我正在努力解决 libgdx 的耳夹三角测量器的问题。它在某个时候进入无限循环并使整个程序崩溃。我记录了视频中发生崩溃的确切位置。
三角仪源代码：
/*
* 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<Vector2> computeTriangles(final List<Vector2> polygon) {
// TODO Check if LinkedList performs better
final ArrayList<Vector2> triangles = new ArrayList<Vector2>();
final ArrayList<Vector2> vertices = new ArrayList<Vector2>(polygon.size());
vertices.addAll(polygon);
if(vertices.size() == 3) {
triangles.addAll(vertices);
return triangles;
}
while(vertices.size() >= 3) {
// TODO Usually(Always?) only the Types of the vertices next to the ear change! --> Improve
final int vertexTypes[] = this.classifyVertices(vertices);
final int vertexCount = vertices.size();
for(int index = 0; index < vertexCount; index++) {
if(this.isEarTip(vertices, index, vertexTypes)) {
this.cutEarTip(vertices, index, triangles);
break;
}
}
}
return triangles;
}
private static boolean areVerticesClockwise(final ArrayList<Vector2> pVertices) {
final int vertexCount = pVertices.size();
float area = 0;
for(int i = 0; i < 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 < 0) {
return true;
} else {
return false;
}
}
/**
* @param pVertices
* @return An array of length <code>pVertices.size()</code> filled with either {@link EarClippingTriangulator#CONCAVE} or
* {@link EarClippingTriangulator#CONVEX}.
*/
private int[] classifyVertices(final ArrayList<Vector2> 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 < 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) < 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 <code>true</code> when the Triangles contains one or more vertices, <code>false</code> otherwise.
*/
private static boolean isAnyVertexInTriangle(final ArrayList<Vector2> 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 < 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) && (currentVertexY != pY1)) || ((currentVertexX != pX2) && (currentVertexY != pY2)) || ((currentVertexX != pX3) && (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 > 0 && areaSign2 > 0 && areaSign3 > 0) {
return true;
} else if(areaSign1 <= 0 && areaSign2 <= 0 && areaSign3 <= 0) {
return true;
}
// }
}
i++;
}
return false;
}
private boolean isEarTip(final ArrayList<Vector2> 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<Vector2> pVertices, final int pEarTipIndex, final ArrayList<Vector2> 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() >= 3) {
EarClippingTriangulator.removeCollinearNeighborEarsAfterRemovingEarTip(pVertices, pEarTipIndex);
}
}
private static void removeCollinearNeighborEarsAfterRemovingEarTip(final ArrayList<Vector2> 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() > 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<Vector2> 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<Vector2> 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<Vector2> pVertices, final int pIndex) {
return pIndex == 0 ? pVertices.size() - 1 : pIndex - 1;
}
private static int computeNextIndex(final List<Vector2> pVertices, final int pIndex) {
return pIndex == pVertices.size() - 1 ? 0 : pIndex + 1;
}
}
上面链接的源代码中的@ 53# 行发生崩溃...
在computeTriangles 函数中的while 循环具有以下条件：while(vertices.size() >= 3) { ...