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RBD Disconnected Faces with Multiple packed objects

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Hello everyone,

Currently trying to get rbd Disconnected Faces to work over multiple packed geo that is pre-fractured.

I noticed the same geo passed unpacked into the sop level Bullet solver node works and before impact the node removes inside cracks (glass) as expected and upon impact brings it back.

Same geo setup as packed geometry, into a dop net, run sim (runs fine), unpack and applying rbd Disconnected Faces, just doesn't want to work. The inside cracks are there with the same threshold. I can see faceid and primdist in the spreadsheet. Just wondering if someone has seen this issue before. Screenshots attached for ref.

Any suggestions would be welcome.





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Adding this because it's the first post that comes up on Google. So even though it's old maybe it will help someone.

The problem is that often your primitive numbers get scrambled in the simulation as houdini adds new primitives on fracturing,etc. Disconnected faces then looks up the prim number of the matching face, but ends up looking up the wrong face because the numbers are all different. Since it's statistically very unlikely that this random face is touching, it doesn't delete anything.

The solution is to use an Enumerate SOP before you pack your simulation geo. This will count through the primitives and save the number in any old variable, say "primindex".

Then after your sim and after you unpack it, you can use a Sort SOP to sort by attribute and sort by "primindex". And voila, now your prim numbers are back to original and set Disconnected Faces SOP to delete connected and you're in business.

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Thanks for this Geoff, makes sense what you wrote.

I was thinking the same that prim nums are getting messed up perhaps during the packed sim but just wasn't sure.

I will try this out and report back :) Thanks so much.

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