| #include "mplot.h" |
| /* arc plotting routine */ |
| /* from x1,y1 to x2,y2 */ |
| /* with center xc,yc and radius rr */ |
| /* integrates difference equation */ |
| /* negative rr draws counterclockwise */ |
| #define PI4 0.7854 |
| void rarc(double x1, double y1, double x2, double y2, double xc, double yc, double rr){ |
| register double dx, dy, a, b; |
| double ph, dph, rd, xnext; |
| register int n; |
| dx = x1 - xc; |
| dy = y1 - yc; |
| rd = sqrt(dx * dx + dy * dy); |
| if (rd / e1->quantum < 1.0) { |
| move(xc, yc); |
| vec(xc, yc); |
| return; |
| } |
| dph = acos(1.0 - (e1->quantum / rd)); |
| if (dph > PI4) |
| dph = PI4; |
| ph=atan2((y2-yc),(x2 - xc)) - atan2(dy, dx); |
| if (ph < 0) |
| ph += 6.2832; |
| if (rr < 0) |
| ph = 6.2832 - ph; |
| if (ph < dph) |
| plotline(x1, y1, x2, y2); |
| else { |
| n = ph / dph; |
| a = cos(dph); |
| b = sin(dph); |
| if (rr < 0) |
| b = -b; |
| move(x1, y1); |
| while ((n--) >= 0) { |
| xnext = dx * a - dy * b; |
| dy = dx * b + dy * a; |
| dx = xnext; |
| vec(dx + xc, dy + yc); |
| } |
| } |
| } |
