| #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); | |
| } | |
| } | |
| } |