     
     /// flag that indicates if rotation is done with two fingers or one.
     /// when the chart is inside a scrollview, you need a two-finger rotation because a one-finger rotation eats up all touch events.
+    ///
+    /// On iOS this will disable one-finger rotation.
+    /// On OSX this will keep two-finger multitouch rotation, and one-pointer mouse rotation.
     /// 
     /// **default**: false
     public var rotationWithTwoFingers: Bool

    private var _decelerationDisplayLink: NSUIDisplayLink!
    private var _decelerationAngularVelocity: CGFloat = 0.0
    
    public override func nsuiTouchesBegan(touches: Set<NSUITouch>, withEvent event: NSUIEvent?)
    {
        // if rotation by touch is enabled

    {
        super.nsuiTouchesCancelled(touches, withEvent: event)
        
        processRotationGestureCancelled()
    }
    #endif
    
    #if os(OSX)
    public override func mouseDown(theEvent: NSEvent)
    {
        // if rotation by touch is enabled
        if rotationEnabled
        {
            stopDeceleration()
        
            let location = self.convertPoint(theEvent.locationInWindow, fromView: nil)
            
            processRotationGestureBegan(location: location)
        }
        
        if !_isRotating
        {
            super.mouseDown(theEvent)
        }
    }
    
    public override func mouseDragged(theEvent: NSEvent)
    {
        if rotationEnabled
        {
            let location = self.convertPoint(theEvent.locationInWindow, fromView: nil)
            
            processRotationGestureMoved(location: location)
        }
        
        if !_isRotating
        {
            super.mouseDragged(theEvent)
        }
    }
    
    public override func mouseUp(theEvent: NSEvent)
    {
        if !_isRotating
        {
            super.mouseUp(theEvent)
        }
        
        if rotationEnabled
        {
            let location = self.convertPoint(theEvent.locationInWindow, fromView: nil)
            
            processRotationGestureEnded(location: location)
        }
        
        if _isRotating
        {
            _isRotating = false
        }
    }
    #endif
    
    private func resetVelocity()
    {
