-sa option in gltfpack causes texture mapping issues after simplification

[Yeah-Zi]

When simplifying a model using the gltfpack tool, enabling the -sa (simplify attributes) parameter causes texture mapping to become incorrect or distorted. The UV coordinates appear to be mismatched or improperly preserved, leading to visible artifacts on the model's surface.

before simplify:

after simplify:

I’d appreciate any suggestions or guidance on how to address this issue

[Yeah-Zi]

Here is a sample glTF file for testing purposes.
Gltf.zip

[zeux]

-sa stands for “aggressive simplification” and has these artifacts by design. You’re looking for -sv. This naming is not ideal but -sa was introduced long before attribute simplification, so the name had to be preserved.

[zeux]

Looking at the model, it doesn't seem to be UV mapped properly, while the texture contains reasonable parts of the buildings, they are mapped in a strange manner with overlaps between shells and such. The default simplification mode thus mostly refuses to simplify this because any changes in topology would break the texturing, and using aggressive simplification breaks the texturing. So I think even modulo the settings confusion, this is more or less expected behavior. Some future improvements to aggressive simplification are tracked in #71, but I'm not sure to what extent they will help here and when I'll have time to look into that one.