Originally Posted by gnoop
EathQuake, I am talking about highlight reflection, not fresnel environment one.
You are not always see much dimmer highlight on rougher surface if that rough surface is constructed of very reflective wet grains.
So that energy conservation being right in theory , in practice just doesn't allow to compensate enough for not precise enough surface representation.
I bet that night photo would be pretty hard to recreate in typical i game PBR without special anisotropic highlights and rather specular/glossiness than metallic/roughness approach
Sorry it's taken a while for me to get back to this, but I made a quick example.
The reflections in those night photos are extremely easy to replicate as long as you have a modern reflectivity BRDF like Blinn-Phong or GGX. Phong might not work very well. You certainly don't need to use an anisotropic shader.
Energy conservation/metalness maps/etc are also not in any way a limiting factor here either. Wet surfaces don't magically become more reflective, they just get a bit darker (albedo) and smoother as the water fills in all the pores/cracks/etc.
The only difference between the wet and dry materials is the wet has a slightly darkened albedo, and the gloss map has been edited to be glossier(brighter). Both materials use a fixed 0.04 reflectivity value, the same that you would find in a metalness PBR workflow, and fresnel of 1 (typically a locked value in PBR systems).
Fresnel is very important for this type of material, because you're likely to see it at a grazing angle. That's why it looks so reflective. It's not because it's wet, it's because of the gloss value and fresnel.
To illustrate how Fresnel works, look at an object at various angles. You'll notice that as you shift from a grazing angle to a straight on angle, the material looks less reflective.
Here will Fresnel at 1 and 0, you can see how important it is to making a surface like road look wet.
Again, no tricks, no breaking the PBR system, no special shaders, just a couple simple parametric changes to the material gives you the difference between wet and dry.