Fix T45171: FBX importer can't handle mesh bound to multiple armatures.

There were two issues here:

I) Since an object can only have *one* parent, it it gets created only during its parent's creation,
   we could end in situation where we would be creating an armature that would need its 'fake' children
   mesh objects, before we have actually created this mesh object (which would only happen during creation
   of the only armature that would be its *real* parent).
   This was solved by decoupling object creation/instancing and creation of objets' relationships.

II) We were only storing one set of binding data (matrices) per mesh, which obviously failed when
    binding several armatures to a single mesh.
    Simply fixed by storing one set of binding data per mesh per armature.
    FBX can store on set of binding matrices per mesh per bone, but this is not supported by Blender!

1 files changed, 86 insertions, 23 deletions

diff --git a/io_scene_fbx/import_fbx.py b/io_scene_fbx/import_fbx.py
index 4b8f3ebb..851339d6 100644
--- a/io_scene_fbx/import_fbx.py
+++ b/io_scene_fbx/import_fbx.py
@@ -1453,7 +1453,7 @@ class FbxImportHelperNode:
     It tries to keep the correction data in one place so it can be applied consistently to the imported data.
     """
 
-    __slots__ = ('_parent', 'anim_compensation_matrix', 'armature_setup', 'bind_matrix',
+    __slots__ = ('_parent', 'anim_compensation_matrix', 'armature_setup', 'armature', 'bind_matrix',
                  'bl_bone', 'bl_data', 'bl_obj', 'bone_child_matrix', 'children', 'clusters',
                  'fbx_elem', 'fbx_name', 'fbx_transform_data', 'fbx_type', 'has_bone_children', 'ignore', 'is_armature',
                  'is_bone', 'is_root', 'matrix', 'matrix_as_parent', 'matrix_geom', 'meshes', 'post_matrix', 'pre_matrix')
@@ -1469,6 +1469,7 @@ class FbxImportHelperNode:
         self.is_root = False
         self.is_bone = is_bone
         self.is_armature = False
+        self.armature = None                    # For bones only, relevant armature node.
         self.has_bone_children = False          # True if the hierarchy below this node contains bones, important to support mixed hierarchies.
         self.ignore = False                     # True for leaf-bones added to the end of some bone chains to set the lengths.
         self.pre_matrix = None                  # correction matrix that needs to be applied before the FBX transform
@@ -1483,7 +1484,7 @@ class FbxImportHelperNode:
 
         self.meshes = None                      # List of meshes influenced by this bone.
         self.clusters = []                      # Deformer Cluster nodes
-        self.armature_setup = None              # mesh and armature matrix when the mesh was bound
+        self.armature_setup = {}                # mesh and armature matrix when the mesh was bound
 
         self._parent = None
         self.children = []
@@ -1636,6 +1637,12 @@ class FbxImportHelperNode:
         for child in self.children:
             child.find_correction_matrix(settings, correction_matrix_inv)
 
+    def find_armature_bones(self, armature):
+        for child in self.children:
+            if child.is_bone:
+                child.armature = armature
+                child.find_armature_bones(armature)
+
     def find_armatures(self):
         needs_armature = False
         for child in self.children:
@@ -1646,18 +1653,21 @@ class FbxImportHelperNode:
             if self.fbx_type in {b'Null', b'Root'}:
                 # if empty then convert into armature
                 self.is_armature = True
+                armature = self
             else:
                 # otherwise insert a new node
                 armature = FbxImportHelperNode(None, None, None, False)
                 armature.fbx_name = "Armature"
                 armature.is_armature = True
 
-                for child in self.children[:]:
+                for child in self.children:
                     if child.is_bone:
                         child.parent = armature
 
                 armature.parent = self
 
+            armature.find_armature_bones(armature)
+
         for child in self.children:
             if child.is_armature or child.is_bone:
                 continue
@@ -1812,7 +1822,13 @@ class FbxImportHelperNode:
 
         return bone
 
-    def build_node(self, fbx_tmpl, settings):
+    def build_node_obj(self, fbx_tmpl, settings):
+        if self.bl_obj:
+            return self.bl_obj
+
+        if self.is_bone or not self.fbx_elem:
+            return None
+
         # create when linking since we need object data
         elem_name_utf8 = self.fbx_name
 
@@ -1841,7 +1857,29 @@ class FbxImportHelperNode:
             for child in self.children:
                 if child.ignore:
                     continue
-                child_obj = child.build_skeleton_children(fbx_tmpl, settings, scene)
+                child.build_skeleton_children(fbx_tmpl, settings, scene)
+            return None
+        else:
+            # child is not a bone
+            obj = self.build_node_obj(fbx_tmpl, settings)
+
+            for child in self.children:
+                if child.ignore:
+                    continue
+                child.build_skeleton_children(fbx_tmpl, settings, scene)
+
+            # instance in scene
+            obj_base = scene.objects.link(obj)
+            obj_base.select = True
+
+            return obj
+
+    def link_skeleton_children(self, fbx_tmpl, settings, scene):
+        if self.is_bone:
+            for child in self.children:
+                if child.ignore:
+                    continue
+                child_obj = child.bl_obj
                 if child_obj:
                     child_obj.parent = self.bl_obj  # get the armature the bone belongs to
                     child_obj.parent_bone = self.bl_bone
@@ -1858,20 +1896,15 @@ class FbxImportHelperNode:
                     child_obj.matrix_basis = child.get_matrix()
             return None
         else:
-            # child is not a bone
-            obj = self.build_node(fbx_tmpl, settings)
+            obj = self.bl_obj
 
             for child in self.children:
                 if child.ignore:
                     continue
-                child_obj = child.build_skeleton_children(fbx_tmpl, settings, scene)
+                child_obj = child.link_skeleton_children(fbx_tmpl, settings, scene)
                 if child_obj:
                     child_obj.parent = obj
 
-            # instance in scene
-            obj_base = scene.objects.link(obj)
-            obj_base.select = True
-
             return obj
 
     def set_pose_matrix(self, arm):
@@ -1997,13 +2030,42 @@ class FbxImportHelperNode:
                 if child.ignore:
                     continue
                 child_obj = child.build_skeleton_children(fbx_tmpl, settings, scene)
+
+            return arm
+        elif self.fbx_elem:
+            obj = self.build_node_obj(fbx_tmpl, settings)
+
+            # walk through children
+            for child in self.children:
+                child.build_hierarchy(fbx_tmpl, settings, scene)
+
+            # instance in scene
+            obj_base = scene.objects.link(obj)
+            obj_base.select = True
+
+            return obj
+        else:
+            for child in self.children:
+                child.build_hierarchy(fbx_tmpl, settings, scene)
+
+            return None
+
+    def link_hierarchy(self, fbx_tmpl, settings, scene):
+        if self.is_armature:
+            arm = self.bl_obj
+
+            # Link bone children:
+            for child in self.children:
+                if child.ignore:
+                    continue
+                child_obj = child.link_skeleton_children(fbx_tmpl, settings, scene)
                 if child_obj:
                     child_obj.parent = arm
 
             # Add armature modifiers to the meshes
             if self.meshes:
                 for mesh in self.meshes:
-                    (mmat, amat) = mesh.armature_setup
+                    (mmat, amat) = mesh.armature_setup[self]
                     me_obj = mesh.bl_obj
 
                     # bring global armature & mesh matrices into *Blender* global space.
@@ -2024,7 +2086,7 @@ class FbxImportHelperNode:
                     # we can compute inverse parenting matrix of the mesh.
                     me_obj.matrix_parent_inverse = amat.inverted_safe() * mmat * me_obj.matrix_basis.inverted_safe()
 
-                    mod = mesh.bl_obj.modifiers.new(elem_name_utf8, 'ARMATURE')
+                    mod = mesh.bl_obj.modifiers.new(arm.name, 'ARMATURE')
                     mod.object = arm
 
             # Add bone weights to the deformers
@@ -2035,22 +2097,20 @@ class FbxImportHelperNode:
                     child.set_bone_weights()
 
             return arm
-        elif self.fbx_elem:
-            obj = self.build_node(fbx_tmpl, settings)
+        elif self.bl_obj:
+            obj = self.bl_obj
 
             # walk through children
             for child in self.children:
-                child_obj = child.build_hierarchy(fbx_tmpl, settings, scene)
+                child_obj = child.link_hierarchy(fbx_tmpl, settings, scene)
                 child_obj.parent = obj
 
-            # instance in scene
-            obj_base = scene.objects.link(obj)
-            obj_base.select = True
-
             return obj
         else:
             for child in self.children:
-                child.build_hierarchy(fbx_tmpl, settings, scene)
+                child.link_hierarchy(fbx_tmpl, settings, scene)
+
+            return None
 
 
 def is_ascii(filepath, size):
@@ -2527,7 +2587,7 @@ def load(operator, context, filepath="",
                                 # when actually binding them via the modifier.
                                 # Note we assume all bones were bound with the same mesh/armature (global) matrix,
                                 # we do not support otherwise in Blender anyway!
-                                mesh_node.armature_setup = (mesh_matrix, armature_matrix)
+                                mesh_node.armature_setup[helper_node.armature] = (mesh_matrix, armature_matrix)
                                 meshes.add(mesh_node)
 
                 helper_node.clusters.append((fbx_cluster, meshes))
@@ -2544,6 +2604,9 @@ def load(operator, context, filepath="",
         # build the Object/Armature/Bone hierarchy
         root_helper.build_hierarchy(fbx_tmpl, settings, scene)
 
+        # Link the Object/Armature/Bone hierarchy
+        root_helper.link_hierarchy(fbx_tmpl, settings, scene)
+
         # root_helper.print_info(0)
     _(); del _