io_scene_fbx/import_fbx.py

@@ -3470,12 +3470,36 @@ def load(operator, context, filepath="",
     def _():
         fbx_tmpl = fbx_template_get((b'Geometry', b'KFbxShape'))
 
+        # - FBX             | - Blender equivalent
+        # Mesh              | `Mesh`
+        # BlendShape        | `Key`
+        # BlendShapeChannel | `ShapeKey`, but without its `.data`.
+        # Shape             | `ShapeKey.data`, but also includes normals and the values are relative to the base Mesh
+        #                   | instead of being absolute. The data is sparse, so each Shape has an "Indexes" array too.
+        #                   | FBX 2020 introduced 'Modern Style' Shapes that also support tangents, binormals, vertex
+        #                   | colors and UVs, and can be absolute values instead of relative, but 'Modern Style' Shapes
+        #                   | are not currently supported.
+        #
+        # The FBX connections between Shapes and Meshes form multiple many-many relationships:
+        # Mesh >-< BlendShape >-< BlendShapeChannel >-< Shape
+        # In practice, the relationships are almost never many-many and are more typically 1-many or 1-1:
+        #   Mesh --- BlendShape:
+        #     usually 1-1 and the FBX SDK might enforce that each BlendShape is connected to at most one Mesh.
+        #   BlendShape --< BlendShapeChannel:
+        #     usually 1-many.
+        #   BlendShapeChannel --- or uncommonly --< Shape:
+        #     usually 1-1, but 1-many is a documented feature.
         mesh_to_shapes = {}
-        for s_uuid, s_item in fbx_table_nodes.items():
+        for s_uuid, (fbx_sdata, _bl_sdata) in fbx_table_nodes.items():
-            fbx_sdata, bl_sdata = s_item = fbx_table_nodes.get(s_uuid, (None, None))
             if fbx_sdata is None or fbx_sdata.id != b'Geometry' or fbx_sdata.props[2] != b'Shape':
                 continue
 
+            # Rarely, an imported FBX file will have duplicate connections. For Shape Key related connections, FBX
+            # appears to ignore the duplicates, or overwrite the existing duplicates such that the end result is the
+            # same as ignoring them, so we keep sets of the seen connections for each FBX type and ignore any duplicates
+            # we find.
+            seen_s2bc_connections = set()
+
             # shape -> blendshapechannel -> blendshape -> mesh.
             for bc_uuid, bc_ctype in fbx_connection_map.get(s_uuid, ()):
                 if bc_ctype.props[0] != b'OO':
@@ -3483,18 +3507,32 @@ def load(operator, context, filepath="",
                 fbx_bcdata, _bl_bcdata = fbx_table_nodes.get(bc_uuid, (None, None))
                 if fbx_bcdata is None or fbx_bcdata.id != b'Deformer' or fbx_bcdata.props[2] != b'BlendShapeChannel':
                     continue
+                connection_key = (s_uuid, bc_uuid)
+                if connection_key in seen_s2bc_connections:
+                    continue
+                seen_s2bc_connections.add(connection_key)
+                seen_bc2bs_connections = set()
                 for bs_uuid, bs_ctype in fbx_connection_map.get(bc_uuid, ()):
                     if bs_ctype.props[0] != b'OO':
                         continue
                     fbx_bsdata, _bl_bsdata = fbx_table_nodes.get(bs_uuid, (None, None))
                     if fbx_bsdata is None or fbx_bsdata.id != b'Deformer' or fbx_bsdata.props[2] != b'BlendShape':
                         continue
+                    connection_key = (bc_uuid, bs_uuid)
+                    if connection_key in seen_bc2bs_connections:
+                        continue
+                    seen_bc2bs_connections.add(connection_key)
+                    seen_bs2m_connections = set()
                     for m_uuid, m_ctype in fbx_connection_map.get(bs_uuid, ()):
                         if m_ctype.props[0] != b'OO':
                             continue
                         fbx_mdata, bl_mdata = fbx_table_nodes.get(m_uuid, (None, None))
                         if fbx_mdata is None or fbx_mdata.id != b'Geometry' or fbx_mdata.props[2] != b'Mesh':
                             continue
+                        connection_key = (bs_uuid, m_uuid)
+                        if connection_key in seen_bs2m_connections:
+                            continue
+                        seen_bs2m_connections.add(connection_key)
                         # Blenmeshes are assumed already created at that time!
                         assert(isinstance(bl_mdata, bpy.types.Mesh))
                         # Group shapes by mesh so that each mesh only needs to be processed once for all of its shape