In regards to the OG question. I'd choose Arnold over RS for your volumes and FLIP fluid meshes.
It's much more mature, and has all the control you want, scattering, etc. You also won't hit memory
limits with your volumes either.
RS Volume tech lacks Multiscatter, so, it cant get that depth look right now - fair point.
If you are looking at pyro stuff, well, 3delight is around 5x faster
Yes, ever since 3Delight dropped, FB has been flooded with VDB renders, but that was until Emergen stole that spotlight. The next drop of Embergen in the next few weeks will cement its place in the lead for VDB sim(s) at least. They just added HDR and other realtime render improvements, but, I dunno how viable those are, since I havent tested it.
Daryl, GPU is not the future of rendering, it is great for what it is targeted at, but in no way is it
coming to any decent sized production any time soon.
Could not disagree with you more - all of the industry is moving that way, to the GPU. The biggest hurdle is VRAM, but, the next PCIe lane drop will lower that barrier - where you'll begin to see synergy between RAM/VRAM.
Daryl, regarding hydra delegates. The notion of using hydra as a path to final frame renders is insane, and not
something anyone is seriously contemplating at all. Treat hydra delegates as nice viewport IPR to get a feel for
your scene, and general look dev. Then it's off to final frame rendering via the usual path.
That's not my understanding of what USD represents in its totality to the Industry, and the reason SideFX invested so heavily in creating this new context called LOPs.
That is EXACTLY what SideFX ( and several other Hydra compliant engines ) are contemplating - final frame rendering via USD (more specifically Hydra). If, as you say, production GPU is not the end goal, they why create Karma at all? SideFX already has a CPU engine!
The entire point of USD/Hydra is the ‘U’ in USD, which is the same reason we have a crap ton of render engine options right now in Houdini, more than we've ever had - Hydra!
Its so that you can author fully described 3D scenes in USD, and preview them in the Hydra viewport (along with all your AOVs, right there in the same viewport) and render them on the command line, thru the Hydra interface for final frame rendering. The same Hydra interface I preview the scene with, is the exact same Hydra interface that is used to render the final frame on the command line - and that's the point, and that's what justifies all this upheaval that LOPs brought.
The best indicator of what's to come on GPU, is Storm, its the only Hydra engine that supports GPU USD (directly resolving the USD stage on the GPU) - it is lightening fast, and it recently got Volume support (bye bye 3Delight, even more). I asked SideFX when they'd update to the new USD spec. and they said the next major Houdini version drop - so we'll have to wait on that to play with it in Houdini.
In the end, use whatever you want to create your pixels.