Hiding geometry in this fashion is usually accomplished with shading and/or
render passes, not geometry operators.
If using render passes, simply make a constant black object as the volume
and unplug it from the primary ray port of it's material shader. Particles
inside the volume will not render in the final image. You might have to use
a constant material shader with other trickery as this behavior tends to
change with the version of mental ray.
Purely with shaders you'd check the incoming ray to see if it's a primary
ray (from camera) or secondary ray (from sibling or specified volume). If
the latter, the particle is hidden or made transparent (or reverse if you
prefer different behavior). The general logic is the same for other
renderers. The advantage to the shading implementation is it's as granular
as the pixel rendered, and computation is negligible.
Doing it in ICE will take the particle all or nothing resulting in some
'popping' of the particles as they enter/exit the volume and hide suddenly
because you're getting the entire particle/object, not just the portion that
enters/leaves the volume. Not to mention the ICE version will be a rather
intensive operation having to cut geometry each frame leading to slower
renders, potentially great memory consumption, and instability - but that's
relative to what is being cut and hidden.
Matt
Date: Wed, 20 Jan 2016 16:29:21 +0100 (CET)
From: Morten Bartholdy <[email protected]>
Subject: Re: Hiding geometry inside volume?
To: "[email protected]"
Content-Type: text/plain; charset="utf-8"
I was thinking it might be possible to cache the RBD sim out with Alembic
and use that for deleting polys.
I guess I will have to do a simple test.
MB
