Unity通过脚本实现不规则多边形的碰撞检测

先上效果图

可能大家都已经对Polygon Collider 2D这个组件已经非常的熟悉，就是一个判断多边形碰撞的组件，我们可以通过编辑形状大小来实现对不同多边形的碰撞检测。
但是如果遇到较为复杂的多边形，我们在调节时就可能会相对困难，例如下边这个复杂的多边形

在这里分享一个脚本，可以去识别多边形最边缘的边，把最边缘的边赋值给Polygon Collider 2D，就可以使得Polygon Collider 2D的大小完美贴合多边形的边缘。

查找边缘的主要算法就是取到多边形内不共用的边（可以发现只有边缘的边是不被三角形共用的，被三角形公用的边都在内部）

代码：

using UnityEngine;
using System.Collections.Generic;
using UnityEditor;[RequireComponent(typeof(MeshFilter))]
[RequireComponent(typeof(PolygonCollider2D))]
[ExecuteInEditMode]
public class Mesh2DColliderMaker : MonoBehaviour {/// <summary>/// 定义一个结构体，用来表示边/// </summary>struct Edge2D{public Vector2 a;public Vector2 b;public override bool Equals(object obj){if (obj is Edge2D){var edge = (Edge2D)obj;//An edge is equal regardless of which order it's points are inreturn (edge.a == a && edge.b == b) || (edge.b == a && edge.a == b);}return false;}public override int GetHashCode(){return a.GetHashCode() ^ b.GetHashCode();}public override string ToString(){return string.Format("[" + a.x + "," + a.y + "->" + b.x + "," + b.y + "]");}}MeshFilter filter;PolygonCollider2D polyCollider;void Start() {filter = GetComponent<MeshFilter>();polyCollider = GetComponent<PolygonCollider2D>();CreatePolygon2DColliderPoints();}void Update(){        }public void CreatePolygon2DColliderPoints(){var edges = BuildEdgesFromMesh();var paths = BuildColliderPaths(edges);ApplyPathsToPolygonCollider(paths);}/// <summary>/// 对多边形碰撞体设置路径/// </summary>/// <param name="paths"></param>private void ApplyPathsToPolygonCollider(List<Vector2[]> paths) {if (paths == null)return;polyCollider.pathCount = paths.Count;for (int i = 0; i < paths.Count; i++) {var path = paths [i];polyCollider.SetPath(i, path);}}/// <summary>/// 通过mesh去找所有的边，存到一个字典里/// 如果 int = 1 则证明是边缘的边，如果 int = 2 则证明则是公用的（不是边缘）/// </summary>/// <returns>返回存Edge2D的字典</returns>private Dictionary<Edge2D, int> BuildEdgesFromMesh() {var mesh = filter.sharedMesh;if (mesh == null)return null;var verts = mesh.vertices;var tris = mesh.triangles;var edges = new Dictionary<Edge2D, int>();for (int i = 0; i < tris.Length - 2; i += 3) {var faceVert1 = verts[tris[i]];var faceVert2 = verts[tris[i + 1]];var faceVert3 = verts[tris[i + 2]];Edge2D[] faceEdges;faceEdges = new Edge2D[] {new Edge2D{ a = faceVert1, b = faceVert2 },new Edge2D{ a = faceVert2, b = faceVert3 },new Edge2D{ a = faceVert3, b = faceVert1 },};foreach(var edge in faceEdges) {if (edges.ContainsKey(edge))edges[edge]++;elseedges[edge] = 1;}}return edges;}private List<Vector2[]> BuildColliderPaths(Dictionary<Edge2D, int> allEdges) {if (allEdges == null)return null;  var outerEdges = GetOuterEdges(allEdges);var paths = new List<List<Edge2D>>();List<Edge2D> path = null;while (outerEdges.Count > 0) {if (path == null) {path = new List<Edge2D>();path.Add (outerEdges[0]);paths.Add (path);outerEdges.RemoveAt(0);}bool foundAtLeastOneEdge = false;int i = 0;while (i < outerEdges.Count) {var edge = outerEdges [i];bool removeEdgeFromOuter = false;if (edge.b == path[0].a) {path.Insert (0, edge);removeEdgeFromOuter = true;}else if (edge.a == path[path.Count - 1].b) {path.Add(edge);removeEdgeFromOuter = true;}if (removeEdgeFromOuter) {foundAtLeastOneEdge = true;outerEdges.RemoveAt(i);} elsei++;}if (!foundAtLeastOneEdge)path = null;}var cleanedPaths = new List<Vector2[]>();foreach(var builtPath in paths) {var coords = new List<Vector2>();foreach(var edge in builtPath)coords.Add (edge.a);cleanedPaths.Add (CoordinatesCleaned(coords));}        return cleanedPaths;}/// <summary>/// 取到边缘的边（即字典中int = 1的值）/// </summary>/// <param name="allEdges"></param>/// <returns>边缘的边</returns>private List<Edge2D> GetOuterEdges(Dictionary<Edge2D, int> allEdges){var outerEdges = new List<Edge2D>();foreach (var edge in allEdges.Keys){var numSharedFaces = allEdges[edge];if (numSharedFaces == 1)outerEdges.Add(edge);}return outerEdges;}private bool CoordinatesFormLine(Vector2 a, Vector2 b, Vector2 c){//If the area of a triangle created from three points is zero, they must be in a line.float area = a.x * ( b.y - c.y ) + b.x * ( c.y - a.y ) + c.x * ( a.y - b.y );return Mathf.Approximately(area, 0f);}private Vector2[] CoordinatesCleaned(List<Vector2> coordinates) {List<Vector2> coordinatesCleaned = new List<Vector2> ();coordinatesCleaned.Add (coordinates [0]);var lastAddedIndex = 0;for (int i = 1; i < coordinates.Count; i++) {var coordinate = coordinates [i];Vector2 lastAddedCoordinate = coordinates [lastAddedIndex];Vector2 nextCoordinate = (i + 1 >= coordinates.Count) ? coordinates[0] : coordinates [i + 1];if (!CoordinatesFormLine(lastAddedCoordinate, coordinate, nextCoordinate)) {coordinatesCleaned.Add (coordinate);lastAddedIndex = i;                           }}return coordinatesCleaned.ToArray ();}}

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