iOS - 从底部填充 UIBezierPath 的动画

我有一个UIBezierPath内部定制UIView, draw()。我想填充该路径，假设从下到上是一个矩形。我怎样才能实现这个。

From Here http://jamesonquave.com/blog/fun-with-cashapelayer/我见过使用CAShapeLayer这是可能的。这对于动画来说效果很好，但是矩形上的填充没有从下到上发生。请指导。

这就是你所要求的吗？

func zoom() {
    let startPath = UIBezierPath(rect: CGRect(x: 0, y: self.frame.size.height-30, width: self.frame.size.width, height: 30))
    let endPath = UIBezierPath(rect: CGRect(x: 0, y: 0, width: self.frame.size.width, height: self.frame.size.height))

    let rectangleLayer = CAShapeLayer()
    rectangleLayer.path = startPath.cgPath
    rectangleLayer.fillColor = UIColor.cyan.cgColor
    self.layer.addSublayer(rectangleLayer)

    let zoomAnimation = CABasicAnimation()
    zoomAnimation.keyPath = "path"
    zoomAnimation.duration = 2.0
    zoomAnimation.toValue = endPath.cgPath
    zoomAnimation.fillMode = kCAFillModeForwards
    zoomAnimation.isRemovedOnCompletion = false
    rectangleLayer.add(zoomAnimation, forKey: "zoom")
}