Static Proxy Volume Excessively Evaluates?

[Atom]

Hi All,

I have a FLIP scene with a single static object collider.  I have prepared a VDB version to supply as the Proxy Volume for the Static Object. When I populate the proxy volume field Houdini goes off into la-la land running a single core process, I assume to generate the proxy volume for FLIP collision. Eventually my collision object appears in the viewport and looks ok. So I click play and once again Houdini drops down into single core process mode and takes forever to crank out a FLIP frame, but it works. I think, ok I guess the solver had to generate the proxy volume at the start of a new simulation. So I wait again and the solver moves on to the next frame.

The same thing happens again, a slow single core process to convert the proxy volume. I might expect this kind of operation if I were supplying a deforming geometric collision object my object is static and that checkbox is off by default.

I put a switch on the static solver to illustrate the point. If I switch off collision the sim immediately jumps into multi-core simulation mode and moves along at a good pace.

Is this bug, do proxy volumes evaluate every frame for static geometry?

ap_cmf_excessive_proxy_volume_update.hiplc

Edited January 17, 2017 by Atom

[rbowden]

You need to check off collision guide if you want to run the simulation in the viewport. When you have Collision Guide turned on, houdini calculates that mesh you are seeing in the viewport per frame. I DLed your file and turned that off and everything seems to play fine (after putting the switch you have in there back to 0).

Edited January 17, 2017 by rbowden

[Guest tar]

35 minutes ago, Atom said:

Is this bug

I'm not quite sure you have realised but you can dive into the Static Object and check out the setup? The whole purpose of Houdini over something blackbox like, like Maya, is that you can modify and learn from when has been setup.  The default position of 'is this a bug' to anything that doesn't work as you expect it to is almost the antithesis of why people use Houdini IMO.

It's like using a tutorial in C++ and then saying, hey when I use this tutorial in my program and it doesn't work, is there a bug in C++...

[Atom]

Thank you Ryan! That works.

[Skybar]

Turn on perfomance monitor, check what takes up the time. Easy way to pinpoint problems. 

[Earller]

Thanks everyone — this thread helped clarify a lot.

Just to add for anyone else running into this: yes, even for static objects, if you’re using a VDB Proxy Volume, Houdini still seems to evaluate the proxy each frame unless you explicitly manage when and how it’s updated. Disabling the Collision Guide (as Ryan pointed out) makes a huge difference, especially in viewport playback — it's not just cosmetic, it actually controls whether Houdini recalculates that VDB every frame.

Also, diving into the Static Object DOP and checking out the internals is super useful. You can often lock in your VDB or pre-cache it manually if you're hitting perf issues.

Highly recommend enabling the Performance Monitor too — it really does help track where the time is going if you're not sure what’s dragging down the sim.

TL;DR: It's not a bug, just a gotcha. VDB-based proxy collisions are powerful but require a little setup awareness, even for static colliders.