The CAEmitterLayer class provides a particle emitter system for Core Animation. The particles are defined by instances of CAEmitterCell.
The particles are drawn above the layer’s background color and border.
var emitter = CAEmitterLayer()
emitter.emitterPosition = CGPoint(x: frame.size.width / 2.0, y: -20)
emitter.emitterShape = kCAEmitterLayerLine
emitter.emitterSize = CGSize(width: frame.size.width, height: 1)
emitter.emitterCells = cells
layer.addSublayer(emitter)