Behavior¶

Behavior effects coordinate neighborhoods, populations, persistent states, and procedural growth.

Where to find it¶

Lists: Effects > Add Effect... > Behavior. Nodes: Pro Physics > Shift+A > Behavior.

Behavior effects¶

These effects are available in Lists and Nodes. Named particle groups let one behavior distinguish populations without requiring separate simulations. In Nodes, branching and Physics Groups can also route populations through different behavior chains before the streams are merged.

Flocking¶

Combines separation, alignment, and cohesion steering. Optional predator, prey, and scene-target behaviors use the same neighborhood solve.

Build a basic flock¶

1. Emit particles with enough initial velocity to establish a heading.
2. Add Flocking.
3. Set Perception Radius large enough for particles to find nearby flock members.
4. Set Max Speed to the desired travel-speed ceiling.
5. Set Max Force to limit how abruptly headings can change.
6. Increase Separation and set Separation Distance to prevent crowding.
7. Add Alignment to match headings and Cohesion to move particles toward their local center.

The three steering terms have different roles:

• Separation pushes away from close neighbors. Separation Distance is the near range used for this crowding response.
• Alignment turns a particle toward the local average heading.
• Cohesion steers toward the local average position.

Perception Radius controls the broader neighborhood used by the flock. A radius that is too small produces disconnected individuals; a very large radius increases neighborhood work and can make the whole population react too uniformly. Max Force limits all steering contributions, while Max Speed limits the resulting motion.

Predators and prey¶

Particle groups define each role. Select Predator Group and Prey Group by name, using the same groups assigned by their emitters or by Change Group.

• Enable Predators makes ordinary flock members flee the selected Predator Group. Avoid Distance starts the response, and Avoid Strength controls it.
• Enable Prey Seeking makes affected predator particles seek the selected Prey Group. Prey Strength controls pursuit.
• Retarget Threshold requires a new prey candidate to be sufficiently closer than the current target before a predator switches. This prevents rapid target changes.
• Retarget Variation and Retarget Seed vary that threshold stably per predator, reducing synchronized pursuit.

A common two-population setup uses one Flocking effect filtered to prey with predator avoidance enabled, and another filtered to predators with prey seeking enabled. This keeps each population's general flock settings independent.

Static target¶

Enable Target attracts the affected flock toward the origin of Target Object. Target Strength controls that steering contribution. The target does not replace separation, alignment, or cohesion, so the flock can stay organized while moving toward an animated object.

Tuning order¶

Tune Separation first, then Alignment, then Cohesion. Add target or predator/prey behavior after the base flock is stable. If particles twitch, reduce Max Force, reduce competing strengths, or increase Perception Radius enough to avoid rapidly changing sparse neighborhoods.

Network¶

Changes particle direction at deterministic per-particle intervals to create grid paths or repeated random turns.

• Mode selects Grid or Random Turn. Grid turns motion by 90 degrees along world axes. Random Turn rotates by the configured angle around a random axis.
• Interval (frames) is the average time between direction changes.
• The first Randomness varies that interval per particle. Zero synchronizes the timing; higher values spread turns across the population.
• Turn Angle, available in Random Turn mode, sets the base rotation angle.
• The second Randomness, available in Random Turn mode, varies Turn Angle per particle.
• Corner Radius rounds a turn into a circular transition. Zero creates a sharp corner.
• Seed selects another deterministic schedule and random-turn variation.

Grid mode is world aligned. Rotate initial velocity when a different starting axis is needed. For a readable network, first use zero timing randomness and sharp corners, establish Interval, then add Corner Radius and randomness.

Particle Self Gravity¶

Attracts or repels particles according to their current mass in 3D or a selected 2D plane. It uses a hierarchical GPU solver and has its own accuracy, bounds, and stability controls.

See Particle Self Gravity.

Infection¶

Propagates persistent susceptible, incubating, infected, and immune states. It supports several initial seed modes, neighborhood transmission limits, incubation sources, lifecycle behavior, color output, and optional assignment of state groups.

See Infection, Explosion and Limit.

Dendrite¶

Grows persistent hierarchical branches and retains branch history for geometry output. Its ordered direction, split, terminate, radius, and custom-data layers are designed for networks, roots, crystals, and related growth systems.

See Dendrite.