Update CombineMeshes extension to match behavior

Author: adamgraham

Runtime/Extensions/MeshFilterExtensions.cs

@@ -5,6 +5,9 @@
 
 namespace Zigurous.Graphics
 {
+    /// <summary>
+    /// Extension methods for mesh filters.
+    /// </summary>
     public static class MeshFilterExtensions
     {
         /// <summary>
@@ -48,24 +51,32 @@ public static void SaveMesh(this MeshFilter filter, string assetName)
         /// Combines the meshes of the mesh filters into one mesh.
         /// </summary>
         /// <param name="filters">The mesh filters to combine.</param>
+        /// <param name="combinedMeshName">The name of the new combined mesh.</param>
         /// <param name="optimizeMesh">Optimizes the combined mesh data to improve rendering performance.</param>
         /// <param name="recalculateBounds">Recalculates the bounding volume of the combined mesh.</param>
         /// <returns>The combined mesh.</returns>
-        public static Mesh CombineMeshes(this MeshFilter[] filters, bool optimizeMesh = true, bool recalculateBounds = true)
+        public static Mesh CombineMeshes(this MeshFilter[] filters, string combinedMeshName = "Combined Mesh", bool optimizeMesh = true, bool recalculateBounds = true)
         {
             CombineInstance[] combine = new CombineInstance[filters.Length];
 
+            int submesh = 0;
+
             for (int i = 0; i < filters.Length; i++)
             {
-                MeshFilter child = filters[i];
+                MeshFilter filter = filters[i];
+
+                if (filter.mesh == null) {
+                    continue;
+                }
+
                 CombineInstance instance = new CombineInstance();
-                instance.mesh = child.mesh;
-                instance.transform = Matrix4x4.TRS(child.transform.localPosition, child.transform.localRotation, child.transform.localScale);
-                combine[i] = instance;
+                instance.mesh = filter.mesh;
+                instance.transform = filter.transform.localToWorldMatrix;
+                combine[submesh++] = instance;
             }
 
             Mesh combinedMesh = new Mesh();
-            combinedMesh.name = "Combined Mesh";
+            combinedMesh.name = combinedMeshName;
             combinedMesh.CombineMeshes(combine);
 
             if (optimizeMesh) {