MeshPhysicalMaterial: .clearcoat -> .clearcoatIntensity

Discussion continued from #18684

I suggest renaming MeshPhysicalMaterial.clearcoat to .clearcoatIntensity. It is an intensity value in [0, 1].

[WestLangley]

OK, closing…

[donmccurdy]

Nested sub-properties (material.clearcoat.intensity) are one naming pattern, prefixed properties (material.clearcoatIntensity) are another. Neither is incorrect, but the latter is more consistent with e.g. material.emissiveIntensity and the many .____Map properties.

To date, we don’t have any .fooIntensity properties except those that are paired with a .foo property they modify, like emissive or envMap. I’d prefer that our long term goal be to align with other PBR models rather than creating new models and new names, so IMHO the term .clearcoat is more future-proof.

You’ll find the correct inplementations in 3DS Max, Unreal or even BabylonJS:

Unreal engine calls this “clear coat”, as far as I can see, and states: “Amount of clear coat layer, 0 acts like the standard shading model, 1 is the full clear coat model.” This aligns with Autodesk Standard Surface, Filament, glTF, Houdini, and Blender. I don’t think we should rename the property, diverging from others further.