Triggers

Triggers can be used to fire logic when an Actor intersects with a Collider, this is useful for in game switches, doors, or other in game sensors.

Under the hood, triggers are just Actors that have sugar to help wire up and fire logic on collision start or end events.

Trigger

By default triggers will fire when any geometry in your game intersects with the trigger area. Triggers are also not visible by default, generally you will layer triggers on top of your scene. They can be given a finite amount of repeat triggers with the repeat, a value of -1 means repeat forever.

// Example trigger will fire on any geometry
const trigger = new ex.Trigger({
  width: 100,
  height: 100,
  pos: ex.vec(100, 100),
  repeat: -1,
  action: () => {
    console.log('triggered')
  },
})

However this might not be desired all the time, you may have a specific Actor, such as a player, that you want to trigger on. Using a target will override any filter's provided.

const player = new ex.Actor({...})

// Example trigger will fire on any geometry
const trigger = new ex.Trigger({
  width: 100,
  height: 100,
  pos: ex.vec(100, 100),
  target: player, // only trigger logic on player
  action: () => {
    console.log('triggered')
  },
})

Filtering Triggers

Sometimes your trigger logic needs to be more complicated than just a target, this can be accomplished with a filter function. Returning a truethy value out of the function will allow the trigger to fire.

This need not be just logic on actors, you can use this for more complex game logic like "Only allow the trigger if there is a key in the inventory"

const player = new ex.Actor({...})

// Example trigger will fire on any geometry
const trigger = new ex.Trigger({
  width: 100,
  height: 100,
  pos: ex.vec(100, 100),
  filter: (actor) => {
    if (actor.name === 'player' && keyInInventory && isLevel42) {
      return true;
    }
  },
  action: () => {
    console.log('triggered')
  },
})

Additionally it is also possible to use collision groups to filter collisions between triggers and other actors because triggers are also actors.

const PlayerGroup = ex.CollisionGroupManager.create('player')

const player = new ex.Actor({
  name: 'player',
  pos: ex.vec(0, 100),
  width: 16,
  height: 16,
  collisionType: ex.CollisionType.Active,
  collisionGroup: PlayerGroup,
  color: ex.Color.Red,
})

player.vel.x = 10

export const trigger = new ex.Trigger({
  width: 16,
  height: 16,
  pos: ex.vec(100, 100),
  repeat: -1,
  action: () => {
    console.log('triggered')
  },
})
trigger.body.group = ex.CollisionGroup.collidesWith([PlayerGroup])