SpriteKit Collisions called multiple times

Question

I'm new to SpriteKit and am learning by making a flappy bird style game.

I am using a bird node whose PhyshicsBody is bound to the texture.

The issue is that occasionally when the bird hits the score node its registering multiple collisions. I have added an if to remove the nodes the first time the function is called but I am still registering multiple collisions.

With that if statement I would have thought this would prevent the issue, why would this still be occurring?

Function of interest:

 func didBegin(_ contact: SKPhysicsContact) {

        if moving.speed > 0 {
            if ( contact.bodyA.categoryBitMask & scoreCategory ) == scoreCategory || ( contact.bodyB.categoryBitMask & scoreCategory ) == scoreCategory {
                // Bird has contact with score entity

                if(contact.bodyB.node != nil && contact.bodyA.node != nil){
                score += 1
                scoreLabelNode.text = String(score)

                    if (contact.bodyA.node?.name == "scoreArea") {
                        contact.bodyA.node?.removeFromParent()
                    } else if contact.bodyB.node?.name == "scoreArea" {
                        contact.bodyB.node?.removeFromParent()
                    }

                // Add a little visual feedback for the score increment
                scoreLabelNode.run(SKAction.sequence([SKAction.scale(to: 1.5, duration:TimeInterval(0.1)), SKAction.scale(to: 1.0, duration:TimeInterval(0.1))]))
                }
            } }

Full code:

import SpriteKit

class GameScene: SKScene, SKPhysicsContactDelegate{
    let verticalPipeGap = 250.0

    var bird:SKSpriteNode!
    var skyColor:SKColor!
    var pipeTextureUp:SKTexture!
    var pipeTextureDown:SKTexture!
    var movePipesAndRemove:SKAction!
    var moving:SKNode!
    var pipes:SKNode!
    var canRestart = Bool()
    var scoreLabelNode:SKLabelNode!
    var score = NSInteger()
    var contactState = false


    let birdCategory: UInt32 = 1 << 0
    let worldCategory: UInt32 = 1 << 1
    let pipeCategory: UInt32 = 1 << 2
    let scoreCategory: UInt32 = 1 << 3

    override func didMove(to view: SKView) {

        canRestart = true

        // setup physics
        self.physicsWorld.gravity = CGVector( dx: 0.0, dy: -5.0 )
        self.physicsWorld.contactDelegate = self

        // setup background color
        skyColor = SKColor(red: 81.0/255.0, green: 192.0/255.0, blue: 201.0/255.0, alpha: 1.0)
        self.backgroundColor = skyColor

        moving = SKNode()
        self.addChild(moving)
        pipes = SKNode()
        moving.addChild(pipes)

        // ground
        let groundTexture = SKTexture(imageNamed: "land")
        groundTexture.filteringMode = .nearest // shorter form for SKTextureFilteringMode.Nearest

        let moveGroundSprite = SKAction.moveBy(x: -groundTexture.size().width * 2.0, y: 0, duration: TimeInterval(0.02 * groundTexture.size().width * 2.0))
        let resetGroundSprite = SKAction.moveBy(x: groundTexture.size().width * 2.0, y: 0, duration: 0.0)
        let moveGroundSpritesForever = SKAction.repeatForever(SKAction.sequence([moveGroundSprite,resetGroundSprite]))

        for i in 0 ..< 2 + Int(self.frame.size.width / ( groundTexture.size().width * 2 )) {
            let i = CGFloat(i)
            let sprite = SKSpriteNode(texture: groundTexture)
            sprite.setScale(2.0)
            sprite.position = CGPoint(x: i * sprite.size.width, y: sprite.size.height / 2.0)
            sprite.run(moveGroundSpritesForever)
            moving.addChild(sprite)
        }

        // skyline
        let skyTexture = SKTexture(imageNamed: "sky")
        skyTexture.filteringMode = .nearest

        let moveSkySprite = SKAction.moveBy(x: -skyTexture.size().width * 2.0, y: 0, duration: TimeInterval(0.1 * skyTexture.size().width * 2.0))
        let resetSkySprite = SKAction.moveBy(x: skyTexture.size().width * 2.0, y: 0, duration: 0.0)
        let moveSkySpritesForever = SKAction.repeatForever(SKAction.sequence([moveSkySprite,resetSkySprite]))

        for i in 0 ..< 2 + Int(self.frame.size.width / ( skyTexture.size().width * 2 )) {
            let i = CGFloat(i)
            let sprite = SKSpriteNode(texture: skyTexture)
            sprite.setScale(2.0)
            sprite.zPosition = -20
            sprite.position = CGPoint(x: i * sprite.size.width, y: sprite.size.height / 2.0 + groundTexture.size().height * 2.0)
            sprite.run(moveSkySpritesForever)
            moving.addChild(sprite)
        }

        // create the pipes textures
        pipeTextureUp = SKTexture(imageNamed: "PipeUp")
        pipeTextureUp.filteringMode = .nearest
        pipeTextureDown = SKTexture(imageNamed: "PipeDown")
        pipeTextureDown.filteringMode = .nearest

        // create the pipes movement actions
        let distanceToMove = CGFloat(self.frame.size.width + 2.0 * pipeTextureUp.size().width)
        let movePipes = SKAction.moveBy(x: -distanceToMove, y:0.0, duration:TimeInterval(0.01 * distanceToMove))
        let removePipes = SKAction.removeFromParent()
        movePipesAndRemove = SKAction.sequence([movePipes, removePipes])

        // spawn the pipes
        let spawn = SKAction.run(spawnPipes)
        let delay = SKAction.wait(forDuration: TimeInterval(2.0))
        let spawnThenDelay = SKAction.sequence([spawn, delay])
        let spawnThenDelayForever = SKAction.repeatForever(spawnThenDelay)
        self.run(spawnThenDelayForever)

        // setup our bird
        let birdTexture1 = SKTexture(imageNamed: "bird-02")
        birdTexture1.filteringMode = .nearest
        let birdTexture2 = SKTexture(imageNamed: "bird-02")
        birdTexture2.filteringMode = .nearest

        let anim = SKAction.animate(with: [birdTexture1, birdTexture2], timePerFrame: 0.2)
        let flap = SKAction.repeatForever(anim)

        bird = SKSpriteNode(texture: birdTexture1)

        bird.position = CGPoint(x: self.frame.size.width * 0.35, y:self.frame.size.height * 0.6)
        bird.run(flap)


        bird.physicsBody = SKPhysicsBody(texture: bird.texture!,
                                         size: bird.texture!.size())
        bird.setScale(0.4)
        bird.physicsBody?.isDynamic = true
        bird.physicsBody?.allowsRotation = false

        bird.physicsBody?.categoryBitMask = birdCategory
        bird.physicsBody?.collisionBitMask = worldCategory | pipeCategory
        bird.physicsBody?.contactTestBitMask = worldCategory | pipeCategory

        self.addChild(bird)

        // create the ground
        let ground = SKNode()
        ground.position = CGPoint(x: 0, y: groundTexture.size().height)
        ground.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: self.frame.size.width, height: groundTexture.size().height * 2.0))
        ground.physicsBody?.isDynamic = false
        ground.physicsBody?.categoryBitMask = worldCategory
        self.addChild(ground)

        // Initialize label and create a label which holds the score
        score = 0
        scoreLabelNode = SKLabelNode(fontNamed:"MarkerFelt-Wide")
        scoreLabelNode.position = CGPoint( x: self.frame.midX, y: 3 * self.frame.size.height / 4 )
        scoreLabelNode.zPosition = 100
        scoreLabelNode.text = String(score)
        self.addChild(scoreLabelNode)

    }

    func spawnPipes() {
        let pipePair = SKNode()
        pipePair.position = CGPoint( x: self.frame.size.width + pipeTextureUp.size().width * 2, y: 0 )
        pipePair.zPosition = -10

        let height = UInt32( self.frame.size.height / 4)
        let y = Double(arc4random_uniform(height) + height)

        let pipeDown = SKSpriteNode(texture: pipeTextureDown)
        pipeDown.setScale(2.0)
        pipeDown.position = CGPoint(x: 0.0, y: y + Double(pipeDown.size.height) + verticalPipeGap)


        pipeDown.physicsBody = SKPhysicsBody(rectangleOf: pipeDown.size)
        pipeDown.physicsBody?.isDynamic = false
        pipeDown.physicsBody?.categoryBitMask = pipeCategory
        pipeDown.physicsBody?.contactTestBitMask = birdCategory
        pipePair.addChild(pipeDown)

        let pipeUp = SKSpriteNode(texture: pipeTextureUp)
        pipeUp.setScale(2.0)
        pipeUp.position = CGPoint(x: 0.0, y: y)

        pipeUp.physicsBody = SKPhysicsBody(rectangleOf: pipeUp.size)
        pipeUp.physicsBody?.isDynamic = false
        pipeUp.physicsBody?.categoryBitMask = pipeCategory
        pipeUp.physicsBody?.contactTestBitMask = birdCategory
        pipePair.addChild(pipeUp)

        let contactNode = SKNode()
        contactNode.name = "scoreArea"
        contactNode.position = CGPoint( x: pipeDown.size.width + bird.size.width / 2, y: self.frame.midY )
        contactNode.physicsBody = SKPhysicsBody(rectangleOf: CGSize( width: pipeUp.size.width, height: self.frame.size.height ))
        contactNode.physicsBody?.isDynamic = false
        contactNode.physicsBody?.categoryBitMask = scoreCategory
        contactNode.physicsBody?.contactTestBitMask = birdCategory
        pipePair.addChild(contactNode)

        pipePair.run(movePipesAndRemove)
        pipes.addChild(pipePair)

    }

    func resetScene (){
        // Move bird to original position and reset velocity
        bird.position = CGPoint(x: self.frame.size.width / 2.5, y: self.frame.midY)
        bird.physicsBody?.velocity = CGVector( dx: 0, dy: 0 )
        bird.physicsBody?.collisionBitMask = worldCategory | pipeCategory
        bird.speed = 1.0
        bird.zRotation = 0.0

        // Remove all existing pipes
        pipes.removeAllChildren()
        contactState = false
        // Reset _canRestart
        canRestart = false

        // Reset score
        score = 0
        scoreLabelNode.text = String(score)

        // Restart animation
        moving.speed = 1
    }
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        if moving.speed > 0  {
            for _ in touches { // do we need all touches?
                bird.physicsBody?.velocity = CGVector(dx: 0, dy: 0)
                bird.physicsBody?.applyImpulse(CGVector(dx: 0, dy: 120))
            }
        } else if canRestart {
            self.resetScene()
        }
    }

    override func update(_ currentTime: TimeInterval) {
        /* Called before each frame is rendered */
        let value = bird.physicsBody!.velocity.dy * ( bird.physicsBody!.velocity.dy < 0 ? 0.003 : 0.001 )
        bird.zRotation = min( max(-1, value), 0.5 )
    }



    func didBegin(_ contact: SKPhysicsContact) {

        if moving.speed > 0 {
            if ( contact.bodyA.categoryBitMask & scoreCategory ) == scoreCategory || ( contact.bodyB.categoryBitMask & scoreCategory ) == scoreCategory {
                // Bird has contact with score entity

                if(contact.bodyB.node != nil && contact.bodyA.node != nil){
                score += 1
                scoreLabelNode.text = String(score)

                    if (contact.bodyA.node?.name == "scoreArea") {
                        contact.bodyA.node?.removeFromParent()
                    } else if contact.bodyB.node?.name == "scoreArea" {
                        contact.bodyB.node?.removeFromParent()
                    }

                // Add a little visual feedback for the score increment
                scoreLabelNode.run(SKAction.sequence([SKAction.scale(to: 1.5, duration:TimeInterval(0.1)), SKAction.scale(to: 1.0, duration:TimeInterval(0.1))]))
                }
            } else {

                moving.speed = 0
                bird.physicsBody?.collisionBitMask = worldCategory
                bird.run(  SKAction.rotate(byAngle: CGFloat(Double.pi) * CGFloat(bird.position.y) * 0.01, duration:1), completion:{self.bird.speed = 0 })


                // Flash background if contact is detected
                self.removeAction(forKey: "flash")
                self.run(SKAction.sequence([SKAction.repeat(SKAction.sequence([SKAction.run({
                    self.backgroundColor = SKColor(red: 1, green: 0, blue: 0, alpha: 1.0)
                }),SKAction.wait(forDuration: TimeInterval(0.05)), SKAction.run({
                    self.backgroundColor = self.skyColor
                }), SKAction.wait(forDuration: TimeInterval(0.05))]), count:4), SKAction.run({
                    self.canRestart = true
                })]), withKey: "flash")
            }
        }
    }
}

Possible duplicate of [Why are didBeginContact called multiple times?](https://stackoverflow.com/questions/24228274/why-are-didbegincontact-called-multiple-times) — Knight0fDragon, Mar 08 '19 at 15:59

score 0 · Answer 1 · answered Mar 07 '19 at 17:02

This is a common issue for people just starting game development with physics.

func didBegin(_ contact: SKPhysicsContact) gets called 60 times a second (optimally). so that means that when your "bird" collides with an object it gets detected 60 times a second. You need to put a flag somewhere to determine if the bird has collided with an object and thus not make those collision checks anymore if the flag is true.

Seeing as you don't have bird in it's own class you can just put a variable in your GameScene to store this collision.

private var isDead = false

then when the object collides with a pipe set it to true

isDead = true

and finally use this when checking for collisions

if moving.speed > 0 && !isDead {
}

or I would prefer at the beginning of your didBegin func. this way saves you and "if" nest in your code

guard moving.speed > 0, !isDead else { return }

The issue is not because of didBegin contact being called over multiple frames, the issue is the moving object has multiple contact points over the same frame. Everything else in this answer is correct (It is a shame that documents is gone, a few of us went into great detail over this matter) — Knight0fDragon, Mar 08 '19 at 15:58

SpriteKit Collisions called multiple times

1 Answers1