Root/
| 1 | /* |
| 2 | * v2d_intersect.c - Intersect two lines |
| 3 | * |
| 4 | * Written 2012 by Werner Almesberger |
| 5 | * Copyright 2012 Werner Almesberger |
| 6 | * |
| 7 | * This library is free software; you can redistribute it and/or |
| 8 | * modify it under the terms of the GNU Lesser General Public |
| 9 | * License as published by the Free Software Foundation; either |
| 10 | * version 2.1 of the License, or (at your option) any later version. |
| 11 | */ |
| 12 | |
| 13 | |
| 14 | #include <math.h> |
| 15 | |
| 16 | #include "poly2d.h" |
| 17 | |
| 18 | |
| 19 | #define EPSILON 1e-6 |
| 20 | |
| 21 | |
| 22 | /* |
| 23 | * Solve |
| 24 | * |
| 25 | * ax+by = e |
| 26 | * cx+dy = f |
| 27 | * |
| 28 | * with Cramer's rule: |
| 29 | * http://en.wikipedia.org/wiki/Cramer's_rule |
| 30 | */ |
| 31 | |
| 32 | static int cramer2(double a, double b, double c, double d, double e, double f, |
| 33 | double *x, double *y) |
| 34 | { |
| 35 | double det; |
| 36 | |
| 37 | det = a*d-b*c; |
| 38 | if (fabs(det) < EPSILON) |
| 39 | return 0; |
| 40 | *x = (e*d-b*f)/det; |
| 41 | *y = (a*f-e*c)/det; |
| 42 | return 1; |
| 43 | } |
| 44 | |
| 45 | |
| 46 | int v2d_intersect(const struct v2d *a0, const struct v2d *a1, |
| 47 | const struct v2d *b0, const struct v2d *b1, |
| 48 | double *na, double *nb) |
| 49 | { |
| 50 | double ax, ay, bx, by, dx, dy; |
| 51 | double a, b; |
| 52 | |
| 53 | ax = a1->x-a0->x; |
| 54 | ay = a1->y-a0->y; |
| 55 | |
| 56 | bx = b1->x-b0->x; |
| 57 | by = b1->y-b0->y; |
| 58 | |
| 59 | dx = b0->x-a0->x; |
| 60 | dy = b0->y-a0->y; |
| 61 | |
| 62 | if (!cramer2(ax, -bx, ay, -by, dx, dy, &a, &b)) |
| 63 | return 0; |
| 64 | if (na) |
| 65 | *na = a; |
| 66 | if (nb) |
| 67 | *nb = b; |
| 68 | return a >= 0 && a <= 1 && b >= 0 && b <= 1 ? 1 : -1; |
| 69 | } |
| 70 |
Branches:
master
