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#ifndef lint |
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static const char RCSid[] = "$Id$"; |
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#endif |
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/* |
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* triangulate.c |
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* |
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* Adapted by Greg Ward on 1/23/14. |
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* Copyright 2014 Anyhere Software. All rights reserved. |
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* |
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*/ |
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|
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/* COTD Entry submitted by John W. Ratcliff [[email protected]] |
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|
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// ** THIS IS A CODE SNIPPET WHICH WILL EFFICIEINTLY TRIANGULATE ANY |
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// ** POLYGON/CONTOUR (without holes) AS A STATIC CLASS. THIS SNIPPET |
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// ** IS COMPRISED OF 3 FILES, TRIANGULATE.H, THE HEADER FILE FOR THE |
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// ** TRIANGULATE BASE CLASS, TRIANGULATE.CPP, THE IMPLEMENTATION OF |
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// ** THE TRIANGULATE BASE CLASS, AND TEST.CPP, A SMALL TEST PROGRAM |
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// ** DEMONSTRATING THE USAGE OF THE TRIANGULATOR. THE TRIANGULATE |
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// ** BASE CLASS ALSO PROVIDES TWO USEFUL HELPER METHODS, ONE WHICH |
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// ** COMPUTES THE AREA OF A POLYGON, AND ANOTHER WHICH DOES AN EFFICENT |
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// ** POINT IN A TRIANGLE TEST. |
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// ** SUBMITTED BY JOHN W. RATCLIFF ([email protected]) July 22, 2000 |
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*/ |
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|
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#include <stdio.h> |
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#include <stdlib.h> |
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#include "triangulate.h" |
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|
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#ifndef true |
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#define true 1 |
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#define false 0 |
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#endif |
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|
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static const double EPSILON = 0.0000000001; |
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|
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static int |
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polySnip(const Vert2_list *contour, int u, int v, int w, int n, int *V) |
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{ |
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int p; |
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double Ax, Ay, Bx, By, Cx, Cy, Px, Py, cross; |
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|
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Ax = contour->v[V[u]].mX; |
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Ay = contour->v[V[u]].mY; |
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|
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Bx = contour->v[V[v]].mX; |
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By = contour->v[V[v]].mY; |
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|
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Cx = contour->v[V[w]].mX; |
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Cy = contour->v[V[w]].mY; |
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|
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cross = ((Bx - Ax)*(Cy - Ay)) - ((By - Ay)*(Cx - Ax)); |
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if (EPSILON > cross) return EPSILON > -cross ? -1 : false; /* Negative if colinear points */ |
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|
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for (p=0;p<n;p++) |
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{ |
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if( (p == u) | (p == v) | (p == w) ) continue; |
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Px = contour->v[V[p]].mX; |
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Py = contour->v[V[p]].mY; |
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if ((Px == Ax && Py == Ay) || (Px == Bx && Py == By) || |
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(Px == Cx && Py == Cy)) continue; /* Handle donuts */ |
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if (insideTriangle(Ax,Ay,Bx,By,Cx,Cy,Px,Py)) return false; |
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} |
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|
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return true; |
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} |
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|
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Vert2_list * |
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polyAlloc(int nv) |
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{ |
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Vert2_list *pnew; |
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|
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if (nv < 3) return NULL; |
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|
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pnew = (Vert2_list *)malloc(sizeof(Vert2_list) + sizeof(Vert2)*(nv-3)); |
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if (pnew == NULL) return NULL; |
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pnew->nv = nv; |
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pnew->p = NULL; |
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|
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return pnew; |
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} |
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|
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double |
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polyArea(const Vert2_list *contour) |
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{ |
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double A=0.0; |
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int p, q; |
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|
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for(p = contour->nv-1, q = 0; q < contour->nv; p=q++) |
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{ |
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A += contour->v[p].mX*contour->v[q].mY - contour->v[q].mX*contour->v[p].mY; |
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} |
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return A*0.5; |
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} |
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|
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/* |
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InsideTriangle decides if a point P is Inside of the triangle |
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defined by A, B, C. |
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*/ |
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int |
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insideTriangle(double Ax, double Ay, |
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double Bx, double By, |
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double Cx, double Cy, |
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double Px, double Py) |
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|
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{ |
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double ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy; |
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double cCROSSap, bCROSScp, aCROSSbp; |
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|
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ax = Cx - Bx; ay = Cy - By; |
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bx = Ax - Cx; by = Ay - Cy; |
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cx = Bx - Ax; cy = By - Ay; |
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apx= Px - Ax; apy= Py - Ay; |
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bpx= Px - Bx; bpy= Py - By; |
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cpx= Px - Cx; cpy= Py - Cy; |
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|
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aCROSSbp = ax*bpy - ay*bpx; |
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cCROSSap = cx*apy - cy*apx; |
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bCROSScp = bx*cpy - by*cpx; |
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|
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return ((aCROSSbp >= 0.0) && (bCROSScp >= 0.0) && (cCROSSap >= 0.0)); |
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}; |
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|
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int |
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polyTriangulate(const Vert2_list *contour, tri_out_t *cb) |
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{ |
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/* allocate and initialize list of Vertices in polygon */ |
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|
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int nv, m, u, v, w, count, result; |
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int *V; |
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|
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if ( contour->nv < 3 ) return false; |
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|
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V = (int *)malloc(sizeof(int)*contour->nv); |
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if (V == NULL) return false; |
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|
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/* we want a counter-clockwise polygon in V */ |
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|
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if ( 0.0 < polyArea(contour) ) |
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for (v=0; v<contour->nv; v++) V[v] = v; |
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else |
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for(v=0; v<contour->nv; v++) V[v] = (contour->nv-1)-v; |
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|
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nv = contour->nv; |
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|
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/* remove nv-2 Vertices, creating 1 triangle every time */ |
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count = 2*nv; /* error detection */ |
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|
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for(m=0, v=nv-1; nv>2; ) |
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{ |
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/* if we loop, it is probably a non-simple polygon */ |
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if (0 >= count--) |
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{ |
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/* Triangulate: ERROR - probable bad polygon */ |
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return false; |
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} |
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|
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/* three consecutive vertices in current polygon, <u,v,w> */ |
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u = v ; if (nv <= u) u = 0; /* previous */ |
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v = u+1; if (nv <= v) v = 0; /* new v */ |
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w = v+1; if (nv <= w) w = 0; /* next */ |
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|
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result = polySnip(contour, u, v, w, nv, V); |
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if (result > 0) /* successfully found a triangle */ |
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{ |
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int a,b,c; |
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|
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/* true names of the vertices */ |
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a = V[u]; b = V[v]; c = V[w]; |
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|
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/* output Triangle */ |
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if (!(*cb)(contour, a, b, c)) return false; |
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|
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m++; |
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} |
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if (result) /* successfully found a triangle or three consecutive colinear points */ |
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{ |
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int s,t; |
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|
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/* remove v from remaining polygon */ |
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for(s=v,t=v+1;t<nv;s++,t++) V[s] = V[t]; nv--; |
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|
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/* reset error detection counter */ |
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count = 2*nv; |
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} |
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} |
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|
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free(V); |
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|
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return true; |
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} |
