Calvin ✨

So traditionally you have three maps- albedo, normals and a third packed with metal, rough ness and AO (I call this one the masks map). Each of these three has 3 channels, R G B. That's nine channels.

Okay, so you can ditch the blue channel of the normal map these days as you can derive this in the shader. Z= sqrt (1 - saturate(xx + yy)) This gives you a free channel in your normal map.

So breath of the wild packs roughness into that blue channel. The logic here is they don't use AO, and unless a metalness map is needed, they just use two maps... albedo and normal (normal X, normal Y, roughness). Okay...

So if you are using PBR, you still need an Ambient Occlusion channel. So rather than pack roughness into the normal blue channel, it makes sense to put the AO channel in there- because material variants will change the albedo, metal and roughness but never the ao.

So, if we do that, we can pack roughness into the alpha of the albedo- store this as linear, and do the gamma for the albedo in the shader. That means only two texture samples for the majority of environmental maps- wood, dirt, mud, stone, leaves etc.

So thats a huge improvement when you are always hitting your 16 sample limit on blended materials. However, here is where my crazy train is headed... what if we can cram metallic into that too?

PBR materials are either metallic or dielectric. The metallic map is therefore mostly black and white, with the grey pixels used for anti-aliasing and dialetric grime on metal surfaces. What if instead of using a whole channel for that, we use part of the roughness?