Quick particle question - what is the correct way to add an emitter to an actor?

[chrisk-7777]

Probably a simple question, but my smooth brain isn't working atm:

Works

const game = new ex.Engine({
  width: 400,
  height: 400
});

const emitter = new ex.ParticleEmitter({
  width: 10,
  height: 10,
  x: 10,
  y: 10,
  emitterType: ex.EmitterType.Rectangle,
  radius: 5,
  minVel: 100,
  maxVel: 200,
  minAngle: 0,
  maxAngle: 6.2,
  emitRate: 300,
  opacity: 0.5,
  fadeFlag: true,
  particleLife: 1000,
  maxSize: 10,
  minSize: 1,
  startSize: 5,
  endSize: 100,
  acceleration: ex.vec(10, 80),
  beginColor: ex.Color.Chartreuse,
  endColor: ex.Color.Magenta
});

game.start();
game.add(emitter)

Does not work

const game = new ex.Engine({
  width: 400,
  height: 400
});

const actor = new ex.Actor({
  anchor: ex.vec(0.5, 0.5),
  pos: game.screen.center,
  color: ex.Color.Red,
  radius: 5,
});

const emitter = new ex.ParticleEmitter({
  width: 10,
  height: 10,
  x: 10,
  y: 10,
  emitterType: ex.EmitterType.Rectangle,
  radius: 5,
  minVel: 100,
  maxVel: 200,
  minAngle: 0,
  maxAngle: 6.2,
  emitRate: 300,
  opacity: 0.5,
  fadeFlag: true,
  particleLife: 1000,
  maxSize: 10,
  minSize: 1,
  startSize: 5,
  endSize: 100,
  acceleration: ex.vec(10, 80),
  beginColor: ex.Color.Chartreuse,
  endColor: ex.Color.Magenta
});

game.start();
game.add(actor);
actor.addChild(emitter);

Link: https://codepen.io/chrisk7777/pen/poLroev?editors=0010

I note in the docs that it refers to actor.add() , but I think that might be out of date? So I'm taking a stab at addChild
https://excaliburjs.com/docs/particles

I'm happy to open a doc PR once its all sussed out.

Side question

I noticed in one of the issues that using the particleSprite may not be a good idea. Is that still the case?

[eonarheim]

@chrisk-7777 In theory adding an emitter as a child to an entity should work, very possibly a bug with particle emitters... I'm looking into it.

I think the docs are out of date for sure 👍

I think it's fine to use particleSprite now, the reason that message was there was in the past sprite modifications were expensive to animate. I think that's some stale information/documentation. Apologies, the particle emitter api is definitely one of the oldest in Excalibur and needs some work, it's definitely not the most friendly.

[eonarheim]

Can confirm, the ParticleEmitter has at least 2 bugs:

1. fix: [#2419] child entities inherit parent's scene #2430 fixes an issue in the latest alpha, which prevents the ParticleEmitter from adding particles to the current scene in v0.27.0
   

   a. To work around this in the non-alpha you could manually add the scene to the emitter emitter.scene = game.currentScene

2. There is another bug where it doesn't respect the parented transform when generating particles, so it will only generate particles in world space as if there was no parent entity. There is a possible workaround by setting the emitter position to be based on the parent.

   emitter.onPreUpdate = () => {
     emitter.pos = actor.pos;
   }
   

[chrisk-7777]

That's fantastic, works perfectly. I'll hold off until this alpha makes it to a release and I'll put together some docs (this also gives me time to get my head around it)

Updated codepen: https://codepen.io/chrisk7777/pen/poLroev?editors=0010

Thanks as always!

[eonarheim]

Awesome this looks super cool!

Almost forgot, but here is the bug #2437

[chrisk-7777]

Its amazing what you can with a few lines in excaliburjs.
I'm still getting my head around the sprite emitter, but I'll loop back to that in a bit

Thanks for the link to the bug