Add zooming to focused attachment view

Packages/ComposeUI/Sources/ComposeUI/Controllers/FocusedAttachmentController.swift

@@ -35,9 +35,17 @@ class FocusedAttachmentController: ViewController {
             VStack(spacing: 0) {
                 Spacer(minLength: 0)
                 
-                ControllerView(controller: { controller.thumbnailController })
-                    .environment(\.attachmentThumbnailConfiguration, .init(contentMode: .fit, fullSize: true))
-                    .matchedGeometryDestination(id: attachment.id)
+                let attachmentView =
+                    ControllerView(controller: { controller.thumbnailController })
+                        .environment(\.attachmentThumbnailConfiguration, .init(contentMode: .fit, fullSize: true))
+                        .matchedGeometryDestination(id: attachment.id)
+                if #available(iOS 16.0, *) {
+                    ZoomableScrollView {
+                        attachmentView
+                    }
+                } else {
+                    attachmentView
+                }
                 
                 Spacer(minLength: 0)
                 

Packages/ComposeUI/Sources/ComposeUI/Views/ZoomableScrollView.swift

@@ -0,0 +1,111 @@
+//
+//  ZoomableScrollView.swift
+//  ComposeUI
+//
+//  Created by Shadowfacts on 4/29/23.
+//
+
+import SwiftUI
+
+@available(iOS 16.0, *)
+struct ZoomableScrollView<Content: View>: UIViewControllerRepresentable {
+    let content: Content
+    
+    init(@ViewBuilder content: () -> Content) {
+        self.content = content()
+    }
+    
+    func makeUIViewController(context: Context) -> Controller {
+        return Controller(content: content)
+    }
+
+    func updateUIViewController(_ uiViewController: Controller, context: Context) {
+        uiViewController.host.rootView = content
+    }
+    
+    class Controller: UIViewController, UIScrollViewDelegate {
+        let scrollView = UIScrollView()
+        let host: UIHostingController<Content>
+        
+        private var lastIntrinsicSize: CGSize?
+        private var contentViewTopConstraint: NSLayoutConstraint!
+        private var contentViewLeadingConstraint: NSLayoutConstraint!
+        private var hostBoundsObservation: NSKeyValueObservation?
+        
+        init(content: Content) {
+            self.host = UIHostingController(rootView: content)
+            
+            super.init(nibName: nil, bundle: nil)
+        }
+        
+        required init?(coder: NSCoder) {
+            fatalError("init(coder:) has not been implemented")
+        }
+        
+        override func viewDidLoad() {
+            super.viewDidLoad()
+            
+            scrollView.delegate = self
+            scrollView.bouncesZoom = true
+            scrollView.translatesAutoresizingMaskIntoConstraints = false
+            view.addSubview(scrollView)
+            
+            host.sizingOptions = .intrinsicContentSize
+            host.view.backgroundColor = .clear
+            host.view.translatesAutoresizingMaskIntoConstraints = false
+            addChild(host)
+            scrollView.addSubview(host.view)
+            host.didMove(toParent: self)
+            
+            contentViewLeadingConstraint = host.view.leadingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor)
+            contentViewTopConstraint = host.view.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor)
+            
+            NSLayoutConstraint.activate([
+                scrollView.frameLayoutGuide.leadingAnchor.constraint(equalTo: view.leadingAnchor),
+                scrollView.frameLayoutGuide.trailingAnchor.constraint(equalTo: view.trailingAnchor),
+                scrollView.frameLayoutGuide.topAnchor.constraint(equalTo: view.topAnchor),
+                scrollView.frameLayoutGuide.bottomAnchor.constraint(equalTo: view.bottomAnchor),
+                
+                contentViewLeadingConstraint,
+                contentViewTopConstraint,
+            ])
+        }
+        
+        override func viewDidLayoutSubviews() {
+            super.viewDidLayoutSubviews()
+            
+            if host.view.intrinsicContentSize != lastIntrinsicSize {
+                self.lastIntrinsicSize = host.view.intrinsicContentSize
+                
+                let maxHeight = view.bounds.height - view.safeAreaInsets.top - view.safeAreaInsets.bottom
+                let maxWidth = view.bounds.width - view.safeAreaInsets.left - view.safeAreaInsets.right
+                let heightScale = maxHeight / host.view.intrinsicContentSize.height
+                let widthScale = maxWidth / host.view.intrinsicContentSize.width
+                let minScale = min(widthScale, heightScale)
+                let maxScale = minScale >= 1 ? minScale + 2 : 2
+                print("min: \(minScale), max: \(maxScale)")
+                scrollView.minimumZoomScale = minScale
+                scrollView.maximumZoomScale = maxScale
+                scrollView.zoomScale = minScale
+            }
+            
+            centerImage()
+        }
+        
+        func viewForZooming(in scrollView: UIScrollView) -> UIView? {
+            return host.view
+        }
+        
+        func scrollViewDidZoom(_ scrollView: UIScrollView) {
+            centerImage()
+        }
+        
+        func centerImage() {
+            let yOffset = max(0, (view.bounds.size.height - host.view.bounds.height * scrollView.zoomScale) / 2)
+            contentViewTopConstraint.constant = yOffset
+
+            let xOffset = max(0, (view.bounds.size.width - host.view.bounds.width * scrollView.zoomScale) / 2)
+            contentViewLeadingConstraint.constant = xOffset
+        }
+    }
+}