SDL Guide 中文译版(二)[4]

例2-8 sdl和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