Sharp distribution on Glossy and Glass (and possibly others)

Inspired in part by starting to read through The Cycles Encyclopedia by the folks at Blender Diplom, I’m going through the different shaders, testing out the various options to see what they do. As I’ve gone through them, I’ve noticed that when the distribution on the glossy and glass shaders (those are the only two I’ve encountered it on so far, I’m sure it will be at least on the Anisotropic and possibly some others) is set to sharp, you get essentially the same result as if you have any of the other distribution methods with a roughness of 0, regardless of what the roughness is set to. In other words, every value I’ve tested for roughness gives the same result when the distribution is set to sharp. (OKay… I think that’s clear, right?)

I’m sure there’s a reason for this. So my question is what is this reason? Why would that be useful?

Thanks! :smiley:

I always thought of “sharp” as being a kind of override, which a) allows to quickly add a mirror like reflection to a material without having to move the roughness slider and which b) also saves on resources. From my understanding GGX, Beckmann and the like are kind of advanced algorithms, which can even affect render times when their respective roughness is set to 0. So, if you want a fully mirror-reflective material anyway, “sharp” is the low-cost way to go.

Then again this might be complete nonsense…