How to properly remove node when out of screen bounds?

Question

I\'m working on a sprite-kit game where nodes spawn below the lowest point on the screen and gravity is set to have them float to the top of the screen. Everything works per

Answer 1

With Swift 1.1 / iOS 8, you can use the following pattern in order to solve your problem.

---

1. Init your scene's physicsBody property with the following code:

physicsBody = SKPhysicsBody(edgeLoopFromRect: frame) // or CGRectInset(frame, -10, -10) if you need insets 

2. Create category masks for your scene and your sprite nodes:

let boundaryCategoryMask: UInt32 =  0x1 << 1
let someNodeCategoryMask: UInt32 =  0x1 << 2

3. Set the proper categoryBitMask, collisionBitMask and contactTestBitMask for your scene and sprite nodes physicsBody properties:

// Scene
physicsBody!.categoryBitMask = boundaryCategoryMask

// Sprite node
/* ... */
someNode.physicsBody!.categoryBitMask = someNodeCategoryMask
someNode.physicsBody!.contactTestBitMask = boundaryCategoryMask 

---

As an example, the following Swift SKScene implementation shows you how to remove all sprite nodes that go beyond your scene's frame:

class GameScene: SKScene, SKPhysicsContactDelegate {

    let boundaryCategoryMask: UInt32 =  0x1 << 1
    let squareCategoryMask: UInt32 =  0x1 << 2


    override func didMoveToView(view: SKView) {
        // Scene
        backgroundColor = SKColor.whiteColor()
        physicsWorld.contactDelegate = self
        physicsBody = SKPhysicsBody(edgeLoopFromRect: frame)
        physicsBody!.categoryBitMask = boundaryCategoryMask

        // Square
        let square = SKSpriteNode(color: SKColor.redColor(), size: CGSize(width: 80, height: 80))
        square.zPosition = 0.1
        square.position = CGPoint(x: size.width / 2.0 - square.size.width / 2, y: size.height - square.size.height)
        square.physicsBody = SKPhysicsBody(rectangleOfSize: square.frame.size)
        square.physicsBody!.dynamic = true
        square.physicsBody!.affectedByGravity = true
        square.physicsBody!.categoryBitMask = squareCategoryMask
        // square.physicsBody!.collisionBitMask = 0 // don't set collisions (you don't want any collision)
        square.physicsBody!.contactTestBitMask = boundaryCategoryMask // this will trigger -didBeginContact: and -didEndContact: 
        addChild(square)
    }

    override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
        // Check if the array containing the scene’s children is empty
        println("children: \(children)")
    }

    func didBeginContact(contact: SKPhysicsContact) {
        if contact.bodyA.categoryBitMask == squareCategoryMask {
            contact.bodyA.node?.removeFromParent()
            println("square removed")
        }

        if contact.bodyB.categoryBitMask == squareCategoryMask {
            contact.bodyB.node?.removeFromParent()
            println("square removed")
        }
    }

    func didEndContact(contact: SKPhysicsContact) {
        /* ... */
    }

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

}