MeshPhysicalMaterial: Support specular attenuation of environment maps

[WestLangley]

This is a follow-on to #22156.

.specularIntensity now attenuates all specular reflections.

.specularIntensity does not attenuate clearcoat, however. I think that is consistent with the glTF spec.

clearcoat is itself an attenuation parameter, so I think this is OK.

[mrdoob]

Thanks!

[WestLangley]

.specularIntensity does not attenuate clearcoat, however. I think that is consistent with the glTF spec.

Use case: a Lambertian surface with a clearcoat.

/ping @donmccurdy Does that sound OK to you?

[donmccurdy]

This sounds like the right decision to me, but didn't find a clear answer in the clearcoat discussion section. @emackey we clarify that base IOR does not affect clearcoat, is it safe to say that KHR_materials_specular does not either?

[emackey]

@emackey we clarify that base IOR does not affect clearcoat, is it safe to say that KHR_materials_specular does not either?

Yes. You're right that we don't explicitly state specular's lack of effect on clearcoat the way we do with IOR. But the result is the same: Clearcoat is an independent layer, not perturbed by any specular or IOR settings on the layer below.