#include <stdio.h>
#include <stdlib.h>
#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>

#define TRUE 1
#define FALSE 0

int DrawGLScene(GLfloat rquad);
int InitGL(GLvoid);
void Reshape(int xres, int yres);

int main(void)
{
    SDL_Surface * screen;
    SDL_Event event;
    int STATE = 0;
    GLfloat rotquad = 0.0f;
    
    if (SDL_Init(SDL_INIT_AUDIO | SDL_INIT_VIDEO) < 0)
    {
        printf("%s\n", SDL_GetError());
        exit(EXIT_FAILURE);
    }
    
    atexit(SDL_Quit);
    
    SDL_GL_SetAttribute(SDL_GL_RED_SIZE,   8);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE,  8);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    
    screen = SDL_SetVideoMode(640, 480, 0, SDL_OPENGL);
    
    if (screen == NULL)
    {
        printf("%s\n", SDL_GetError());
        exit(EXIT_FAILURE);
    }
    
    Reshape(screen->w, screen->h);
    rotquad = 0.2f;
    
    if (!InitGL())
    {
        printf("Error when initializing OpenGL.\n");
        exit(EXIT_FAILURE);
    }
     
    while (!STATE)
    {
        while (SDL_PollEvent(&event))
        {
            if (event.type == SDL_QUIT)
                STATE = 1;
                
            if (event.type == SDL_KEYDOWN)
                if (event.key.keysym.sym == SDLK_ESCAPE)
                    STATE = 1;
        }
        
        if (!DrawGLScene(rotquad))
            STATE = 1;
            
        rotquad += 0.2;
    }
   
    exit(EXIT_SUCCESS);
}

int InitGL(GLvoid)
{
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glEnable(GL_DEPTH_TEST);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3f(1.0, 1.0, 1.0);
    glLoadIdentity();
    glTranslatef(0.0, 0.0, -6.0);
    
    return TRUE;
}

int DrawGLScene(GLfloat rquad)
{ 
    glRotatef(rquad, 1.0f, 0.0f, 0.0f);
   
    glBegin(GL_QUADS);
        glColor3f(0.0f, 0.0f, 0.0f);
        glVertex3f(-0.5, -0.5, 0.0);
        glColor3f(0.0f, 1.0f, 0.0f);
        glVertex3f(-0.5, 0.5, 0.0);
        glColor3f(1.0f, 0.0f, 0.0f);
        glVertex3f(0.5, 0.5, 0.0);
        glColor3f(0.5f, 0.5f, 0.5f);
        glVertex3f(0.5, -0.5, 0.0);
    glEnd();
    
    SDL_GL_SwapBuffers();
    
    return TRUE;
}

void Reshape(int xres, int yres)
{
    if (yres == 0)
        yres = 1;
        
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0f, xres / yres, 1.5f, 20.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}