It’s something I call “RiFog Plus”; and I have no idea if it will be shareable when I’m done with it. For simple reasons: a) it’s built off the “RiFog” example from the shader builder volume folder; b) the altitude code is lifted as-is from the altitude fog shader I found in the RIB Mosaic package (the RIB Mosaic itself doesn’t seem to work with the latest Blender builds, pity); c) I want to add good AA’d noise to it, and the only way I can do it is by copying some publicly available noise code. The whole copyright law thing is something I don’t understand well, and when it comes to re-using bits of these sample shaders, I don’t understand it at all.
Anyway, what it is is an aerial perspective shader, very simple and almost free in terms of rendertime. Not a real volume. But it should be really really useful for outdoor renders… especially with the noise part in.
I guess I should also add parameters to control the distribution – I already have a multiplier in the distance exponent (simulates the “density” of the fog, i.e. falloff), and I guess a similar one should be there for the altitude part, to have the transitional region more compressed or spread wider. And simple switches to disable either of the distributions in case they aren’t required for a particular look.