Houdini - Moving Geometry with Particles
Transform Pieces moves stuff around with points.
[Above] We use one point to move one box.
Transform Pieces takes three inputs:
[ A ] Points to transform. [ B ] Points that will move the A-points. [ C ] Rest positions of B before the move.
Houdini binds the A-points to the B-points by matching a user-specified attribute that exists on both.
In our tree, Assemble packs the box – reducing it to a single A-point – which is then driven by the single B-point. Both points have s@name = "box".
The packing is unneccessary, but it’s cheaper. If we bypass the Assemble, all the points of the box will have the same @name and will be bound to a computed centroid. This centroid is then driven by the matching B-point (which essentially has the same effect as packing).
Using a POP Simulation to drive Packed Primitives
We can animate the B-points however we want, which includes running them through a POP Simulation:
Here’s the generalized framework:
The idea is: take any geo, break and pack the pieces, then simulate only the points. Use those simulated points to move the broken pieces.
Transform Pieces also works like Copy to Points. It understands point attributes like @orient and @pscale.
Since we don’t compute @orient, the pieces use @v – coming out of the sim – to work out orientation. We do compute @pscale so the pieces “dissolve away” (aka scale to 0) over time.