//这里的lazy：是懒加载 就是OC中重写get，set方法 
lazy var waveDisplaylink = CADisplayLink()//相比NSTimer下，这里用CADisplayLink主要是精确点，其频率：1/60 
lazy var firstWaveLayer = CAShapeLayer() 
lazy var secondWaveLayer = CAShapeLayer() 
/// 基础描述 正弦函数 
///  y=Asin(ωx+φ）+ b 
///  A : wavaA 
///  w : 1/waveW 
///  φ : offsetφ 
///  b : b 
private var waveA: CGFloat = 0 
private var waveW: CGFloat = 0 
private var offsetX: CGFloat = 0 
private var b : CGFloat = 0 
//水纹的移动的速度 
var waveSpeed : CGFloat = 0 

//MARK: - 数据的初始化 
private func initData(){ 
  waveSpeed = 0.05 
  waveA = 8 
  // 设置周期 :( 2* M_PI)/waveW = bounds.size.width 。因为涉及的是layer，所以只谈bounds,不说frame 
  waveW = 2 * CGFloat(M_PI) / bounds.size.width 
  b = bounds.size.height / 2 
} 

private func configUI(){ 
   firstWaveLayer.fillColor = UIColor.init(colorLiteralRed: 69/255.0, green: 255/255.0, blue: 255/255.0, alpha: 0.5).cgColor 
   secondWaveLayer.fillColor = UIColor.init(colorLiteralRed: 69/255.0, green: 255/255.0, blue: 255/255.0, alpha: 0.5).cgColor 
   layer.addSublayer(firstWaveLayer) 
   layer.addSublayer(secondWaveLayer) 
   waveDisplaylink = CADisplayLink(target: self, selector: #selector(getCurrentWave)) 
   waveDisplaylink.add(to: RunLoop.current, forMode: .commonModes) 
 } 

@objc private func getCurrentWave() { 
  offsetX += waveSpeed 
  setCurrentStatusWavePath() 
} 
//MARK: - 关键部分 
private func setCurrentStatusWavePath() { 
  // 创建一个路径 
  let firstPath = CGMutablePath() 
  var firstY = bounds.size.width/2 
  firstPath.move(to: CGPoint(x: 0, y: firstY)) 
  for i in 0...Int(bounds.size.width) { 
    firstY = waveA * sin(waveW * CGFloat(i) + offsetX) + b 
    firstPath.addLine(to: CGPoint(x: CGFloat(i), y: firstY)) 
  } 
   
  firstPath.addLine(to: CGPoint(x: bounds.size.width, y: bounds.size.height)) 
  firstPath.addLine(to: CGPoint(x: 0, y: bounds.size.height)) 
  firstPath.closeSubpath() 
  firstWaveLayer.path = firstPath 
   
  // 创建一个路径 
  let secondPath = CGMutablePath() 
  var secondY = bounds.size.width/2 
  secondPath.move(to: CGPoint(x: 0, y: secondY)) 
   
  for i in 0...Int(bounds.size.width) { 
    secondY = waveA * sin(waveW * CGFloat(i) + offsetX - bounds.size.width/2 ) + b 
    secondPath.addLine(to: CGPoint(x: CGFloat(i), y: secondY)) 
  } 
  secondPath.addLine(to: CGPoint(x: bounds.size.width, y: bounds.size.height)) 
  secondPath.addLine(to: CGPoint(x: 0, y: bounds.size.height)) 
  secondPath.closeSubpath() 
  secondWaveLayer.path = secondPath 
}