Spawn operator

The Spawn operator spawns new particles from existing particles.


Spawn Rollout

Spawn

On Entry

Spawns child particles the first time a particle enters the operator

  • Delete parent: controls whether the parent is deleted after children are spawned.
Per Second

Spawns child particles at a rate per second over time.

  • Rate: the spawn rate per second.

The rate per frame can be calculated as (rate / framerate).

  • Variation %: the per-particle percentage of variation to apply.
  • Simulate substeps: controls whether particle positions will be interpolated along their velocity by a random value, to simulate substep spawning.

By Travel Distance

Spawns child particles along the trajectories of their parents, at defined spatial increments.

  • Step Size: the distance a parent particle must travel before spawning a child particle.

If a parent particle travels a distance greater than the step size value over a particular step of the simulation, the distance traveled will be properly subdivided such that child particles will be spawned at equal distance intervals.

  • Variation %: the per-particle percentage of variation to apply.
Voxels Inside Shape

Spawns child particles inside voxels within the overall volume of a parent particle’s shape mesh.

  • Voxel size: the size of individual voxels, in which particles will be spawned.

  • Accuracy: controls the accuracy of the raycaster used to compute information about whether a particle is inside or outside of a shape mesh’s volume.

If a parent particle’s shape mesh is not closed, or is self-intersecting, increasing the accuracy value can improve results and reduce artifacts.

  • Min surface distance: particles within this distance from the parent particle’s shape mesh will be culled.
Marked for Collision Spawn

Spawns child particles if their parent was marked by a Collision operator as having colliding with a surface at the end of the previous time step.

At PhysX Contact Points

Spawns child particles at contact reports reported by the PhysX solver located on a parent particle’s PhysX hull.

  • Simulation groups: controls which particle simulation groups value the PhysX contacts must satisfy, in order to spawn particles.

By filtering desired simulation groups, you can control which types of PhysX contacts will spawn particles.


  • Spawn %: the percentage of parent particles that will spawn child particles.

  • Offspring: the number of child particles a particular parent particle will spawn, per time step.

  • Variation %: the per-particle percentage of variation to apply.

Age

  • Restart particle age: controls whether spawned particles will have their age reset, or instead inherit the age of their parent.

Parent/child info

  • Remember parent: controls whether the particle will internally remember which particle is its parent.

Uniqueness

  • Seed: the seed value for all varied parameters.

Position Rollout

Position

  • Parent particle position: spawned particles will be located at the position of their parent.

  • Parent shape surface: spawned particles will be located at a random position on their parent particle’s shape surface.

  • Mat ID enabled: controls whether particles will only be spawned on faces with a specific material ID.

  • Mat ID: the specific material ID of faces particles will be spawned on.

  • Offset: the distance from the parent particle’s shape surface, along its face normals, to offset spawned particles.

  • Variation %: the per-particle percentage of variation to apply.
  • Align to Surface: controls whether particles will be aligned to the surface of their parent.

Inherited Properties Rollout

Velocity

  • Inherited %: controls how much velocity child particles will inherit from their parent.

  • Variation %: the per-particle percentage of variation to apply.
  • Divergence: controls how much child particle velocity vectors will diverge from that of their parent.

  • Noise amount: controls the amount of noise variation that will be applied to child particle velocity vectors.

  • Noise scale: controls the scale of the noise variation applied to child particle velocity vectors.

Spin

  • Inherited %: controls how much spin child particles will inherit from their parent.

  • Variation %: the per-particle percentage of variation to apply.
  • Divergence: controls how much child particle spin vectors will diverge from that of their parent.

Scale

  • Inherited %: controls how much scale child particles will inherit from their parent.

  • Variation %: the per-particle percentage of variation to apply.

Limits and Filters Rollout

Particle Filter

  • Min volume: parent particles with a shape mesh volume below this value will not spawn children.

  • Min velocity: parent particles with a velocity magnitude below this value will not spawn children.

  • Min impulse: parent particles with PhysX contacts whose impulse is below this threshold will not spawn children.

Spawn Limits (per step)

  • Per particle: limits the total number of children that an individual particle can spawn, per time step.

  • Total: limits the total number of children that can be spawned, per time step.