SKPhysicsBody scale with parent scaling - ios

Question

I have a node, A, in a parent node, B.
I'm using setScale on node B to give the illusion of zooming, but when I do that, node A and all of its siblings do not have the expected physics bodies.
Even though A appears smaller and smaller, its physics body stays the same size. This leads to wacky behavior.
How can I "zoom out" and still have sensible physics?

Answer 1

SKPhysicsBody cannot be scaled. As a hack you could destroy the current physics body and add a smaller one as you scale up or down but unfortunately this is not a very efficient solution.

Answer 2

The SKCameraNode (added in iOS9) sounds perfect for your scenario. As opposed changing the scale of every node in the scene, you would change the scale of only the camera node.
Firstly, you need to add an SKCameraNode to your scene's hierarchy (this could all be done in the Sprite Kit editor too).
override func didMoveToView(view: SKView) {
super.didMoveToView(view)
let camera = SKCameraNode()
camera.position = CGPoint(x: size.width / 2, y: size.height / 2)
self.addChild(camera)
self.camera = camera
}
Secondly, since SKCameraNode is a node you can apply SKActions to it. For a zoom out effect you could do:
guard let camera = camera else { return }
let scale = SKAction.scaleBy(2, duration: 5)
camera.runAction(scale)
For more information have a look at the WWDC 2015 talk: What's New In Sprite Kit.

Answer 3

A simple example that shows that a physics body scales/behaves appropriately when its parent node is scaled. Tap to add sprites to the scene.
class GameScene: SKScene {
var toggle = false
var node = SKNode()
override func didMoveToView(view: SKView) {
self.physicsBody = SKPhysicsBody(edgeLoopFromRect: view.frame)
scaleMode = .ResizeFill
view.showsPhysics = true
addChild(node)
let shrink = SKAction.scaleBy(0.25, duration: 5)
let grow = SKAction.scaleBy(4.0, duration: 5)
let action = SKAction.sequence([shrink,grow])
node.runAction(SKAction.repeatActionForever(action))
}
override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
/* Called when a touch begins */
for touch in (touches as! Set<UITouch>) {
let location = touch.locationInNode(node)
let sprite = SKSpriteNode(imageNamed:"Spaceship")
if (toggle) {
sprite.physicsBody = SKPhysicsBody(circleOfRadius: sprite.size.width/2.0)
}
else {
sprite.physicsBody = SKPhysicsBody(rectangleOfSize: sprite.size)
}
sprite.xScale = 0.125
sprite.yScale = 0.125
sprite.position = location
node.addChild(sprite)
toggle = !toggle
}
}
}