iOS CAEmitterCell trail

[moonman239]

So I have decided to build my star burst animation from the ground up using Core Animation. I have a bunch of little stars, created using a CAEmitterCell, that come out of this bigger star. What I want to do is have each little star leave a trail as it goes along. I know I can draw a CGPath on a UIView.

Edit: Found my answer: Just create another emitter cell for the trail, and add it to the existingCells property of the first emitter cell.

 

[moonman239]

I got it working (sort of). What I need to do now is make it so that the first emitter cell's emitter emits the trail particles so that the trail particles don't go over the star. I'm thinking I can do this by setting the first emitter cell's emitterLatitude and/or emitterLongitude properties.

Here's my code:

    CALayer *viewLayer = [self.view layer];
    // Create a particle emission layer and set its properties.
    layer = [CAEmitterLayer layer];
    NSString *imagePath = [[NSBundle mainBundle] pathForResource:@"star copy" ofType:@"png"];
    UIImage *image = [UIImage imageWithContentsOfFile:imagePath];
    id cgimage = (__bridge id)[image CGImage];
    [[layer contents] addObject:cgimage];
    CGRect rect = viewLayer.frame;
    [layer setFrame:rect];
    layer.emitterPosition = layer.position; //
    layer.emitterSize = [image size];
    layer.emitterShape = kCAEmitterLayerCircle;
    layer.lifetime = 3;
    // Create an emitter cell for the little stars.
    CAEmitterCell *emitterCell = [CAEmitterCell emitterCell];
    emitterCell.contents = cgimage;
    emitterCell.birthRate = 4;
    emitterCell.lifetime = 2;
    emitterCell.lifetimeRange = 1;
    emitterCell.velocity = 300;
    emitterCell.velocityRange = 20;
    emitterCell.emissionRange = M_PI * 2.0f;
    // Create the trail.
    CAEmitterCell *trailEmitterCell = [CAEmitterCell emitterCell];
    trailEmitterCell.velocity = 0;
    trailEmitterCell.birthRate = 50;
    trailEmitterCell.lifetime = 0.2;
    trailEmitterCell.emissionRange = 1.0f;
    NSString *trailImagePath = [[NSBundle mainBundle] pathForResource:@"r" ofType:@"png"];
    id trailImage = (__bridge id)[[UIImage imageWithContentsOfFile:trailImagePath] CGImage];
    trailEmitterCell.contents = trailImage;
    [emitterCell setEmitterCells:[NSArray arrayWithObject:trailEmitterCell]];
    layer.emitterCells = [NSArray arrayWithObject:emitterCell];
    [viewLayer addSublayer:layer];