Particle simulations

The particle solver (POP Solver node, short for Particle OPerator) imports particles and rules from a traditional Houdini particle system into a dynamics simulation so the particles can interact with dynamics objects. You can also import geometry and treat its points as if they were particles. This lets you simulate various types of springy and squishy objects.

Importing particles always involves at least two dynamics nodes: a POP Object node to set up a dynamics object to represent the particles, and a POP Solver node that references a POP network to use to direct the particles.

The most important thing to remember when importing particles into dynamics is that both particle system and RBD forces apply to the particles.

For example, if you have a downward “gravity” force in the particle system, and a downward “gravity” force in the dynamics network, you’ll want to make sure they don’t both apply to the imported particles (either by importing the particles from a point before the particle gravity, or keeping the imported particles in a branch of the dynamics network away from the dynamics gravity), or else both forces will be applied to the particles.

See relationships for how to make particles interact with other objects.

The Create particles and Drive particles shelf tabs contain tools for creating and manipulating traditional particle systems.

The POP Object tool on the Create Particles shelf tab will take the selected particle object and import it into dynamics for you. In the dynamics network, it creates a POP Object node, an Object Position node to grab the particle object’s transform, and a POP Solver pointed at the particle network.

The Squishy Object tool on the Create Particles shelf tab will create an object that uses a particle/dynamics simulation to simulate a soft-body object.

• POP Solver dynamics node - set the POP path to the particle system you want to import.

• POP Object dynamics node - imports geometry and uses its points as particles.

• POP Shape Match dynamics node - Applies forces to particles to make them form a shape defined by geometry (usually the initial shape of the geometry the points come from). This is how the squishy object you can create from the shelf works.

• Object Position dynamics node - Copies the transform from an object into a dynamics object’s Position data.