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140 lines
3.1 KiB
140 lines
3.1 KiB
#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <assert.h>
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#include "triangulate.h"
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static const float EPSILON=0.0000000001f;
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float Triangulate::Area(const Vector2dVector &contour)
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{
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int n = contour.size();
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float A=0.0f;
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for(int p=n-1,q=0; q<n; p=q++)
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{
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A+= contour[p].GetX()*contour[q].GetY() - contour[q].GetX()*contour[p].GetY();
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}
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return A*0.5f;
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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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bool Triangulate::InsideTriangle(float Ax, float Ay,
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float Bx, float By,
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float Cx, float Cy,
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float Px, float Py)
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{
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float ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy;
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float cCROSSap, bCROSScp, aCROSSbp;
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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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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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return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f));
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};
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bool Triangulate::Snip(const Vector2dVector &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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float Ax, Ay, Bx, By, Cx, Cy, Px, Py;
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Ax = contour[V[u]].GetX();
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Ay = contour[V[u]].GetY();
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Bx = contour[V[v]].GetX();
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By = contour[V[v]].GetY();
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Cx = contour[V[w]].GetX();
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Cy = contour[V[w]].GetY();
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if ( EPSILON > (((Bx-Ax)*(Cy-Ay)) - ((By-Ay)*(Cx-Ax))) ) return false;
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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[p]].GetX();
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Py = contour[V[p]].GetY();
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if (InsideTriangle(Ax,Ay,Bx,By,Cx,Cy,Px,Py)) return false;
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}
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return true;
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}
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bool Triangulate::Process(const Vector2dVector &contour,Vector2dVector &result)
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{
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/* allocate and initialize list of Vertices in polygon */
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int n = contour.size();
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if ( n < 3 ) return false;
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int *V = new int[n];
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/* we want a counter-clockwise polygon in V */
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if ( 0.0f < Area(contour) )
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for (int v=0; v<n; v++) V[v] = v;
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else
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for(int v=0; v<n; v++) V[v] = (n-1)-v;
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int nv = n;
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/* remove nv-2 Vertices, creating 1 triangle every time */
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int count = 2*nv; /* error detection */
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for(int 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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/* three consecutive vertices in current polygon, <u,v,w> */
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int 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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int w = v+1; if (nv <= w) w = 0; /* next */
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if ( Snip(contour,u,v,w,nv,V) )
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{
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int a,b,c,s,t;
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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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/* output Triangle */
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result.push_back( contour[a] );
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result.push_back( contour[b] );
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result.push_back( contour[c] );
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m++;
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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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/* resest error detection counter */
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count = 2*nv;
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}
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}
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delete V;
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return true;
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}
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