test/Assets/Editor/MeshColliderGeneratorWindow.cs

using System.Collections.Generic;
using System.IO;
using UnityEditor;
using UnityEngine;

public class MeshColliderGeneratorWindow : EditorWindow
{
    private const string GeneratedMeshFolder = "Assets/GeneratedColliders";
    [SerializeField]
    private List<GameObject> targetRoots = new List<GameObject>();

    [SerializeField]
    private bool includeInactive = true;

    [SerializeField]
    private float xScale = 1f;

    [SerializeField]
    private bool skipIfExists = true;

    [SerializeField]
    private bool setConvex = false;

	[SerializeField]
	private bool extrudeAlongNormals = false;

	[SerializeField]
	private float extrusionDistance = 0f;

    private SerializedObject serializedObjectRef;
    private SerializedProperty targetsProp;

    [MenuItem("Tools/Mesh Collider Generator")] 
    public static void ShowWindow()
    {
        var window = GetWindow<MeshColliderGeneratorWindow>(true, "Mesh Collider Generator");
        window.minSize = new Vector2(420, 320);
        window.Show();
    }

    private void OnEnable()
    {
        serializedObjectRef = new SerializedObject(this);
        targetsProp = serializedObjectRef.FindProperty("targetRoots");
    }

    private void OnGUI()
    {
        serializedObjectRef.Update();

        EditorGUILayout.LabelField("Target GameObjects", EditorStyles.boldLabel);
        EditorGUILayout.HelpBox("Assign one or more root GameObjects. All children will be scanned.", MessageType.Info);
        EditorGUILayout.PropertyField(targetsProp, true);

        EditorGUILayout.Space();
        EditorGUILayout.LabelField("Options", EditorStyles.boldLabel);
        includeInactive = EditorGUILayout.Toggle(new GUIContent("Include Inactive", "Scan inactive children too"), includeInactive);
        xScale = EditorGUILayout.FloatField(new GUIContent("X Scale", "Local X scale for the generated collider GameObject"), Mathf.Max(0f, xScale));
		skipIfExists = EditorGUILayout.Toggle(new GUIContent("Skip If MeshCollider Exists", "Skip if the target object already has a MeshCollider"), skipIfExists);
        setConvex = EditorGUILayout.Toggle(new GUIContent("Set Convex", "Set MeshCollider.convex on generated colliders"), setConvex);

		EditorGUILayout.Space();
		EditorGUILayout.LabelField("Extrusion", EditorStyles.boldLabel);
		extrudeAlongNormals = EditorGUILayout.Toggle(new GUIContent("Extrude Along Normals", "If enabled, duplicates the mesh and offsets vertices along their normals for the collider"), extrudeAlongNormals);
		using (new EditorGUI.DisabledScope(!extrudeAlongNormals))
		{
			extrusionDistance = EditorGUILayout.FloatField(new GUIContent("Extrusion Distance", "Distance to offset vertices along normals (units). Positive = expand, negative = shrink."), extrusionDistance);
		}

        EditorGUILayout.Space();
        using (new EditorGUI.DisabledScope(targetsProp.arraySize == 0))
        {
            if (GUILayout.Button("Scan And Generate"))
            {
                GenerateForTargets();
            }
        }

        serializedObjectRef.ApplyModifiedProperties();
    }

    private void GenerateForTargets()
    {
        var totalCreated = 0;
        try
        {
            Undo.IncrementCurrentGroup();
            var undoGroup = Undo.GetCurrentGroup();

            for (int i = 0; i < targetRoots.Count; i++)
            {
                var root = targetRoots[i];
                if (root == null)
                {
                    continue;
                }

                var meshFilters = root.GetComponentsInChildren<MeshFilter>(includeInactive);
                foreach (var meshFilter in meshFilters)
                {
                    if (meshFilter == null)
                    {
                        continue;
                    }

                    var meshRenderer = meshFilter.GetComponent<MeshRenderer>();
                    if (meshRenderer == null)
                    {
                        continue;
                    }

                    var sourceMesh = meshFilter.sharedMesh;
                    if (sourceMesh == null)
                    {
                        continue;
                    }

                    var parent = meshFilter.transform;

					var targetGo = parent.gameObject;
					if (skipIfExists && targetGo.GetComponent<MeshCollider>() != null)
					{
						continue;
					}

					var meshCollider = Undo.AddComponent<MeshCollider>(targetGo);

					var workingMesh = sourceMesh;
					if (extrudeAlongNormals && !Mathf.Approximately(extrusionDistance, 0f))
					{
						var extruded = CreateExtrudedMesh(workingMesh, extrusionDistance);
						if (extruded != null)
						{
							workingMesh = extruded;
						}
					}

					var uniformScale = Mathf.Approximately(xScale, 0f) ? 0.0001f : xScale;
					if (!Mathf.Approximately(uniformScale, 1f))
					{
						var scaled = CreateScaledMesh(workingMesh, uniformScale);
						if (scaled != null)
						{
							workingMesh = scaled;
						}
					}

					meshCollider.sharedMesh = workingMesh;
					meshCollider.convex = setConvex;

                    totalCreated++;
                }
            }

            Undo.CollapseUndoOperations(Undo.GetCurrentGroup());
            EditorUtility.DisplayDialog("Mesh Collider Generator", $"Created {totalCreated} collider object(s).", "OK");
        }
        catch (System.SystemException e)
        {
            Debug.LogError($"Mesh Collider generation failed: {e.Message}\n{e}");
        }
    }

	private static Mesh CreateExtrudedMesh(Mesh source, float distance)
	{
		if (source == null)
		{
			return null;
		}

		if (!source.isReadable)
		{
			Debug.LogWarning($"Source mesh '{source.name}' is not readable. Using original mesh for collider.");
			return null;
		}

		var vertices = source.vertices;
		var normals = source.normals;
		var triangles = source.triangles;

		if (normals == null || normals.Length != vertices.Length)
		{
			var temp = new Mesh();
			temp.vertices = vertices;
			temp.triangles = triangles;
			temp.RecalculateNormals();
			normals = temp.normals;
		}

		var newVertices = new Vector3[vertices.Length];
		for (int i = 0; i < vertices.Length; i++)
		{
			newVertices[i] = vertices[i] + normals[i] * distance;
		}

		var extruded = new Mesh();
		extruded.name = string.IsNullOrEmpty(source.name) ? "ExtrudedMesh" : source.name + "_Extruded";
		extruded.vertices = newVertices;
		extruded.triangles = triangles;
		extruded.RecalculateBounds();

		SaveMeshAsset(extruded, source);

		return extruded;
	}

	private static Mesh CreateScaledMesh(Mesh source, float uniformScale)
	{
		if (source == null)
		{
			return null;
		}

		if (Mathf.Approximately(uniformScale, 1f))
		{
			return null;
		}

		if (!source.isReadable)
		{
			Debug.LogWarning($"Source mesh '{source.name}' is not readable. Using original mesh for collider.");
			return null;
		}

		var vertices = source.vertices;
		var triangles = source.triangles;

		var newVertices = new Vector3[vertices.Length];
		for (int i = 0; i < vertices.Length; i++)
		{
			newVertices[i] = vertices[i] * uniformScale;
		}

		var scaled = new Mesh();
		scaled.name = string.IsNullOrEmpty(source.name) ? "ScaledMesh" : source.name + "_Scaled_Collider";
		scaled.vertices = newVertices;
		scaled.triangles = triangles;
		scaled.RecalculateBounds();
		SaveMeshAsset(scaled, source);
		return scaled;
	}

	private static void SaveMeshAsset(Mesh mesh, Mesh sourceForPath)
	{
		if (mesh == null)
		{
			return;
		}

		string baseFolder = GeneratedMeshFolder;
		if (sourceForPath != null)
		{
			var srcPath = AssetDatabase.GetAssetPath(sourceForPath);
			if (!string.IsNullOrEmpty(srcPath))
			{
				var dir = Path.GetDirectoryName(srcPath);
				if (!string.IsNullOrEmpty(dir) && AssetDatabase.IsValidFolder(dir.Replace('\\','/')))
				{
					baseFolder = dir.Replace('\\','/');
				}
			}
		}

		if (!AssetDatabase.IsValidFolder(baseFolder))
		{
			// Fallback: ensure default folder exists
			if (!AssetDatabase.IsValidFolder(GeneratedMeshFolder))
			{
				var parts = GeneratedMeshFolder.Split('/');
				for (int i = 1; i < parts.Length; i++)
				{
					var parentPath = string.Join("/", parts, 0, i);
					var thisFolder = string.Join("/", parts, 0, i + 1);
					if (!AssetDatabase.IsValidFolder(thisFolder))
					{
						AssetDatabase.CreateFolder(parentPath, parts[i]);
					}
				}
			}
			baseFolder = GeneratedMeshFolder;
		}

		var sanitizedName = SanitizeFileName(string.IsNullOrEmpty(mesh.name) ? "GeneratedMesh" : mesh.name);
		var combined = baseFolder.EndsWith("/") ? baseFolder + sanitizedName + ".asset" : baseFolder + "/" + sanitizedName + ".asset";
		var path = AssetDatabase.GenerateUniqueAssetPath(combined.Replace('\\','/'));
		AssetDatabase.CreateAsset(mesh, path);
		AssetDatabase.SaveAssets();
	}

	private static string SanitizeFileName(string name)
	{
		foreach (var c in Path.GetInvalidFileNameChars())
		{
			name = name.Replace(c, '_');
		}
		return name;
	}
}