Merge pull request #406 from Unity-Technologies/UNI-36617-fix-skinned-mesh-update

UNI-36617 fix skinned mesh bone update

Author: vkovec

Packages/com.unity.formats.fbx/Editor/Scripts/FbxPrefabAutoUpdater.cs

@@ -1164,6 +1164,17 @@ public HashSet<String> GetNodesToRename()
                     return m_nodesToRename;
                 }
 
+                /// <summary>
+                /// Get the equivalent transform on the linked prefab for the given fbx transform.
+                /// e.g. if there is a transform called Bone1 in the fbx, find the transform called Bone1 in the prefab.
+                /// </summary>
+                /// <returns>The linked prefab transform that matches the given fbx transform or null if not found</returns>
+                private Transform GetMatchingPrefabTransform(Transform fbxTransform, Transform fbxAssetRoot, Transform prefabAssetRoot)
+                {
+                    var transformPath = AnimationUtility.CalculateTransformPath(fbxTransform, fbxAssetRoot);
+                    return prefabAssetRoot.Find(transformPath);
+                }
+
                 /// <summary>
                 /// Then we act -- in a slightly different order:
                 /// 1. Create all the new nodes we need to create.
@@ -1355,6 +1366,42 @@ public HashSet<GameObject> ImplementUpdates(FbxPrefab prefabInstance)
                             }
                             // Now set the values.
                             UnityEditor.EditorJsonUtility.FromJsonOverwrite(fbxComponent.jsonValue, prefabComponent);
+
+                            // if the prefab component is a skinned mesh renderer, then make sure to update the bone list so that
+                            // the bones are in the prefab, and not the fbx
+                            if (prefabComponent is SkinnedMeshRenderer)
+                            {
+                                var skinnedMeshComponent = prefabComponent as SkinnedMeshRenderer;
+                                var rootBone = skinnedMeshComponent.rootBone;
+                                var bones = skinnedMeshComponent.bones;
+
+                                var fbxAssetTransform = m_fbxPrefabUtility.GetFbxAsset().transform;
+                                
+                                var rootPrefabTransform = GetMatchingPrefabTransform(rootBone, fbxAssetTransform, prefabRoot);
+                                if (rootPrefabTransform == null)
+                                {
+                                    Debug.LogWarningFormat("FbxPrefabAutoUpdater: Could not find root bone {0} for {1} skinned mesh in linked prefab", rootBone.name, skinnedMeshComponent.name);
+                                }
+                                skinnedMeshComponent.rootBone = rootPrefabTransform;
+
+                                var prefabBones = new Transform[bones.Length];
+                                for (int i = 0; i < bones.Length; i++)
+                                {
+                                    var bone = bones[i];
+
+                                    var prefabTransform = GetMatchingPrefabTransform(bone, fbxAssetTransform, prefabRoot);
+                                    if (prefabTransform == null)
+                                    {
+                                        Debug.LogWarningFormat("FbxPrefabAutoUpdater: Could not find bone {0} for {1} skinned mesh", bone.name, skinnedMeshComponent.name);
+                                        continue;
+                                    }
+
+                                    prefabBones[i] = prefabTransform;
+                                }
+                                skinnedMeshComponent.bones = prefabBones;
+
+                                continue;
+                            }
                         }
                     }
                     return updatedNodes;