CAEmitterLayer emits random unwanted particles on touch events

Question

I'm trying to set up a CAEmitterLayer to make a confetti effect, and I've run into two issues:

1. Whenever I set the birthRate on my cells to something non-zero to start the animation I get a flurry of cells placed randomly on screen, which animate normally, and then the emitter continues to emit properly after that.
2. Whenever the emitterCells are drawing things on screen, any time I touch the screen, the emitter draws emitterCells in (seemingly) random locations that exist for a (seemingly) random amount of time. Nothing in the emitter is tied to any touch events (i.e. I'm not intentionally drawing anything on a touch event), but the layer is in a view that has multiple embedded views. The more I touch, the more cells show up.

Here's my code for setting up the emitter, and then starting and stopping it (once I've called the stop function, then taps on the screen cease creating new random elements):

- (void)setupConfetti
{
    self.confettiLayer = [CAEmitterLayer layer];
    [self.view.layer addSublayer:self.confettiLayer];
    [self.view.layer setNeedsDisplay];

    self.confettiLayer.emitterPosition = CGPointMake(1024.0/2,-50.0);
    self.confettiLayer.emitterSize = CGSizeMake(1000.0, 10.0);
    self.confettiLayer.emitterShape = kCAEmitterLayerLine; 
    self.confettiLayer.renderMode =kCAEmitterLayerUnordered;

    CAEmitterCell *confetti = [CAEmitterCell emitterCell];

    confetti1.contents =  (id)[[UIImage imageNamed:@"confetti.png"] CGImage];

    confetti.emissionLongitude = M_PI;
    confetti.emissionLatitude = 0;
    confetti.lifetime = 5;
    confetti.birthRate = 0.0;
    confetti.velocity = 125;
    confetti.velocityRange = 50;
    confetti.yAcceleration = 50;
    confetti.spin = 0.0;
    confetti.spinRange = 10;
    confetti.name = @"confetti1";

    self.confettiLayer.emitterCells = [NSArray arrayWithObjects:confetti, nil];
}

To start the confetti:

- (void)startConfettiAnimation
{
    [self.confettiLayer setValue:[NSNumber numberWithInt:10.0] forKeyPath:@"emitterCells.confetti.birthRate"];
}

And to stop it:

- (void)stopConfettiAnimation
{
    [self.confettiLayer setValue:[NSNumber numberWithInt:0.0] forKeyPath:@"emitterCells.confetti.birthRate"];
}

Again, once it gets started, after the initial flurry of random elements, this works just fine: everything animates normally, and when the birthRate is later set to zero, it ends gracefully. It just seems to respond to touch events, and I have no idea why. I've tried adding the emitterLayer to a different view, disabling user interaction on that view, and then adding it as a subview of the main view, and that didn't seem to work.

Any help/insight would be much appreciated!

Thanks, Sam

Answer 1

I know this is an old post, but I also had this problem. Jackslash answers it well in this post: iOS 7 CAEmitterLayer spawning particles inappropriately

You need to set beginTime on your emitter layer to begin at the current time with CACurrentMediaTime(). It seems the problem we have occurs because the emitter started already in the past.

emitter.beginTime = CACurrentMediaTime();

Answer 2

Could it be that you aren't checking to see if the particle is emitting like in the Wenderlich example Artur Ozieranski posted? I'm not seeing the doubling as long as the check is in place.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    [fireView setEmitterPositionFromTouch: [touches anyObject]];
    [fireView setIsEmitting:YES];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [fireView setIsEmitting:NO];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
    [fireView setIsEmitting:NO];
}
-(void)setIsEmitting:(BOOL)isEmitting
{
    //turn on/off the emitting of particles
    [fireEmitter setValue:[NSNumber numberWithInt:isEmitting?200:0] forKeyPath:@"emitterCells.fire.birthRate"];
}