Merge pull request #1777 from KhronosGroup/donmccurdy-clearcoat-texture-linear

Clarify linear space for clearcoat textures

Author: emackey

extensions/2.0/Khronos/KHR_materials_clearcoat/README.md

@@ -79,7 +79,7 @@ color = (f_emissive + f_diffuse + f_specular) * (1.0 - clearcoatBlendFactor * cl
 
 If `clearcoatFactor` (in the extension) is zero, the whole clearcoat layer is disabled.
 
-The values for clearcoat layer intensity and clearcoat roughness can be defined using factors, textures, or both. If the `clearcoatTexture` or `clearcoatRoughnessTexture` is not given, respective texture components are assumed to have a value of 1.0. If both factors and textures are present, the factor value acts as a linear multiplier for the corresponding texture values.
+The values for clearcoat layer intensity and clearcoat roughness can be defined using factors, textures, or both. If the `clearcoatTexture` or `clearcoatRoughnessTexture` is not given, respective texture components are assumed to have a value of 1.0. All clearcoat textures contain RGB components in linear space. If both factors and textures are present, the factor value acts as a linear multiplier for the corresponding texture values.
 
 If `clearcoatNormalTexture` is not given, no normal mapping is applied to the clear coat layer, even if normal mapping is applied to the base material.  Otherwise, `clearcoatNormalTexture` may be a reference to the same normal map used by the base material, or any other compatible normal map.