_AddTimer.

Return Value

Returns a boolean value indicating success.

Examples

SDL_RemoveTimer(my_timer_id);

See Also

SDL_AddTimer

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SDL_AddTimer | Up | SDL_SetTimer

SDL Library Documentation

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SDL_SetTimer

Name

SDL_SetTimer -- Set a callback to run after the specified number of milliseconds has elapsed.

Synopsis

#include "SDL.h"

int SDL_SetTimer(Uint32 interval, SDL_TimerCallback callback);

Callback

/* Function prototype for the timer callback function */ typedef Uint32 (*SDL_TimerCallback)(Uint32 interval);

Description

Set a callback to run after the specified number of milliseconds has elapsed. The callback function is passed the current timer interval and returns the next timer interval. If the returned value is the same as the one passed in, the periodic alarm continues, otherwise a new alarm is scheduled.

To cancel a currently running timer, call SDL_SetTimer(0, NULL);

The timer callback function may run in a different thread than your main constant, and so shouldn't call any functions from within itself.

The maximum resolution of this timer is 10 ms, which means that if you request a 16 ms timer, your callback will run approximately 20 ms later on an unloaded system. If you wanted to set a flag signaling a frame update at 30 frames per second (every 33 ms), you might set a timer for 30 ms (see example below).

If you use this function, you need to pass SDL_INIT_TIMER to SDL_Init().

Note: This function is kept for compatibility but has been superseded by the new timer functions SDL_AddTimer and SDL_RemoveTimer which support multiple timers.

Examples

SDL_SetTimer((33/10)*10, my_callback);

See Also

SDL_AddTimer

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SDL_RemoveTimer | Up |