A replacement for the anchorPoint property that doesn’t make the layer jump

NSView+ChangeAnchorPointWithoutMakingTheLayerJump.swift

//
//  NSView+ChangeAnchorPointWithoutMakingTheLayerJump.swift
//
//  Setting .anchorPoint on a layer makes the layer jump which is most
//  likely not what you want. This extension fixes that. Useful for Core Animation.
//
//  Usage: (e.g., to set the anchor point to the centre)
//
//  myView.setAnchorPoint(CGPointMake(0.5, 0.5))
//
//  Created by Aral Balkan on 18/07/2015.
//  Copyright (c) 2015 Ind.ie. Released under the MIT License.
//

import Cocoa

extension NSView
{
    //
    // Converted to Swift + NSView from: 
    // http://stackoverflow.com/a/10700737
    //
    func setAnchorPoint (anchorPoint:CGPoint)
    {
        if let layer = self.layer
        {
            var newPoint = CGPointMake(self.bounds.size.width * anchorPoint.x, self.bounds.size.height * anchorPoint.y)
            var oldPoint = CGPointMake(self.bounds.size.width * layer.anchorPoint.x, self.bounds.size.height * layer.anchorPoint.y)
            
            newPoint = CGPointApplyAffineTransform(newPoint, layer.affineTransform())
            oldPoint = CGPointApplyAffineTransform(oldPoint, layer.affineTransform())
            
            var position = layer.position
            
            position.x -= oldPoint.x
            position.x += newPoint.x
            
            position.y -= oldPoint.y
            position.y += newPoint.y
            
            layer.position = position
            layer.anchorPoint = anchorPoint
        }
    }
}