Root/
| 1 | /* |
| 2 | * p2d_attrib.c - Determine various polygon attributes |
| 3 | * |
| 4 | * Written 2012, 2015 by Werner Almesberger |
| 5 | * Copyright 2012, 2015 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 <stdbool.h> |
| 15 | #include <stdio.h> |
| 16 | #include <math.h> |
| 17 | #include <assert.h> |
| 18 | |
| 19 | #include "poly2d.h" |
| 20 | |
| 21 | |
| 22 | /* |
| 23 | * Angle in counter-clockwise direction to turn at point B when coming from A |
| 24 | * in order to face towards C. |
| 25 | */ |
| 26 | |
| 27 | static double angle_3(const struct v2d *a, const struct v2d *b, |
| 28 | const struct v2d *c) |
| 29 | { |
| 30 | double ax, ay, bx, by; |
| 31 | double cs, aa, bb; |
| 32 | double cross, angle; |
| 33 | |
| 34 | ax = b->x - a->x; |
| 35 | ay = b->y - a->y; |
| 36 | bx = c->x - b->x; |
| 37 | by = c->y - b->y; |
| 38 | |
| 39 | cross = ax * by - ay * bx; |
| 40 | if (!cross) |
| 41 | return 0; |
| 42 | |
| 43 | aa = hypot(ax, ay); |
| 44 | bb = hypot(bx, by); |
| 45 | |
| 46 | cs = (ax * bx + ay * by) / aa / bb; |
| 47 | if (cs <= -1) |
| 48 | angle = 180; |
| 49 | else if (cs >= 1) |
| 50 | angle = 0; |
| 51 | else |
| 52 | angle = acos(cs) / M_PI * 180.0; |
| 53 | return cross >= 0 ? angle : -angle; |
| 54 | } |
| 55 | |
| 56 | /* |
| 57 | * If we predominantly turn to the right, then the path must be clockwise. |
| 58 | */ |
| 59 | |
| 60 | bool p2d_is_cw(const struct p2d *p) |
| 61 | { |
| 62 | const struct v2d *v; |
| 63 | double a = 0; |
| 64 | |
| 65 | assert(p2d_vertices(p) >= 3); |
| 66 | assert(p2d_is_closed(p)); |
| 67 | assert(p2d_no_intersect(p)); |
| 68 | |
| 69 | v = p->v; |
| 70 | do { |
| 71 | a += angle_3(v, v->next, v->next->next); |
| 72 | v = v->next; |
| 73 | } |
| 74 | while (v != p->v); |
| 75 | assert(!isnan(a)); /* require -std=c99 or -std=gnu99 */ |
| 76 | return a < 0; |
| 77 | } |
| 78 | |
| 79 | |
| 80 | bool p2d_is_closed(const struct p2d *p) |
| 81 | { |
| 82 | return p->v == p->last || p->last->next; |
| 83 | } |
| 84 | |
| 85 | |
| 86 | /* |
| 87 | * Known bug: if the polygon intersects on a vertex, the intersection may |
| 88 | * go unnoticed. |
| 89 | */ |
| 90 | |
| 91 | bool p2d_no_intersect(const struct p2d *p) |
| 92 | { |
| 93 | const struct v2d *v, *u; |
| 94 | |
| 95 | v = p->v; |
| 96 | while (v) { |
| 97 | u = v->next; |
| 98 | if (!u || u == p->v) |
| 99 | return 1; |
| 100 | u = u->next; |
| 101 | if (!u || u == p->v) |
| 102 | return 1; |
| 103 | while (u && u->next && u->next != v) { |
| 104 | if (v2d_intersect(v, v->next, u, u->next, |
| 105 | NULL, NULL) > 0) |
| 106 | return 0; |
| 107 | u = u->next; |
| 108 | if (u == p->v) |
| 109 | break; |
| 110 | } |
| 111 | v = v->next; |
| 112 | if (v == p->v) |
| 113 | break; |
| 114 | } |
| 115 | return 1; |
| 116 | } |
| 117 | |
| 118 | |
| 119 | unsigned p2d_vertices(const struct p2d *p) |
| 120 | { |
| 121 | const struct v2d *v; |
| 122 | unsigned n = 0; |
| 123 | |
| 124 | v = p->v; |
| 125 | while (v) { |
| 126 | n++; |
| 127 | v = v->next; |
| 128 | if (v == p->v) |
| 129 | break; |
| 130 | } |
| 131 | return n; |
| 132 | } |
| 133 |
Branches:
master
