I am trying to solve a problem without success and am hoping someone could help.

I have looked for similar posts but haven't been able to find anything which solves my problem.

My Scenario is as follows: I have a UIView on which a number of other UIViews can be placed. These can be moved, scaled and rotated using gesture recognisers (There is no issue here). The User is able to change the Aspect Ratio of the Main View (the Canvas) and my problem is trying to scale the content of the Canvas to fit into the new destination size.

There are a number of posts with a similar theme e.g:

calculate new size and location on a CGRect

How to create an image of specific size from UIView

But these don't address the changing of ratios multiple times.

My Approach:

When I change the aspect ratio of the canvas, I make use of AVFoundation to calculate an aspect fitted rectangle which the subviews of the canvas should fit:

let sourceRectangleSize = canvas.frame.size

canvas.setAspect(aspect, screenSize: editorLayoutGuide.layoutFrame.size)
view.layoutIfNeeded()

let destinationRectangleSize = canvas.frame.size

let aspectFittedFrame = AVMakeRect(aspectRatio:sourceRectangleSize, insideRect: CGRect(origin: .zero, size: destinationRectangleSize))
ratioVisualizer.frame = aspectFittedFrame

The Red frame is simply to visualise the Aspect Fitted Rectangle. As you can see whilst the aspect fitted rectangle is correct, the scaling of objects isn't working. This is especially true when I apply scale and rotation to the subviews (CanvasElement).

The logic where I am scaling the objects is clearly wrong:

@objc
private func setRatio(_ control: UISegmentedControl) {
  guard let aspect = Aspect(rawValue: control.selectedSegmentIndex) else { return }
  
  let sourceRectangleSize = canvas.frame.size
 
  canvas.setAspect(aspect, screenSize: editorLayoutGuide.layoutFrame.size)
  view.layoutIfNeeded()
 
  let destinationRectangleSize = canvas.frame.size
  
  let aspectFittedFrame = AVMakeRect(aspectRatio:sourceRectangleSize, insideRect: CGRect(origin: .zero, size: destinationRectangleSize))
  ratioVisualizer.frame = aspectFittedFrame
  
  let scale = min(aspectFittedFrame.size.width/canvas.frame.width, aspectFittedFrame.size.height/canvas.frame.height)
  
  for case let canvasElement as CanvasElement in canvas.subviews {
  
    canvasElement.frame.size = CGSize(
      width: canvasElement.baseFrame.width * scale,
      height: canvasElement.baseFrame.height * scale
    )
    canvasElement.frame.origin = CGPoint(
      x: aspectFittedFrame.origin.x + canvasElement.baseFrame.origin.x * scale,
      y:  aspectFittedFrame.origin.y + canvasElement.baseFrame.origin.y * scale
    )
  }
}

I am enclosing the CanvasElement Class as well if this helps:

final class CanvasElement: UIView {
  
  var rotation: CGFloat = 0
  var baseFrame: CGRect = .zero

  var id: String = UUID().uuidString
  
  // MARK: - Initialization
  
  override init(frame: CGRect) {
    super.init(frame: frame)
    storeState()
    setupGesture()
  }
  
  required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
  }
  
  // MARK: - Gesture Setup
  
  private func setupGesture() {
    let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(panGesture(_:)))
    let pinchGestureRecognizer = UIPinchGestureRecognizer(target: self, action: #selector(pinchGesture(_:)))
    let rotateGestureRecognizer = UIRotationGestureRecognizer(target: self, action: #selector(rotateGesture(_:)))
    addGestureRecognizer(panGestureRecognizer)
    addGestureRecognizer(pinchGestureRecognizer)
    addGestureRecognizer(rotateGestureRecognizer)
  }
  
  // MARK: - Touches
  
  override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesBegan(touches, with: event)
    moveToFront()
  }
  
  //MARK: - Gestures
  
  @objc
  private func panGesture(_ sender: UIPanGestureRecognizer) {
    let move = sender.translation(in: self)
    transform = transform.concatenating(.init(translationX: move.x, y: move.y))
    sender.setTranslation(CGPoint.zero, in: self)
    storeState()
  }
  
  @objc
  private func pinchGesture(_ sender: UIPinchGestureRecognizer) {
    transform = transform.scaledBy(x: sender.scale, y: sender.scale)
    sender.scale = 1
    storeState()
  }
  
  @objc
  private func rotateGesture(_ sender: UIRotationGestureRecognizer) {
    rotation += sender.rotation
    transform = transform.rotated(by: sender.rotation)
    sender.rotation = 0
    storeState()
  }
  
  // MARK: - Miscelaneous
  
  func moveToFront() {
    superview?.bringSubviewToFront(self)
  }
  
  public func rotated(by degrees: CGFloat) {
    transform = transform.rotated(by: degrees)
    rotation += degrees
  }
  
  func storeState() {
    print("""
    Element Frame = \(frame)
    Element Bounds = \(bounds)
    Element Center = \(center)
    """)
    baseFrame = frame
  }
}

Any help or advise, approaches, with some actual examples would be great. Im not expecting anyone to provide full source code, but something which I could use as a basis.

Thank you for taking the time to read my question.