     func addPipes() {
         let pipe1Texture    = SKTexture(imageNamed: "pipe1.png")
         let pipe2Texture    = SKTexture(imageNamed: "pipe2.png")
-        let gap             = bird.size.height * 3
+        let gapHeight       = bird.size.height * 3
         let updown          = CGFloat(arc4random() % UInt32(self.frame.size.height / 2))
         let offset          = updown - self.frame.size.height / 4
 


        pipe1 = SKSpriteNode(texture: pipe1Texture)

        pipe1.position = CGPoint(x: CGRectGetMaxX(self.frame) + self.frame.size.width, y: CGRectGetMidY(self.frame) + pipe1Texture.size().height / 2 + gap / 2 + offset)
        pipe1.runAction(moveandRemove)

        pipe1.physicsBody = SKPhysicsBody(rectangleOfSize: pipe1Texture.size())

        pipe2.physicsBody?.collisionBitMask      = ColliderType.Object.rawValue

        self.addChild(pipe2)

        // Scoring gap

        let gap = SKSpriteNode(color: UIColor.whiteColor(), size: CGSizeMake(pipe1.size.width, gapHeight))

        gap.position = CGPoint(x: CGRectGetMidX(self.frame) + self.frame.size.width, y: CGRectGetMidY(self.frame) + offset)
        gap.runAction(moveandRemove)

        gap.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(pipe1.size.width, gapHeight))
        gap.physicsBody?.dynamic = false

        gap.physicsBody?.categoryBitMask       = ColliderType.Gap.rawValue
        gap.physicsBody?.contactTestBitMask    = ColliderType.Bird.rawValue
        gap.physicsBody?.collisionBitMask      = ColliderType.Gap.rawValue

        self.addChild(gap)
    }
}
