Hide the window from DWM until we're finished with initialization

.github/actions/spelling/allow/apis.txt

@@ -30,6 +30,7 @@ DERR
 dlldata
 DONTADDTORECENT
 DWORDLONG
+DWMWA
 endfor
 enumset
 environstrings

src/cascadia/TerminalApp/AppLogic.h

@@ -198,6 +198,7 @@ namespace winrt::TerminalApp::implementation
         FORWARDED_TYPED_EVENT(FullscreenChanged, winrt::Windows::Foundation::IInspectable, winrt::Windows::Foundation::IInspectable, _root, FullscreenChanged);
         FORWARDED_TYPED_EVENT(ChangeMaximizeRequested, winrt::Windows::Foundation::IInspectable, winrt::Windows::Foundation::IInspectable, _root, ChangeMaximizeRequested);
         FORWARDED_TYPED_EVENT(AlwaysOnTopChanged, winrt::Windows::Foundation::IInspectable, winrt::Windows::Foundation::IInspectable, _root, AlwaysOnTopChanged);
+        FORWARDED_TYPED_EVENT(Initialized, winrt::Windows::Foundation::IInspectable, winrt::Windows::Foundation::IInspectable, _root, Initialized);
         FORWARDED_TYPED_EVENT(RaiseVisualBell, winrt::Windows::Foundation::IInspectable, winrt::Windows::Foundation::IInspectable, _root, RaiseVisualBell);
         FORWARDED_TYPED_EVENT(SetTaskbarProgress, winrt::Windows::Foundation::IInspectable, winrt::Windows::Foundation::IInspectable, _root, SetTaskbarProgress);
         FORWARDED_TYPED_EVENT(IdentifyWindowsRequested, Windows::Foundation::IInspectable, Windows::Foundation::IInspectable, _root, IdentifyWindowsRequested);

src/cascadia/TerminalApp/AppLogic.idl

@@ -121,6 +121,7 @@ namespace TerminalApp
         event Windows.Foundation.TypedEventHandler<Object, Object> FullscreenChanged;
         event Windows.Foundation.TypedEventHandler<Object, Object> ChangeMaximizeRequested;
         event Windows.Foundation.TypedEventHandler<Object, Object> AlwaysOnTopChanged;
+        event Windows.Foundation.TypedEventHandler<Object, Object> Initialized;
         event Windows.Foundation.TypedEventHandler<Object, Object> RaiseVisualBell;
         event Windows.Foundation.TypedEventHandler<Object, Object> SetTaskbarProgress;
         event Windows.Foundation.TypedEventHandler<Object, Object> IdentifyWindowsRequested;

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -658,7 +658,7 @@ namespace winrt::TerminalApp::implementation
     // - <none>
     // Return Value:
     // - <none>
-    void TerminalPage::_CompleteInitialization()
+    winrt::fire_and_forget TerminalPage::_CompleteInitialization()
     {
         _startupState = StartupState::Initialized;
 
@@ -678,10 +678,48 @@ namespace winrt::TerminalApp::implementation
         if (_tabs.Size() == 0 && !(_shouldStartInboundListener || _isEmbeddingInboundListener))
         {
             _LastTabClosedHandlers(*this, nullptr);
+            co_return;
         }
         else
         {
-            _InitializedHandlers(*this, nullptr);
+            // GH#11561: When we start up, our window is initially just a frame
+            // with a transparent content area. We're gonna do all this startup
+            // init on the UI thread, so the UI won't actually paint till it's
+            // all done. This results in a few frames where the frame is
+            // visible, before the page paints for the first time, before any
+            // tabs appears, etc.
+            //
+            // To mitigate this, we're gonna wait for the UI thread to finish
+            // everything it's gotta do for the initial init, and _then_ fire
+            // our Initialized event. By waiting for everything else to finish
+            // (CoreDispatcherPriority::Low), we let all the tabs and panes
+            // actually get created. In the window layer, we're gonna cloak the
+            // window till this event is fired, so we don't actually see this
+            // frame until we're actually all ready to go.
+            //
+            // This will result in the window seemingly not loading as fast, but
+            // it will actually take exactly the same amount of time before it's
+            // usable.
+            //
+            // We also experimented with drawing a solid BG color before the
+            // initialization is finished. However, there are still a few frames
+            // after the frame is displayed before the XAML content first draws,
+            // so that didn't actually resolve any issues.
+
+            // Capture calling context.
+            winrt::apartment_context ui_thread;
+            auto weak{ get_weak() };
+
+            // Switch to the BG thread -
+            co_await winrt::resume_background();
+
+            // Then enqueue the rest of this function for after the UI thread settles.
+            co_await wil::resume_foreground(Dispatcher(), CoreDispatcherPriority::Low);
+
+            if (auto self{ weak.get() })
+            {
+                _InitializedHandlers(*self, nullptr);
+            }
         }
     }
 

src/cascadia/TerminalApp/TerminalPage.h

@@ -146,7 +146,7 @@ namespace winrt::TerminalApp::implementation
         TYPED_EVENT(AlwaysOnTopChanged, IInspectable, IInspectable);
         TYPED_EVENT(RaiseVisualBell, IInspectable, IInspectable);
         TYPED_EVENT(SetTaskbarProgress, IInspectable, IInspectable);
-        TYPED_EVENT(Initialized, IInspectable, winrt::Windows::UI::Xaml::RoutedEventArgs);
+        TYPED_EVENT(Initialized, IInspectable, IInspectable);
         TYPED_EVENT(IdentifyWindowsRequested, IInspectable, IInspectable);
         TYPED_EVENT(RenameWindowRequested, Windows::Foundation::IInspectable, winrt::TerminalApp::RenameWindowRequestedArgs);
         TYPED_EVENT(IsQuakeWindowChanged, IInspectable, IInspectable);
@@ -385,7 +385,7 @@ namespace winrt::TerminalApp::implementation
 
         void _StartInboundListener();
 
-        void _CompleteInitialization();
+        winrt::fire_and_forget _CompleteInitialization();
 
         void _FocusActiveControl(IInspectable sender, IInspectable eventArgs);
 

src/cascadia/TerminalApp/TerminalPage.idl

@@ -51,7 +51,7 @@ namespace TerminalApp
         event Windows.Foundation.TypedEventHandler<Object, Object> FocusModeChanged;
         event Windows.Foundation.TypedEventHandler<Object, Object> FullscreenChanged;
         event Windows.Foundation.TypedEventHandler<Object, Object> AlwaysOnTopChanged;
-        event Windows.Foundation.TypedEventHandler<Object, Windows.UI.Xaml.RoutedEventArgs> Initialized;
+        event Windows.Foundation.TypedEventHandler<Object, Object> Initialized;
         event Windows.Foundation.TypedEventHandler<Object, Object> SetTaskbarProgress;
         event Windows.Foundation.TypedEventHandler<Object, Object> IdentifyWindowsRequested;
         event Windows.Foundation.TypedEventHandler<Object, RenameWindowRequestedArgs> RenameWindowRequested;

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -377,6 +377,7 @@ void AppHost::Initialize()
     _revokers.FullscreenChanged = _logic.FullscreenChanged(winrt::auto_revoke, { this, &AppHost::_FullscreenChanged });
     _revokers.FocusModeChanged = _logic.FocusModeChanged(winrt::auto_revoke, { this, &AppHost::_FocusModeChanged });
     _revokers.AlwaysOnTopChanged = _logic.AlwaysOnTopChanged(winrt::auto_revoke, { this, &AppHost::_AlwaysOnTopChanged });
+    _revokers.Initialized = _logic.Initialized(winrt::auto_revoke, { this, &AppHost::_AppInitializedHandler });
     _revokers.RaiseVisualBell = _logic.RaiseVisualBell(winrt::auto_revoke, { this, &AppHost::_RaiseVisualBell });
     _revokers.SystemMenuChangeRequested = _logic.SystemMenuChangeRequested(winrt::auto_revoke, { this, &AppHost::_SystemMenuChangeRequested });
     _revokers.ChangeMaximizeRequested = _logic.ChangeMaximizeRequested(winrt::auto_revoke, { this, &AppHost::_ChangeMaximizeRequested });
@@ -533,6 +534,14 @@ LaunchPosition AppHost::_GetWindowLaunchPosition()
 // - None
 void AppHost::_HandleCreateWindow(const HWND hwnd, RECT proposedRect, LaunchMode& launchMode)
 {
+    // GH#11561: Hide the window until we're totally done being initialized.
+    // More commentary in TerminalPage::_CompleteInitialization
+    BOOL cloak = TRUE;
+    LOG_IF_FAILED(DwmSetWindowAttribute(hwnd,
+                                        DWMWA_CLOAK,
+                                        &cloak,
+                                        sizeof(cloak)));
+
     launchMode = _logic.GetLaunchMode();
 
     // Acquire the actual initial position
@@ -1547,3 +1556,15 @@ void AppHost::_CloseRequested(const winrt::Windows::Foundation::IInspectable& /*
     const auto pos = _GetWindowLaunchPosition();
     _logic.CloseWindow(pos);
 }
+
+void AppHost::_AppInitializedHandler(const winrt::Windows::Foundation::IInspectable& /*sender*/,
+                                     const winrt::Windows::Foundation::IInspectable& /*arg*/)
+{
+    // GH#11561: We're totally done being initialized. Uncloak the window, making it visible.
+    // More commentary in TerminalPage::_CompleteInitialization
+    BOOL cloak = FALSE;
+    LOG_IF_FAILED(DwmSetWindowAttribute(_window->GetHandle(),
+                                        DWMWA_CLOAK,
+                                        &cloak,
+                                        sizeof(cloak)));
+}

src/cascadia/WindowsTerminal/AppHost.h

@@ -52,6 +52,9 @@ class AppHost
                                   const winrt::Windows::Foundation::IInspectable& arg);
     void _AlwaysOnTopChanged(const winrt::Windows::Foundation::IInspectable& sender,
                              const winrt::Windows::Foundation::IInspectable& arg);
+    void _AppInitializedHandler(const winrt::Windows::Foundation::IInspectable& sender,
+                                const winrt::Windows::Foundation::IInspectable& arg);
+
     void _RaiseVisualBell(const winrt::Windows::Foundation::IInspectable& sender,
                           const winrt::Windows::Foundation::IInspectable& arg);
     void _WindowMouseWheeled(const til::point coord, const int32_t delta);
@@ -144,6 +147,7 @@ class AppHost
         winrt::TerminalApp::AppLogic::FullscreenChanged_revoker FullscreenChanged;
         winrt::TerminalApp::AppLogic::FocusModeChanged_revoker FocusModeChanged;
         winrt::TerminalApp::AppLogic::AlwaysOnTopChanged_revoker AlwaysOnTopChanged;
+        winrt::TerminalApp::AppLogic::Initialized_revoker Initialized;
         winrt::TerminalApp::AppLogic::RaiseVisualBell_revoker RaiseVisualBell;
         winrt::TerminalApp::AppLogic::SystemMenuChangeRequested_revoker SystemMenuChangeRequested;
         winrt::TerminalApp::AppLogic::ChangeMaximizeRequested_revoker ChangeMaximizeRequested;