Now that fluids (minus white water) are ported over to SOPs, I’m wondering - are there any use cases or scenarios that can only be accomplished in DOPs?

Cheers

The advantage of setting up dynamics in dops is that you aren't limited to the functionality the sop level wrappers provide. Just like any HDA in Houdini, if it doesn't do what you need, you either crack it open and modify it or make what you need from scratch.

Personally I even prefer setting up simple sims in dops still as I only use the nodes/microsolvers that I actually need rather than scrolling through a ton of parameters on the sop wrapper that aren't relevant.

That’s what I mean - what are those sop level functionality limitations?

Other than just seeing too many parameters that one doesn’t need is there anything that can only be done in SOPs?

For example, it is very difficult to use sop solver with rbd bullet solver in a sop level.

ifree
For example, it is very difficult to use sop solver with rbd bullet solver in a sop level.

And coming from a newbie - under which circumstances would you want to do that?

Not an RBD example but say you wanted to have a flip sim dissolve some geometry like it was lava or something.
You could use a sop solver in dops to perform some sdf boolean operation bewteen the current state of the fluid and the collider geo then send the updated collider back to the simulation.

But if you're a newbie it's fine to use the sop tools if that's what you're comfortable with, it's a great place to start learning about the different solvers. Use them until you can't accomplish what you need to accomplish, then - if you have the interest - dive into the dop net and start poking around.

But no one is going to say learning dops is pointless, at the end of the day it's all dops anyways so the more you know the better.
It's just probably not necessary for most people anymore.

It's like vex - you can use Houdini without writing a single line. But one day you'll want to build something where you have no choice but to use vex, so it doesn't hurt to know it.

In summary: Don't learn dops if you don't want to, do if you do.

Great explanation. Thank you!

ifree
For example, it is very difficult to use sop solver with rbd bullet solver in a sop level.

Could you expand on that? I'd love to hear what difficulties users are running into and how we can make that easier.

Diving into the rbd bullet solver and dropping a SOP Solver should be plug and play. In 19.0 we added DOP subnet multi-output support so you can choose whether you want it to be evaluated as a "pre" or a "post"-solve process.
The new "SOP Solver (Constraint Geometry)" is all setup to allow you to work on both the RBD pieces and the constraints simultaneously without having to fumble with the convoluted "Invoke Compiled Block" options - it is a compile block, so you do need to be a little familiar with how these work however.

We do try and provide hooks for customisation wherever possible. Having said that, the main limitation with the SOP based solvers is coupling (i.e RBDs and fluids, wires and RBDs, vellum and fluids etc...) - you'll have to roll your own in DOPs for that.

Another limitation of the RBD Bullet Solver SOP is dynamic fracturing, or generally modifying the RBD pieces' geometry (beyond using transforms on the packed fragments) - while the solver itself will allow that, none of the outputs are currently setup in a way that will allow you to retrieve those modified pieces - you'd have to create a dop import node yourself and retrieve the dop geometry directly from there.
In 19.5 we added support for scaling RBD pieces so you shouldn't need to unpack and scale the geometry itself and force a geometry update which was unnecessarily costly.