MeshPhysicalMaterial: .sheen -> .sheenTint

[WestLangley]

To accommodate upcoming changes to MeshPhysicalMaterial, .sheen is renamed to .sheenTint.

At a later time, additional properties will be added:

sheenTintMap
sheenRoughness
sheenRoughnessMap

This nomenclature is consistent with the properties .specularTint and .attenuationTint.

sheenTint is a THREE.Color. it is never null.

A new convenience method THREE.Color.isBlack() is added which can be used to test for zero values.

As per the glTF spec, the sheen layer is disabled when the color is black.

[WestLangley]

Note: webgl_materials_physical_sheen.html needs to be rewritten. I have not modified it.

[mrdoob]

Thanks!

[Mugen87]

sheenTint is a THREE.Color. it is never null.

#22379 (comment). I vote to keep null for optional shader features.

[WestLangley]

sheenTint is a THREE.Color. it is never null.

... I vote to keep null for optional shader features.

We set optional material texture properties to null.

.emissive is a THREE.Color and it is not set to null; it is set to zero.

Same for sheenTint.

[Mugen87]

The difference is that emissive does not influence a GLSL define. That is true for sheenTint.

In other words changing the default value of emissive does not produce a shader permutation whereas sheenTint does.

[WestLangley]

That is not the user's concern.

[Mugen87]

Don't get me wrong, I'm fine with your alternative approach. I just though because of #17700 (comment) we want to use null for such use cases.

[mrdoob]

Would it make sense to add a sheen (float) property that behaves like clearcoat and transmission?
It'd basically multiply sheenTint.

[WestLangley]

Personally, I think clearcoat should be named clearcoatIntensity. Ditto for transmissionIntensity. They are not booleans.

EDIT: ...but I do not have a strongly feeling about it. It is OK as-is.

Would it make sense to add a sheen (float) property that behaves like clearcoat and transmission?
It'd basically multiply sheenTint.

Regarding sheen, we will be having

sheenTint
sheenTintMap
sheenRoughness
sheenRoughnessMap

Adding sheenIntensity seems natural IMO, but the glTF spec does not call for it.

EDIT: In Version 2022x of the Dassault spec, sheenIntensity has been removed -- consistent with the glTF spec.