         
     }
     
-    //MARK: White StatusBar : better look
+    //MARK: White StatusBar : just for a better look
     override func preferredStatusBarStyle() -> UIStatusBarStyle {
         return .LightContent
     }

        
        //add observers to stop and resume your animation when application goes background
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "resumeanimation:", name: UIApplicationDidBecomeActiveNotification, object: nil)
        
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "stopanimation:", name: UIApplicationDidEnterBackgroundNotification, object: nil)

    }

class ViewController: UIViewController {

    let DEFAULT_BACKGROUND_IMAGE = "2801-11"
    let REFERENCE_ANIMATION_DURATION = 40
    let REFERENCE_ANIMATION_FAST_RETURN_DURATION = 3
    let REFERENCE_MAX_TRAILING_CONTRAINT_CONSTANT = -400
    
    
    enum direction
    {
