1 |
greg |
2.1 |
#ifndef lint |
2 |
greg |
2.3 |
static const char RCSid[] = "$Id: triangulate.c,v 2.2 2014/01/24 01:26:44 greg Exp $"; |
3 |
greg |
2.1 |
#endif |
4 |
|
|
/* |
5 |
|
|
* triangulate.c |
6 |
|
|
* |
7 |
|
|
* Adapted by Greg Ward on 1/23/14. |
8 |
|
|
* Copyright 2014 Anyhere Software. All rights reserved. |
9 |
|
|
* |
10 |
|
|
*/ |
11 |
|
|
|
12 |
|
|
/* COTD Entry submitted by John W. Ratcliff [[email protected]] |
13 |
|
|
|
14 |
|
|
// ** THIS IS A CODE SNIPPET WHICH WILL EFFICIEINTLY TRIANGULATE ANY |
15 |
|
|
// ** POLYGON/CONTOUR (without holes) AS A STATIC CLASS. THIS SNIPPET |
16 |
|
|
// ** IS COMPRISED OF 3 FILES, TRIANGULATE.H, THE HEADER FILE FOR THE |
17 |
|
|
// ** TRIANGULATE BASE CLASS, TRIANGULATE.CPP, THE IMPLEMENTATION OF |
18 |
|
|
// ** THE TRIANGULATE BASE CLASS, AND TEST.CPP, A SMALL TEST PROGRAM |
19 |
|
|
// ** DEMONSTRATING THE USAGE OF THE TRIANGULATOR. THE TRIANGULATE |
20 |
|
|
// ** BASE CLASS ALSO PROVIDES TWO USEFUL HELPER METHODS, ONE WHICH |
21 |
|
|
// ** COMPUTES THE AREA OF A POLYGON, AND ANOTHER WHICH DOES AN EFFICENT |
22 |
|
|
// ** POINT IN A TRIANGLE TEST. |
23 |
|
|
// ** SUBMITTED BY JOHN W. RATCLIFF ([email protected]) July 22, 2000 |
24 |
|
|
*/ |
25 |
|
|
|
26 |
|
|
#include <stdio.h> |
27 |
|
|
#include <stdlib.h> |
28 |
|
|
#include "triangulate.h" |
29 |
|
|
|
30 |
|
|
#ifndef true |
31 |
|
|
#define true 1 |
32 |
|
|
#define false 0 |
33 |
|
|
#endif |
34 |
|
|
|
35 |
|
|
static const double EPSILON = 0.0000000001; |
36 |
|
|
|
37 |
|
|
static int |
38 |
|
|
polySnip(const Vert2_list *contour, int u, int v, int w, int n, int *V) |
39 |
|
|
{ |
40 |
|
|
int p; |
41 |
|
|
double Ax, Ay, Bx, By, Cx, Cy, Px, Py; |
42 |
|
|
|
43 |
|
|
Ax = contour->v[V[u]].mX; |
44 |
|
|
Ay = contour->v[V[u]].mY; |
45 |
|
|
|
46 |
|
|
Bx = contour->v[V[v]].mX; |
47 |
|
|
By = contour->v[V[v]].mY; |
48 |
|
|
|
49 |
|
|
Cx = contour->v[V[w]].mX; |
50 |
|
|
Cy = contour->v[V[w]].mY; |
51 |
|
|
|
52 |
|
|
if ( EPSILON > (((Bx-Ax)*(Cy-Ay)) - ((By-Ay)*(Cx-Ax))) ) return false; |
53 |
|
|
|
54 |
|
|
for (p=0;p<n;p++) |
55 |
|
|
{ |
56 |
greg |
2.3 |
if( (p == u) | (p == v) | (p == w) ) continue; |
57 |
greg |
2.1 |
Px = contour->v[V[p]].mX; |
58 |
|
|
Py = contour->v[V[p]].mY; |
59 |
|
|
if (insideTriangle(Ax,Ay,Bx,By,Cx,Cy,Px,Py)) return false; |
60 |
|
|
} |
61 |
|
|
|
62 |
|
|
return true; |
63 |
|
|
} |
64 |
|
|
|
65 |
|
|
Vert2_list * |
66 |
|
|
polyAlloc(int nv) |
67 |
|
|
{ |
68 |
|
|
Vert2_list *pnew; |
69 |
|
|
|
70 |
|
|
if (nv < 3) return NULL; |
71 |
|
|
|
72 |
|
|
pnew = (Vert2_list *)malloc(sizeof(Vert2_list) + sizeof(Vert2)*(nv-3)); |
73 |
|
|
if (pnew == NULL) return NULL; |
74 |
|
|
pnew->nv = nv; |
75 |
|
|
pnew->p = NULL; |
76 |
|
|
|
77 |
|
|
return pnew; |
78 |
|
|
} |
79 |
|
|
|
80 |
|
|
double |
81 |
|
|
polyArea(const Vert2_list *contour) |
82 |
|
|
{ |
83 |
|
|
double A=0.0; |
84 |
|
|
int p, q; |
85 |
|
|
|
86 |
|
|
for(p = contour->nv-1, q = 0; q < contour->nv; p=q++) |
87 |
|
|
{ |
88 |
|
|
A += contour->v[p].mX*contour->v[q].mY - contour->v[q].mX*contour->v[p].mY; |
89 |
|
|
} |
90 |
|
|
return A*0.5; |
91 |
|
|
} |
92 |
|
|
|
93 |
|
|
/* |
94 |
|
|
InsideTriangle decides if a point P is Inside of the triangle |
95 |
|
|
defined by A, B, C. |
96 |
|
|
*/ |
97 |
|
|
int |
98 |
|
|
insideTriangle(double Ax, double Ay, |
99 |
|
|
double Bx, double By, |
100 |
|
|
double Cx, double Cy, |
101 |
|
|
double Px, double Py) |
102 |
|
|
|
103 |
|
|
{ |
104 |
|
|
double ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy; |
105 |
|
|
double cCROSSap, bCROSScp, aCROSSbp; |
106 |
|
|
|
107 |
|
|
ax = Cx - Bx; ay = Cy - By; |
108 |
|
|
bx = Ax - Cx; by = Ay - Cy; |
109 |
|
|
cx = Bx - Ax; cy = By - Ay; |
110 |
|
|
apx= Px - Ax; apy= Py - Ay; |
111 |
|
|
bpx= Px - Bx; bpy= Py - By; |
112 |
|
|
cpx= Px - Cx; cpy= Py - Cy; |
113 |
|
|
|
114 |
|
|
aCROSSbp = ax*bpy - ay*bpx; |
115 |
|
|
cCROSSap = cx*apy - cy*apx; |
116 |
|
|
bCROSScp = bx*cpy - by*cpx; |
117 |
|
|
|
118 |
|
|
return ((aCROSSbp >= 0.0) && (bCROSScp >= 0.0) && (cCROSSap >= 0.0)); |
119 |
|
|
}; |
120 |
|
|
|
121 |
|
|
int |
122 |
|
|
polyTriangulate(const Vert2_list *contour, tri_out_t *cb) |
123 |
|
|
{ |
124 |
|
|
/* allocate and initialize list of Vertices in polygon */ |
125 |
|
|
|
126 |
|
|
int nv, m, u, v, w, count; |
127 |
|
|
int *V; |
128 |
|
|
|
129 |
|
|
if ( contour->nv < 3 ) return false; |
130 |
|
|
|
131 |
|
|
V = (int *)malloc(sizeof(int)*contour->nv); |
132 |
|
|
if (V == NULL) return false; |
133 |
|
|
|
134 |
|
|
/* we want a counter-clockwise polygon in V */ |
135 |
|
|
|
136 |
greg |
2.2 |
if ( 0.0 < polyArea(contour) ) |
137 |
greg |
2.1 |
for (v=0; v<contour->nv; v++) V[v] = v; |
138 |
|
|
else |
139 |
|
|
for(v=0; v<contour->nv; v++) V[v] = (contour->nv-1)-v; |
140 |
|
|
|
141 |
|
|
nv = contour->nv; |
142 |
|
|
|
143 |
|
|
/* remove nv-2 Vertices, creating 1 triangle every time */ |
144 |
|
|
count = 2*nv; /* error detection */ |
145 |
|
|
|
146 |
|
|
for(m=0, v=nv-1; nv>2; ) |
147 |
|
|
{ |
148 |
|
|
/* if we loop, it is probably a non-simple polygon */ |
149 |
greg |
2.3 |
if (0 >= count--) |
150 |
greg |
2.1 |
{ |
151 |
greg |
2.3 |
/* Triangulate: ERROR - probable bad polygon */ |
152 |
greg |
2.1 |
return false; |
153 |
|
|
} |
154 |
|
|
|
155 |
|
|
/* three consecutive vertices in current polygon, <u,v,w> */ |
156 |
|
|
u = v ; if (nv <= u) u = 0; /* previous */ |
157 |
|
|
v = u+1; if (nv <= v) v = 0; /* new v */ |
158 |
|
|
w = v+1; if (nv <= w) w = 0; /* next */ |
159 |
|
|
|
160 |
|
|
if ( polySnip(contour,u,v,w,nv,V) ) |
161 |
|
|
{ |
162 |
|
|
int a,b,c,s,t; |
163 |
|
|
|
164 |
|
|
/* true names of the vertices */ |
165 |
|
|
a = V[u]; b = V[v]; c = V[w]; |
166 |
|
|
|
167 |
|
|
/* output Triangle */ |
168 |
greg |
2.2 |
if (!(*cb)(contour, a, b, c)) return false; |
169 |
greg |
2.1 |
|
170 |
|
|
m++; |
171 |
|
|
|
172 |
|
|
/* remove v from remaining polygon */ |
173 |
|
|
for(s=v,t=v+1;t<nv;s++,t++) V[s] = V[t]; nv--; |
174 |
|
|
|
175 |
greg |
2.3 |
/* reset error detection counter */ |
176 |
greg |
2.1 |
count = 2*nv; |
177 |
|
|
} |
178 |
|
|
} |
179 |
|
|
|
180 |
|
|
free(V); |
181 |
|
|
|
182 |
|
|
return true; |
183 |
|
|
} |