arc

下载来的一个看图软件的源代码

/* s and e are integers modulo 360 (degrees), with 0 degrees
  being the rightmost extreme and degrees changing clockwise.
  cx and cy are the center in pixels; w and h are the horizontal 
  and vertical diameter in pixels. Nice interface, but slow, since
  I don't yet use Bresenham (I'm using an inefficient but
  simple solution with too much work going on in it; generalizing
  Bresenham to ellipses and partial arcs of ellipses is non-trivial,
  at least for me) and there are other inefficiencies (small circles
  do far too much work). */

void gdImageArc(gdImagePtr im, int cx, int cy, int w, int h, int s, int e, int color)
{
	int i;
	int lx = 0, ly = 0;
	int w2, h2;
	w2 = w/2;
	h2 = h/2;
	while (e < s) {
		e += 360;
	}
	for (i=s; (i <= e); i++) {
		int x, y;
		x = ((long)gdCosT[i % 360] * (long)w2 / 1024) + cx; 
		y = ((long)gdSinT[i % 360] * (long)h2 / 1024) + cy;
		if (i != s) {
			gdImageLine(im, lx, ly, x, y, color);	
		}
		lx = x;
		ly = y;
	}
}