这是启动和停止粒子系统的正确方法吗？

Question

I'm currently practicing with particle systems and I was wondering if the following code is the right way to stop and start a particle when a button is tapped?

The code works fine, I touch the start button and the particle starts, I touch the stop button and the particle stops but I'm not sure if removeFromSuperLayer is the right method to use. As I said, the code does what I need but I just want to make sure that the particle won't keep running in the background even after calling removeFromSuperLayer and end-up wasting resources.

- (IBAction)stopAnimation:(id)sender
{
    [emitterLayer removeFromSuperlayer];
}

- (IBAction)startAnimation:(id)sender
{
    [self particle];
}

-(void) particle
{
    emitterLayer = [CAEmitterLayer layer]; 
    emitterLayer.emitterPosition = CGPointMake(50 ,50); 
    emitterLayer.emitterZPosition = 10; 
    emitterLayer.emitterSize = CGSizeMake(10,10); 
    emitterLayer.emitterShape = kCAEmitterLayerSphere; 

    CAEmitterCell *emitterCell = [CAEmitterCell emitterCell]; 
    emitterCell.scale = 0.1; 
    emitterCell.scaleRange = 0.2; 
    emitterCell.emissionRange = (CGFloat)M_PI_2; 
    emitterCell.lifetime = 10; 
    emitterCell.birthRate = 5; 
    emitterCell.velocity = 20; 
    emitterCell.velocityRange = 50; 
    emitterCell.yAcceleration = 0; 

    emitterCell.contents = (id)[[UIImage imageNamed:@"particleImage.png"] CGImage]; 
    emitterLayer.emitterCells = [NSArray arrayWithObject:emitterCell]; 

    [self.view.layer addSublayer:emitterLayer]; 
}

Thanks a lot

Answer 1

You could use a method in which you put the following:

- (void)stopEmitting
{   
    self.emitterCell.birthRate = 0.0f;
}

With this you should be able to stop the emitting, without having to remove and re-create the layer each time when the start button is pressed.

To start again, simply do:

- (void)startEmitting
{
    self.emitterCell.birthRate = <VAlUE HERE (greater than 0)>;
}

Hope this helps.

Answer 2

It's funny but just modifying the birthRate like this self.emitterCell.birthRate = 0.0f; in a method doesn't stop the emitterCell, in fact it looks like if it appends instead of stopping it, in other words if I change it to self.emitterCell.birthRate = 100; it adds 100 more particles to the existing particles. Lucky I found the solution.

I basically had to give my emitterCell a name emitterCell.name = @"_myCell"; and then in my stop method modify it like this [emitterLayer setValue:[NSNumber numberWithInteger:0] forKeyPath:@"emitterCells._myCell.birthRate"]; and it worked.

This is what I did that worked. This is assuming you already have an image in your project named myImage.

#import "SpriteViewController.h"

@implementation SpriteViewController

CAEmitterLayer *emitterLayer;

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)stopAnimation:(id)sender
{
    [emitterLayer setValue:[NSNumber numberWithInteger:0] forKeyPath:@"emitterCells._myCell.birthRate"]; // new code
}

- (IBAction)startAnimation:(id)sender
{
    [self particle];
}

-(void) particle
{
    emitterLayer = [CAEmitterLayer layer];
    emitterLayer.emitterPosition = CGPointMake(50 ,50);
    emitterLayer.emitterZPosition = 10;
    emitterLayer.emitterSize = CGSizeMake(10,10);
    emitterLayer.emitterShape = kCAEmitterLayerSphere;

    CAEmitterCell *emitterCell = [CAEmitterCell emitterCell];
    emitterCell.name = @"_myCell";// new code
    emitterCell.scale = 0.1;
    emitterCell.scaleRange = 0.2;
    emitterCell.emissionRange = (CGFloat)M_PI_2;
    emitterCell.lifetime = 10;
    emitterCell.birthRate = 5;
    emitterCell.velocity = 20;
    emitterCell.velocityRange = 50;
    emitterCell.yAcceleration = 0;

    emitterCell.contents = (id)[[UIImage imageNamed:@"myImage.png"] CGImage];
    emitterLayer.emitterCells = [NSArray arrayWithObject:emitterCell];

    [self.view.layer addSublayer:emitterLayer];
}
@end

Answer 3

Rather than change the birthRate of the each of the emitterCells you can change the birthrate of the emitterLayer itself.

- (void)stopEmitting
{   
    self.emitterLayer.birthRate = 0;
}

- (void)startEmitting
{
    self.emitterLayer.birthRate = 1;
}