Particle System ‣ Physics



Boids particle systems are controlled by a limited artificial intelligence, which can be programmed to follow basic rules and behaviors. They are ideal for simulating flocks, swarms, herds and schools of various kind of animals, insects and fishes or predators vs. preys simulations. They can react on the presence of other objects and on the members of their own system. Boids can handle only a certain amount of information, therefore the sequence of the Boid Brain rules is very important. In certain situations only the first three parameter are evaluated.




Particle System ‣ Physics ‣ Movement

Boids try to avoid objects with activated Collision. They try to reach goal objects, and fly from "predators" according to the Boid Brain settings.

Boids can different physics depending on whether they are in the air, or on land (on collision object).

Allow Flight

Allow boids to move in the air.

Allow Land

Allow boids to move on land.

Allow Climbing

Allow boids to climb goal objects.

Max Air Speed

Set the Maximum velocity in the air.

Min Air Speed

Set the Minimum velocity in the air.

Max Air Acceleration

Lateral acceleration in air, percentage of the max velocity (turn). Defines how fast a boid is able to change direction.

Max Air Angular Velocity

Tangential acceleration in air, percent 180 degrees. Defines how much the boid can suddenly accelerate in order to fulfill a rule.

Air Personal Space

Radius of boids personal space in air. Percentage of particle size.

Landing Smoothness

How smoothly the boids land.

Max Land Speed

Set the Maximum velocity on land.

Jump Speed

Maximum speed for jumping.

Max Land Acceleration

Lateral acceleration on land, percent of max velocity (turn). Defines how fast a boid is able to change direction.

Max Land Angular Velocity

Tangential acceleration on land, percent 180 degrees. Defines how much the boid can suddenly accelerate in order to fulfill a rule.

Land Personal Space

Radius of boids personal space on land. Percentage of particle size.

Land Stick Force

How strong a force must be to start effecting a boid on land.

Collision Collection

Only collide with objects in this collection.




Particle System ‣ Physics ‣ Battle


Initial boid health when born.


Maximum caused damage per second on attack.


Boid will fight this time stronger than enemy.


Accuracy of attack.


Maximum distance of which a boid can attack.




Particle System ‣ Physics ‣ Misc


Amount of rotation around velocity vector on turns. Banking of 1.0 gives a natural banking effect.


Amount of rotation around side vector.


Boid height relative to particle size.




Particle System ‣ Physics ‣ Relations


This list view allows you to set up other particle systems to react with the boids.

Target Object

A data ID to select an object with a particle system set on.


Index of the Object's particle system as set in the list view in the particle panel.


Setting the type to Enemy will cause the systems to fight with each other.


Will make the systems work together.


Will not cause them to align or fight with each other.


Boids will try to avoid deflector objects according to the Collision rule's weight. It works best for convex surfaces (some work needed for concave surfaces).

Force Fields

As other physics types, Boids is also influenced by external force fields.

In addition, special Boid force fields can be used with the Boids physics. These effectors could be predators (positive Strength) that boids try to avoid, or targets (negative Strength) that boids try to reach according to the (respectively) Avoid and Goal rules of the Boid Brain.

Boid Brain



Particle System ‣ Physics ‣ Boid Brain

The Boid Brain panel controls how the boids particles will react with each other. The boids' behavior is controlled by a list of rules. Only a certain amount of information in the list can be evaluated. If the memory capacity is exceeded, the remaining rules are ignored.

The rules are by default parsed from top-list to bottom-list (thus giving explicit priorities), and the order can be modified using the little arrows buttons on the right side.

Rule Evaluation

There are three ways to control how rules are evaluated:


All rules are averaged.


A random rule is selected for each boid.


Uses fuzzy logic to evaluate rules. Rules are gone through top to bottom. Only the first rule that affect above the Rule Fuzziness threshold is evaluated. The value should be considered how hard the boid will try to respect a given rule (a value of 1 means the Boid will always stick to it, a value of 0 means it will never). If the boid meets more than one conflicting condition at the same time, it will try to fulfill all the rules according to the respective weight of each.


A given boid will try as much as it can to comply to each of the rules it is given, but it is more than likely that some rule will take precedence on other in some cases. For example, in order to avoid a predator, a boid could probably "forget" about Collision, Separate and Flock rules, meaning that "while panicked" it could well run into obstacles, e.g. even if instructed not to, most of the time.

In Air

The current rule affects boids while they are flying.

On Land

The current rule affects boids while they are not flying.

Goal Rule

Seek goal.


Specifies the goal object. If not specified, Boid force fields with negative Strength are used as goals.


Predict target's movements.

Avoid Rule

Avoid "predators".


Specifies the object to avoid. If not specified, Boid force fields with positive Strength are used as predators.


Predict target's movements.

Fear Factor

Avoid object if danger from it is above this threshold.

Avoid Collision Rule

Avoid objects with activated Deflection.


Avoid collision with other boids.


Avoid collision with deflector objects.

Look Ahead

Time to look ahead in seconds.

Separate Rule

Boids move away from each other.

Flock Rule

Copy movements of neighboring boids, but avoid each other.

Follow Leader Rule

Follows a leader object instead of a boid.


Distance behind leader to follow.


Follow the leader in a line.

Queue Size

How many boids that are allowed to follow in a line.

Average Speed Rule

Maintain average velocity.


Percentage of maximum speed.


How fast velocity's direction is randomized.


How much velocity's Z component is kept constant.

Fight Rule

Move toward nearby boids.

Fight Distance

Attack boids at a maximum of this distance.

Flee Distance

Flee to this distance.