Swift: Centre point of fingers in UIRotationGesture in wrong place in SKView?

Question

I'm trying to build a board game whereby the board is built of sprites and you can look over them birds eye view style with an SKCamera node. I've gotten the pan, zoom and rotate down but they don't feel natural as wherever I put my fingers on the screen it will rotate about the centre of the camera node.

To remedy this, I was going to create a SKNode and place this in-between where the fingers are as an anchor for the camera's rotation and zooming.

However I can't get the location of the centre point of the fingers to line up with the right coords in the gamescene.

I've created some red boxes to debug and find my problem and looks as so:

Where-ever I place my fingers in the entire game scene to rotate it, the centre where it thinks it should be is always in that red blob.

The SKView is placed on the storyboard as a SpriteKit view and is bound to the left and right edges of the screen with top and bottom padding:

Inside of viewcontroller:

    @IBOutlet weak var Gameview: SKView!

    override func viewDidLoad() {
        super.viewDidLoad()
        let scene = GameScene(size:Gameview.frame.size)
        Gameview.presentScene(scene)
    }

Inside of GameScene.swift, let a = sender.location(in: self.view) seems to be where the problem lies.

class GameScene: SKScene, UIGestureRecognizerDelegate {

    var newCamera: SKCameraNode!

    let rotateRec = UIRotationGestureRecognizer()
    let zoomRec = UIPinchGestureRecognizer()
    //let panRec = UIPanGestureRecognizer()


    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer,
                           shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer)
        -> Bool {return true}



    override func didMove(to view: SKView) {

        rotateRec.addTarget(self, action: #selector(GameScene.rotatedView (_:) ))
        rotateRec.delegate = self
        self.view!.addGestureRecognizer(rotateRec)

        zoomRec.addTarget(self, action: #selector(GameScene.zoomedView (_:) ))
        zoomRec.delegate = self
        self.view!.addGestureRecognizer(zoomRec)

        //panRec.addTarget(self, action: #selector(GameScene.pannedView (_:) ))
        //self.view!.addGestureRecognizer(panRec)


        newCamera = SKCameraNode()
        newCamera.position = CGPoint(x: self.size.width / 2, y: self.size.height / 2)
        self.addChild(newCamera)
        self.camera = newCamera

        //drawBoard()
        //I removed this function as it had nothing to do with the question

    }

    @objc func rotatedView(_ sender:UIRotationGestureRecognizer) {
        print(sender.location(in: self.view))
        let square = SKSpriteNode(color: #colorLiteral(red: 0.7450980544, green: 0.1568627506, blue: 0.07450980693, alpha: 1), size: CGSize(width: 10, height: 10))
        let a = sender.location(in: self.view)
        let b = -a.x
        let c = -a.y
        let d = CGPoint(x: b, y: c)


        square.position = d
        self.addChild(square)


        newCamera.zRotation += sender.rotation
        sender.rotation = 0
        if sender.state == .ended {
            let rotateAmount = abs(Double(newCamera.zRotation) * Double(180) / Double.pi)
            let remainder = abs(rotateAmount.truncatingRemainder(dividingBy: 90))
            //print(rotateAmount)
            //print(remainder)
            if remainder < 10 {
                newCamera.zRotation = CGFloat((rotateAmount-remainder)*Double.pi/180)
            } else if remainder > 80 {
                newCamera.zRotation = CGFloat((rotateAmount-remainder+90)*Double.pi/180)
            }

        }

    }



    @objc func zoomedView(_ sender:UIPinchGestureRecognizer) {
        let pinch = SKAction.scale(by: 1/sender.scale, duration: 0.0)
        newCamera.run(pinch)
        sender.scale = 1.0
    }

    //@objc func pannedView(_ sender:UIPanGestureRecognizer) {
    //    sender.translation(in: )
    //}


    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        for touch in touches {
            let location = touch.location(in: self)
            let previousLocation = touch.previousLocation(in: self)
            let deltaY = location.y - previousLocation.y
            let deltax = location.x - previousLocation.x
            newCamera!.position.y -= deltaY
            newCamera!.position.x -= deltax
        }
    }
}

I did remove the function drawboard() as it was redundant in context to the question.

Answer 1

You needed to convert the coords from the sender.location to the coords in the skview using the functions shown in the page:

https://developer.apple.com/documentation/spritekit/skscene

--> https://developer.apple.com/documentation/spritekit/skscene/1520395-convertpoint

in the rotatedview() function, putting the code:

let bluesquare = SKSpriteNode(color: #colorLiteral(red: 0.2392156869, green: 0.6745098233, blue: 0.9686274529, alpha: 1), size: CGSize(width: 10, height: 10))

let a = sender.location(in: self.view)
bluesquare.position = self.convertPoint(fromView: a)

self.addChild(bluesquare)

...will add blue sprites where the centre of your two fingers are.