usr/src/lib/libplot/hp2648/circle.c

#ifndef lint
static char sccsid[] = "@(#)circle.c    4.1 (Berkeley) %G%";
#endif

#include "hp2648.h"

circle (xc,yc,r)
int xc,yc,r;
{
        double costheta,sintheta,x,y,xn;
        int xi,yi;

        if(r<1){
                point(xc,yc);
                return;
        }
        sintheta = 1.0/r;
        costheta = pow(1-sintheta*sintheta,0.5);
        xi = x = r;
        yi = y = 0;
        do {
                point(xc+xi,yc+yi);
                xn = x;
                xi = x = x*costheta + y*sintheta;
                yi = y = y*costheta - xn*sintheta;
        } while( ! (yi==0 && xi >= r-1));
}