PBR：The roughness property (in the metallic/roughness workflow) or the micro-surface property (in the specular/glossiness workflow) will also be used to blur the reflection (see below for more details).
This is possible by using a specular map: in this case, the alpha component of the texture is used as the glossiness value (so, 1-roughness). I will update the documentation to mention this.
When there is no texture, it is difficult to calculate the roughness because the standard material has a specularPower (which corresponds to the glossiness), but this value is not between 0 and 1, it is not bounded… I suppose we could still set a hard limit when calculating the roughness…
