#include <gd.h>

/* D(R,y) = |P2-P| = ceil(sqrt(R2-y2)) - sqrt(R2-y2) */
static double D(int r, int y)
{
	return ceil(sqrt(r*r - y*y)) - sqrt(r*r - y*y);
}
static gdImagePtr HmmPtr;
static void hmm(int x,int y,double I, int k)
{
	int r = (k >> 16) & 255,
	    g = (k >> 8) & 255,
	    b = (k) & 255;
	int c = gdImageGetPixel(HmmPtr, x,y);
	
	//c=0;
	r = ((c >> 16) & 255)   * (1-I) + r * I;
	g = ((c >> 8) & 255)    * (1-I) + g * I;
	b = (c & 255)           * (1-I) + b * I;
	
	//printf("%X: %d %d %d\n", k, r,g,b);
	
	c = b + g*256 + r*256*256;
	//c = gdImageColorAllocate(HmmPtr, r,g,b);
	gdImageSetPixel(HmmPtr, x,y, c);
}
static void putpixel(int cx,int cy, int x,int y,double I, int c)
{
	hmm(cx + y, cy + x, I, c);
	hmm(cx - y, cy + x, I, c);
	hmm(cx + y, cy - x, I, c);
	hmm(cx - y, cy - x, I, c);
	
	hmm(cx + x, cy + y, I, c);
	hmm(cx - x, cy + y, I, c);
	hmm(cx + x, cy - y, I, c);
	hmm(cx - x, cy - y, I, c);
}
static void WUCircle(int cx,int cy, int R, int filled, int c)
{
   int x = R;
   int y = 0;
   int ax;
   double T = 0;
   double I = 0.93;
   if(filled)for(ax=0; ax<x; ++ax)putpixel(cx,cy, ax,y,1, c);
   putpixel(cx,cy, x,y,I, c);
   while (x>y)
   {
   	  ++y;
      if (D(R,y) < T) --x;
      putpixel(cx,cy, x,y,I*(1-D(R,y)), c);
      if(!filled)putpixel(cx,cy, x-1,y,I*D(R,y), c);
      if(filled)for(ax=0; ax<x; ++ax)putpixel(cx,cy, ax,y,1, c);
      T = D(R,y);
   }
}

static void DrawFilledCircle(gdImagePtr im, int cx,int cy, int R, int c)
{
	HmmPtr=im;
	WUCircle(cx,cy, R, 1, c);
}
static void DrawCircle(gdImagePtr im, int cx,int cy, int R, int c)
{
	HmmPtr=im;
	WUCircle(cx,cy, R, 0, c);
}