MeshPhysicalMaterial: Support clearcoatMap, clearcoatRoughnessMap

[donmccurdy]

MeshPhysicalMaterial currently offers:

• clearcoat
• clearcoatRoughness
• clearcoatNormalMap

The glTF extension KHR_materials_clearcoat will also require texture versions of the first two, which I'd propose adding to (only) MeshPhysicalMaterial:

• clearcoatMap
• clearcoatRoughnessMap

[donmccurdy]

/cc @arobertson0 @bhouston

[donmccurdy]

In progress: #18682

[donmccurdy]

Fixed by #18769.

[WestLangley]

@donmccurdy What support do you intend for clearcoat/roughness map offset/repeat settings?

Currently, it is not considered in the offset/repeat priority list.

[WestLangley]

https://stackoverflow.com/questions/63559688/three-meshphysicalmaterial-clearcoatnormalmap-repeatwrapping

[donmccurdy]

Hm. My first reaction would be uv2 for clearcoatNormalMap, uv1 for everything else. It would be nice to get out of having to hardcode those pairings. 😅

[WestLangley]

Should the clearcoat normal/roughness map be added to the priority list so -- at a minimum -- offset/repeat is honored if it is the only map.

[PaulMitch]

Are there any known limitations apart from performance that is stopping repeat texturing of the clear coat normal?
I'm happy to have a look into it if someone can point me where to start.

[WestLangley]

This is a long-standing issue. For the primary uv set, three.js only supports one offset/repeat pair per material. See #8278.

three.js/src/renderers/webgl/WebGLMaterials.js

Lines 177 to 183 in c3c03a7

	// uv repeat and offset setting priorities
	// 1. color map
	// 2. specular map
	// 3. normal map
	// 4. bump map
	// 5. alpha map
	// 6. emissive map

[PaulMitch]

Ok, thanks for the info. So in a perfect world we'd need 3 UV sets as AO works great on UV set 2. So the clearcoat normals would have to be moved to UV set 3 :)