#include <iostream>
#include <cstdlib>
#include <cassert>
#include <cstddef>
#include <cmath>
#include <SDL/SDL.h>
#include <GL/gl.h>
#include <GL/glu.h>
using namespace std;

#define PI 3.14159
#define DISPLAY_INTERVAL 30     // in milli-secs

void draw()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
    // draw here
    
    glFlush();
}

void on_key(SDL_keysym* key)
{
    switch (key->sym)
    {
        case SDLK_ESCAPE:
            SDL_Quit();
			exit(0);
            break;
    }
}

void init(Uint32 width, Uint32 height)
{
    glClearColor(0, 0, 0.5, 0);
    
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    double ratio = double(width)/height;
    gluOrtho2D(-1*ratio, ratio, -1, 1);
    
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

int main()
{
    if (SDL_Init(SDL_INIT_AUDIO | SDL_INIT_VIDEO | SDL_INIT_TIMER) < 0)
    {
        cout << "SDL init error!" << endl;
        return 1;
    }
    
    // Check that we are using 32 bpp, and tell the user to change it to 32 if not.
    // Required for the X-Window System, since the bpp cannot be changed without 
    // restarting the display server.
    const SDL_VideoInfo* vinfo = SDL_GetVideoInfo();
    assert(vinfo);
    if (vinfo->vfmt->BitsPerPixel != 32)
    {
        cout << "Error: Your video is not set to use 32 bits-per-pixel, which is" << endl;
        cout << "       required by this program. Please change it to 32-bits" << endl;
        cout << "       and restart this program." << endl;
        exit(EXIT_FAILURE);
    }
    
    // Set opengl specific stuff
    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_ALPHA_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 1);
    
    Uint32 flags = SDL_OPENGL;
    char c;
    cout << "Do you want to use fullscreen mode? (Y/N)";
    cin >> c;
    if (c == 'Y' || c == 'y')
        flags |= SDL_FULLSCREEN;
    
    // Open screen
    SDL_Surface* screen = SDL_SetVideoMode(640, 480, 32, flags);
    assert(screen);
    init(648, 480);         // opengl-specific initialisation
    
    while (1)
    {
        static Uint32 next_time;
        Uint32 now = SDL_GetTicks();
        if (now < next_time)
            SDL_Delay(next_time - now);
        next_time += DISPLAY_INTERVAL;
        
        // Check for events
        SDL_Event event;
        while (SDL_PollEvent(&event))
        {
            switch (event.type)
            {
                case SDL_KEYDOWN:
                    on_key(&event.key.keysym);
                    break;
                case SDL_QUIT:
					SDL_Quit();
					exit(0);
                    break;
            }
        }
        
        // Draw the scene
        draw();
        SDL_GL_SwapBuffers();
    }
    
    return 0;
}