Automatically Create Polygon Collider 2D From 2D Mesh in Unity
I was working on a 2D game in Unity and needed some way to automatically create a collider for a complex 2D level mesh. Editing a Polygon Collider 2D in the editor was out of the question, since there were thousands of vertices. I ended up writing a script that analyzes the MeshFilter of the mesh, and programmatically creates a Polygon Collider 2D for it. It also supports meshes that have mutliple non-connected components.

How to Use It
To use it, create a ColliderCreator C# script, copy the code in, and add the Script component to a GameObject that has a 2D mesh. When you hit Play, the script will generate a Polygon Collider 2D for that GameObject based on the mesh. While the game is running, it's best to save the generated PolygonCollider2D using Copy Component, and paste it into the prefab. Then the script won't have to run every time.

ColliderCreator C# Code
`using System.Collections.Generic;using UnityEngine;public class ColliderCreator : MonoBehaviour{ void Start() { // Stop if no mesh filter exists or there's already a collider if (GetComponent<PolygonCollider2D>() || GetComponent<MeshFilter>() == null) { return; } // Get triangles and vertices from mesh int[] triangles = GetComponent<MeshFilter>().mesh.triangles; Vector3[] vertices = GetComponent<MeshFilter>().mesh.vertices; // Get just the outer edges from the mesh's triangles (ignore or remove any shared edges) Dictionary<string, KeyValuePair<int, int>> edges = new Dictionary<string, KeyValuePair<int, int>>(); for (int i = 0; i < triangles.Length; i += 3) { for (int e = 0; e < 3; e++) { int vert1 = triangles[i + e]; int vert2 = triangles[i + e + 1 > i + 2 ? i : i + e + 1]; string edge = Mathf.Min(vert1, vert2) + ":" + Mathf.Max(vert1, vert2); if (edges.ContainsKey(edge)) { edges.Remove(edge); } else { edges.Add(edge, new KeyValuePair<int, int>(vert1, vert2)); } } } // Create edge lookup (Key is first vertex, Value is second vertex, of each edge) Dictionary<int, int> lookup = new Dictionary<int, int>(); foreach (KeyValuePair<int, int> edge in edges.Values) { if (lookup.ContainsKey(edge.Key) == false) { lookup.Add(edge.Key, edge.Value); } } // Create empty polygon collider PolygonCollider2D polygonCollider = gameObject.AddComponent<PolygonCollider2D>(); polygonCollider.pathCount = 0; // Loop through edge vertices in order int startVert = 0; int nextVert = startVert; int highestVert = startVert; List<Vector2> colliderPath = new List<Vector2>(); while (true) { // Add vertex to collider path colliderPath.Add(vertices[nextVert]); // Get next vertex nextVert = lookup[nextVert]; // Store highest vertex (to know what shape to move to next) if (nextVert > highestVert) { highestVert = nextVert; } // Shape complete if (nextVert == startVert) { // Add path to polygon collider polygonCollider.pathCount++; polygonCollider.SetPath(polygonCollider.pathCount - 1, colliderPath.ToArray()); colliderPath.Clear(); // Go to next shape if one exists if (lookup.ContainsKey(highestVert + 1)) { // Set starting and next vertices startVert = highestVert + 1; nextVert = startVert; // Continue to next loop continue; } // No more verts break; } } }}`

## Old Version

The old version of the code was much slower. You can still see it below, but I highly recommend using the above one.

`using UnityEngine;using System.Collections.Generic;public class ColliderCreator : MonoBehaviour{ private int currentPathIndex = 0; private PolygonCollider2D polygonCollider; private List<Edge> edges = new List<Edge>(); private List<Vector2> points = new List<Vector2>(); private Vector3[] vertices; void Start() { // Get the polygon collider (create one if necessary) polygonCollider = GetComponent<PolygonCollider2D>(); if (polygonCollider == null) { polygonCollider = gameObject.AddComponent<PolygonCollider2D>(); } // Get the mesh's vertices for use later vertices = GetComponent<MeshFilter>().mesh.vertices; // Get all edges from triangles int[] triangles = GetComponent<MeshFilter>().mesh.triangles; for (int i = 0; i < triangles.Length; i += 3) { edges.Add(new Edge(triangles[i], triangles[i + 1])); edges.Add(new Edge(triangles[i + 1], triangles[i + 2])); edges.Add(new Edge(triangles[i + 2], triangles[i])); } // Find duplicate edges List<Edge> edgesToRemove = new List<Edge>(); foreach (Edge edge1 in edges) { foreach (Edge edge2 in edges) { if (edge1 != edge2) { if (edge1.vert1 == edge2.vert1 && edge1.vert2 == edge2.vert2 || edge1.vert1 == edge2.vert2 && edge1.vert2 == edge2.vert1) { edgesToRemove.Add(edge1); } } } } // Remove duplicate edges (leaving only perimeter edges) foreach (Edge edge in edgesToRemove) { edges.Remove(edge); } // Start edge trace edgeTrace(edges[0]); } void edgeTrace(Edge edge) { // Add this edge's vert1 coords to the point list points.Add(vertices[edge.vert1]); // Store this edge's vert2 int vert2 = edge.vert2; // Remove this edge edges.Remove(edge); // Find next edge that contains vert2 foreach (Edge nextEdge in edges) { if (nextEdge.vert1 == vert2) { edgeTrace(nextEdge); return; } } // No next edge found, create a path based on these points polygonCollider.pathCount = currentPathIndex + 1; polygonCollider.SetPath(currentPathIndex, points.ToArray()); // Empty path points.Clear(); // Increment path index currentPathIndex ++; // Start next edge trace if there are edges left if (edges.Count > 0) { edgeTrace(edges[0]); } }}class Edge{ public int vert1; public int vert2; public Edge(int Vert1, int Vert2) { vert1 = Vert1; vert2 = Vert2; }}`
SticKai   Feb 02, 2024
Hey bro um I was just wondering why the script doesn't get rid of the initial polygon, otherwise it works great!
SteveB   Sep 14, 2022
Man, this is what I was searching for. The mesh colliders from imported geometry simply didn't work so i needed to somehow create my own after import. Absolutely brilliant! Thanks!
YoYo   Aug 02, 2021
Thankyou!! Exactly what I was looking for!
Vov   Aug 31, 2020
Ignore my last comment, not sure what causes it but I'm getting an out of memory error on some quite complex shapes
Vov   Aug 31, 2020
Absolutely great, except... Where one mesh is interpreted as 2 shapes despite sharing 1 vertex, the routine goes into an infinite loop. You can reproduce this by creating 2 squares diagonally next to each other sharing 1 corner vertex. For now I've just commented out the part where it cycles around to address additional shapes because I don't need it anyway :)
Ä°brahim Ã‡imentepe   Jun 15, 2020
This is absolutely perfect mate. Thank you very much!
Abood   Oct 25, 2018
This is perfect! I was looking for something like this but I only have one problem which is when I have a mesh that has a hole in it, for example, the collider covers the inner gap too how can I fix that?
JÃ´natas Q. Lima   Apr 22, 2018
I'm so grateful. I researched for a long time how to let the shape of the collider equal the sprite. I failed a lot, when I found an answer, it did not work, or sometimes I did not find anything. Until that came this wonderful site, even though a mesh collider was generated from the 2d mesh I modified that part: ushort [] triangles = GetComponent <SpriteRenderer> (). sprite.triangles; Vector3 [] vertices = GetComponent <SpriteRenderer> (). Sprite.vertices; Now the collider is generated based on the shape of the Sprite. I solved my problem. Many thanks H3X3D!