How to move sprite to center while is in a path and then return to the original path?

Question

I am making a game in which a sprite is rotating around a big circle and I want that when touches began the sprite moves to another circle that is in the center of the screen and now the sprite rotatate around it, and when the touches began occurs again the sprite return to the big circle. In my code the sprite moves to the -sprite.position.x * 2 so that makes that the sprite move to the oposite side of the big circle. How can I solve that?

Answer 1

One of the easiest ways to move an object in a circular path is to

1. Create a SKNode container
2. Create a sprite
3. Add the container to the scene
4. Add the sprite to the container
5. Set the sprite's x position to the radius of the circular path
6. Rotate the container

If you want to move the sprite to the another circle with a different radius,

7. change the sprite's x position
8. move the container's position (optional)

If you want to change the direction of the rotation,

9. reverse the container's rotation

Here's an example:

// Define circle
struct Circle {
    var position:CGPoint
    var radius:CGFloat
}

class GameScene: SKScene {
    // 1. Create container node
    let node = SKNode()
    // 2. Create a sprite
    let sprite = SKSpriteNode(color:SKColor.blueColor(),size:CGSizeMake(10,10))
    var rotation:CGFloat = CGFloat(M_PI)
    var circles:[Circle] = []

    override func didMoveToView(view: SKView) {
        scaleMode = .ResizeFill

        circles.append(Circle(position: view.center, radius: 80))
        circles.append(Circle(position: view.center, radius: 40))
        // 3. Add the container to the scene
        addChild(node)

        // 4. Add the sprite to the container
        node.addChild(sprite)
        // 5. Set the sprite's x position to the radius of the circular path
        if let circle = nextCircle() {
            node.position = circle.position
            sprite.position = CGPoint(x:circle.radius, y:0)
            // 6. Rotate the container
            rotate()
        }
    }

    // Rotate the container
    func rotate() {
        let action = SKAction.rotateByAngle(rotation, duration: 4)
        node.runAction(SKAction.repeatActionForever(action),withKey: "rotate")
    }

    // 9. Reverse the container's rotation
    func reverse() {
        rotation = -rotation
    }

    // Stop rotating the container
    func stopRotation() {
        if node.actionForKey("rotate") != nil {
            node.removeActionForKey("rotate")
        }
    }

    // Returns the next circle's parameters and rotates the array
    func nextCircle() -> Circle? {
        guard let circle = circles.first else {
            return nil
        }
        // Move the current circle to the back of the queue
        circles.append(circles.removeAtIndex(0))
        return circle
    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        /* Change the sprite's x-position  */
        if sprite.actionForKey("move") == nil {
            stopRotation()
            // 7. change the sprite's x position
            // 8. move the container's position (optional)
            if let circle = nextCircle() {
                let radius = CGPoint(x:circle.radius, y:0)
                let moveCenter = SKAction.moveTo(circle.position, duration: 3)
                let move = SKAction.moveTo(radius, duration: 3)
                let rotate = SKAction.runBlock {
                    self.rotate()
                }
                sprite.runAction(SKAction.sequence([move, rotate]), withKey: "move")
                node.runAction(moveCenter, withKey: "move")
            }
        }
    }
}