随着精灵向上移动，屏幕上会出现更多跳跃垫

Question

我正在尝试制作类似涂鸦跳跃的游戏。我想做到这一点，作为一个精灵，我的主角，在某个Y点之上移动，出现更多的跳跃垫，给它一种跳跃越来越高的错觉。

我该怎么做呢？任何例子都会很好。我在Xcode 7中使用SpriteKit。

到目前为止，这是我的代码：

import SpriteKit
import Foundation

class GameScene: SKScene {

    var mainSprite = SKSpriteNode()

    var wallPair = SKNode()

    var ground = SKSpriteNode()

    var moveAndRemove = SKAction()

    override func didMoveToView(view: SKView) {
        /* Setup your scene here */
        mainSprite.size = CGSize(width: 30, height: 30)
        mainSprite.color = SKColor.redColor();
        mainSprite.position = CGPoint(x: self.frame.width / 2, y: self.frame.height / 2 - 100)
        self.addChild(mainSprite)

        ground.size = CGSize(width: self.frame.width, height: 300)
        ground.color = SKColor.brownColor()
        ground.position = CGPoint(x: self.frame.width / 2, y: 0)
        self.addChild(ground)


    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
       /* Called when a touch begins */
        createWallMap()


        for touch in touches {
            let location = touch.locationInNode(self)


        }
    }

    override func update(currentTime: CFTimeInterval) {
        /* Called before each frame is rendered */
    }

    func createWalls(height: CGFloat) {
        wallPair = SKNode()
        wallPair.name = "wallPair"
        let rightWall = SKSpriteNode(imageNamed: "LeftWall.png") // I know it is opposite. Named the image wrong
        let leftWall = SKSpriteNode(imageNamed: "RightWall.png")
        rightWall.setScale(0.9)
        leftWall.setScale(0.9)
        rightWall.color = SKColor.redColor()
        leftWall.color = SKColor.blueColor()
        rightWall.position = CGPoint(x: self.frame.width / 2 + 340, y: height)
        leftWall.position = CGPoint(x: self.frame.width / 2 - 340, y: height)
        wallPair.addChild(rightWall)
        wallPair.addChild(leftWall)
        let randomPosition = CGFloat.random(min: -140, max: 140)
        wallPair.position.x = wallPair.position.x + randomPosition
        //wallPair.runAction(moveAndRemove)

        self.addChild(wallPair)
    }