message: Don't use clear coat roughness as base roughness if clear coat is 0
  This change finds the max of the clear coat and base layer roughness
  then lerps the base layer roughness according to the amount of clear
  coat.
diff: @@ -130,7 +130,8 @@ void getRoughnessPixelParams(const MaterialInputs material, inout PixelParams pi
  // This is a hack but it will do: the base layer must be at least as rough
  // as the clear coat layer to take into account possible diffusion by the
  // top layer
  - perceptualRoughness = max(perceptualRoughness, pixel.clearCoatPerceptualRoughness);
  + float basePerceptualRoughness = max(perceptualRoughness, pixel.clearCoatPerceptualRoughness);
  + perceptualRoughness = mix(perceptualRoughness, basePerceptualRoughness, pixel.clearCoat);
  #endif
  // Remaps the roughness to a perceptually linear roughness (roughness^2)
  