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Behaviour structure

Evacu-agent pedestrians all have the ability to contain multiple sets of behaviours. Each set of behaviours will be exhibited in a given environment or scenario, such as in crowded stadiums or in evacuation events.

Behaviours and sets of behaviours are structured in a hierarchy, with the currently active set of behaviours modelled as a reactive subsumption hierarchy. This hierarchy represents the preference in which behaviours will be triggered, with the highest priority behaviour being considered first and the lowest priority behaviour being considered last.

The behaviour hierarchy is a child of the Pedestrian GameObject as described in the diagram below:

Behaviour structure breakdown diagram

The structure

Behaviour structure breakdown diagram

Behaviour Controller

BehaviourController - Each pedestrian has exactly one of these controllers. It is responsible for maintaining a List<BehaviourCollection> which stores all behaviours a pedestrian is able to perform. It also tracks the active BehaviourCollection, so that the collection of behaviours appropriate for the current context can be dereferenced.

FixedUpdate() is used to call currentBehaviourCollection.PerformBehaviours().

Behaviour Collection

BehaviourCollection - Models a set of related behaviours that a pedestrian is able to use in a given context. It does this via storing a List<BehaviourStrategy>.

The sole method PerformBehaviours() then iterates over this collection of BehaviourStrategy, calling behaviourStrategy.ShouldTriggerBehaviour() which checks to see if the conditions of each given behaviour to trigger are currently met.

If conditions are correct for a given behaviour to execute then behaviourStrategy.PerformBehaviour() is called on that BehaviourStrategy.

Note the iteration stops once a behaviour has been triggered, to ensure only one behaviour is executed per iteration.

Behaviour Strategy

BehaviourStrategy - Is responsible for modelling a single behaviour, such as entering a building or choosing a path of nodes to visit.

This is an abstract class containing two abstract methods:

  1. public abstract bool ShouldTriggerBehaviour() - In each behaviour this method contains logic to check whether the behaviour should be executed. This is done through using percept information such as that obtained from the FieldOfView.

  2. public abstract void PerformBehaviour() - In each behaviour this method contains the logic for execution of that given behaviour, for example choosing a path of nodes to visit.

Below is an example of a BehaviourStrategy called WaitAtDestinationBehaviour. It checks to see if a pedestrian is at its destination in ShouldTriggerBehaviour() and stops the pedestrian moving in PerformBehaviour().

public override bool ShouldTriggerBehaviour()
    float distanceToDestination = Vector3.Distance(transform.position, groupCollection.GroupDestination);
    return distanceToDestination <= RadiusToDestination;

public override void PerformBehaviour()

Behaviour Type Order and Behaviour Type

Behaviour Type Order

BehaviourTypeOrder - This is responsible for storing the List<BehaviourStrategy> for a given BehaviourCollection for different types of pedestrians. The order that behaviours is stored here is important as elements closer to index 0 will be considered for execution first, and only one behaviour is triggered per iteration.

BehaviourTypeOrder is an abstract class declaring one protected property and one abstract method:

  1. protected List<BehaviourType> behaviourTypes - Models the List<BehaviourStrategy> used for defining the preference order of behaviour execution. This is set up in Awake() of each BehaviourTypeOrder.

  2. public abstract List<BehaviourType> GetBehaviourTypes() - Returns behaviourTypes.

Behaviour Type

BehaviourType - This is responsible for storing a reference to a BehaviourStrategy script that will be instantiated and added to a BehaviourCollection for a pedestrian to use.

This is an abstract class declaring two methods:

  1. public abstract Type GetBehaviourStrategyClass<T>() where T : BehaviourStrategy; - Returns a type of BehaviourStrategy to be instantiated.

  2. public abstract float GetBehaviourStrategyChance() - Returns a float between 0 and 1 that represents the chance of a BehaviourStrategy being added to a BehaviourCollection. Currently this is not used but it is intended to allow pedestrians drawing behaviours from the same BehaviourTypeOrder to have non-uniform behaviour.


In the example below, FriendGroupLeaderTypeOrder defines the preference order of behaviours to be used by a FriendGroupLeaderPedestrian.

The private classes are used to populate behaviour types which store references to two BehaviourStrategy:

  1. GenericEnterLeaveBuildingBehaviour.
  2. GenericPathCreationBehaviour.

The List<BehaviourType> behaviourTypes object is instantiated and populated in Awake().

When behaviourTypes is passed to a pedestrian it will allow the BehaviourStrategy to be instantiated and added in the correct order, where GenericEnterLeaveBuildingBehaviour will be added first, GenericPathCreationBehaviour second and the rest of the BehaviourType in the correct order.

This means that whilst the BehaviourCollection containing these behaviours is actively being iterated over, the behaviours will be iterated over in the order they are added, giving highest priority to GenericEnterLeaveBuildingBehaviour.

public class FriendGroupLeaderTypeOrder : BehaviourTypeOrder
    private void Awake()
        behaviourTypes = new List<BehaviourType>()
            new GenericPathCreationBehaviourType(),
            new GenericEnterLeaveBuildingBehaviourType(),
            new WaitForFollowersBehaviourType(),
            new WaitAtDestinationBehaviourType(),
            new FriendGroupBoidBehaviourType(),
            new GenericNoNewBehaviourType()

    public override List<BehaviourType> GetBehaviourTypes() => behaviourTypes;

    private class GenericEnterLeaveBuildingBehaviourType : BehaviourType
        private readonly float behaviourStrategyChanceToUse = 1f;

        public override Type GetBehaviourStrategyClass<BehaviourStrategy>() => typeof(GenericEnterLeaveBuildingBehaviour);
        public override float GetBehaviourStrategyChance() => behaviourStrategyChanceToUse;

    private class GenericPathCreationBehaviourType : BehaviourType
        private readonly float behaviourStrategyChanceToUse = 1f;

        public override Type GetBehaviourStrategyClass<BehaviourStrategy>() => typeof(GenericPathCreationBehaviour);
        public override float GetBehaviourStrategyChance() => behaviourStrategyChanceToUse;

  // Further details omitted

Adding a new behaviour to an existing Behaviour Collection

  1. Create a new script that extends BehaviourStrategy in an appropriate folder in Assets/Scripts/EvacuAgent with a folder suffixed with Behaviours or add a new folder also suffixed with Beahviours. The new script should be suffixed with Behaviour.

  2. Add a private class extending BehaviourType in the appropriate BehaviourTypeOrder. Inside the class, the method GetBehaviourStrategyChance() should return a float between 0 and 1. The return type of GetBehaviourStrategyClass() should look similar to typeof(NewBehaviourScriptType).

  3. The new private class should be instantiated in behaviourTypes in the Awake() method of the BehaviourTypeOrder.

Adding a new Behaviour Collection

  1. Create a new script extending BehaviourTypeOrder in Assets/Scripts/EvacuAgent/BehaviourTypes suffixed with Behaviours. The script name should be suffixed with TypeOrder.

  2. Add an Awake() method which instantiates behaviourTypes.

  3. Ensure that GetBehaviourTypes() returns behaviourTypes.

  4. Add the necessary number of private classes that extend BehaviourType as described in Adding a new behaviour to an existing Behaviour Collection: Step 2.

  5. Populate the behaviourTypes instance with the BehaviourType created in the previous step. Remember that order of these is important, behaviours will be iterated from element 0 to element N.

  6. Add the new BehaviourTypeOrder script to the appropriate pedestrian prefab using Add Component as seen in the diagram below in red. This should make the BehaviourTypeOrder appear on the GameObject, as seen in green. Finally drag and drop the BehaviourTypeOrder into the slot marked in blue.

Adding BehaviourTypeOrder Example