make vertical moving background - ios

Question

I'm beginner in Spritekit and I try to make background move vertically
I did know how
this what in the controller
class GameViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let scene = GameScene(size: view.bounds.size)
let skView = view as! SKView
skView.showsFPS = true
skView.showsNodeCount = true
skView.ignoresSiblingOrder = true
scene.scaleMode = .resizeFill
skView.presentScene(scene)
}
and this the scene
class GameScene: SKScene {
var background = SKSpriteNode()
override func didMove(to view: SKView) {
let backgroundTexture = SKTexture(imageNamed: "bbbgg.png")
let shiftBackground = SKAction.moveBy(x: 0, y: -backgroundTexture.size().height, duration: 5)
let replaceBackground = SKAction.moveBy(x: 0, y:backgroundTexture.size().height, duration: 0)
let movingAndReplacingBackground = SKAction.repeatForever(SKAction.sequence([shiftBackground,replaceBackground]))
for i in 1...3{
background=SKSpriteNode(texture:backgroundTexture)
background.position = CGPoint(x: 0, y: 0)
background.size.height = self.frame.height
background.run(movingAndReplacingBackground)
self.addChild(background)
}
}
}
the problem is the background move horizontally and after it arrives to the end of screen disappear, then begins move from the beginning of the screen again
I want it work vertically without disappearing

Answer 1

The background move horizontally because declarations of moveBy (shiftBackground, replaceBackground) works on the x axe (horizontally). You need to work on the y axe (vertically).
let shiftBackground = SKAction.moveBy(x: 0, y: -backgroundTexture.size().height, duration: 5)
let replaceBackground = SKAction.moveBy(x: 0, y: backgroundTexture.size().height, duration: 0)
At the first line, the background move from it position to it position - it height. At the second line, it return to it first position (I think moveBy is relative).
_
The background move again because you use the function SKAction.repeatForever (movingAndReplacingBackground). I think you can remove it.
let movingAndReplacingBackground = SKAction.sequence([shiftBackground,replaceBackground])
Edit :
I forget the loop.
In the loop, you give to the background an initial position.
background.position = CGPoint(x: backgroundTexture.size().width/2 + (backgroundTexture.size().width * CGFloat(i)), y: self.frame.midY)
Try to replace it by 0, middle if you want an immediately visible background
background.position = CGPoint(x: 0, y: self.frame.midY)
Or -height, 0 if you want the background appear by the top of the screen. In this case you need to replace shiftBackground and replaceBackground
background.position = CGPoint(x: -backgroundTexture.size().height, y: 0)
and
let shiftBackground = SKAction.moveBy(x: 0, y: backgroundTexture.size().height, duration: 5)
let replaceBackground = SKAction.moveBy(x: 0, y: 0, duration: 0)
I'm not sure, but I think, if you want only one mouvement, you can remove th sequence :
class GameScene: SKScene {
var background = SKSpriteNode()
override func didMove(to view: SKView) {
let backgroundTexture = SKTexture(imageNamed: "bbbgg.png")
let scrollByTopBackground = SKAction.moveBy(x: O, y: backgroundTexture.size().height, duration: 5)
background = SKSpriteNode(texture:backgroundTexture)
background.position = CGPoint(x: -backgroundTexture.size().height, y: self.frame.midY)
background.size.height = self.frame.height
background.run(scrollByTopBackground)
self.addChild(background)
}
}
Edit to answer you, try this...
class GameScene: SKScene {
var background = SKSpriteNode()
override func didMove(to view: SKView) {
let backgroundTexture = SKTexture(imageNamed: "bbbgg.png")
let shiftBackground = SKAction.moveBy(x: 0, y: -backgroundTexture.size().height, duration: 5)
let replaceBackground = SKAction.moveBy(x: 0, y:backgroundTexture.size().height, duration: 0)
let movingAndReplacingBackground = SKAction.repeatForever(SKAction.sequence([shiftBackground,replaceBackground]))
for i in 0...2 {
background=SKSpriteNode(texture:backgroundTexture)
background.position = CGPoint(x: 0, y: self.frame.midY + (backgroundTexture.size().height * CGFloat(i)))
background.size.height = self.frame.height
background.run(movingAndReplacingBackground)
self.addChild(background)
}
}