1 #include "mplot.h"
parabola(double x0,double y0,double x1,double y1,double xb,double yb)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 }
33