GLTF inverse bind matrix remapping (bind poses) not fully supported
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Gaia Clary
## Summary
GLB/GLTF uploads can produce different rigged mesh deformation than DAE uploads from the same source model when the model uses a bind pose that differs from the viewer skeleton rest pose.
## Context
Bind pose support is not directly exposed by Blender itself, although other tools such as Maya support this workflow. Both Collada/DAE and GLB/GLTF can represent bind-posed models through inverse bind matrices.
The Avastar Blender add-on explicitly adds bind pose support and collada support to Blender-5, so this issue can be reproduced and tested using Blender-5 with Avastar.
## Steps to Reproduce in Blender
- In Blender, create or open a rigged mesh that uses a bind pose different from the default viewer skeleton rest pose. typical use case: A-posed models with A-Pose as restpose.
- Export the same model from Blender as DAE.
- Export the same model from Blender as GLB/GLTF.
- Upload/import both files into the viewer.
- Compare the imported results at the vertex/deformation level.
## Actual Result
The GLB/GLTF import can deform differently from the DAE import, even though both files were exported from the same source model.
Visible differences can include child joint twists.
## Expected Result
DAE and GLB/GLTF exports from the same bind-posed source model should import with equivalent vertex-level deformation.
Mesh edges may differ depending on exporter triangulation, but the rigged vertex positions and deformation should match.
## Test Notes
This was tested with Blender using Avastar bind pose support by exporting the same bind-posed model as both DAE and GLB/GLTF, then comparing the uploaded viewer results.
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Dan Linden
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Dan Linden
Thank you for the report, Gaia!
Issue tracked at https://github.com/secondlife/viewer/issues/5786. We have no estimate when it may be implemented. Please see future updates here.
If you can send files that demonstrate the issue to bug-attachments@lindenlab.com it would be appreciated. Please reference the issue name in the email subject line.