1 #include "mplot.h"
2 /*		arc plotting routine		*/
3 /*		from x1,y1 to x2,y2		*/
4 /*	with center xc,yc and radius rr	*/
5 /*	integrates difference equation		*/
6 /*	negative rr draws counterclockwise	*/
7 #define PI4 0.7854
8 void rarc(double x1, double y1, double x2, double y2, double xc, double yc, double rr){
9 	register double dx, dy, a, b;
10 	double	ph, dph, rd, xnext;
11 	register int	n;
12 	dx = x1 - xc;
13 	dy = y1 - yc;
14 	rd = sqrt(dx * dx + dy * dy);
15 	if (rd / e1->quantum < 1.0) {
16 		move(xc, yc);
17 		vec(xc, yc);
18 		return;
19 	}
20 	dph = acos(1.0 - (e1->quantum / rd));
21 	if (dph > PI4)
22 		dph = PI4;
23 	ph=atan2((y2-yc),(x2 - xc)) - atan2(dy, dx);
24 	if (ph < 0)
25 		ph += 6.2832;
26 	if (rr < 0)
27 		ph = 6.2832 - ph;
28 	if (ph < dph)
29 		plotline(x1, y1, x2, y2);
30 	else {
31 		n = ph / dph;
32 		a = cos(dph);
33 		b = sin(dph);
34 		if (rr < 0)
35 			b = -b;
36 		move(x1, y1);
37 		while ((n--) >= 0) {
38 			xnext = dx * a - dy * b;
39 			dy = dx * b + dy * a;
40 			dx = xnext;
41 			vec(dx + xc, dy + yc);
42 		}
43 	}
44 }