1 files changed, 32 insertions, 0 deletions
diff --git a/src/cmd/plot/libplot/parabola.c b/src/cmd/plot/libplot/parabola.c
new file mode 100644
index 00000000..212b9c97
--- /dev/null
+++ b/src/cmd/plot/libplot/parabola.c
@@ -0,0 +1,32 @@
+#include "mplot.h"
+void parabola(double x0, double y0, double x1, double y1, double xb, double yb){
+	register double x, y, t;
+	double	c0x, c0y, c1x, c1y;
+	double	dt, d2, d1;
+	d1 = sqrt((xb - x0) * (xb - x0) + (yb - y0) * (yb - y0));
+	d2 = sqrt((xb - x1) * (xb - x1) + (yb - y1) * (yb - y1));
+	if (d1 <= e1->quantum || d2 <= e1->quantum) { 
+		plotline(x0, y0, x1, y1); 
+		return; 
+	}
+	c0x = x0 + x1 - 2. * xb; 
+	c1x = 2. * (xb - x0);
+	c0y = y0 + y1 - 2. * yb; 
+	c1y = 2. * (yb - y0);
+	move(x0, y0);
+	dt = e1->quantum / d1;
+	dt /= e1->grade;
+	for (t = dt; t < 0.5; t += dt) {
+		x = (c0x * t + c1x) * t + x0;
+		y = (c0y * t + c1y) * t + y0;
+		vec(x, y);
+	}
+	dt = e1->quantum / d2;
+	dt /= e1->grade;
+	for (; t < 1.0; t += dt) {
+		x = (c0x * t + c1x) * t + x0;
+		y = (c0y * t + c1y) * t + y0;
+		vec(x, y);
+	}
+	vec(x1, y1);
+}