Turns out glTF doesn't actually put metalness into R and roughness into
G, even though the naming suggests that. This was done originally, but
then they changed that in order to be compatible with UE4 and allow for
a more efficient storage of an occlusion map.
Because this feels extremely arbitrary, the docs have added rationale
for each of the packing variants, and I'm also renaming the packed
attribute and checks to imply the red channel isn't used.
Well, "basic". Practically mirrors glTF PBR materials:
- builtin metallic/roughness
- the KHR_materials_pbrSpecularGlossiness extension
- extra normal/occlusion/emission maps
- exposes the implicit metallic/roughness and specular/glossiness
packing, but also allows separate maps with arbitrary packings as
well as two-channel normal maps (instead of three-channel)
- provides convenience checks for the most common packing schemes
including MSFT_packing_normalRoughnessMetallic and the three variants
of MSFT_packing_occlusionRoughnessMetallic
- teaches PhongMaterialData to recognize packed specular/glossiness
maps as well
Next up is exposing at least one layer extension, and then I'm done
here.
Vladimír Vondruš