Generate 2D polygon collider from 3D mesh

Question

My game use 2d physic, but 3D graphics. The unity editor automatically generates a collider polygon using the sprite of the desired shape. If for example on a sprite a circle is drawn on a transparent background, then the generated collider polygon will be round. When the 2D scene mode is fixed, if you click on the 3d mesh model - it is outlined in orange (as can be seen in the screenshot), I want to make the polygon a collider polygon of the same shape as if it was a sprite. Tell me, please, how can I do this except to manually sketch the collider polygon? I need to algorithm working on at least simple examples as in the screenshot alt text

Answer 1

I was looking for this exact solution myself (All that dragging around polygon points was driving me insane).

Here's an editor script I wrote that will match any PolygonCollider2D to the MeshFilter on a GameObject.

Just plop it into an Editor folder, highlight the GameObject, and click Update Polygon Colliders up in the Tools menu, or Ctrl/Cmd+T

Seems to work well with ProBuilder and in Prefab Edit Mode. I'm sure this can be greatly improved upon, feel free!

GIANT credit goes to @Bunny83 for their EdgeHelper class! Wouldn't work nearly as well without it. :)

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEditor;
 using System;
 using UnityEditor.SceneManagement;
 using System.Linq;
 
 public static class SetPolygonCollider3D
 {
     [MenuItem("Tools/Update Polygon Colliders %t", false, -1)]
     static void UpdatePolygonColliders()
     {
         Transform transform = Selection.activeTransform;
         if(transform == null)
         {
             Debug.LogWarning("No valid GameObject selected!");
             return;
         }
 
         EditorSceneManager.MarkSceneDirty(transform.gameObject.scene);
 
         MeshFilter[] meshFilters = transform.GetComponentsInChildren<MeshFilter>();
         
         foreach(MeshFilter meshFilter in meshFilters)
         {
             if(meshFilter.GetComponent<PolygonCollider2D>() != null)
             {
                 UpdatePolygonCollider2D(meshFilter);
             }
         }
     }
 
     static void UpdatePolygonCollider2D(MeshFilter meshFilter)
     {
         if(meshFilter.sharedMesh == null)
         {
             Debug.LogWarning(meshFilter.gameObject.name + " has no Mesh set on its MeshFilter component!");
             return;
         }
 
         PolygonCollider2D polygonCollider2D = meshFilter.GetComponent<PolygonCollider2D>();
         polygonCollider2D.pathCount = 1;
 
         List<Vector3> vertices =  new List<Vector3>();
         meshFilter.sharedMesh.GetVertices(vertices);
 
         var boundaryPath = EdgeHelpers.GetEdges(meshFilter.sharedMesh.triangles).FindBoundary().SortEdges();
 
         Vector3[] yourVectors = new Vector3[boundaryPath.Count];
         for(int i = 0; i < boundaryPath.Count; i++)
         {
             yourVectors[i] = vertices[ boundaryPath[i].v1 ];
         }
         List<Vector2> newColliderVertices = new List<Vector2>();
 
         for(int i=0; i < yourVectors.Length; i++)
         {
             newColliderVertices.Add(new Vector2(yourVectors[i].x, yourVectors[i].y));
         }
 
         Vector2[] newPoints = newColliderVertices.Distinct().ToArray();
 
         EditorUtility.SetDirty(polygonCollider2D);
 
         polygonCollider2D.SetPath(0, newPoints);
         Debug.Log(meshFilter.gameObject.name + " PolygonCollider2D updated.");
     }
 }
 
 public static class EdgeHelpers
 {
     public struct Edge
     {
         public int v1;
         public int v2;
         public int triangleIndex;
         public Edge(int aV1, int aV2, int aIndex)
         {
             v1 = aV1;
             v2 = aV2;
             triangleIndex = aIndex;
         }
     }
 
     public static List<Edge> GetEdges(int[] aIndices)
     {
         List<Edge> result = new List<Edge>();
         for (int i = 0; i < aIndices.Length; i += 3)
         {
             int v1 = aIndices[i];
             int v2 = aIndices[i + 1];
             int v3 = aIndices[i + 2];
             result.Add(new Edge(v1, v2, i));
             result.Add(new Edge(v2, v3, i));
             result.Add(new Edge(v3, v1, i));
         }
         return result;
     }
 
     public static List<Edge> FindBoundary(this List<Edge> aEdges)
     {
         List<Edge> result = new List<Edge>(aEdges);
         for (int i = result.Count-1; i > 0; i--)
         {
             for (int n = i - 1; n >= 0; n--)
             {
                 if (result[i].v1 == result[n].v2 && result[i].v2 == result[n].v1)
                 {
                     // shared edge so remove both
                     result.RemoveAt(i);
                     result.RemoveAt(n);
                     i--;
                     break;
                 }
             }
         }
         return result;
     }
     public static List<Edge> SortEdges(this List<Edge> aEdges)
     {
         List<Edge> result = new List<Edge>(aEdges);
         for (int i = 0; i < result.Count-2; i++)
         {
             Edge E = result[i];
             for(int n = i+1; n < result.Count; n++)
             {
                 Edge a = result[n];
                 if (E.v2 == a.v1)
                 {
                     // in this case they are already in order so just continoue with the next one
                     if (n == i+1)
                         break;
                     // if we found a match, swap them with the next one after "i"
                     result[n] = result[i + 1];
                     result[i + 1] = a;
                     break;
                 }
             }
         }
         return result;
     }
 }

Generate 2D polygon collider from 3D mesh

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