Spawn SKSpriteNode objects at random times

Question

I am making a game where I would like to spawn obstacles at random times. The obstacles are going to make contact with the player.

Here the code that I have:

var obstacle : SKSpriteNode?

func createObstacles() {
let obstaclesArray = ["obstacle_1", "obstacle_2", "obstacle_3", "obstacle_4", "obstacle_5"]
let randomObs = obstaclesArray.randomElement()
let selectedTexture = SKTexture(imageNamed: randomObs!)
obstacle = SKSpriteNode(imageNamed: randomObs!)
obstacle?.physicsBody = SKPhysicsBody(texture: selectedTexture, size: selectedTexture.size())
obstacle?.position = CGPoint(x: scene!.size.width/2 + selectedTexture.size().width, y: -120)
obstacle?.zPosition = -15
if let obs = obstacle?.physicsBody {
obs.affectedByGravity = true
obs.allowsRotation = false
obs.isDynamic = true
obs.restitution = 0
obs.categoryBitMask = obstacleCategory
obs.collisionBitMask = floorCategory
obs.contactTestBitMask = heroCategory
}
addChild(obstacle!)
}

func spawnObstacles() {
let wait = SKAction.wait(forDuration: 1, withRange: 0.4)
let spawn = SKAction.run {
createObstacles()
}
let moveLeft = SKAction.moveBy(x: -scene!.size.width - obstacle.size.width - 10, y: 0, duration: 2)
let sequence = SKAction.sequence([wait, spawn, moveLeft, SKAction.removeFromParent()])
self.run(SKAction.repeatForever(sequence))
}

I read some a similar questions but the response is my same code but it is not working. Spawning a Spritekit node at a random time

I also tried other way:

var randDelay = Double.random(in: 0.7 ..< 1.4)
DispatchQueue.main.asyncAfter(deadline: randDelay, execute: {
    if self.canCreateObstacle == true {
    self.spawnObstacle()
    }})

But it is not working and everytime I restart the game it seems like the function is being called two times, if I restart the game a third time it is called 3 times and so on.

Anyone with a good and clean solution to spawn objects at random times?

Answer 1

Do not use DispatchQueue Set up a repeating sequential action using wait(forDuration:withRange:) like you previously had.

https://developer.apple.com/documentation/spritekit/skaction/1417760-wait

First, create a generic node used to spawn obstacles, then attach this generic node to the scene.
Finally assign the repeating sequential action to this node. Boom, you are done.

The reason why you want to assign it to a random node is because you want to be able to give your game the opportunity to stop generating obstacles, plus you alter the speed property to make the node generate nodes faster or slower.

You also want to detach the spawning/waiting from the moving/destroying, because as of right now, your code is confused. You are saying move the scene left for 2 seconds, then wait a random amount of time to spawn the next enemy, but I think you are trying to just spawn enemies on a time interval and move the enemy to the left.

Your scene code should look something like this

class GameScene : SKScene{
    let obstacleGenerator = SKNode()
    func didMove(to: view){


        let wait = SKAction.wait(forDuration: 1, withRange: 0.4)
        let spawn = SKAction.run({createObstacles()})

        let sequence = SKAction.sequence([wait, spawn])
        obstacleGenerator.run(SKAction.repeatForever(sequence))
        addChild(obstacleGenerator)

    }

    func createObstacles() {
        let obstaclesArray = ["obstacle_1", "obstacle_2", "obstacle_3", "obstacle_4", "obstacle_5"]
        let randomObs = obstaclesArray.randomElement()
        let selectedTexture = SKTexture(imageNamed: randomObs!)
        obstacle = SKSpriteNode(imageNamed: randomObs!)

        obstacle.position = CGPoint(x: scene!.size.width/2 + selectedTexture.size().width, y: -120)
        obstacle.zPosition = -15
        let body = SKPhysicsBody(texture: selectedTexture, size: selectedTexture.size())
        body.affectedByGravity = true
        body.allowsRotation = false
        body.isDynamic = true
        body.restitution = 0
        body.categoryBitMask = obstacleCategory
        body.collisionBitMask = floorCategory
        body.contactTestBitMask = heroCategory
        obstacle.physicsBody = body
        addChild(obstacle!)
        let moveLeft = SKAction.moveBy(x: -scene!.size.width - obstacle.size.width - 10, y: 0, duration: 2)
        let seq = SKAction.sequence([moveLeft,SKAction.removeFromParent()])
        obstacle.run(seq)
    }
}

Now as for your spawning increasing with each reset, you never post how you are resetting. I am going to assume you never remove the previous action upon reset, and this is why your rate increases. It is always better to just create a new GameScene instance when doing a reset.