animating the CAEmitterCell Color property

Question

I have a CAEmitterCell and I have set it up with a specific colour. The documentation says that this property is animatable, and I would like to animate this between a number of different colours for the different players in my game (all of whom choose their color at the start).

Here is my EmitterCell when I set it up:

//
    // Emitter Cells
    //

    // 'New Emitter' cell configuration
    newEmitter = [CAEmitterCell emitterCell];
    newEmitter.scaleSpeed = 10;
    newEmitter.lifetime = 2.481715;
    newEmitter.velocity = 332.3636968085106;
    newEmitter.contents = newemitterImg;
    newEmitter.name = @"New Emitter";
    newEmitter.color = [[UIColor colorWithRed:0.50 green:0.00 blue:1.00 alpha:1.00] CGColor];
    newEmitter.scaleRange = 4.178236607142859;
    newEmitter.lifetimeRange = 1.6;
    newEmitter.greenRange = -2.775558e-17;
    newEmitter.birthRate = 40;
    newEmitter.emissionRange = -6.283185306666667;
    newEmitter.scale = 0;

    //
    // Emitter Cell Chains
    //
    emitter.emitterCells = [NSArray arrayWithObjects:newEmitter, nil];

And here is where I am testing the color change in this case just bouncing between two different colors:

-(void)changeColor {

    if (color == 0) {
        color = 1;
        NSLog(@"color = 1");

        [UIView animateWithDuration:1.5 delay:0 options:0 animations:^{
            newEmitter.color = [[UIColor colorWithRed:0.50 green:0.00 blue:1.00 alpha:1.00] CGColor];
        } completion:^(BOOL finished) {[self performSelector:@selector(changeColor) withObject:nil afterDelay:2];}];
    } else {
        color = 0;
        NSLog(@"color = 0");
        [UIView animateWithDuration:1.5 delay:0 options:0 animations:^{
            newEmitter.color = [[UIColor colorWithRed:1.00 green:0.50 blue:0.10 alpha:1.00] CGColor];
        } completion:^(BOOL finished) {[self performSelector:@selector(changeColor) withObject:nil afterDelay:2];}];
    }

}

However, when I run this the color never changes. Have I misunderstood the nature of "Animatable" here, or do I just need to go about it differently for a CAEmitterCell?

Answer 1

CAEmitterCells are, in fact, different. To get animations working on them, you need to take these steps:

1.Assign a name to your CAEmitterCell, e.g.:

newEmitter.name = @"fire";

2.Access the animation property for this emitter through the CAEmitterLayer instance:

//Set first before doing CABasicAnimation so it sticks
newEmitter.redSpeed = 1.0;

//Access the property with this key path format: @"emitterCells.<name>.<property>"
CABasicAnimation *anim = [CABasicAnimation animationWithKeyPath:@"emitterCells.fire.redSpeed"];
anim.fromValue = @(0.0);
anim.toValue = @(1.0);
anim.duration = 1.5;
anim.fillMode = kCAFillModeForwards;
[emitter addAnimation:anim forKey:@"emitterAnim"];