Import: exception for 'Node' object has no attribute 'blender_bone_name'

[scurest]

Traceback (most recent call last):
  File "/home/scurest/.config/blender/2.79/scripts/addons/io_scene_gltf2/__init__.py", line 468, in execute
    return self.import_gltf2(context)
  File "/home/scurest/.config/blender/2.79/scripts/addons/io_scene_gltf2/__init__.py", line 487, in import_gltf2
    BlenderGlTF.create(self.gltf_importer)
  File "/home/scurest/.config/blender/2.79/scripts/addons/io_scene_gltf2/blender/imp/gltf2_blender_gltf.py", line 35, in create
    BlenderScene.create(gltf, scene_idx)
  File "/home/scurest/.config/blender/2.79/scripts/addons/io_scene_gltf2/blender/imp/gltf2_blender_scene.py", line 78, in create
    BlenderSkin.create_vertex_groups(gltf, skin_id)
  File "/home/scurest/.config/blender/2.79/scripts/addons/io_scene_gltf2/blender/imp/gltf2_blender_skin.py", line 163, in create_vertex_groups
    obj.vertex_groups.new(name=gltf.data.nodes[bone].blender_bone_name)
AttributeError: 'Node' object has no attribute 'blender_bone_name'

Test file

Not sure what's wrong, but maybe caused by a mesh being instantiated on one of the joints of its skin.

[julienduroure]

Your node idx 0 is at the same time a mesh (mesh idx 0), and is listed in joints list.
In Blender, your node can't be at same time a mesh and a bone. Will check what spec says about that.

• If this is something possible in glTF2.0, we will have to find a way to manage it.
• If not possible in glTF2.0, will add some checks to avoid exception traceback

@donmccurdy is this something allowed in glTF2.0 spec?

[donmccurdy]

See KhronosGroup/glTF#1433 — this is valid, and if we interpret a node referencing a mesh to mean that node "is" a mesh, then a node can simultaneously be a mesh, a bone, a camera, and a light. The robust way to deal with that is to consider nodes empties, and whatever things they reference become children without a transform of their own.

A lot of tools want to avoid overcomplicating the node hierarchy and optimistically flatten, so I'm sure the importer is not the only tool that will have trouble with this asset. I would suggest we handle this as best we can on import, but avoid writing dual-purpose nodes from the exporter like this.

I'm tempted to say this should be tightened up in a future version of the spec, to reduce edge cases.

[emackey]

I'm tempted to say this should be tightened up in a future version of the spec, to reduce edge cases.

Agreed. It might be helpful to inquire the history of this. Were multi-purpose nodes intentionally allowed at some point, or were they just an artifact of the schema's ability to assign one of each thing to a node?

[julienduroure]

Note for importer implementation: I will work first on a version where node can be multiple "things" except joints. This will be the more easy part, even it will not solve this issue.
Then I will work on second part, node being able to be joint and something else

[scurest]

Note that this same error occurs if a mesh is skinned by joints not in the same scene. See KhronosGroup/glTF#1558.

[julienduroure]

Started a simple implementation on branch importer_multipletype
Only for objects for now (that means that the bug is not solved yet, because this is a object / rig case)