Collision operator

The Collision operator can be used to collide particles with scene geometry.


Collisions Rollout

Colliders

  • Input object list: the list of input collider objects.

The Collider operator supports static/deforming geometry objects, as well as built-in Deflector/SDeflector spacewarps.

Collision Radius

  • Absolute radius: the collision radius of each particle will be set to a specific value.

  • Radius: the specific collision radius value.

  • Shape radius: the collision radius of each particle will be set to each particle’s shape mesh radius.

  • Scale radius: the collision radius of each particle will be set to each particle’s maximum scale dimension.

  • Multiplier: the multiplier to apply to shape/scale radius values.

Test TRUE if Particle

  • Collides: the test condition will be satisfied as soon as a particle collides with a collider object.

  • Collides multiple times: the test condition will be satisfied as soon as a particle collides with a collider a specified number of times.

  • Count: the number of times a particle must hit a collider in order to satisfy the test condition.

Particle Interaction

  • Bounce: Particles will bounce off colliders.

  • Continue: Particle will not be affected by colliders (but may still satisfy the test condition).

  • Collide with front faces: particles will only collide with the fronts of faces.

  • Collide with back faces: particles will only collide with the backs of faces.

  • Collide with both: particles will collide with fronts and backs of faces.

  • Pass-Through %: controls the number of particles that are allowed to pass through the collider.

Geometry Surface Interaction

Bounce
  • Bounce %: the bounce velocity of particles, relative to their travel velocity.

  • Variation %: the per-particle percentage of variation to apply.
  • Diverge %: the percentage of divergence to apply to bounce vectors.

  • Threshold: particles whose travel velocity magnitude is below this value will not bounce.

Friction
  • Friction %: the friction applied to particles, relative to their travel velocity.

  • Variation %: the per-particle percentage of variation to apply.
  • Threshold: particles whose travel velocity magnitude is below this value will be treated with 100% friction.

Motion Inheritance
  • Inherit %: the percentage of collider surface velocity that particles will inherit.

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

  • Apply to Spacewarps: controls whether Collision operator values relating to bounce/friction/inheritance will override the corresponding values within an input deflector/sdeflector’s own settings.

Collision Offset

  • Distance: the distance above a face a particle will be placed after colliding with it.

Values above 0 help prevent floating-point precision errors during collision detection calculations. Values that are too large will create visible jittering artifacts.

Collision Spawn

  • Mark for collision spawn: collided particles will be internally marked so that they may satisfy the entry test (collision) condition of a Spawn operator.

Use this setting in combination with a Spawn operator to spawn child particles at each collision point.

Evaluation Timing

  • In order: the operator will evaluate in order with its surrounded operators.

  • After secondary solvers: the operator will evaluate at the end of the simulation step, after secondary solvers (bind, wobble, etc) have computed their velocities.

For accurate collisions, the operator should evaluate after secondary solvers (since those solvers may inject velocities into the simulation which will affect collisions). However, in certain circumstances you may not want the operator to evaluate after secondary solvers (if you’re using the operator to immediately send particles to another event). In that case, “in order” should be selected as the timing method.

Display

  • Display collision spheres: displays collision spheres for each partilce in the viewport.

Uniqueness

  • Seed: the seed value for all varied parameters.