Godot 4.3 and 4.4 model importer renames skeleton bones, breaking animation retargeting and bone map support

[Azzara]

Tested versions

• Reproducible in Godot 4.3.0 up to 4.4.1 (newest current version)
• Not reproducible in Godot 4.2.2

System information

Windows 10, Godot 4.2.2 / 4.3.0 / 4.4.1

Issue description

I have a library of character models stored as a single GLB file.
The characters have similar but not always identical humanoid skeletons.
I have created bone maps for the humanoid characters but some extra bones remain unmapped.
Since Godot 4.3.0 all bones in the GLB file are treated as belonging to a single skeleton and duplicate names are silently renamed even though there should be no conflict. The new import feature "Import as Skeleton Bones" is explicitly turned off (default).

This is what the bone names on the second skeleton in the GLB look like in Godot 4.2:

This is what happens to the skeleton bone names if imported into Godot 4.3 or higher:

For the MRP example I downloaded free assets from here (only the two characters are included in the MRP):
https://syntystore.com/products/polygon-starter-pack

Steps to reproduce

I have attached a tiny Godot 4.2 project to demonstrate the issue.
It contains a single GLB file called "Humans.glb".
The GLB contains 2 rigged characters. Each character model has its own mesh and skeleton.
There is also a bone map with a humanoid profile included in the project.
This setup work perfectly in Godot 4.2.2.

Try upgrading the project to Godot 4.3 or higher.
The setup no longer works.
Godot now insists that the bones on the second skeleton have different names with the suffix "_2".
It is no longer possible to import the model into Godot. For example the bone "Eyebrows" will always have different names among skeletons, which breaks animation retargeting.
This is a breaking change but if fails silently so I only realized it's happening just now.

In my opinion the problem is caused by the new feature "Import as Skeleton Bones" which can't be fully disabled even though it's turned off by default.

Minimal reproduction project (MRP)

SkeletonBug.zip

[AThousandShips]

This is already tracked in:

• Different skeletons in an imported scene can't have same bone names #93758

See also:

• Godot's GLB Importer in MacOSX adds "_2" suffix randomly to bone names, it doesn't in Windows #96248

This is apparently by design, CC @aaronfranke

[Azzara]

I would prefer it if "Import as Skeleton Bones: OFF" simply doesn't rename bones, like it didn't before the feature existed.

My workflow is to import each Blender collection as a single GLB file into Godot.
I don't export single files because it is too much work to configure the import settings of each file in Godot and I don't know how to do that in code or how to import everything without selecting each file and clicking "Import".
Instead I have a post-import script in Godot which splits the assets into their own scene files and saves them where they belong (based on my personal preferences and heuristics).

Asset packs can be huge. What is the intended approach which avoids clicking "Import" 1000+ times?

[aaronfranke]

@Azzara It is intended to make names unique regardless of that setting. However, perhaps we need to change this to per-skeleton uniqueness. I don't think the cases of multiple skeletons have been extensively tested. Note that this gets tricky for skeletons with bone attachments, since they are nodes as well, and so need to be considered in both checks and kept in sync.

[Azzara]

@aaronfranke I haven't discovered any problems with having multiple skeletons in Godot 4.2 (yet). I often have multiple rigged objects in the same collection - capes, bows, characters, etc.

I don't have a strong oppinion on bone attachments. I went out of my way to remove them from the MRP. Here is an example with the accessories still attached.
Humans_With_Hair.zip

I guess the least intrusive approach would be to not create a new bone for bone attachments at all.
In Blender the "Hairstyle" object is attached directly to the "Head" bone and it has its own transform. This approach could work in Godot as well, since bone attachments have their own transforms too. There is no need for the GLB-importer to append a new "Hairstyle" bone to the original skeleton. This would solve the potential naming conflicts even when "Import as Skeleton Bones" merges the skeletons.
I'm not suggesting that the bone attachment import should be changed too, just saying that it might work.

[aaronfranke]

@Azzara Not adding an unnecessary bone to the skeleton is something I've fixed in PR #104184, but it's not merged yet. However we still need to handle the case regardless, because it can happen for things that are bones anyway, or sit between bones in the hierarchy. I'll take a look within the next week probably.

[aaronfranke]

I have opened PR #106537 to fix this on import. I also made sure it works with PR #104184 (can be merged in either order).