Я считаю, что анимация Siri создается с помощью CAEmitterLayer и CAEmitterCell, а затем анимируется с помощью основной анимации, но я могу быть совершенно неправ. Вот некоторый код, который имитирует эффект:
// create emitter layer
self.emitterLayer = [CAEmitterLayer layer];
self.emitterLayer.frame = CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height);
self.emitterLayer.emitterMode = kCAEmitterLayerOutline;
self.emitterLayer.emitterShape = kCAEmitterLayerLine;
self.emitterLayer.renderMode = kCAEmitterLayerAdditive;
[self.emitterLayer setEmitterSize:CGSizeMake(4, 4)];
// create the ball emitter cell
CAEmitterCell *ball = [CAEmitterCell emitterCell];
ball.color = [[UIColor colorWithRed:111.0/255.0 green:80.0/255.0 blue:241.0/255.0 alpha:0.10] CGColor];
ball.contents = (id)[[UIImage imageNamed:@"ball.png"] CGImage]; // ball.png is simply an image of white circle
[ball setName:@"ball"];
self.emitterLayer.emitterCells = [NSArray arrayWithObject:ball];
[self.view.layer addSublayer:self.emitterLayer];
float factor = 1.5; // you should play around with this value
[self.emitterLayer setValue:[NSNumber numberWithInt:(factor * 500)] forKeyPath:@"emitterCells.ball.birthRate"];
[self.emitterLayer setValue:[NSNumber numberWithFloat:factor * 0.25] forKeyPath:@"emitterCells.ball.lifetime"];
[self.emitterLayer setValue:[NSNumber numberWithFloat:(factor * 0.15)] forKeyPath:@"emitterCells.ball.lifetimeRange"];
// animation code
CAKeyframeAnimation* circularAnimation = [CAKeyframeAnimation animationWithKeyPath:@"emitterPosition"];
CGMutablePathRef path = CGPathCreateMutable();
CGRect pathRect = CGRectMake(0, 0, 200, 200); // define circle bounds with rectangle
CGPathAddEllipseInRect(path, NULL, pathRect);
circularAnimation.path = path;
CGPathRelease(path);
circularAnimation.duration = 2;
circularAnimation.repeatDuration = 0;
circularAnimation.repeatCount = 3;
circularAnimation.calculationMode = kCAAnimationPaced;
[self.emitterLayer addAnimation:circularAnimation forKey:@"circularAnimation"];
Классы CAEmitterCell и CAEmitterLayer имеют много свойств, поэтому обратитесь к документации для получения дополнительной информации.