#include <stdlib.h>
#if defined(_MSC_VER)
#include "SDL.h"
#else
#include "SDL/SDL.h"
#endif

SDL_Surface *screen;

void render()
{   
  // Lock surface if needed
  if (SDL_MUSTLOCK(screen)) 
    if (SDL_LockSurface(screen) < 0) 
      return;

  // Ask SDL for the time in milliseconds
  int tick = SDL_GetTicks();

  // Declare a couple of variables
  int i, j, yofs, ofs;

  // Draw to screen
  yofs = 0;
  for (i = 0; i < 480; i++)
    {
      for (j = 0, ofs = yofs; j < 640; j++, ofs++)
	{
	  ((unsigned int*)screen->pixels)[ofs] = i * i + j * j + tick;
	}
      yofs += screen->pitch / 4;
    }

  // Unlock if needed
  if (SDL_MUSTLOCK(screen)) 
    SDL_UnlockSurface(screen);

  // Tell SDL to update the whole screen
  SDL_UpdateRect(screen, 0, 0, 640, 480);    
}


// Entry point
int main(int argc, char *argv[])
{
  // Initialize SDL's subsystems - in this case, only video.
  if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) 
    {
      fprintf(stderr, "Unable to init SDL: %s\n", SDL_GetError());
      exit(1);
    }

  // Register SDL_Quit to be called at exit; makes sure things are
  // cleaned up when we quit.
  atexit(SDL_Quit);
    
  // Attempt to create a 640x480 window with 32bit pixels.
  screen = SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE);
  
  // If we fail, return error.
  if ( screen == NULL ) 
    {
      fprintf(stderr, "Unable to set 640x480 video: %s\n", SDL_GetError());
      exit(1);
    }

  // Main loop: loop forever.
  while (1)
    {
      // Render stuff
      render();

      // Poll for events, and handle the ones we care about.
      SDL_Event event;
      while (SDL_PollEvent(&event)) 
	{
	  switch (event.type) 
	    {
	    case SDL_KEYDOWN:
	      break;
	    case SDL_KEYUP:
	      // If escape is pressed, return (and thus, quit)
	      if (event.key.keysym.sym == SDLK_ESCAPE)
		return 0;
	      break;
	    case SDL_QUIT:
	      return(0);
	    }
	}
    }
  return 0;
}