Behaviors

BehaviorSystem runs the behaviors attached to actors.

To write a behavior and attach it in the editor, see Behaviors in Game Code.

Setting it up

1. In the Systems tab, add Behavior System.
2. Add BehaviorSystem, Behaviors and the project’s gameBehaviors to the engine:

import { Engine, BehaviorSystem, Behaviors } from 'dacha';

const engine = new Engine({
  config,
  systems: [BehaviorSystem, ...gameSystems],
  components: [Behaviors, ...gameComponents],
  assets: [],
  resources: {
    [BehaviorSystem.systemName]: [...gameBehaviors],
  },
});

The Behaviors component

The component has one field, list. It holds the behaviors of the actor, in the order they run. Each entry has three fields:

Field	What it is
id	An identifier for the entry. The editor creates it
name	The behaviorName of the class to create
options	Values for the behavior’s fields. The system passes them to the constructor

When instances are created and destroyed

BehaviorSystem is a scene system, so each scene gets its own copy. It creates the behavior instances for an actor when:

• the scene becomes active,
• an actor with Behaviors is added to the active scene,
• an actor in the active scene gets a Behaviors component.

It calls destroy on the instances of an actor when:

• the actor is removed from the scene,
• the Behaviors component is removed from the actor,
• the scene is destroyed.

Changing behaviors at runtime

The system reads Behaviors only when it creates the instances. If you update the component later, the running instances do not change.

To change the behaviors of an actor, replace the whole component:

actor.setComponent(
  new Behaviors({
    list: [{ id: 'patrol', name: 'Patrol', options: { speed: 2 } }],
  }),
);

setComponent removes the old component first, so the system destroys the old instances. Then it adds the new component, so the system creates instances from the new list.

Where behaviors run in the frame

When BehaviorSystem gets its turn in the systems list, it calls update and fixedUpdate on every behavior of every actor.

API reference

• BehaviorSystem
• Behaviors
• Behavior