I've got a 2d fluid simulation in geometry nodes (which works). I want to displace in Z depending on the luminance of a texture (which also works), but the particles jiggle about too much, which I don't want. So I had the idea to dampen the motion by rigging up a spring simulation which stores the z component of each particle, then moves them each frame based on how far away they are from where they should be.

But I can't get this bit to work. I'm storing z-pos as a custom attribute, but I can't work out how to reference this in the right way so it's looking at the value from the last frame. Oh, and the node setup I've put in for this bit doesn't work either.

Here's the bit that works: enter image description here

The node graph with nodes expanded: enter image description here

And the result if i connect it... enter image description here

The (2d) simulation itself is cached. But it doesn't matter if I roll back to frame 1 and play from there, I still get nothing.

FWIW the geometry is generated by the fluid sim itself, circled in red. enter image description here

What am I doing wrong?



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