reflective ao in reflection and ramp based glossiness correct?

[thebeals]

I have two questions that I've been wondering about for some time now.

I have been seeing more and more lately artists placing a reflective ambient occlusion in their reflectivity slot to occlude reflections. Their reasoning is that this is the physically correct way to do reflections and so you won't get a hall of mirrors effect. Is this correct? I understand the hall of mirrors thing, but what real world effect causes reflections to be occluded like this? Or is this simply an optimization/artistic choice?



I have also been told that glossiness needs to be mapped to an angle of view ramp like a facing ratio or fresnel effect because glossiness gets sharper the more of a glancing angle you are at. Is this correct and if so why? I understand an object gets more reflective the more perpendicular the point is to you, but is glossiness the same way too?

Thanks for any clarification!

[Remydrh]

I have been seeing more and more lately artists placing a reflective ambient occlusion in their reflectivity slot to occlude reflections.

This was typically done so you could map a reflection of an environment directly to the object and then use the occlusion to darken areas where that light is reflected away. This meant the reflection mapping looked more realistic without have to raytrace anything.

You can find that workflow here: www.lamrug.org/resources/doc/occlusion_tutorial.pdf

I have also been told that glossiness needs to be mapped to an angle of view ramp like a facing ratio or fresnel effect because glossiness gets sharper the more of a glancing angle you are at. Is this correct and if so why?

This is a physical property of glossy reflections in the real world. The mia_material does this automatically/correctly using a micro-facet model. It's possible that workflow is from old shaders like blinn and phong. I would not recommend using those at all. This workflow is no longer necessary with modern shaders.

[thebeals]

huh, that is good to know. Thanks for the answer! I could not figure out for the life of me why someone would use these methods with the current workflows involving more physically based methods. Good to know it's just left over methods/methods used in special circumstances.

I've used the ao as a light/environment shader before, but never realized that's where this reflective ao in refl. trick came from. Neat stuff. Thanks again!