     let layer:CALayer
     let maskColor:UIColor?
     let fPlus:Bool
+}
+
+private enum BackgroundMode: Int {
+    case checker = 0
+    case black = 1
+    case white = 2
+    case limit = 3
 }
 
 protocol SNTrimControllerDelegate : class {

    
    @IBAction func switchBackground() {
        print("switchBackground")
    }
    
    @IBAction func undo() {

        }
        checkerImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        let temp = backgroundMode
        backgroundMode = .limit
        backgroundMode = temp
    }

    override func didReceiveMemoryWarning() {
