Particles2D don't disable emitting after one-shot, when starting off-screen

[KoBeWi]

Godot version:
3.2 alpha2

Issue description:
When you create Particles2D, enable one_shot and start emitting when particles are outside visible radius, the emitting is never disabled and will start only when particles are again on screen. This is annoying, because I wan't to e.g. play explosion, but are too far to see it and then it will happen when I get close, even though it should be already finished. One shot should affect emitting whether particles are rendering or not.

Steps to reproduce:

1. Create Particles2D
2. Enable one_shot
3. Pan viewport away from particles
4. Enable emitting
5. Wait a bit
6. Pan to particles again
7. They will start emitting only then :<

[Ranoller]

Maybe related: #18242

[KoBeWi]

Still valid in 3.2.3
Will test in 4.0 when 2D particles are reintroduced.

[KoBeWi]

Still valid™ in 26b86c1

[Calinou]

Related to #17903.

Can you reproduce this with GPUParticles3D located outside the camera frustum?

[KoBeWi]

Yeah, same issue in 3D

[vfreitas-]

Still valid in 3.4.4-stable. Having the same issue =/

To help anybody with this issue:

To fix it I added a VisibilityNotifier2D to my explosion scene (where the Particles2D is the root) and changed my code to queue_free the scene if not emitting or if not on the screen.

func _ready():
	emitting = true
	one_shot = true
	
func _process(_delta):
	if not emitting or not $VisibilityNotifier2D.is_on_screen():
		queue_free()

Worked well for my case.

[svendixon]

I'm not sure this is really an issue. I know it seems like it's broken, it tripped me up.

But I think you should be using the particles visibility_rect for 2D, and visibility_aabb for 3D, here. This is what it's for. Your particle will run even if you go off screen and come back depending on how large the rect is. It's a bit silly, but one_shot particles in particular should probably have an almost infinitely large rect so the particle can run and finish even when it's far off the screen.

Performance shouldn't really be much of an issue here because they're one_shot particles that stop emitting after their lifetime ends and you can then queue_free() them if you want. However, if you have something generating these particles off screen, and you're worried about performance, you can use a VisibilityNotifier2D for 2D, or VisibilityNotifier for 3D, so they don't continue to create the particles when they themselves are off screen.

[KoBeWi]

Seems like #20160 is related.