How to make a volume with gradient falloff?

[Anonymous]

Hi everyone, I'm trying to make a localized atmosphere object- something to simulate thick atmosphere at a bottom of a valley and thin at the top. I've tried using a ramp on a standard volume material, but I get all sorts of strange effects due to the ramp using screen space or something... not sure why, but each object within the volume has a different looking application of that volume. I've tried putting the ramp through a camera projection, but still wasn't able to get any good results. Finally I put a gradient bitmap through a camera projection, into the projection color and the mask slots, and I got something that sorta works. However, it's super unwieldy, because the volume needs to be connected to the camera, and can't be scaled without ruining the careful placement of the gradient through the camera projection. I'd love to be able to have an atmosphere object I could just plop into an area and resize and reposition at will. There must be a better way to do this! Anyone have some good ideas that I'm overlooking? Thanks!

[lee_griggs]

Can't you just scale the volume in X and Z so that you don't see the edge?

Wouldn't fog work better for this?

[Anonymous]

Lee, thanks for replying! In this particular image, I could scale the x and y, yes, but that's not really the issue. I don't think fog is a good solution, as I want to be able to localize the effect, and I would also like to be able to get the cool shadows that a volume enables. What I'm really interested in are techniques to create smooth falloff gradients on volumes without the strange visual artifacts that occur with the screen-space issues with ramps. Any ideas? Thanks so much for your time. 🙂

[lee_griggs]

Why are you using a bitmap and not a ramp RGB?

Maybe something like UV Projection, UV Transform, or Triplanar projection would help control how the ramp is placed?