C++ HDK - interact with rigid bodies

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Are there any pointers as two how to approach a coupled solve between a custom SIM_solver derived DOP solver and houdini/bullet rigid bodies.

There is some discussion about it in this older post: https://www.sidefx.com/forum/topic/25444/#post-118354 [www.sidefx.com]

The last paragraph interests me most. I can get to the SIM_Object instances that represent the rigid bodies. But how would I go about applying forces or impulses on them? The SIM_Object does not seem to have an interface for that.

Any help appreciated,

Rog
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You should create impact data on the objects, which will then be read by the Bullet solver on the next feedback iteration:
SIM_Impacts *impacts = SIM_DATA_CREATE(*obj, SIM_NEWFEEDBACK_DATANAME, SIM_Impacts, SIM_DATA_RETURN_EXISTING);
impacts->addPrimitiveImpact(...)
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Thanks!!

Trying that now!
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Great, that works, mostly.

I had to use SIM_FEEDBACK_DATANAME instead of SIM_NEWFEEDBACK_DATANAME for the bullet packed rbd object to react.

Also, as I was debugging this, I noticed that if I combine this test solver (ripped of from the SnowSolver example) that as soon as I merge in a bullet solved packedrbd the solveSingleObjectSubclass function will get called twice per timestep. I double checked that no substepping is on the DOP network node, nor the Bullet Solver node. Is there an obvious explanation for this?

Thanks again,
Rog
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If you check the current simulation time in the solver, you're likely re-simulating the same timestep again according to the Max Feedback Loops parameter on the DOP network.
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You are right! It is related to the Max Feedback Loops being 2 and the merge relationship being set to mutual.

I'm afraid to admit that in my 10 years of dopsing around I had never given that parameter much thought.

Is there any more information apart from the normal houdini docs on how to deal with feedback loops? Is there a way of flagging to SIM_engine or as return value that there is no, or no more, interaction? So we can avoid unnecessarily re-simulating?

Sorry if these questions are a bit scattered. The information may be hidden inside the HDK docs but I haven't stumbled across it or put it together.

And thanks for your quick replies so far, really appreciated!

Rog
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The absence of any feedback subdata will terminate the feedback loop, so just be careful to only create it once there are impacts.
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Aha, that makes sense!

Thanks
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