Mask.swift

// You'll need this https://gist.github.com/jorgenisaksson/76a8dae54fd3dc4e31c2

extension NSBezierPath {
    func toCGPath () -> CGPath? {
        if self.elementCount == 0 {
            return nil
        }

        let path = CGPathCreateMutable()
        var didClosePath = false

        for i in 0...self.elementCount-1 {
            var points = [NSPoint](count: 3, repeatedValue: NSZeroPoint)

            switch self.elementAtIndex(i, associatedPoints: &points) {
            case .MoveToBezierPathElement:CGPathMoveToPoint(path, nil, points[0].x, points[0].y)
            case .LineToBezierPathElement:CGPathAddLineToPoint(path, nil, points[0].x, points[0].y)
            case .CurveToBezierPathElement:CGPathAddCurveToPoint(path, nil, points[0].x, points[0].y, points[1].x, points[1].y, points[2].x, points[2].y)
            case .ClosePathBezierPathElement:CGPathCloseSubpath(path)
            didClosePath = true;
            }
        }

        if !didClosePath {
            CGPathCloseSubpath(path)
        }

        return CGPathCreateCopy(path)
    }
}

var isFirst = false {
        didSet {
            if isFirst {
                let mask = NSBezierPath(roundedRect: NSRect(x: 0, y: 0, width: self.frame.width, height: self.frame.height + 10), xRadius: 10.0, yRadius: 10.0)
                mask.fill()
                let maskShape = CAShapeLayer()
                maskShape.path = mask.toCGPath()
                self.layer?.mask = maskShape
            } else {
                
            }
        }
    }