root/libgd/gd_arc.c

DEFINITIONS

1. gdImageEllipse
2. gdImageFilledEllipse

#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;
        }
}