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

#define WIDTH   500
#define HEIGHT  500

#define ADDR_DIFF(x, y) ((unsigned long) (y) - (unsigned long) (x))

void init(void)
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glEnable(GL_DEPTH_TEST);
    glShadeModel(GL_SMOOTH);
    glViewport(0, 0, WIDTH, HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, (GLfloat)WIDTH/(GLfloat)WIDTH, 1.0, 30.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.0, 0.0, -3.6);
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    static const GLfloat data[][2][4] = {
        {{-0.8, -0.8, 0.0, 1.0}, {1.0, 0.0, 0.0, 1.0}},
        {{0.8, -0.8, 0.0, 1.0}, {0.0, 1.0, 0.0, 1.0}},
        {{0.8, 0.8, 0.0, 1.0}, {0.0, 0.0, 1.0, 1.0}},
        {{-0.8, 0.8, 0.0, 1.0}, {0.0, 0.4, 1.0, 1.0}}
    };
    static const GLbyte indexes[] = {1, 0, 2, 3};
    GLuint buffers[2];
    glGenBuffers(sizeof(buffers)/sizeof(buffers[0]), buffers);
    glBindBuffer(GL_ARRAY_BUFFER, buffers[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, buffers[1]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indexes), indexes,
            GL_STATIC_DRAW);

    glBindBuffer(GL_ARRAY_BUFFER, buffers[0]);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, buffers[1]);
    glVertexPointer(3, GL_FLOAT, ADDR_DIFF(&data[0], &data[1]),
            (void *) ADDR_DIFF(&data, &data[0][0][0]));
    glColorPointer(4, GL_FLOAT, ADDR_DIFF(&data[0], &data[1]),
            (void *) ADDR_DIFF(&data, &data[0][1][0]));
    glDrawElements(GL_TRIANGLE_STRIP, 4, GL_UNSIGNED_BYTE, NULL);
    SDL_GL_SwapBuffers();
}

int main(int argc, char *argv[])
{
    if (SDL_Init(SDL_INIT_VIDEO))
    {
        printf("Failed to initialize SDL!\n");
        return 1;
    }

    atexit(SDL_Quit);

    SDL_Surface *screen;
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    if (!(screen = SDL_SetVideoMode(WIDTH, HEIGHT, 16, SDL_OPENGL)))
    {
        printf("Failed to set video mode!\n");
        SDL_Quit();
        return 2;
    }
    SDL_WM_SetCaption(argv[0], argv[0]);

    init();
    display();
    SDL_Event event;
    while (SDL_WaitEvent(&event))
    {
        if (event.type == SDL_QUIT)
            break;
        else if (event.type == SDL_KEYDOWN)
        {
            if (event.key.keysym.sym == SDLK_ESCAPE)
                break;
        }
    }
}