#include <stdlib.h>
#include <unistd.h>
#include "SDL/SDL.h"
#include <math.h>

#define XRES 640
#define YRES 480
#define BALLSIZE 40
#define NUMCOL 3
#define PERCOL 4
#define PAGES (NUMCOL*PERCOL)

SDL_Surface *screen;
SDL_Surface *page[PAGES];
SDL_Surface *ball[NUMCOL];

int bcols[][3] = { { 0x68, 0x68, 0xff },
                   { 0xff, 0x68, 0x68 },
                   { 0x68, 0xff, 0x68 } };

int cpage=0;

void putpixel(SDL_Surface *surface, int x, int y, Uint32 pixel) {
	int bpp = surface->format->BytesPerPixel;
	/* Here p is the address to the pixel we want to set */
	Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;
	switch(bpp) {
	 case 1:
		*p = pixel;
		break;
	 case 2:
		*(Uint16 *)p = pixel;
		break;
	 case 3:
		if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {
			p[0] = (pixel >> 16) & 0xff;
			p[1] = (pixel >> 8) & 0xff;
			p[2] = pixel & 0xff;
		}
		else {
			p[0] = pixel & 0xff;
			p[1] = (pixel >> 8) & 0xff;
			p[2] = (pixel >> 16) & 0xff;
		}
		break;
	 case 4:
		*(Uint32 *)p = pixel;
		break;
	}
} 

void drawball(int xofs, int yofs, int a) {
	SDL_Rect drect = { xofs, yofs, ball[a]->w, ball[a]->h };
	SDL_BlitSurface(ball[a], NULL, page[cpage], &drect);
}

int main() {
	int size=BALLSIZE;
	int hsize=size/2;
	
	if(SDL_Init(SDL_INIT_VIDEO)<0) {
		fprintf(stderr, "failed to initialise sdl: %s\n", SDL_GetError());
		exit(1);
	};
	
	atexit(SDL_Quit);
	
	screen = SDL_SetVideoMode(XRES, YRES, 16, SDL_DOUBLEBUF|SDL_HWSURFACE);
	if(!screen) {
		fprintf(stderr, "failed to set video mode: %s\n", SDL_GetError());
		exit(1);
	}
	
	{
		int n;
		for(n=0; n<PAGES; n++)
			page[n] = SDL_CreateRGBSurface(SDL_HWSURFACE, screen->w, screen->h, 16, screen->format->Rmask, screen->format->Gmask, screen->format->Bmask, 0);
	}
	
	{
		Uint32 col;
		int x, y, n;
		double dist, bright;
		
                for(n=0; n<NUMCOL; n++) {
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
			ball[n]=SDL_CreateRGBSurface(0, BALLSIZE, BALLSIZE, 24, 0xf80000, 0x0e7000, 0x001f00, 0x0000ff);
#else
			ball[n]=SDL_CreateRGBSurface(0, BALLSIZE, BALLSIZE, 24, 0x00001f, 0x0007e0, 0x00f800, 0xff0000);
#endif
			if(!ball[n]) {
				fprintf(stderr, "Failed to create surface: %s\n", SDL_GetError());
				exit(1);
			}
		
			for(y=0; y<size; y++) {
				for(x=0; x<size; x++) {
					dist=hypot(x-hsize, y-hsize);
					if(dist > hsize)
						continue;
					bright=1-(dist/size);
					col=SDL_MapRGBA(ball[n]->format, bcols[n][0]*bright, bcols[n][1]*bright, bcols[n][2]*bright, 0xd0*((1.0+(dist/hsize))/2.0));
					putpixel(ball[n], x, y, col);
				}
			}
		}
	}
		
	/* Lock the screen for direct access to the pixels */
	if(SDL_MUSTLOCK(screen)) {
		if(SDL_LockSurface(screen) < 0) {
			fprintf(stderr, "Can't lock screen: %s\n", SDL_GetError());
			exit(1);
		}
	}
	
	{
		SDL_Event event;
		float f=0.0;
		int i=-10;
		int pause=0, dir=1;
		int x,y;
		int quit=0;
		
		while(!quit) {
			if(i>=10)
				dir=-1;
			else if(i<=-10)
				dir=1;
	
			while(f>=1.0) {
				i+=dir;
				f-=1.0;
			}
			
			{
				int j;
				for(j=0; j<NUMCOL; j++) {
					x=(int)((((cos(f*2*M_PI)/2))+0.5)*(screen->w-size));
					y=(int)((((sin(f*2*M_PI)/2)*(i/10.0))+0.5)*(screen->h-size));
					drawball(x, y, j);
					cpage=(cpage+PERCOL)%(PAGES);
				}
			}
			cpage=(cpage+1)%(PAGES);
			f+=0.02/PERCOL;
			
			SDL_BlitSurface(page[cpage], NULL, screen, NULL);
			SDL_Flip(screen);
			
			do {
//				usleep(1000000);
				
				for(x=0; x<750000; x++)
					y=x;
				
				while(SDL_PollEvent(&event))
					if(event.type == SDL_KEYDOWN)
						if(event.key.keysym.sym == SDLK_ESCAPE)
							quit=1;
						else if(event.key.keysym.sym == SDLK_SPACE)
							pause=!pause;
			} while(pause && !quit);
		}
	}
	
	if(SDL_MUSTLOCK(screen)) {
		SDL_UnlockSurface(screen);
	}
	
	SDL_Quit();
	exit(0);
}