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
rarc(double x1,double y1,double x2,double y2,double xc,double yc,double rr)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 }
45