macos: drag preview is an image of the surface

macos/Sources/Ghostty/Surface View/SurfaceGrabHandle.swift

@@ -5,6 +5,7 @@ extension Ghostty {
     /// Only appears when hovering in the top region of the surface.
     struct SurfaceGrabHandle: View {
         private let handleHeight: CGFloat = 10
+        private let previewScale: CGFloat = 0.2
         
         let surfaceView: SurfaceView
         
@@ -34,7 +35,35 @@ extension Ghostty {
                 Spacer()
             }
             .frame(maxWidth: .infinity, maxHeight: .infinity)
-            .draggable(surfaceView)
+            .draggable(surfaceView) {
+                SurfaceDragPreview(surfaceView: surfaceView, scale: previewScale)
+            }
+        }
+    }
+    
+    /// A miniature preview of the surface view for drag operations that updates periodically.
+    private struct SurfaceDragPreview: View {
+        let surfaceView: SurfaceView
+        let scale: CGFloat
+        
+        var body: some View {
+            // We need to use a TimelineView to ensure that this doesn't
+            // cache forever. This will NOT let the view live update while
+            // being dragged; macOS doesn't seem to allow that. But it will
+            // make sure on new drags the screenshot is updated.
+            TimelineView(.periodic(from: .now, by: 1.0 / 30.0)) { _ in
+                if let snapshot = surfaceView.asImage {
+                    Image(nsImage: snapshot)
+                        .resizable()
+                        .aspectRatio(contentMode: .fit)
+                        .frame(
+                            width: snapshot.size.width * scale,
+                            height: snapshot.size.height * scale
+                        )
+                        .clipShape(RoundedRectangle(cornerRadius: 8))
+                        .shadow(radius: 10)
+                }
+            }
         }
     }
 }

macos/Sources/Ghostty/Surface View/SurfaceView+Image.swift

@@ -0,0 +1,28 @@
+#if canImport(AppKit)
+import AppKit
+#elseif canImport(UIKit)
+import UIKit
+#endif
+
+extension Ghostty.SurfaceView {
+    #if canImport(AppKit)
+    /// A snapshot image of the current surface view.
+    var asImage: NSImage? {
+        guard let bitmapRep = bitmapImageRepForCachingDisplay(in: bounds) else {
+            return nil
+        }
+        cacheDisplay(in: bounds, to: bitmapRep)
+        let image = NSImage(size: bounds.size)
+        image.addRepresentation(bitmapRep)
+        return image
+    }
+    #elseif canImport(UIKit)
+    /// A snapshot image of the current surface view.
+    var asImage: UIImage? {
+        let renderer = UIGraphicsImageRenderer(bounds: bounds)
+        return renderer.image { _ in
+            drawHierarchy(in: bounds, afterScreenUpdates: true)
+        }
+    }
+    #endif
+}

macos/Sources/Ghostty/Surface View/SurfaceView_AppKit.swift

@@ -2213,6 +2213,7 @@ extension Ghostty.SurfaceView {
 
         return NSAttributedString(string: plainString, attributes: attributes)
     }
+    
 }
 
 /// Caches a value for some period of time, evicting it automatically when that time expires.