SKSpriteNode slows down but shouldn't

Question

I am trying to get my "word" to float across the screen; constant velocity, no impacts, no gravity, no friction. Everything works except the word slows down.

Code for creating word:

func createWordNode (word: String, atPos: CGPoint) -> SKSpriteNode {

    let doneSize = CGSize(width: 50, height: 50)

    let wordSprite = SKSpriteNode()
    wordSprite.size = CGSize(width: doneSize.width * CGFloat(word.len()), height: doneSize.height)
    wordSprite.position = atPos
    wordSprite.blendMode = .replace
    wordSprite.zPosition = zlvlBG + 1

    let ltrs = Array(word.uppercased().characters)

    for i in 0 ... ltrs.count - 1 {

        let done = SKSpriteNode(imageNamed: "LetterTiles/Tile" + String(ltrs[i]) + ".png")
        done.size = doneSize
        done.position = CGPoint(x: doneSize.width * CGFloat(Double(i) - 1.5), y: 0)
        done.blendMode = .replace
        done.zPosition = zlvlBG + 1

        wordSprite.addChild(done)

    }

    wordSprite.physicsBody?.restitution = 1
    wordSprite.physicsBody?.friction = 0
    wordSprite.physicsBody?.linearDamping = 0
    wordSprite.physicsBody?.angularDamping = 0
    wordSprite.physicsBody?.mass = 2000

    wordSprite.physicsBody = SKPhysicsBody(rectangleOf: wordSprite.size)
    wordSprite.physicsBody?.collisionBitMask = 0
    wordSprite.physicsBody?.contactTestBitMask = 0
    wordSprite.physicsBody?.categoryBitMask = categoryWords
    wordSprite.physicsBody?.fieldBitMask = 0

    wordSprite.physicsBody?.isDynamic = true
    wordSprite.physicsBody?.affectedByGravity = false
    wordSprite.physicsBody?.allowsRotation = false

    var velocity = CGVector()
    velocity.dx = 100
    velocity.dy = 0
    wordSprite.physicsBody?.velocity = velocity
    wordSprite.physicsBody?.applyImpulse(velocity)

    wordSprite.name = "Word:" + word


    return wordSprite
}

I call function like:

addChild (createWordNode(word: "Done", atPos: CGPoint(x:-500, y:450)))

Any ideas why word slows down? Thanks.

Answer 1

It looks like you are creating an object that doesn't need to be in the physics simulation. So you may want to reconsider simply dropping the physics related code and update the nodes position manually.

That being said if you wish this node to remain in the Physics simulation. You need to add the SKPhysicsBody to the SKSpriteNode before you start trying to modify properties. e.g.

wordSprite.physicsBody = SKPhysicsBody(rectangleOf: wordSprite.size)
wordSprite.physicsBody?.restitution = 1
wordSprite.physicsBody?.friction = 0
wordSprite.physicsBody?.linearDamping = 0
wordSprite.physicsBody?.angularDamping = 0
wordSprite.physicsBody?.mass = 2000