 
     // MARK: - Constants
 
+    private let fadeInDuration: NSTimeInterval = 1.0
     private let animationDuration: NSTimeInterval = 2.0
     private let animationDelay: NSTimeInterval = 0.5
 


        doubleTapGestureImageView.alpha = 0.0
        doubleTapGestureImageView.hidden = false
        UIView.animateWithDuration(1.0, animations: {
            self.doubleTapGestureImageView.alpha = 1.0
            }, completion: { _ in
                UIView.animateKeyframesWithDuration(self.animationDuration, delay: self.animationDelay, options: .Repeat, animations: {


        panGestureImageView.alpha = 0.0
        panGestureImageView.hidden = false
        UIView.animateWithDuration(fadeInDuration, animations: {
            self.panGestureImageView.alpha = 1.0
            }, completion: { _ in
                UIView.animateKeyframesWithDuration(self.animationDuration, delay: self.animationDelay, options: [.Autoreverse, .Repeat], animations: {
