1 #include "mplot.h"
2 void parabola(double x0, double y0, double x1, double y1, double xb, double yb){
3 	register double x, y, t;
4 	double	c0x, c0y, c1x, c1y;
5 	double	dt, d2, d1;
6 	d1 = sqrt((xb - x0) * (xb - x0) + (yb - y0) * (yb - y0));
7 	d2 = sqrt((xb - x1) * (xb - x1) + (yb - y1) * (yb - y1));
8 	if (d1 <= e1->quantum || d2 <= e1->quantum) { 
9 		plotline(x0, y0, x1, y1); 
10 		return; 
11 	}
12 	c0x = x0 + x1 - 2. * xb; 
13 	c1x = 2. * (xb - x0);
14 	c0y = y0 + y1 - 2. * yb; 
15 	c1y = 2. * (yb - y0);
16 	move(x0, y0);
17 	dt = e1->quantum / d1;
18 	dt /= e1->grade;
19 	for (t = dt; t < 0.5; t += dt) {
20 		x = (c0x * t + c1x) * t + x0;
21 		y = (c0y * t + c1y) * t + y0;
22 		vec(x, y);
23 	}
24 	dt = e1->quantum / d2;
25 	dt /= e1->grade;
26 	for (; t < 1.0; t += dt) {
27 		x = (c0x * t + c1x) * t + x0;
28 		y = (c0y * t + c1y) * t + y0;
29 		vec(x, y);
30 	}
31 	vec(x1, y1);
32 }