1 files changed, 44 insertions, 0 deletions
diff --git a/src/cmd/plot/libplot/rarc.c b/src/cmd/plot/libplot/rarc.c
new file mode 100644
index 00000000..9c8ccf15
--- /dev/null
+++ b/src/cmd/plot/libplot/rarc.c
@@ -0,0 +1,44 @@
+#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);
+		}
+	}
+}