Archived GLTF extension for specular/glossy materials. KHR_materials_pbrSpecularGlossiness is an archived GLTF extension. This means that it is deprecated and not recommended for new files. However, it is still supported for loading old files. https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Archived/KHR_materials_pbrSpecularGlossiness The reflected diffuse factor of the material. The diffuse texture. The glossiness or smoothness of the material. The specular-glossiness texture. The specular RGB color of the material. The alpha channel is unused.