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SOP animation in DOPs

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I believe this is my first post here, so hello everyone.


I'm trying to wrap my head around SOPs-DOPs interaction.


I would like my objects (be it rigid bodies, RBD fracture objects, packed or unpacked) to follow animation from SOPs rather closely, but also collide with each other and respond to forces.


Let's say I have boxes copied over a grid, and the copies are animated with time offset. They move and rotate, penetrating eachother at some point - that's where collisions should come into play.


What would be the best way to approach this?

- POP Attract force in / alongside RBD Solver

- A custom POP / DOP Force - essentially also an attract force

- Trying to update position / velocity / force every frame, using SOP Solver?

- Reference Frame Force + SOP Geometry node?


Sorry if this is basic stuff.

Edited by jamnique
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Hello. You could attach constraints(my favourite is springs) to each rigid body. It's easy to make one end of the constraint follow the animated data, and the other end be dragging the rbd to get it as close as possible to that point. This can be really effective in certain situations.

I'm not near Houdini right now so I can't build you an example setup, but there are a few hip files for this on my blog(the address is in my signature)

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Thank you Richard. That's a very cool blog you've got there.


Based on one of your examples I've managed to assemble a working scene with a constraint network with spring / hard constraints. This works great for piece transformations.


However, I would like to stick to SOP rotations as well. In such case, would constraints still be the way to go? There is an RBD Angular Constraint, but can be made to reference a sop goal for each piece?

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Yes, constraints can apply to just rotation, and can follow sop data. The help card for the DOP node Constraint Network is a mine of good info.

Another way to do this is to set the rotation of each piece via a sop solver each frame.

I personally find packed primitives way easier to understand in DOPs. Because you operate on them as points, the SOP Solver seems easier to work with.

Sorry I'm being no help with example files. I'm never near Houdini at the moment.

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