Point displacement.

[Dubbie99]

I would really love to able to displace points at rendertime. A vector displacement to be precise.

The problem this would solve is it would allow us to have planar foam sims, and then displace them to match an ocean surface at rendertime. This would allow changing spectrum settings without having to recache millions of particles.

It seems like this would be a simple feature to add.... (bet you love people saying this)

[Gosho.Genchev]

Hey Dubbie99 ,

That's an interesting suggestion! I'm wondering if it's something that needs to be done at render-time, though - you'll inevitably end up with a slowdown, no matter how it's implemented.

Wouldn't that be far simpler to accomplish prior to caching out, by simply sampling the spectra and adding the result to the point positions? There's a VEX function for that, and an example for doing precisely the requested thing at the bottom ( https://www.sidefx.com/docs/houdini/...an_sample.html )

Displace the point position by an ocean spectrum stored in a file.
@P += ocean_sample("spectrum.bgeo", 0, 1, 2, 0.7, time 0, 0, @P);

edit: I missed that part

This would allow changing spectrum settings without having to recache millions of particles.

Indeed that would be the bottleneck here. Sadly I'm not sure that sampling a volume at render-time to get the displacement vectors, and translating millions of particles would be an improvement over the re-caching :/

Best regards!

[Dubbie99]

The one thing it does save is data on disk. And in theory, moving a few million points in ram should only take a few seconds with properly written code. (Or less! - V-Ray can trace millions of rays per second, and that code has to do a lot more than adding a couple of vector3's)

This WOULD be a big improvement to writing a new cache to disk.

[Dubbie99]

This is becoming more a more of a pain not to have.
Lots of things come up where it would be super useful to be able to displace points.