artemis-odb-eeel

Easy Entity Event Listening

EEEL is a drop in plugin for Artemis-odb

EEEL provided an easy interface to subscribe to Entity events, using either Annotations, or registration.

EEEL also provides an event bus to dispatch entity-bound events, and listen to events based on the related entitie’s aspect.

Susbscribing to Aspects

The first step to using EEEL is to add the plugin to your world:

WorldConfiguration config = new WorldConfigurationBuilder()
  .with(new EEELPlugin())
  ...
  .build();
world = new World(config);

Any system can then subscribe to entities.

Using Annotations

Any system can subscribe to Aspects by using the @Inserted and @Removed annotations, along side the @All, @One and @Exclude annotations.

class MySystem extends BaseSystem {
  
  @Inserted
  @All(Position.class)
  public void handlePositionEntityInsert(int entityId) {
    //do Something
  }
  
  @Inserted
  @All({life.class, damage.class})
  @Exclude(invurnerable.class)
  public void handleDamage(int entityId) {
    //do Something
  }
  
  @Removed
  @All(Position.class)
  public void handleRemoved(int entityId) {
    //do Something
  }
  
  @Inserted
  @Removed
  @All(TestComponent.class)
  public void addedOrRemoved(int entityId) {
    //do something
  }
 
  
  ...
}

As you can see, EEEL removes the need for event listeners, and thus makes complex systems much easier to manage.

Annotations in other objects

You can register any other objects to listen to events using the EEELSystem.register function:

world.getSystem(EEELSystem.class).register(MyListener);

Using method registration

Its possible you may not want to use Annotations due to the cost associated with invoking methods. This is why EEEL also provides a way to directly register methods (or lambdas) to be called. This is also useful if you need to register eventListeners on the fly.

This is does easily with the EEELSystem.inserted and EEELSystem.removed methods.

class MySystem extends BaseSystem {
    
    EEELSystem eeel;
    
    protected void initialize() {
        eeel.inserted(Aspect.all(health.class, attack.class), this::handleAttack);
        eeel.removed(Aspect.all(health.class), this::handleDead);
    }
    
    public handleAttack(int entity) {
        //do something
    }
    
    public handleDead(int entity) {
        //do something
    }
    
    ...
}

This example shows the use of Method references, but lambdas can be used in the same way:

eeel.inserted(Aspect.all(Position.class), entity -> {
   //do something
});

Custom Events

EEEL custom events is an experimental, proof of concept feature. EEEL also provides an Event Bus for custom events. Events can be dispatched for individual entities, and systems can subscribe to events according to their matching apsects.

Dispatching events

EEElEventSystem eventSystem;

 public void CalculateDamage(int entity) {
     int damage = 5;
     eventSystem.dispatchEvent(new DamageEvent(damage), entity);
 }

subscribing to events

EEELEventSystem eventSystem;

public void initialize() {
    eventSystem.registerEvent(this::onDamage, DamageEvent.class, Aspect.all(Health.class).exclude(Armor.class));
}

public void onDamage(DamageEvent event, int entity) {
    //do something
}

Getting started

Maven

<dependency>
	<groupId>net.fbridault.eeel</groupId>
	<artifactId>artemis-odb-eeel</artifactId>
	<version>1.2</version>
</dependency>

Gradle

dependencies { compile "net.fbridault.eeel:artemis-odb-eeel:1.2.1" }