SpriteKit: How do I remove objects once they leave the screen? - swift

Question

I have a rock sprite that it is falling and every time it goes out of the screen I want to reset it back to the top and have it fall again. It should be a continuous cycle. Here's my code:
import SpriteKit
import GameplayKit
class GameScene: SKScene {
func addRock(){
var rock = self.childNode(withName: "rock")
rock?.physicsBody?.affectedByGravity = true
//self.addChild(rock!)
}
override func sceneDidLoad() {
//bRock = self.childNode(withName: "rock")
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
//addRock()
var rock = self.childNode(withName: "rock")
rock?.physicsBody?.affectedByGravity = true
/*if (Int((rock?.position.y)!) < Int((self.view?.scene?.view?.bounds.minY)!)){
print("out of screen")
rock?.removeFromParent()
addRock()
}*/
}
override func update(_ currentTime: TimeInterval) {
// Called before each frame is rendered
var rock = self.childNode(withName: "rock")
//rock?.physicsBody?.affectedByGravity = true
if (!intersects(rock!)){
print("out of screen")
rock?.removeFromParent()
addRock()
}
}
}
I have the rock coming on the screen and then falling. Once it leaves the screen, it does not reset and I get an error. I tried placing the reset code in both the touchesBegan and update functions but neither work. If someone could guide me to the correct path, that would be greatly appreciated.

Answer 1

The problem you're having is that you're removing the rock node from the scene but the addRock method doesn't actually add a new rock, it just finds the existing node if there is one and sets a property on its physicsBody. Instead of removing the node, you should just change its position.
Assuming your scene has the default anchor point of (0,0), you can reset the position like this:
override func update(_ currentTime: TimeInterval) {
// Called before each frame is rendered
if let rock = self.childNode(withName: "rock") {
if !intersects(rock!) {
print("out of screen")
rock.position.y = size.height/2 // divided by 2 as discussed in comments
}
}
That will reset the rock's position to the top of the scene and it should resume falling from there.

Answer 2

Three ways:
the same rock is newly located at the right place after leaving the screen, so you just need to set the position of it in (misnamed) addRock (resetRock should be better): rock.position = CGPoint(...). But beware that you also need to reset its velocity, etc, as it was previously moved by physical laws...
create a new rock each time one leaves the screen in addRock: let rock = SKSpriteNode(...)... (and all the initializing code for it. Much simpler as all its physical parameters will be initialized with right values by default.
create a clone of an initial rock. I suppose you have a model of it in your sks file, then don't name it rock but something like (rockModel), and just clone it in addRock with giving it the right name rock. Don't forget to remove the model from the scene at the beginning. This is the usual way to do it.

Answer 3

You could also think about using a series of move actions in a sequence to control the rock's behaviour. Given the move actions are already defined, in your defined sequence, pass in sequence[(falling, hide, backtotop, unhide)] - Repeat Forever.
As long as the rocks don't actually interact with anything and are just for the backdrop/background, hiding and unhiding them is a good way to give the affect they are falling.