I'm interested in discussing the theory of how a volumetric smoke/cloud/gas renderer like Digital Domain's STORM works. What exactly are the particles, at render time. Planes, spheres? What is their shape, texture and lighting?
I've read lots of articles on volumetric rendering, ray-casting and what-not, but few deal with in-depth theory about how to light smoke puffs for rendering, like you can see in Digital Domain's three-colored particle lighting passes.
Check these Digital Domain making-of's to see what I mean:
xXx avalanche ("Computer Generated Avalanche" pass)
Motorola Pebl (rising smoke and blowing dust)
Now, I'm not a programmer, but I do like to have basic understand of the tech stuff anyway. So, here's what I'm thinking:
- They can't be lighting a cloud of billboards, because billboards don't react too well to directional lighting..
- Unless of course the billboards are normal mapped to simulate more round shapes?
- They can also be "spheric billboards", meaning a cluster of spheres, all camera-mapped with a billboard type smoke texture? That would give them the visual benefit of billboards, but make them lightable like spheres.
- They could also just be totally normal sphere (with falloff), and the whole volumetric thing is in the lighting?
Any inside knowledge?