How to - Particle material affected by how many particles are behind it.

naked_chicken

I'd like to create a mask for my particle material based on how many particles are behind the current drawing particle. Basically it would be a depth mask but rather than being based on scene depth, it would just take into account the other particles. If the particle looks behind it and sees nothing then it draws black on the mask, if it looks behind it and sees another particle then it draws a shade of grey, if it looks behind it and sees lots of particles then it draws white.

I've tried scene and dest depth but they apparently don't see particles.

Any help would be much appreciated.

SirCalalot

What is the purpose of the particle effect?
Is there a real-world effect that you are trying to imitate, such as water?

Just in case anyone knows of an easier method to get what you are trying to achieve

naked_chicken

a geyser actually. I've got the water for the geyser looking pretty much how I like it but I want to mask out the foam and froth where the geyser is "thickest" ie where there is the highest concentration of particles and keep the foam and froth more visible on the edges and near the top.

imbueFX

Honestly just using translucency is your best bet for what you're talking about. Allowing the varying transparencies to add over one another will mask out exactly in the manner that you're describing.