Gist for the medium article

ig-zoom-1.swift

import Foundation
import UIKit

class ViewController: UIViewController {
  // MARK: - UI Initialization
  
  // The image that we will zoom/drag
  var imageView = UIImageView()
  
  // The dark overlay layer behind the image
  // that will be visible while gestures are recognized
  var overlay: UIView = {
    let view = UIView(frame: UIScreen.main.bounds);
    
    view.alpha = 0
    view.backgroundColor = .black
    
    return view
  }()
  
  // Let's start
  override func viewDidLoad() {
    super.viewDidLoad()
    
    // Here some basic setup
    view.addSubview(overlay)
    view.bringSubviewToFront(imageView)
  }
}