circle.c

<B>Digital的Unix操作系统VAX 4.2源码</B>

#ifndef lint
static char SccsId[] = " @(#)circle.c	4.1	(ULTRIX)	7/2/90";
#endif not(lint)

/*
 * Modification History
 *
 * 	April-11-1989, Pradeep Chetal
 *	Added changes from 4.3Tahoe BSD for lots of new drivers
 */

/*
 * Copyright (c) 1980 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 */

#ifndef lint
static char sccsid[] = "@(#)circle.c	5.1 (Berkeley) 5/7/85";
#endif not lint

#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));
}