Is it possible to make a fluid that's applied to a particle object shade in world space? That is, if you apply a fluid to particles as a shader, you get a million tiny copies of the whole fluid. What I want is one copy of the fluid, at "normal" size, shaded only where the particles exist.
Driving the texture offset/scale with a particleSampler node, as mentioned elsewhere, doesn't help me, because I'm not using texturing. What I'm trying to do is to confine the rendering of an already-simulated 3D fluid to a particular area (basically, to cut the top part off of it). Unfortunately, I'm already driving the Opacity curve with Density, or I'd just use that. A screen space solution (holdout object or garbage mattes) won't work, because of the camera angle. (Imagine looking straight down into a mushroom cloud, and cutting off the top while leaving the stem.)