gistfile1.txt

// A Simple AppKit NSViewControllerRepresentable to wrap a NSViewCOntroller subclass that presents a NSImageView in a NSScrollVIew.
// This was done more or less for educational purposes for myself, but maybe someone will find it helpful

public struct ImageRepresentable: NSViewControllerRepresentable {
    
    public typealias NSViewControllerType = ImageViewController

    let image: NSImage
    let minSize: CGSize?
    
    init(image: NSImage, minSize: CGSize? = nil) {
        self.image = image
        self.minSize = minSize
    }
    
    @Environment(\.dismiss) var dismiss: DismissAction
    
    static var urlIndicator: String { String(describing: Self.self) }
    
    @State private var viewController: ImageViewController?
    
    fileprivate func closeWindow() {
        dismiss()
    }
    
    public func makeNSViewController(context: Context) -> ImageViewController {
        
        ImageViewController(image)
    }
    
    public func updateNSViewController(_ uiViewController: ImageViewController, context: Context) {
        
    }
    
    @available(macOS 14.0, *)
    @MainActor @preconcurrency public func sizeThatFits(_ proposal: ProposedViewSize, nsViewController: ImageViewController, context: Self.Context) -> CGSize? {
        
        let viewSize = nsViewController.scroller.contentSize
        guard let screenSize = NSScreen.main?.frame.size else {
            // this shouldn't really happen, but to be safe..
            return proposal.replacingUnspecifiedDimensions(by: viewSize)
        }
                
        let imageSize = nsViewController.scroller.documentView?.bounds.size ?? image.size
        
        var sizes = [
            screenSize,
            imageSize,
        ]
        
        // if the image is smaller than the screen, then the image size is the smallest it can get
        if let minSize,
           imageSize.width > screenSize.width ||
            imageSize.height > screenSize.height {
            sizes.append(minSize)
        }

        let ideal = sizes.reduce(screenSize) {
            CGSize(width: min($0.width, $1.width),
                   height: min($0.height, $1.height))
        }
        
        // don't allow a zero size ever
        if proposal == .zero {
            return ideal
        }
        return proposal.replacingUnspecifiedDimensions(by: ideal)
    }
}

public class ImageViewController: NSViewController {

    let image: NSImage

    init(_ image: NSImage) {
        self.image = image
        super.init(nibName: nil, bundle: nil)
        self.representedObject = image
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private(set) var scroller: NSScrollView!
    
    public override func loadView() {

        let imageRect = CGRect(origin: .zero, size: image.size)
        let imageView = NSImageView(frame: imageRect)
        imageView.bounds = imageRect
        imageView.image = image
        
        self.scroller = NSScrollView()
        scroller.hasHorizontalScroller = true
        scroller.hasVerticalScroller = true
        scroller.borderType = .noBorder
        scroller.addSubview(imageView)
        scroller.documentView = imageView
        scroller.allowsMagnification = true

        self.view = scroller
        view.frame = CGRect(origin: .zero, size: image.size)
    }
    
    public override func viewWillAppear() {
        super.viewWillAppear()
        
        // NOTE: AppKit uses a Quadrant I coordinate system, so the top of the image is at the highest number
        // NOTE: This code has no effect if called in viewDidLoad(). 
        // It's not until viewWillAppear() that the view is setup in such a way that it works
        let top = NSPoint(x: 0, y: image.size.height)
        scroller?.documentView?.scroll(top)

    }
}