feat: animate compact window transitions

Sources/App/CompactWindow.swift

@@ -1,10 +1,12 @@
 import AppKit
+import QuartzCore
 
 @MainActor
 final class CompactWindowController: NSObject {
     var onChange: (() -> Void)?
     private(set) var isCompact = false
     private(set) var isTransitioning = false
+    static let transitionDuration: TimeInterval = 0.25
 
     var snappingEnabled: Bool {
         didSet {
@@ -54,9 +56,14 @@ final class CompactWindowController: NSObject {
     private var originatedFullScreen = false
     private var videoAspect = 16.0 / 9.0
     private var fittedAspect: Double?
+    private let reduceMotion: () -> Bool
+    private var frameAnimating = false
+    private var frameAnimationGeneration: UInt64 = 0
 
-    init(snappingEnabled: Bool = true) {
+    init(snappingEnabled: Bool = true,
+         reduceMotion: @escaping () -> Bool = { NSWorkspace.shared.accessibilityDisplayShouldReduceMotion }) {
         self.snappingEnabled = snappingEnabled
+        self.reduceMotion = reduceMotion
         super.init()
     }
 
@@ -64,6 +71,7 @@ final class CompactWindowController: NSObject {
 
     func attach(_ window: NSWindow) {
         guard window !== self.window else { return }
+        stopFrameAnimation()
         if let oldWindow = self.window, fullScreenTransition == nil,
            !oldWindow.styleMask.contains(.fullScreen) {
             restoreSnapshot(to: oldWindow)
@@ -105,11 +113,12 @@ final class CompactWindowController: NSObject {
         reconcile()
     }
 
-    func restore(resumeFullScreen: Bool = true) {
+    func restore(resumeFullScreen: Bool = true, animated: Bool = true) {
         guard sessionActive else { return }
         wantsCompact = false
         wantsFullScreen = resumeFullScreen && originatedFullScreen
-        reconcile()
+        if !animated { stopFrameAnimation() }
+        reconcile(animated: animated)
     }
 
     func updateAspect(_ aspect: Double) {
@@ -137,6 +146,7 @@ final class CompactWindowController: NSObject {
             fullScreenTransition = nil
             reconcile()
         case NSWindow.willCloseNotification:
+            stopFrameAnimation()
             restoreDelegate()
             NotificationCenter.default.removeObserver(self)
             window = nil
@@ -204,8 +214,8 @@ final class CompactWindowController: NSObject {
     }
 
     // A toggle changes the destination, never reverses an in-flight native animation.
-    private func reconcile() {
-        guard let window, fullScreenTransition == nil else { return }
+    private func reconcile(animated: Bool = true) {
+        guard let window, fullScreenTransition == nil, !frameAnimating else { return }
         guard sessionActive else {
             setState(compact: isCompact, transitioning: false)
             return
@@ -214,7 +224,7 @@ final class CompactWindowController: NSObject {
             if window.styleMask.contains(.fullScreen) {
                 toggleNativeFullScreen(window, transition: .exiting)
             } else if !isCompact {
-                enterCompact(window)
+                enterCompact(window, animated: animated)
             } else {
                 if fittedAspect != videoAspect { fitCompactWindow(window, initial: false) }
                 setState(compact: true, transitioning: false)
@@ -229,10 +239,17 @@ final class CompactWindowController: NSObject {
             }
             return
         }
-        if snapshot != nil {
-            setState(compact: isCompact, transitioning: true)
-            restoreSnapshot(to: window)
-            setState(compact: false, transitioning: wantsFullScreen)
+        if let snapshot {
+            setState(compact: false, transitioning: animated)
+            window.aspectRatio = .zero
+            window.minSize = .zero
+            window.contentMinSize = .zero
+            animateFrame(snapshot.frame, of: window, animated: animated) { [weak self, weak window] in
+                guard let self, let window else { return }
+                self.restoreSnapshot(to: window)
+                self.reconcile()
+            }
+            return
         }
         if wantsFullScreen {
             toggleNativeFullScreen(window, transition: .entering)
@@ -247,10 +264,10 @@ final class CompactWindowController: NSObject {
         window.toggleFullScreen(nil)
     }
 
-    private func enterCompact(_ window: NSWindow) {
-        setState(compact: false, transitioning: true)
+    private func enterCompact(_ window: NSWindow, animated: Bool) {
         // After didExitFullScreen, this is the normal frame, not the fullscreen frame.
         snapshot = Snapshot(window)
+        setState(compact: true, transitioning: animated)
         window.aspectRatio = .zero
         window.minSize = .zero
         window.contentMinSize = .zero
@@ -267,8 +284,7 @@ final class CompactWindowController: NSObject {
         window.level = .floating
         window.hidesOnDeactivate = false
         window.isMovableByWindowBackground = true
-        fitCompactWindow(window, initial: true)
-        setState(compact: true, transitioning: false)
+        fitCompactWindow(window, initial: true, animated: animated)
     }
 
     private func restoreSnapshot(to window: NSWindow) {
@@ -298,6 +314,42 @@ final class CompactWindowController: NSObject {
         setState(compact: false, transitioning: false)
     }
 
+    private func animateFrame(_ frame: NSRect, of window: NSWindow, animated: Bool,
+                              completion: @escaping @MainActor () -> Void) {
+        guard animated, !reduceMotion(), window.frame != frame else {
+            window.setFrame(frame, display: true)
+            completion()
+            return
+        }
+        frameAnimationGeneration &+= 1
+        let generation = frameAnimationGeneration
+        frameAnimating = true
+        NSAnimationContext.runAnimationGroup { context in
+            context.duration = Self.transitionDuration
+            context.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)
+            window.animator().setFrame(frame, display: true)
+        } completionHandler: { [weak self, weak window] in
+            MainActor.assumeIsolated {
+                guard let self, let window, self.window === window, self.frameAnimating,
+                      self.frameAnimationGeneration == generation else { return }
+                self.frameAnimating = false
+                completion()
+            }
+        }
+    }
+
+    private func stopFrameAnimation() {
+        guard frameAnimating else { return }
+        frameAnimating = false
+        frameAnimationGeneration &+= 1
+        guard let window else { return }
+        // A zero-duration animator update cancels the native in-flight frame animation.
+        NSAnimationContext.runAnimationGroup { context in
+            context.duration = 0
+            window.animator().setFrame(window.frame, display: true)
+        }
+    }
+
     private func setState(compact: Bool, transitioning: Bool) {
         guard isCompact != compact || isTransitioning != transitioning else { return }
         isCompact = compact
@@ -309,9 +361,10 @@ final class CompactWindowController: NSObject {
         (window.screen ?? NSScreen.main)?.visibleFrame ?? window.frame
     }
 
-    private func fitCompactWindow(_ window: NSWindow, initial: Bool) {
+    private func fitCompactWindow(_ window: NSWindow, initial: Bool, animated: Bool = false) {
         let visibleFrame = visibleFrame(for: window)
         let usable = Self.usableFrame(visibleFrame)
+        let aspect = videoAspect
         var frame = Self.initialFrame(aspect: videoAspect, visibleFrame: visibleFrame)
         if !initial {
             frame.size = Self.compactSize(aspect: videoAspect, width: window.frame.width, available: usable.size)
@@ -319,11 +372,14 @@ final class CompactWindowController: NSObject {
             frame.origin.y = min(max(window.frame.minY, usable.minY), usable.maxY - frame.height)
         }
         window.aspectRatio = .zero
-        window.setFrame(frame, display: true)
-        if Self.canFitAspect(videoAspect, available: usable.size) {
-            window.aspectRatio = NSSize(width: videoAspect, height: 1)
+        animateFrame(frame, of: window, animated: animated) { [weak self, weak window] in
+            guard let self, let window else { return }
+            if Self.canFitAspect(aspect, available: usable.size) {
+                window.aspectRatio = NSSize(width: aspect, height: 1)
+            }
+            self.fittedAspect = aspect
+            if initial { self.reconcile() }
         }
-        fittedAspect = videoAspect
     }
 
     nonisolated static func initialFrame(aspect: Double, visibleFrame: NSRect) -> NSRect {