GLTFExporter: Unable to export multi material object.

[Mugen87]

Description of the problem

If you import the following OBJ file into the editor, it looks like so:

house.obj.zip

If you now export to glTF and load it into a glTF viewer, it seems certain parts of the model are missing:

The house model is a multi-material asset. It seems the exporter only respect the parts with the first material applied.

Original issue: https://discourse.threejs.org/t/scene-quality-doesnt-match-when-exported-compared-to-first-time-load-scene/7099

Three.js version

• Dev
• r103
• ...

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• All of them
• Windows
• macOS
• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, ...)

[takahirox]

I'm aware of the root issue but didn't have time to fix.

https://github.com/mrdoob/three.js/blob/dev/examples/js/exporters/GLTFExporter.js#L1361-L1370

cachedData key should take account of group.start and group.count, not only geometry.index.