feat: improve responsiveness of showing the switcher

src/logic/Windows.swift

@@ -314,7 +314,7 @@ class Windows {
     }
 
     // dispatch screenshot requests off the main-thread, then wait for completion
-    static func refreshThumbnails(_ windows: [Window], _ source: RefreshCausedBy) {
+    static func refreshThumbnailsAsync(_ windows: [Window], _ source: RefreshCausedBy) {
         var eligibleWindows = [Window]()
         for window in windows {
             if !window.isWindowlessApp, let cgWindowId = window.cgWindowId, cgWindowId != CGWindowID(bitPattern: -1) {
@@ -322,10 +322,10 @@ class Windows {
             }
         }
         if eligibleWindows.isEmpty { return }
-        screenshotEligibleWindowsAndRefreshUi(eligibleWindows, source)
+        screenshotEligibleWindowsAndUpdateUi(eligibleWindows, source)
     }
 
-    private static func screenshotEligibleWindowsAndRefreshUi(_ eligibleWindows: [Window], _ source: RefreshCausedBy) {
+    private static func screenshotEligibleWindowsAndUpdateUi(_ eligibleWindows: [Window], _ source: RefreshCausedBy) {
         for window in eligibleWindows {
             BackgroundWork.screenshotsQueue.addOperation { [weak window] in
                 if source == .refreshOnlyThumbnailsAfterShowUi && !App.app.appIsBeingUsed { return }

src/ui/App.swift

@@ -206,7 +206,7 @@ class App: AppCenterApplication {
         if !windowsToScreenshot.isEmpty && SystemPermissions.screenRecordingPermission == .granted
                && !Preferences.onlyShowApplications()
                && (!Appearance.hideThumbnails || Preferences.previewFocusedWindow) {
-            Windows.refreshThumbnails(windowsToScreenshot, source)
+            Windows.refreshThumbnailsAsync(windowsToScreenshot, source)
             if source == .refreshOnlyThumbnailsAfterShowUi { return }
         }
         guard appIsBeingUsed else { return }
@@ -216,12 +216,7 @@ class App: AppCenterApplication {
         guard appIsBeingUsed else { return }
         Windows.updateFocusedWindowIndex()
         guard appIsBeingUsed else { return }
-        thumbnailsPanel.thumbnailsView.updateItemsAndLayout()
-        guard appIsBeingUsed else { return }
-        thumbnailsPanel.setContentSize(thumbnailsPanel.thumbnailsView.contentView.frame.size)
-        thumbnailsPanel.display()
-        guard appIsBeingUsed else { return }
-        NSScreen.preferred.repositionPanel(thumbnailsPanel)
+        thumbnailsPanel.updateContents()
         guard appIsBeingUsed else { return }
         Windows.voiceOverWindow() // at this point ThumbnailViews are assigned to the window, and ready
         guard appIsBeingUsed else { return }
@@ -267,12 +262,10 @@ class App: AppCenterApplication {
         guard appIsBeingUsed else { return }
         Appearance.update()
         guard appIsBeingUsed else { return }
-        thumbnailsPanel.makeKeyAndOrderFront(nil) // workaround: without this, switching between 2 screens make thumbnailPanel invisible
-        KeyRepeatTimer.toggleRepeatingKeyNextWindow()
-        guard appIsBeingUsed else { return }
         refreshOpenUi([], .showUi)
         guard appIsBeingUsed else { return }
         thumbnailsPanel.show()
+        KeyRepeatTimer.toggleRepeatingKeyNextWindow()
         refreshOpenUi(Windows.list, .refreshOnlyThumbnailsAfterShowUi)
     }
 

src/ui/generic-components/LightImageView.swift

@@ -13,27 +13,46 @@ class LightImageView: NSView {
         super.init(frame: frameRect)
         translatesAutoresizingMaskIntoConstraints = false
         wantsLayer = true
+        // configure the layer for efficient GPU-scaling
         layer!.contentsGravity = .resize
         layer!.magnificationFilter = .trilinear
         layer!.minificationFilter = .trilinear
         layer!.minificationFilterBias = 0.0
         layer!.shouldRasterize = false
+        // disable implicit animations
+        layer!.actions = [
+            "contents": NSNull(),
+            "bounds": NSNull(),
+            "position": NSNull(),
+            "contentsScale": NSNull()
+        ]
     }
 
     func updateWithResizedCopy(_ image: CGImage?, _ size: NSSize) {
         let scaleFactor = NSScreen.preferred.backingScaleFactor
         if let image {
-            CATransaction.begin()
-            // disable implicit fade-in animation from CALayer
-            CATransaction.setDisableActions(true)
             // alternatively, we could set layer!.contentsGravity to .center, and use the lines bellow to resize ourselves
             //     let scaledSize = NSSize(width: size.width * scaleFactor, height: size.height * scaleFactor)
             //     layer!.contents = image.resizedCopyWithCoreGraphics(scaledSize, fixBitmapInfo)
             // it would produce subjectively better quality, but the resizing would be done on the CPU so poor performance
             layer!.contents = image
             layer!.contentsScale = scaleFactor
-            CATransaction.commit()
         }
         frame.size = size
     }
+
+    /// this schedules the image update for the next cycle
+    /// The Panel will show with previous pictures, then they each will get updated quickly. It's a trade-off of getting AltTab interactive faster at the price of wrong data being shown
+    /// I feel the UX is better without it. I may reconsider
+    func updateWithResizedCopyAsync(_ image: CGImage?, _ size: NSSize) {
+        layer!.contentsScale = NSScreen.preferred.backingScaleFactor
+        frame.size = size
+        if let image {
+            // set image on another cycle so it doesn't block initial rendering
+            DispatchQueue.main.async { [weak self] in
+                guard let self else { return }
+                self.layer!.contents = image
+            }
+        }
+    }
 }

src/ui/main-window/ThumbnailsPanel.swift

@@ -30,6 +30,17 @@ class ThumbnailsPanel: NSPanel {
         appearance = NSAppearance(named: Appearance.currentTheme == .dark ? .vibrantDark : .vibrantLight)
     }
 
+    func updateContents() {
+        CATransaction.begin()
+        defer { CATransaction.commit() }
+        CATransaction.setDisableActions(true)
+        thumbnailsView.updateItemsAndLayout()
+        guard App.app.appIsBeingUsed else { return }
+        setContentSize(thumbnailsView.contentView.frame.size)
+        guard App.app.appIsBeingUsed else { return }
+        NSScreen.preferred.repositionPanel(self)
+    }
+
     override func orderOut(_ sender: Any?) {
         if Preferences.fadeOutAnimation {
             NSAnimationContext.runAnimationGroup(