Place anchor point at the centre of the screen while doing gestures

Since the question is mostly answered in the edits, I don't want to repeat myself too much.

Broadly what I changed from the code posted in the original question:

1. Deleted calls to adjustAnchorPoint function in pinch and rotation gesture functions.

2. Placed this piece of code in pan gesture function, so that the anchor point would update its position after panning the photo:

   if gestureRecognizer.state == .ended { self.centerAnchorPoint() }

3. Updated centerAnchorPoint function to work for rotation.

A fully working centerAnchorPoint function (rotation included):

    func centerAnchorPoint() {        // Scale factor        photo.transform = photo.transform.rotated(by: -angle)        let curScale = photo.frame.size.width / photo.layer.bounds.size.width        photo.transform = photo.transform.rotated(by: angle)        // Position of the current anchor point        let currentPosition = photo.layer.anchorPoint        self.setAnchorPoint(CGPoint(x: 0.5, y: 0.5), forView: photo)        // Center of the image        let imageCenter = CGPoint(x: photo.center.x, y: photo.center.y)        self.setAnchorPoint(currentPosition, forView: photo)        // Center of the screen        let screenCenter = CGPoint(x: UIScreen.main.bounds.midX, y: UIScreen.main.bounds.midY)        // Distance between the centers        let distanceX = screenCenter.x - imageCenter.x        let distanceY = screenCenter.y - imageCenter.y        // Apply rotational matrix to the distances        let distX = distanceX*cos(angle)+distanceY*sin(angle)        let distY = -distanceX*sin(angle)+distanceY*cos(angle)        let incrementX = (distX)/(curScale*UIScreen.main.bounds.size.width)        let incrementY = (distY)/(curScale*UIScreen.main.bounds.size.height)        // Find new anchor point        let newAnchorPoint = CGPoint(x: 0.5+incrementX, y: 0.5+incrementY)        self.setAnchorPoint(newAnchorPoint, forView: photo)}

The key things to notice here is that the rotation matrix has to be applied to distanceX and distanceY. The scale factor is also updated to remain the same throughout the rotation.