Continous minimum velocity tracking of a finger on a sprite in spritekit/ios

Question

What is a good way to continuously track the velocity of a user moving their finger up and down on a sprite without lifting the finger? And if they don't go fast enough(set a minimum) to perform an action.

Answer 1

This is some code you can use to drag a sprite across the screen at different speeds depending on your finger acceleration. You can add your own code to detect the magnitude of change and perform whichever action you want..

class GameScene: SKScene {

    // time values
    var delta:NSTimeInterval = NSTimeInterval(0)
    var last_update_time:NSTimeInterval = NSTimeInterval(0)

    // our sprite
    let sprite = SKSpriteNode(color: SKColor.redColor(), size: CGSize(width: 20, height: 30))

    // tracking difference between touches
    var currentTouchY: CGFloat = CGFloat(0)
    var lastTouchY: CGFloat = CGFloat(0)

    // the magnitude of change between current and last touch
    var forceMag: CGFloat = CGFloat(0)
    // max mag so our sprite doesnt travel at crazy speed
    let forceMagMax: CGFloat = CGFloat(7)
    // direction of our sprites travel
    var forceDir: CGFloat = CGFloat(0)
    // arbitrary speed we want sprite to move
    let velocity: CGFloat = CGFloat(70)

    // we use this to stop moving our sprite when we let go
    var intervalsWithoutChange = 0

    override func didMoveToView(view: SKView) {
        sprite.position.x = 100
        sprite.position.y = size.width/2
        self.addChild(sprite)
    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        for touch: AnyObject in touches {
            let location = touch.locationInNode(self)
            let yCoord = location.y

            lastTouchY = yCoord
        }
    }

    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
        for touch: AnyObject in touches {
            let location = touch.locationInNode(self)
            let yCoord = location.y

            intervalsWithoutChange = 0
            currentTouchY = yCoord
            let diff = currentTouchY - lastTouchY
            forceMag = abs(diff)
            forceMag = forceMag > forceMagMax ? forceMagMax : forceMag
            forceDir = diff < 0 ? -1 : 1
            lastTouchY = yCoord
        }
    }

    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        intervalsWithoutChange = 1
        currentTouchY = 0
        lastTouchY = 0
    }

    override func update(currentTime: NSTimeInterval) {

        if last_update_time == 0.0 {
            delta = 0
        } else {
            delta = currentTime - last_update_time
        }

        last_update_time = currentTime

        if intervalsWithoutChange > 0 {
            forceMag -= CGFloat(15) * CGFloat(delta)
        }

        if forceMag < 0.01 {
            forceMag = 0
        }

        let change = forceDir * pow(forceMag, 1.29)

        sprite.position.y += change * CGFloat(delta) * velocity
    }
}