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Initial revision
author Sam Lantinga <slouken@lokigames.com>
date Thu, 26 Apr 2001 16:45:43 +0000
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children 55f1f1b3e27d
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<HTML
><HEAD
><TITLE
>Graphics and Video</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.61
"><LINK
REL="HOME"
TITLE="SDL Library Documentation"
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TITLE="SDL Guide"
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TITLE="Initializing SDL"
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><BODY
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><DIV
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><TABLE
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><TR
><TH
COLSPAN="3"
ALIGN="center"
>SDL Library Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="guidebasicsinit.html"
>Prev</A
></TD
><TD
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>Next</A
></TD
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><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="CHAPTER"
><H1
><A
NAME="GUIDEVIDEO"
>Chapter 2. Graphics and Video</A
></H1
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="GUIDEVIDEOOPENGL"
>Using OpenGL With SDL</A
></H1
><P
>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).</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN65"
>Initialisation</A
></H2
><P
>Initialising SDL to use OpenGL is not very different to initialising SDL normally. There are three differences; you must pass <TT
CLASS="LITERAL"
>SDL_OPENGL</TT
> to <A
HREF="sdlsetvideomode.html"
><TT
CLASS="FUNCTION"
>SDL_SetVideoMode</TT
></A
>, you must specify several GL attributes (depth buffer size, framebuffer sizes) using <A
HREF="sdlglsetattribute.html"
><TT
CLASS="FUNCTION"
>SDL_GL_SetAttribute</TT
></A
> and finally, if you wish to use double buffering you must specify it as a GL attribute, <I
CLASS="EMPHASIS"
>not</I
> by passing the <TT
CLASS="LITERAL"
>SDL_DOUBLEBUF</TT
> flag to <TT
CLASS="FUNCTION"
>SDL_SetVideoMode</TT
>.
<PRE
CLASS="PROGRAMLISTING"
>    /* 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 ) &#60; 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-&#62;vfmt-&#62;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 );
    }</PRE
></P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN77"
>Drawing</A
></H2
><P
>Apart from initialisation, using OpenGL within SDL is the same as using. However if you have request a double buffered display (using <A
HREF="sdlglsetattribute.html"
><TT
CLASS="FUNCTION"
>SDL_GL_SetAttribute</TT
></A
>) and one (which can be checked by using <A
HREF="sdlglgetattribute.html"
><TT
CLASS="FUNCTION"
>SDL_GL_GetAttribute</TT
></A
>), then you must use <A
HREF="sdlglswapbuffers.html"
><TT
CLASS="FUNCTION"
>SDL_GL_SwapBuffers()</TT
></A
> to swap the buffers and update the display.</P
><P
>A full example code listing is now presented below.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN87"
></A
><P
><B
>Example 2-1. gl.c - SDL OpenGL Example</B
></P
><PRE
CLASS="PROGRAMLISTING"
>/*
 * SDL OpenGL Tutorial.
 * (c) Michael Vance, 2000
 * briareos@lokigames.com
 *
 * Distributed under terms of the LGPL. 
 */

#include &#60;SDL/SDL.h&#62;
#include &#60;GL/gl.h&#62;
#include &#60;GL/glu.h&#62;

#include &#60;stdio.h&#62;
#include &#60;stdlib.h&#62;

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-&#62;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( &#38;event ) ) {

        switch( event.type ) {
        case SDL_KEYDOWN:
            /* Handle key presses. */
            handle_key_down( &#38;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 &#62; 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 ) &#60; 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-&#62;vfmt-&#62;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;
}</PRE
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><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="guidebasicsinit.html"
>Prev</A
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ALIGN="center"
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>Home</A
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>Next</A
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