GLTFExporter not accounting for SkinnedMesh bindMatrix

[zach-capalbo]

Describe the bug

Using THREE.GLTFExporter to export a SkinnedMesh with a bindMatrix that is not the identity matrix results in the bindMatrix being lost. If the exported mesh is later imported,

To Reproduce

Steps to reproduce the behavior:

1. Use FBXLoader to load the model from https://sketchfab.com/3d-models/mannequin-anatomy-aid-free-download-2f67c4384e7f4a5b86d84ae9199b7d3b
2. See that mesh is properly aligned with skeleton (See Screenshot 1 below)
3. Export mesh using THREE.GLTFExporter
4. Import model exported in step 3
5. See that mesh is improperly aligned with skeleton (See Screenshot 2 below)

Code

Fix proposed in: #20804

Live example

None at the moment. I can put one together if necessary.

Expected behavior

Skeleton should be properly aligned after being exported and re-imported.

Screenshots

1. Mesh is properly aligned (on original import):

2. Mesh is improperly aligned after importing exported GLB:

Platform:

• Device: Any
• OS: Any
• Browser: Any
• Three.js version: Noticed in 0.111.6/A-FRAME 1.0.4. Still appears to be present in dev

[Mugen87]

Export mesh using THREE.GLTFExporter

How have you exported the model? When I'm trying this from the three.js editor (which uses GLTFExporter), I get the following error:

Uncaught Error: THREE.GLTFExporter: Morph target name not found: 0

[zach-capalbo]

Thanks for looking into this. There may be some unrelated version differences. I'll set up a runnable demo as soon as I get a chance.

[zach-capalbo]

The export error you mentioned seems to be a separate error with animations on morph targets in a number of models that come from FBX files. I'm investigating that as well, but will report it separately & submit a fix if I can pin down the issue.

For this issue here I've created a minimal live example here: https://glitch.com/edit/#!/transparent-brassy-mercury?path=index.html%3A55%3A2

The glitch also demonstrates a manual application of the proposed fix in: #20804

Let me know if there's any thing else you need for this.

[Mugen87]

Thanks for the examples! Yes, I suspect this issues was noticed so far since many assets have an identity matrix as the bind matrix.