Boids

Reference

Panel:Particle System ‣ Physics Type:Boids

Boid Physics settings.

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 Behavior settings is very important. In certain situations only the first three parameter are evaluated.

To view the panel to the right, add a Particle System of type Emitter and look in the middle area of the Particle System tab.

Options

Main

Boids try to avoid objects with activated Deflection. They try to reach objects with positive Force fields, and fly from objects with negative Force fields. The objects have to share one common layer to have an effect. It is not necessary to render this common layer, so you may use invisible influences.

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.

Misc

Banking

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

Pitch

Amount of rotation around side vector.

Height

Boid height relative to particle size.

Battle

Health

Initial boid health when born.

Strength

Maximum caused damage per second on attack.

Aggression

Boid will fight this times stronger than enemy.

Accuracy

Accuracy of attack.

Range

Maximum distance of which a boid can attack.

Relations

Target

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

Object

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

System

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

Alliance

Enemy

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

Friend

Will make the systems work together.

Neutral

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

Details

As mentioned before, very much like Newtonian particles, Boids will react to the surrounding deflectors and fields, according to the needs of the animator.

Deflection

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

For boid physics, spherical force fields define the way the objects having the field are seen by others. So a negative force field (on an object or a particle system) will be a predator to all other boids particle systems, and a positive field will be a goal to all other boids particle systems.

These effectors could be predators (negative Strength) that boids try to avoid, or targets (positive Strength) that boids try to reach according to the (respectively) Avoid and Goal rules’ weights. Force’s effective Strength is multiplied by the actual relevant weight (e.g. if either Strength or Goal is null, then a flock of boids will not track a positive force field).

Boid Brain

The Boid Brain panel controls how the boids particles will react with each other.

Rules

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.

Goal

Seek goal (objects with a force field and positive Strength).

Predict

Predict target’s movements.

Avoid

Avoid «predators» (objects with force fields and negative Strength).

Predict

Predict target’s movements.

Fear Factor

Avoid object if danger from it is above this threshold.

Avoid Collision

Avoid objects with activated Deflection.

Boids

Avoid collision with other boids.

Deflectors

Avoid collision with deflector objects.

Look Ahead

Time to look ahead in seconds.

Separate

Boids move away from each other.

Flock

Copy movements of neighboring boids, but avoid each other.

Follow Leader

Follows a leader object instead of a boid.

Distance

Distance behind leader to follow.

Line

Follow the leader in a line.

Average Speed

Maintain average velocity.

Speed

Percentage of maximum speed.

Wander

How fast velocity’s direction is randomized.

Level

How much velocity’s Z component is kept constant.

Fight

Move toward nearby boids.

Fight Distance

Attack boids at a maximum of this distance.

Flee Distance

Flee to this distance.

Rule Evaluation

There are three ways control how rules are evaluated.

Average

All rules are averaged.

Random

A random rule is selected for each boid.

Fuzzy

Uses fuzzy logic to evaluate rules. Rules are gone through top to bottom. Only the first rule that affect above the fuzziness threshold is evaluated. The value should be considered how hard the boid will try to respect a given rule (a value of 1.000 means the Boid will always stick to it, a value of 0.000 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.

Please note that a given boid will try as much as it can to comply to each of the rules he 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, Crowd and Center rules, meaning that «while panicked» it could well run into obstacles, e.g. even if instructed not to, most of the time.

As a final note, the Collision algorithm is still not perfect and in research progress, so you can expect wrong behaviors at some occasion. It is worked on.