Swift：如何用外面的颜色填充CAShapeLayer圈？

Question

好吧，我对CAShapeLayer很新，但我需要知道如何填充一个CAShapeLayer圆圈，其颜色从外部轮廓开始，然后像这样进入中心 -

我正在使用教程中的修改来绘制我的圈子：

SCM_RIGHTS

然后我像这样添加CircleView -

var circleLayer: CAShapeLayer!

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.backgroundColor = UIColor.clearColor()

        // Use UIBezierPath as an easy way to create the CGPath for the layer.
        // The path should be the entire circle.
        let circlePath = UIBezierPath(arcCenter: CGPoint(x: frame.size.width / 2.0, y: frame.size.height / 2.0), radius: (frame.size.width - 10)/2, startAngle: 0.0, endAngle: CGFloat(M_PI * 2.0), clockwise: true)

        // Setup the CAShapeLayer with the path, colors, and line width
        circleLayer = CAShapeLayer()
        circleLayer.path = circlePath.CGPath
        circleLayer.fillColor = UIColor.clearColor().CGColor
        circleLayer.strokeColor = UIColor.whiteColor().CGColor
        circleLayer.lineWidth = 1.5;

        // Don't draw the circle initially
        circleLayer.strokeEnd = 0.0

        // Add the circleLayer to the view's layer's sublayers
        layer.addSublayer(circleLayer)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func animateCircle(duration: NSTimeInterval) {
        // We want to animate the strokeEnd property of the circleLayer
        let animation = CABasicAnimation(keyPath: "strokeEnd")

        // Set the animation duration appropriately
        animation.duration = duration

        // Animate from 0 (no circle) to 1 (full circle)
        animation.fromValue = 0
        animation.toValue = 1

        // Do a linear animation (i.e. the speed of the animation stays the same)
        animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionLinear)

        // Set the circleLayer's strokeEnd property to 1.0 now so that it's the
        // right value when the animation ends.
        circleLayer.strokeEnd = 1.0

        // Do the actual animation
        circleLayer.addAnimation(animation, forKey: "animateCircle")
    }

}