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Triggers

Triggers are area-based sensor entities that fire events when other entities enter or interact with their bounding box. They are commonly used for map transitions, cutscenes, trap zones, and door switches.

Creating Triggers

Via utiLITI

  1. Add a Trigger entity to your map.
  2. Define the trigger area (bounding box).
  3. Set activation properties and target tags in the Entity Inspector.

Via Code

// Constructor: (activationType, name, message)
Trigger trigger = new Trigger(TriggerActivation.COLLISION, "exit_trigger", "exit_level");
trigger.setLocation(100, 100);
trigger.setWidth(64);
trigger.setHeight(64);

// Add to active environment
Game.world().environment().add(trigger);

Trigger Activation Modes

The TriggerActivation enum defines how the trigger detects activation when instantiated:

  • COLLISION: Activates automatically whenever an entity collides with or enters the trigger bounding box.
  • INTERACT: Activated when game logic explicitly invokes trigger.interact(entity) (e.g. from an input listener or action key).
// Create an interaction trigger: (activationType, name, message)
Trigger talkTrigger = new Trigger(TriggerActivation.INTERACT, "npc_trigger", "talk_elder");

// Explicitly trigger interaction from player input logic
talkTrigger.interact(player);

Trigger Listeners

Activation Listeners

trigger.addActivatedListener(event -> {
  IEntity activator = event.getEntity();
  System.out.println("Trigger activated by: " + activator.getName());

  // Execute trigger logic
  spawnEnemies();
});

Deactivation Listeners

trigger.addDeactivatedListener(event -> {
  System.out.println("Entity left trigger zone: " + event.getEntity().getName());
});

Unified TriggerListener

trigger.addTriggerListener(new TriggerListener() {
  @Override
  public void activated(TriggerEvent event) {
    // Fired on activation
  }

  @Override
  public void deactivated(TriggerEvent event) {
    // Fired on deactivation
  }
});

Common Use Cases

Level Transitions

Trigger exit = new Trigger(TriggerActivation.COLLISION, "exit_to_level2");
exit.addActivatedListener(e -> {
  Game.world().loadEnvironment("level2");
});

Enemy Spawning

Trigger spawnZone = new Trigger(TriggerActivation.COLLISION, "spawn_wave1");
spawnZone.addActivatedListener(e -> {
  for (int i = 0; i < 5; i++) {
    Enemy enemy = new Enemy();
    enemy.setLocation(200 + i * 40, 150);
    Game.world().environment().add(enemy);
  }
});

See Also