Swift SpriteKit: Incorrect sprite position - ios

Question

I've created a new Xcode game project and selected SpriteKit. By default, Xcode provides a game template which I modified to add image. The image was displayed on the screen but in incorrect position. I followed this tutorial to setup the correct scene dimension and it works. But the image is still in incorrect position.
I'm trying to position the image at Y=0, but it appears at the bottom of the screen instead of the top.
Here's what I've done so far.
ViewController Code:
class GameViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillLayoutSubviews() {
super.viewWillLayoutSubviews();
let skView = self.view as! SKView
println(skView)
let scale:CGFloat = UIScreen.mainScreen().scale;
let size = CGSizeMake(skView.frame.size.width*scale, skView.frame.size.height*scale)
if (skView.scene == nil) {
if let scene = GameScene.unarchiveFromFile("GameScene") as? GameScene {
// Configure the view.
skView.showsFPS = true
skView.showsNodeCount = true
skView.ignoresSiblingOrder = true
scene.scaleMode = .AspectFill
scene.size = size
skView.presentScene(scene)
}
}
else {
skView.scene!.size = size;
}
}
override func shouldAutorotate() -> Bool {
return true
}
override func supportedInterfaceOrientations() -> Int {
if UIDevice.currentDevice().userInterfaceIdiom == .Phone {
return Int(UIInterfaceOrientationMask.Portrait.rawValue)
} else {
return Int(UIInterfaceOrientationMask.All.rawValue)
}
}
}
Scene Code:
class GameScene: SKScene {
override func didMoveToView(view: SKView) {
println(self)
self.backgroundColor = UIColor(red: 31.0/255.0, green: 31.0/255.0, blue: 31.0/255.0, alpha: 1.0)
//Add the app logo
let logo = SKSpriteNode(imageNamed:"imgLogo")
logo.position = CGPoint(x:self.frame.size.width/2, y:0)
self.addChild(logo)
let lblTitle = SKLabelNode(fontNamed:"LibelSuit-Regular")
lblTitle.text = "Hello World!";
lblTitle.fontSize = 65;
lblTitle.position = CGPoint(x:CGRectGetMidX(self.frame), y:CGRectGetMidY(self.frame));
self.addChild(lblTitle)
}
}

Answer 1

I assume logo is the red/green boxes on the bottom? If so, y = 0 is the bottom edge, not the top. Try:
logo.position = CGPoint(x:self.frame.size.width/2,
y:self.frame.size.height - logo.size.height / 2)

Answer 2

Unlike game development for other platforms, the y-axis in spritekit runs from down to up instead of up to down. In this case you'd want to replace the 0 with self.frame.size.height
logo.position = CGPoint(x:self.frame.size.width/2, y:0) //Your current code
logo.position = CGPoint(x:self.frame.size.width/2, y:self.frame.size.height)//What you want

Answer 3

Since the Scene anchor point was set to (0,0) - lower left of the screen by default, what I did is to set the anchor point to (0,1) - upper left instead.
self.anchorPoint = CGPointMake(0, 1);
I also set the same anchor point for each child, then I set the Y position to a negative value.
let logo = SKSpriteNode(imageNamed:"imgLogo")
logo.anchorPoint = CGPointMake(0, 1);
logo.position = CGPoint(x:0, y:-180)
self.addChild(logo)
This works perfectly. Appreciate your inputs.

Answer 4

Why would y = 0 be at the top? Just think of it as a graph like the ones you've learned in school. y = 0 is in the bottom and x = 0 is on the left side. So 0,0 would be on the left bottom corner.