Swift Spritekit Scrolling Background - ios

Question

I am trying to find the best method to do a vertically scrolling background in Swift,
without using the Update Method. The Background is 1 Image that should loop infinite.
The Image should be in the middle of the screen (full-size), moving down, and on top of that image should always be another image spawned.
However, mine doesn't work quite right, it spawns 2 images, and than after a delay they pop up and start the Actions again.
Also, it breaks sometimes down from 30 FPS to 26, which I want to avoid.
I hope somebody, who is more into Swift can help me.
let Background = SKTexture(imageNamed: "Background.png")
Background.filteringMode = .Nearest
let BackgroundMove = SKAction.moveByX(0, y: -self.frame.size.height, duration: 10)
let BackgroundReset = SKAction.moveByX(0, y: self.frame.size.height, duration: 0.0)
let BackgroundMoveAndResetForever = SKAction.repeatActionForever(SKAction.sequence([BackgroundMove,BackgroundReset]))
for var i:CGFloat = 0; i < 2.0 + self.frame.size.height / (Background.size().height * 2); ++i {
let sprite = SKSpriteNode(texture: Background)
sprite.size = CGSize(width: self.frame.size.width / 2, height: self.frame.size.height)
sprite.position = CGPointMake(self.frame.size.width / 2, self.frame.size.height / 2 * i)
sprite.zPosition = 1
sprite.runAction(BackgroundMoveAndResetForever)
self.addChild(sprite)
}

Answer 1

This is the code I used to make a background that moves right to left across the screen. It used a loop to generate three backgrounds, all of which formed a line which passed through the screen and returned to their original position when they were done. To convert it to a screen that moves top to bottom, you would have to replace the moveByX SKActions to moveToY, and exchange changing x values with changing y values. Hope this helps!
func makeBackground() {
var backgroundTexture = SKTexture(imageNamed: "img/bg.png")
//move background right to left; replace
var shiftBackground = SKAction.moveByX(-backgroundTexture.size().width, y: 0, duration: 9)
var replaceBackground = SKAction.moveByX(backgroundTexture.size().width, y:0, duration: 0)
var movingAndReplacingBackground = SKAction.repeatActionForever(SKAction.sequence([shiftBackground,replaceBackground]))
for var i:CGFloat = 0; i<3; i++ {
//defining background; giving it height and moving width
background=SKSpriteNode(texture:backgroundTexture)
background.position = CGPoint(x: backgroundTexture.size().width/2 + (backgroundTexture.size().width * i), y: CGRectGetMidY(self.frame))
background.size.height = self.frame.height
background.runAction(movingAndReplacingBackground)
self.addChild(background)
}
}

Answer 2

I wrote this one... It's probably not as short as it could be, but it only uses 2 copies of the image, unlike the one posted above as best-answer. It also allows you to specify a direction (true to scroll right, false to scroll left) and a speed (indicates how many seconds it takes for an image to scroll across the screen, lower numbers = faster). It requires you to specify the view as well, and I haven't tested it with images that aren't the same size as the desired output (although I included scaling, so it probably works)
func scrollingBackground (view: SKView, rightward: Bool, speed: CGFloat) {
let background = SKSpriteNode(imageNamed: "space")
let background2 = SKSpriteNode(imageNamed: "space")
// variables to manage x position, will be set based on which
// direction this will be moving
var b1startX, b2startX, destination, resetPos: CGFloat
// Set values based on desired direction
if(rightward){
b1startX = frame.size.width * -0.5 // value to start offscreen
b2startX = frame.size.width * 0.5 // value to start on screen
destination = frame.size.width * 1.5 // position where image will disappear
resetPos = frame.size.width * -0.5 // position where image will reappear
}
else{
b1startX = frame.size.width * 1.5
b2startX = frame.size.width * 0.5
destination = frame.size.width * -0.5
resetPos = frame.size.width * 1.5
}
background.position = CGPoint(x: b1startX, y: frame.size.height / 2)
background.scale(to: view.bounds.size)
background.zPosition = -1
background2.position = CGPoint(x: b2startX, y: frame.size.height / 2)
background2.scale(to: view.bounds.size)
background2.zPosition = -1
// Define actions based on desired direction
let scrollFromMid = SKAction.moveTo(x: destination, duration: TimeInterval(speed))
let scrollFromLeft = SKAction.moveTo(x: destination, duration: TimeInterval(speed * 2.0))
let resetPosition = SKAction.moveTo(x: resetPos, duration: 0)
//background starts in the default starting position, totally offscreen
background.run(SKAction.repeatForever(SKAction.sequence([scrollFromLeft, resetPosition])))
// background2 starts fully displayed, moves offscreen, then into default loop
background2.run(SKAction.sequence([scrollFromMid, resetPosition,
SKAction.repeatForever(
SKAction.sequence([scrollFromLeft, resetPosition]))
]))
addChild(background)
addChild(background2)
}

Answer 3

when you create the BackgroundReset action you set the y change to a negative value, this will move the background further down the screen. Remove the minus sign to move the background back up the screen.
let BackgroundReset =
SKAction.moveByX(0, y: /* removed minus sign here */ self.frame.size.height * 2, duration: 0.0)