KHR_materials_specularGlossiness is a glTF 2.0 extension. It is not and has never been part of glTF 2.0 core spec.
The Khronos 3d formats working group and PBR Next technical subgroup have been considering discouraging the use of the KHR_materials_specularGlossiness in favor of using KHR_materials_specular once the WG submits it for ratification and it gets ratified. Both extensions, by definition, are not part of the core spec.
Both KHR_materials_specularGlossiness and KHR_materials_specular are implemented in the Babylon.js glTF loader. The latter is marked as experimental.
For the exporter, there are a few options:
- Export KHR_materials_specularGlossiness extension in the glTF.
- Export KHR_materials_specular extension in the glTF.
- Convert specular/glossiness to metallic/roughness via a lossy algorithm.
Or we do some/all of them and let the user choose.
@aWeirdo I don’t know what your scenario is, but if it’s possible, the best course of action is to use metallic/roughness workflow at the source. Then you won’t have any issues.