Fix #1626 Set skinned mesh at root

addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_tree.py

@@ -123,12 +123,6 @@ def recursive_node_traverse(self, blender_object, blender_bone, parent_uuid, par
         node.parent_uuid = parent_uuid
         node.set_blender_data(blender_object, blender_bone)
 
-        # add to parent if needed
-        if parent_uuid is not None:
-            self.add_children(parent_uuid, node.uuid)
-        else:
-            self.roots.append(node.uuid)
-
         # Set blender type
         if blender_bone is not None:
             node.blender_type = VExportNode.BONE
@@ -145,6 +139,8 @@ def recursive_node_traverse(self, blender_object, blender_bone, parent_uuid, par
         else:
             node.blender_type = VExportNode.OBJECT
 
+        force_node_at_world_center = False
+
         # For meshes with armature modifier (parent is armature), keep armature uuid
         if node.blender_type == VExportNode.OBJECT:
             modifiers = {m.type: m for m in blender_object.modifiers}
@@ -160,6 +156,16 @@ def recursive_node_traverse(self, blender_object, blender_bone, parent_uuid, par
                 else:
                     node.armature = parent_uuid
 
+                # In glTF, meshes should be at root, so clearing parent, and setting as root
+                node.parent_uuid = None
+                force_node_at_world_center = True
+
+        # add to parent if needed
+        if node.parent_uuid is not None:
+            self.add_children(parent_uuid, node.uuid)
+        else:
+            self.roots.append(node.uuid)
+
         # For bones, store uuid of armature
         if blender_bone is not None:
             node.armature = armature_uuid
@@ -231,6 +237,12 @@ def recursive_node_traverse(self, blender_object, blender_bone, parent_uuid, par
         if blender_object.is_instancer is True and blender_object.show_instancer_for_render is False:
             node.force_as_empty = True
 
+        # Because no local transforms are set in glTF for skinned meshes, we need to 
+        # artificially set the mesh at world center
+        # This way, any children local transforms will be correclty calculated
+        if force_node_at_world_center is True:
+            node.matrix_world = Matrix.Identity(4)
+
         # Storing this node
         self.add_node(node)