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POEar Clipping Triangulator Crashing
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  1. POEar Clipping Triangulator Crashing
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    copied!<p>i'm struggling with a problem in ear clipping triangulator of libgdx. It goes into infinite loop at some point and crashes the whole program. I recorded where exactly crash occurs on <a href="http://www.youtube.com/watch?v=3Y43KStb6cI" rel="nofollow">a video</a>.</p> <p>Source Code of Triangulator:</p> <pre><code>/* * Copyright 2010 Mario Zechner (contact@badlogicgames.com), Nathan Sweet (admin@esotericsoftware.com), Nicolas Gramlich * * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the * License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" * BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language * governing permissions and limitations under the License. */ package com.badlogic.gdx.math; import java.util.ArrayList; import java.util.Collections; import java.util.List; /** * A simple implementation of the ear cutting algorithm to triangulate simple * polygons without holes. For more information: * http://cgm.cs.mcgill.ca/~godfried/teaching/cg-projects/97/Ian/algorithm2.html * http://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf * * @author badlogicgames@gmail.com * @author Nicolas Gramlich (Improved performance. Collinear edges are now supported.) */ public final class EarClippingTriangulator { private static final int CONCAVE = 1; private static final int CONVEX = -1; private int concaveVertexCount; /** * Triangulates the given (concave) polygon to a list of triangles. The * resulting triangles have clockwise order. * @param polygon the polygon * @return the triangles */ public List&lt;Vector2&gt; computeTriangles(final List&lt;Vector2&gt; polygon) { // TODO Check if LinkedList performs better final ArrayList&lt;Vector2&gt; triangles = new ArrayList&lt;Vector2&gt;(); final ArrayList&lt;Vector2&gt; vertices = new ArrayList&lt;Vector2&gt;(polygon.size()); vertices.addAll(polygon); if(vertices.size() == 3) { triangles.addAll(vertices); return triangles; } while(vertices.size() &gt;= 3) { // TODO Usually(Always?) only the Types of the vertices next to the ear change! --&gt; Improve final int vertexTypes[] = this.classifyVertices(vertices); final int vertexCount = vertices.size(); for(int index = 0; index &lt; vertexCount; index++) { if(this.isEarTip(vertices, index, vertexTypes)) { this.cutEarTip(vertices, index, triangles); break; } } } return triangles; } private static boolean areVerticesClockwise(final ArrayList&lt;Vector2&gt; pVertices) { final int vertexCount = pVertices.size(); float area = 0; for(int i = 0; i &lt; vertexCount; i++) { final Vector2 p1 = pVertices.get(i); final Vector2 p2 = pVertices.get(EarClippingTriangulator.computeNextIndex(pVertices, i)); area += p1.x * p2.y - p2.x * p1.y; } if(area &lt; 0) { return true; } else { return false; } } /** * @param pVertices * @return An array of length &lt;code&gt;pVertices.size()&lt;/code&gt; filled with either {@link EarClippingTriangulator#CONCAVE} or * {@link EarClippingTriangulator#CONVEX}. */ private int[] classifyVertices(final ArrayList&lt;Vector2&gt; pVertices) { final int vertexCount = pVertices.size(); final int[] vertexTypes = new int[vertexCount]; this.concaveVertexCount = 0; /* Ensure vertices are in clockwise order. */ if(!EarClippingTriangulator.areVerticesClockwise(pVertices)) { Collections.reverse(pVertices); } for(int index = 0; index &lt; vertexCount; index++) { final int previousIndex = EarClippingTriangulator.computePreviousIndex(pVertices, index); final int nextIndex = EarClippingTriangulator.computeNextIndex(pVertices, index); final Vector2 previousVertex = pVertices.get(previousIndex); final Vector2 currentVertex = pVertices.get(index); final Vector2 nextVertex = pVertices.get(nextIndex); if(EarClippingTriangulator.isTriangleConvex(previousVertex.x, previousVertex.y, currentVertex.x, currentVertex.y, nextVertex.x, nextVertex.y)) { vertexTypes[index] = CONVEX; } else { vertexTypes[index] = CONCAVE; this.concaveVertexCount++; } } return vertexTypes; } private static boolean isTriangleConvex(final float pX1, final float pY1, final float pX2, final float pY2, final float pX3, final float pY3) { if(EarClippingTriangulator.computeSpannedAreaSign(pX1, pY1, pX2, pY2, pX3, pY3) &lt; 0) { return false; } else { return true; } } private static int computeSpannedAreaSign(final float pX1, final float pY1, final float pX2, final float pY2, final float pX3, final float pY3) { float area = 0; area += pX1 * (pY3 - pY2); area += pX2 * (pY1 - pY3); area += pX3 * (pY2 - pY1); return (int)Math.signum(area); } /** * @return &lt;code&gt;true&lt;/code&gt; when the Triangles contains one or more vertices, &lt;code&gt;false&lt;/code&gt; otherwise. */ private static boolean isAnyVertexInTriangle(final ArrayList&lt;Vector2&gt; pVertices, final int[] pVertexTypes, final float pX1, final float pY1, final float pX2, final float pY2, final float pX3, final float pY3) { int i = 0; final int vertexCount = pVertices.size(); while(i &lt; vertexCount - 1) { if((pVertexTypes[i] == CONCAVE)) { final Vector2 currentVertex = pVertices.get(i); final float currentVertexX = currentVertex.x; final float currentVertexY = currentVertex.y; /* TODO The following condition fails for perpendicular, axis aligned triangles! * Removing it doesn't seem to cause problems. * Maybe it was an optimization? * Maybe it tried to handle collinear pieces ? */ // if(((currentVertexX != pX1) &amp;&amp; (currentVertexY != pY1)) || ((currentVertexX != pX2) &amp;&amp; (currentVertexY != pY2)) || ((currentVertexX != pX3) &amp;&amp; (currentVertexY != pY3))) { final int areaSign1 = EarClippingTriangulator.computeSpannedAreaSign(pX1, pY1, pX2, pY2, currentVertexX, currentVertexY); final int areaSign2 = EarClippingTriangulator.computeSpannedAreaSign(pX2, pY2, pX3, pY3, currentVertexX, currentVertexY); final int areaSign3 = EarClippingTriangulator.computeSpannedAreaSign(pX3, pY3, pX1, pY1, currentVertexX, currentVertexY); if(areaSign1 &gt; 0 &amp;&amp; areaSign2 &gt; 0 &amp;&amp; areaSign3 &gt; 0) { return true; } else if(areaSign1 &lt;= 0 &amp;&amp; areaSign2 &lt;= 0 &amp;&amp; areaSign3 &lt;= 0) { return true; } // } } i++; } return false; } private boolean isEarTip(final ArrayList&lt;Vector2&gt; pVertices, final int pEarTipIndex, final int[] pVertexTypes) { if(this.concaveVertexCount != 0) { final Vector2 previousVertex = pVertices.get(EarClippingTriangulator.computePreviousIndex(pVertices, pEarTipIndex)); final Vector2 currentVertex = pVertices.get(pEarTipIndex); final Vector2 nextVertex = pVertices.get(EarClippingTriangulator.computeNextIndex(pVertices, pEarTipIndex)); if(EarClippingTriangulator.isAnyVertexInTriangle(pVertices, pVertexTypes, previousVertex.x, previousVertex.y, currentVertex.x, currentVertex.y, nextVertex.x, nextVertex.y)) { return false; } else { return true; } } else { return true; } } private void cutEarTip(final ArrayList&lt;Vector2&gt; pVertices, final int pEarTipIndex, final ArrayList&lt;Vector2&gt; pTriangles) { final int previousIndex = EarClippingTriangulator.computePreviousIndex(pVertices, pEarTipIndex); final int nextIndex = EarClippingTriangulator.computeNextIndex(pVertices, pEarTipIndex); if(!EarClippingTriangulator.isCollinear(pVertices, previousIndex, pEarTipIndex, nextIndex)) { pTriangles.add(new Vector2(pVertices.get(previousIndex))); pTriangles.add(new Vector2(pVertices.get(pEarTipIndex))); pTriangles.add(new Vector2(pVertices.get(nextIndex))); } pVertices.remove(pEarTipIndex); if(pVertices.size() &gt;= 3) { EarClippingTriangulator.removeCollinearNeighborEarsAfterRemovingEarTip(pVertices, pEarTipIndex); } } private static void removeCollinearNeighborEarsAfterRemovingEarTip(final ArrayList&lt;Vector2&gt; pVertices, final int pEarTipCutIndex) { final int collinearityCheckNextIndex = pEarTipCutIndex % pVertices.size(); int collinearCheckPreviousIndex = EarClippingTriangulator.computePreviousIndex(pVertices, collinearityCheckNextIndex); if(EarClippingTriangulator.isCollinear(pVertices, collinearityCheckNextIndex)) { pVertices.remove(collinearityCheckNextIndex); if(pVertices.size() &gt; 3) { /* Update */ collinearCheckPreviousIndex = EarClippingTriangulator.computePreviousIndex(pVertices, collinearityCheckNextIndex); if(EarClippingTriangulator.isCollinear(pVertices, collinearCheckPreviousIndex)){ pVertices.remove(collinearCheckPreviousIndex); } } } else if(EarClippingTriangulator.isCollinear(pVertices, collinearCheckPreviousIndex)){ pVertices.remove(collinearCheckPreviousIndex); } } private static boolean isCollinear(final ArrayList&lt;Vector2&gt; pVertices, final int pIndex) { final int previousIndex = EarClippingTriangulator.computePreviousIndex(pVertices, pIndex); final int nextIndex = EarClippingTriangulator.computeNextIndex(pVertices, pIndex); return EarClippingTriangulator.isCollinear(pVertices, previousIndex, pIndex, nextIndex); } private static boolean isCollinear(final ArrayList&lt;Vector2&gt; pVertices, final int pPreviousIndex, final int pIndex, final int pNextIndex) { final Vector2 previousVertex = pVertices.get(pPreviousIndex); final Vector2 vertex = pVertices.get(pIndex); final Vector2 nextVertex = pVertices.get(pNextIndex); return EarClippingTriangulator.computeSpannedAreaSign(previousVertex.x, previousVertex.y, vertex.x, vertex.y, nextVertex.x, nextVertex.y) == 0; } private static int computePreviousIndex(final List&lt;Vector2&gt; pVertices, final int pIndex) { return pIndex == 0 ? pVertices.size() - 1 : pIndex - 1; } private static int computeNextIndex(final List&lt;Vector2&gt; pVertices, final int pIndex) { return pIndex == pVertices.size() - 1 ? 0 : pIndex + 1; } } </code></pre> <p>Crash occurs @ 53# line in the source-code linked above...<br/> while loop in computeTriangles function with following condition : while(vertices.size() >= 3) { ...</p>
 

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