php-src/ext/gd/libgd/gd_arc.c

#if HAVE_GD_BUNDLED
# include "gd.h"
#else
# include <gd.h>
#endif

#include "gd_intern.h"


/**
 * Integer Ellipse functions (gdImageEllipse and gdImageFilledEllipse)
 * Function added by Pierre-Alain Joye 02/08/2003 (paj@pearfr.org)
 * See the ellipse function simplification for the equation
 * as well as the midpoint algorithm.
 */

void gdImageEllipse(gdImagePtr im, int mx, int my, int w, int h, int c)
{
	int x=0,mx1=0,mx2=0,my1=0,my2=0;
	long aq,bq,dx,dy,r,rx,ry,a,b;

	a=w>>1;
	b=h>>1;
	gdImageSetPixel(im,mx+a, my, c);
	gdImageSetPixel(im,mx-a, my, c);
	mx1 = mx-a;my1 = my;
	mx2 = mx+a;my2 = my;

	aq = a * a;
	bq = b * b;
	dx = aq << 1;
	dy = bq << 1;
	r  = a * bq;
	rx = r << 1;
	ry = 0;
	x = a;
	while (x > 0){
		if (r > 0) {
			my1++;my2--;
			ry +=dx;
			r  -=ry;
		}
		if (r <= 0){
			x--;
			mx1++;mx2--;
			rx -=dy;
			r  +=rx;
		}
		gdImageSetPixel(im,mx1, my1, c);
		gdImageSetPixel(im,mx1, my2, c);
		gdImageSetPixel(im,mx2, my1, c);
		gdImageSetPixel(im,mx2, my2, c);
	}
}

void gdImageFilledEllipse (gdImagePtr im, int mx, int my, int w, int h, int c)
{
	int x=0,mx1=0,mx2=0,my1=0,my2=0;
	long aq,bq,dx,dy,r,rx,ry,a,b;
	int i;
	int old_y1,old_y2;

	a=w>>1;
	b=h>>1;

	for (x = mx-a; x <= mx+a; x++) {
		gdImageSetPixel(im, x, my, c);
	}

	mx1 = mx-a;my1 = my;
	mx2 = mx+a;my2 = my;

	aq = a * a;
	bq = b * b;
	dx = aq << 1;
	dy = bq << 1;
	r  = a * bq;
	rx = r << 1;
	ry = 0;
	x = a;
	old_y2=-2;
	old_y1=-2;
	while (x > 0){
		if (r > 0) {
			my1++;my2--;
			ry +=dx;
			r  -=ry;
		}
		if (r <= 0){
			x--;
			mx1++;mx2--;
			rx -=dy;
			r  +=rx;
		}
		if(old_y2!=my2){
			for(i=mx1;i<=mx2;i++){
				gdImageSetPixel(im,i,my1,c);
			}
		}
		if(old_y2!=my2){
			for(i=mx1;i<=mx2;i++){
				gdImageSetPixel(im,i,my2,c);
			}
		}
		old_y2 = my2;
		old_y1 = my1;
	}
}