/// 聚光灯效果的遮罩class SpotlightFilterMaskLayer : CALayer {
    /// 坡度的宽度    var gradientWidth: CGFloat = 40.0
    /// 直径    var diameter: CGFloat = 0 {        didSet {            setNeedsDisplay()        }    }        override func draw(in ctx: CGContext) {        let origin: CGPoint = CGPoint(x: self.bounds.midX, y: self.bounds.midY)                let clearRegionRadius: CGFloat = self.diameter * 0.5        let blurRegionRadius: CGFloat = clearRegionRadius + gradientWidth
        // 创建颜色空间        let baseColorSpace = CGColorSpaceCreateDeviceRGB();        let colours : [CGFloat] = [0.0, 0.0, 0.0, 1,                                   0.0, 0.0, 0.0, 0.2]        let colourLocations : [CGFloat] = [0, 1]                // 创建渐变对象        // - colorSpace: 颜色空间        // - colorComponents: 颜色分量的强度值数组        // - locations: 渐变系数数组        // - count: 设置的渐变系数数组的元素个数        guard let gradient = CGGradient(colorSpace: baseColorSpace,                                        colorComponents: colours,                                        locations: colourLocations,                                        count: 2) else {            return        }
        // 绘制渐变        // - gradient: 渐变对象        // - startCenter: 起点        // - startRadius: 径向半径        // - endCenter: 终点        // - endRadius: 径向半径        // - options: 渐变模式        //   - .drawsBeforeStartLocation 表示向里发散        //  - .drawsAfterEndLocation 表示向外发散        ctx.drawRadialGradient(gradient,                               startCenter: origin,                               startRadius: clearRegionRadius,                               endCenter: origin,                               endRadius: blurRegionRadius,                               options: .drawsBeforeStartLocation);
        ctx.drawPath(using: .fill)    }}

imageView.layer.mask = maskLayer

func begin() {    let fromValue = imageView.bounds    let animation = CABasicAnimation(keyPath: "bounds")    animation.fromValue = fromValue    animation.toValue = CGRect(x: fromValue.origin.x - 100,                               y: fromValue.origin.y - 100,                               width: fromValue.size.width + 200,                               height: fromValue.size.height + 200)
    animation.duration = 1    animation.autoreverses = true    animation.repeatCount = MAXFLOAT    animation.isRemovedOnCompletion = false    maskLayer.add(animation, forKey: nil)}