Keep particles in scene paused after app becomes active

Question

Let me preface this question by saying I know it has been asked a few times, but the most upvoted post here was from back in 2014 and the top answer doesn't seem to work anymore.

Issue

In my game, I have all my 'moving' nodes as children of pauseNode. When the pauses button is pressed or when the player leaves the app, pauseScene() is called:

func pauseScene() {
    self.node.speed = 0
    self.physicsWorld.speed = 0
    self.node.isPaused = true
}

This pauses all sprite nodes and emitter nodes. This keeps the sprite nodes paused if the app transitions from background to foreground state, but the particle emitters seem to resume animating.

Current solution

I solved this issue by triggering pauseScene() after a small delay when the app became active.

override func didMove(to view: SKView) {
     NotificationCenter.default.addObserver(self, selector: #selector(GameScene.applicationDidBecomeActive(notification:)), name: NSNotification.Name.UIApplicationDidBecomeActive, object: app)
}

@objc func applicationDidBecomeActive(notification: NSNotification) {
    NSDelay(0.01) {
        pauseScene()
    }
}

func NSDelay(_ delay:Double, closure:@escaping ()->()) {
    let when = DispatchTime.now() + delay
    DispatchQueue.main.asyncAfter(deadline: when, execute: closure)
}

Goal

While this solution pauses the particles, it is not perfect because they are visible moving for the split second it takes to pause them again (this is the shortest delay that actually re-pauses them).

So, after reading the post I linked above, I tried to override applicationDidBecomeActive() in an SKView subclass as was suggested, but I couldn't get the method to be called. I want to prevent these particles from being unpaused in the first place, if possible. Thanks

score 0 · Answer 1 · answered Feb 02 '19 at 07:27

So, it's been a little over a day and I've found a better solution. A comment in this post suggested having a variable that recorded the status of the scene, and updating it along with the pause/play functions:

var sceneIsPaused = false

func pauseScene() {
    self.node.speed = 0
    self.physicsWorld.speed = 0
    self.node.isPaused = true

    sceneIsPaused = true
}

func playScene() {
    self.node.speed = 1
    self.physicsWorld.speed = 1
    self.node.isPaused = false

    sceneIsPaused = false
}

Then, override SKView's update method and check the state of that variable. If the scene should be paused, pause it. This will mean that if the scene is automatically unpaused it will re-pause the next frame. This is much faster and cleaner than setting a delay:

override func update(_ currentTime: TimeInterval) {
    if (sceneIsPaused == true) {
        self.node.speed = 0
        self.physicsWorld.speed = 0
        self.node.isPaused = true
    }
}

Keep particles in scene paused after app becomes active

Issue

Current solution

Goal

1 Answers1