将内部阴影添加到圈子（UIBezierPath）

Question

我尝试将内部阴影添加到使用UIBezierPath绘制的圆上。但是代码似乎不起作用（对于UIView是有效的）。只需要将阴影添加到圆的顶部即可。

func drawCircleWithShadow() {
    //Draw Circle
    let path = UIBezierPath(arcCenter: CGPoint(x: 100, y: 400), radius: 150, startAngle: 0, endAngle: 6.2831853072, clockwise: true)
    let shapeLayer = CAShapeLayer()
    shapeLayer.path = path.cgPath
    let lightRedColor = UIColor(red: 255.0/255.0, green: 87.0/255.0, blue: 51.0/255.0, alpha: 1)
    shapeLayer.strokeColor = lightRedColor.cgColor
    shapeLayer.fillColor = UIColor.white.cgColor
    shapeLayer.lineWidth = 2.0
    shapeLayer.position = CGPoint(x: 100, y: 100)
    self.view.layer.addSublayer(shapeLayer)

    let innerShadow = CALayer()
    innerShadow.frame = shapeLayer.frame

    //Draw Shadow Arc
    let shadowPath = UIBezierPath(arcCenter: CGPoint(x: 100, y: 400), radius: 150, startAngle: 3.1415926536, endAngle: 4.7123889804, clockwise: true)
    let cutout = shadowPath.reversing()
    shadowPath.append(cutout)
    innerShadow.shadowPath = shadowPath.cgPath
    innerShadow.masksToBounds = true
    innerShadow.shadowColor = UIColor.black.cgColor
    innerShadow.shadowOffset = CGSize(width: 0, height: 3)
    innerShadow.shadowOpacity = 0.15
    innerShadow.shadowRadius = 3
    shapeLayer.addSublayer(innerShadow)
}