Keep Apart Operator

The Keep Apart operator, a member of the Speed operator family, lets you apply forces to particles to cause them to separate, in order to prevent or minimize collisions among particles. Alternatively, you can use a negative force to keep particles from separating too much. The operator works by controlling particle speed and acceleration.

• Particle View > Click Keep Apart in an event or add a Keep Apart operator to the particle system and then select it.

Note: Keep Apart doesn't use particle geometry; rather, it creates a spherical force field centered on the pivot of each particle. You can adjust the size of the force field by changing the particle size.

Tip: In certain cases, the default settings might not be sufficient to keep particles from interpenetrating. For increased separation, use higher values for Force and Accel Limit, choose Relative To Particle Size, and increase the Core % value.

Script Wiring rollout

This rollout appears in the parameters panel below the main operator rollout after you highlight the operator, right-click it, and then choose Use Script Wiring. Thereafter, a check mark appears next to the Use Script Wiring in the right-click menu, and the rollout appears whenever you highlight the operator. To turn off script wiring, choose Use Script Wiring again from the right-click menu.

Script wiring lets you use a script to control the Force and Range parameters, which you normally specify in the operator's parameters. Place a Script operator before the Keep Apart operator in the event, and then use it to define values in the particleFloat and particleVector channels. For an example of a script that sets particleFloat values, see particleFloat Sample Script.

On the Script Wiring rollout, choose either of the following:

Use Script Float As

Choose either of the following:

• Not Used Particle Flow uses the Force setting specified in the Parameters rollout.
• Influence Particle Flow applies the script particleFloat value to the Force value.

Use Script Vector As

Choose one of the following. Choosing Absolute Size Range or Relative Size Range makes the Range settings on the Parameters rollout unavailable.

• Not Used Particle Flow uses the Range settings specified in the Parameters rollout.
• Absolute Size Range Particle Flow applies the script particleVector values to the Absolute Size Range values. The X component of the vector value is used for the core radius, and the Y component for the falloff radius.
• Relative Size Range Particle Flow applies the script particleVector values to the Relative Size Range values. The X component of the vector value is used for the core percent, and the Y component for the falloff percent.

Interface

The user interface appears in the parameters panel, on the right side of the Particle View dialog.

Force

The amount of force applied to the particles. Use positive values to separate particles, or negative values to move them closer together. Default=100.0

Accel[eration] Limit

When on, lets you set a maximum acceleration value that can be applied to particles' motion. When off, Particle Flow uses any necessary acceleration. Default=on, 1000.0.

Tip: Use a lower Accel Limit value for smooth motion, and a higher value when greater accuracy is needed, such as when the particles should hit a small target. You can animate this setting (use Sync By Event Duration) to specify different appropriate values, depending on the required results.

Speed Limit

When on, lets you set a maximum speed value that can be applied to particles' motion. When off, Particle Flow uses any necessary speed. Default=off, 600.0.

Range group

You can set a volume and falloff within which the force takes effect, either as absolute distances or relative to particle size.

• Absolute Size (The default.) Choose this to set the core radius and falloff zone as absolute distances, in system units.

  Core Radius The distance from each particle's pivot point, in system units, within which the force is applied at full strength. Default=10.0

  Falloff Zone The distance beyond the core radius, in system units, over which the force diminishes from full strength to 0. Default=10.0

• Relative to Particle Size Choose this to set the core radius and falloff zone as percentages, relative to the radius of each particle. The particle radius is determined by measuring the distance from the pivot point to the farthest corner of its bounding box.

  Core % The distance from each particle, as a percentage of the particle radius, within which the force is applied at full strength. Default=200.0

  Falloff % The distance beyond the core radius, as a percentage of the radius, over which the force diminishes from full strength to 0. Default=100.0

Variation %

The amount by which range values can vary randomly, as a percentage of the specified values. Particle Flow uses the same random variation value for both Core and Falloff values, whether absolute or relative. Default=0.0

For example, if you choose Absolute Size, set Core Radius to 40 and Falloff Zone to 20, and set Variation % to 50, then each particle's actual core radius will be a random number in the range 20 to 60, and the falloff zone a random number in the range 10 to 30. For each particle, Particle Flow uses the same Variation % value, so if Core Radius is determined to be 20, then Falloff Zone would be 10.

Scope group

By default, the Keep Apart force keeps particles only in the current event (that is, the event that contains the Keep Apart operator) apart from each other when used locally, or particles in each event in the current flow apart when used globally. These settings let you alternatively keep particles away from particles in other events or flows without affecting the behavior of latter. Default=Current Event.

• Current Event Keeps particles in the current event only away from each other.

  When used globally, keeps particles in each event in the current flow apart from each other, but not apart from particles in other events in the flow.

• Current Particle System Keeps particles in the current event away from each other, and away from all other particles in the current flow. The particles not in the current event are not influenced by the Keep Apart operator.

  When used globally, keeps apart and influences all particles in the current flow.

• Selected Events Keeps particles in the current event away from all particles in the events highlighted in the list below this choice. Particles not in the current event are not influenced by the Keep Apart operator.

  When used globally, keeps all particles in the current flow apart from all particles in the events highlighted in the list below this choice, but influences only particles in the current flow.

  After choosing this option, click items in the list to highlight them.

• Selected Particle Systems

  Keeps particles in the current event away from all particles in the flows highlighted in the list below this choice. The particles not in the current event are not influenced by the Keep Apart operator.

  When used globally, keeps all particles in the current flow apart from all particles in the flows highlighted in the list below this choice, but influences only particles in the current flow.

  After choosing this option, click items in the list to highlight them.

Uniqueness group

The Uniqueness setting enables randomization of the Range group Variation % calculations.

Seed

Specifies a randomization value.

New

Calculates a new seed using a randomization formula.