Use standard 1px window borders on NC Island Window

src/cascadia/TerminalApp/App.cpp

@@ -338,7 +338,8 @@ namespace winrt::TerminalApp::implementation
         TerminalSettings settings = _settings->MakeSettings(std::nullopt);
 
         // TODO MSFT:21150597 - If the global setting "Always show tab bar" is
-        // set, then we'll need to add the height of the tab bar here.
+        // set or if "Show tabs in title bar" is set, then we'll need to add
+        // the height of the tab bar here.
 
         return TermControl::GetProposedDimensions(settings, dpi);
     }
@@ -397,6 +398,17 @@ namespace winrt::TerminalApp::implementation
         return point;
     }
 
+    winrt::Windows::UI::Xaml::ElementTheme App::GetRequestedTheme()
+    {
+        if (!_loadedInitialSettings)
+        {
+            // Load settings if we haven't already
+            LoadSettings();
+        }
+
+        return _settings->GlobalSettings().GetRequestedTheme();
+    }
+
     bool App::GetShowTabsInTitlebar()
     {
         if (!_loadedInitialSettings)

src/cascadia/TerminalApp/App.h

@@ -32,6 +32,7 @@ namespace winrt::TerminalApp::implementation
 
         Windows::Foundation::Point GetLaunchDimensions(uint32_t dpi);
         winrt::Windows::Foundation::Point GetLaunchInitialPositions(int32_t defaultInitialX, int32_t defaultInitialY);
+        winrt::Windows::UI::Xaml::ElementTheme GetRequestedTheme();
         LaunchMode GetLaunchMode();
         bool GetShowTabsInTitlebar();
 

src/cascadia/TerminalApp/App.idl

@@ -31,6 +31,7 @@ namespace TerminalApp
 
         Windows.Foundation.Point GetLaunchDimensions(UInt32 dpi);
         Windows.Foundation.Point GetLaunchInitialPositions(Int32 defaultInitialX, Int32 defaultInitialY);
+        Windows.UI.Xaml.ElementTheme GetRequestedTheme();
         LaunchMode GetLaunchMode();
         Boolean GetShowTabsInTitlebar();
         void TitlebarClicked();

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -22,7 +22,7 @@ AppHost::AppHost() noexcept :
 
     if (_useNonClientArea)
     {
-        _window = std::make_unique<NonClientIslandWindow>();
+        _window = std::make_unique<NonClientIslandWindow>(_app.GetRequestedTheme());
     }
     else
     {
@@ -188,54 +188,25 @@ void AppHost::_HandleCreateWindow(const HWND hwnd, RECT proposedRect, winrt::Ter
 
         auto initialSize = _app.GetLaunchDimensions(dpix);
 
-        const short _currentWidth = Utils::ClampToShortMax(
+        const short islandWidth = Utils::ClampToShortMax(
             static_cast<long>(ceil(initialSize.X)), 1);
-        const short _currentHeight = Utils::ClampToShortMax(
+        const short islandHeight = Utils::ClampToShortMax(
             static_cast<long>(ceil(initialSize.Y)), 1);
 
-        // Create a RECT from our requested client size
-        auto nonClient = Viewport::FromDimensions({ _currentWidth,
-                                                    _currentHeight })
-                             .ToRect();
+        RECT islandFrame = {};
+        bool succeeded = AdjustWindowRectExForDpi(&islandFrame, WS_OVERLAPPEDWINDOW, false, 0, dpix);
+        // If we failed to get the correct window size for whatever reason, log
+        // the error and go on. We'll use whatever the control proposed as the
+        // size of our window, which will be at least close.
+        LOG_LAST_ERROR_IF(!succeeded);
 
-        // Get the size of a window we'd need to host that client rect. This will
-        // add the titlebar space.
         if (_useNonClientArea)
         {
-            // If we're in NC tabs mode, do the math ourselves. Get the margins
-            // we're using for the window - this will include the size of the
-            // titlebar content.
-            const auto pNcWindow = static_cast<NonClientIslandWindow*>(_window.get());
-            const MARGINS margins = pNcWindow->GetFrameMargins();
-            nonClient.left = 0;
-            nonClient.top = 0;
-            nonClient.right = margins.cxLeftWidth + nonClient.right + margins.cxRightWidth;
-            nonClient.bottom = margins.cyTopHeight + nonClient.bottom + margins.cyBottomHeight;
-        }
-        else
-        {
-            bool succeeded = AdjustWindowRectExForDpi(&nonClient, WS_OVERLAPPEDWINDOW, false, 0, dpix);
-            if (!succeeded)
-            {
-                // If we failed to get the correct window size for whatever reason, log
-                // the error and go on. We'll use whatever the control proposed as the
-                // size of our window, which will be at least close.
-                LOG_LAST_ERROR();
-                nonClient = Viewport::FromDimensions({ _currentWidth,
-                                                       _currentHeight })
-                                .ToRect();
-            }
-
-            // For client island scenario, there is an invisible border of 8 pixels.
-            // We need to remove this border to guarantee the left edge of the window
-            // coincides with the screen
-            const auto pCWindow = static_cast<IslandWindow*>(_window.get());
-            const RECT frame = pCWindow->GetFrameBorderMargins(dpix);
-            proposedRect.left += frame.left;
+            islandFrame.top = -NonClientIslandWindow::topBorderVisibleHeight;
         }
 
-        adjustedHeight = nonClient.bottom - nonClient.top;
-        adjustedWidth = nonClient.right - nonClient.left;
+        adjustedWidth = -islandFrame.left + islandWidth + islandFrame.right;
+        adjustedHeight = -islandFrame.top + islandHeight + islandFrame.bottom;
     }
 
     const COORD origin{ gsl::narrow<short>(proposedRect.left),
@@ -294,5 +265,5 @@ void AppHost::_UpdateTitleBarContent(const winrt::Windows::Foundation::IInspecta
 // - <none>
 void AppHost::_UpdateTheme(const winrt::TerminalApp::App&, const winrt::Windows::UI::Xaml::ElementTheme& arg)
 {
-    _window->UpdateTheme(arg);
+    _window->OnApplicationThemeChanged(arg);
 }

src/cascadia/WindowsTerminal/BaseWindow.h

@@ -34,10 +34,8 @@ class BaseWindow
             WINRT_ASSERT(that);
             WINRT_ASSERT(!that->_window);
             that->_window = wil::unique_hwnd(window);
-            SetWindowLongPtr(window, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(that));
 
-            EnableNonClientDpiScaling(window);
-            that->_currentDpi = GetDpiForWindow(window);
+            return that->_OnNcCreate(wparam, lparam);
         }
         else if (T* that = GetThisFromHandle(window))
         {
@@ -245,6 +243,20 @@ class BaseWindow
     std::wstring _title = L"";
 
     bool _minimized = false;
+
+    // Method Description:
+    // - This method is called when the window receives the WM_NCCREATE message.
+    // Return Value:
+    // - The value returned from the window proc.
+    virtual [[nodiscard]] LRESULT _OnNcCreate(WPARAM wParam, LPARAM lParam) noexcept
+    {
+        SetWindowLongPtr(_window.get(), GWLP_USERDATA, reinterpret_cast<LONG_PTR>(this));
+
+        EnableNonClientDpiScaling(_window.get());
+        _currentDpi = GetDpiForWindow(_window.get());
+
+        return DefWindowProc(_window.get(), WM_NCCREATE, wParam, lParam);
+    };
 };
 
 template<typename T>

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -243,15 +243,6 @@ IRawElementProviderSimple* IslandWindow::_GetUiaProvider()
     return _pUiaProvider;
 }
 
-RECT IslandWindow::GetFrameBorderMargins(unsigned int currentDpi)
-{
-    const auto windowStyle = GetWindowStyle(_window.get());
-    const auto targetStyle = windowStyle & ~WS_DLGFRAME;
-    RECT frame{};
-    AdjustWindowRectExForDpi(&frame, targetStyle, false, GetWindowExStyle(_window.get()), currentDpi);
-    return frame;
-}
-
 // Method Description:
 // - Called when the window has been resized (or maximized)
 // Arguments:
@@ -300,7 +291,7 @@ void IslandWindow::OnAppInitialized()
 // - arg: the ElementTheme to use as the new theme for the UI
 // Return Value:
 // - <none>
-void IslandWindow::UpdateTheme(const winrt::Windows::UI::Xaml::ElementTheme& requestedTheme)
+void IslandWindow::OnApplicationThemeChanged(const winrt::Windows::UI::Xaml::ElementTheme& requestedTheme)
 {
     _rootGrid.RequestedTheme(requestedTheme);
     // Invalidate the window rect, so that we'll repaint any elements we're

src/cascadia/WindowsTerminal/IslandWindow.h

@@ -23,19 +23,17 @@ class IslandWindow :
 
     [[nodiscard]] virtual LRESULT MessageHandler(UINT const message, WPARAM const wparam, LPARAM const lparam) noexcept override;
     IRawElementProviderSimple* _GetUiaProvider();
-    RECT GetFrameBorderMargins(unsigned int currentDpi);
     void OnResize(const UINT width, const UINT height) override;
     void OnMinimize() override;
     void OnRestore() override;
     virtual void OnAppInitialized();
     virtual void SetContent(winrt::Windows::UI::Xaml::UIElement content);
+    virtual void OnApplicationThemeChanged(const winrt::Windows::UI::Xaml::ElementTheme& requestedTheme);
 
     virtual void Initialize();
 
     void SetCreateCallback(std::function<void(const HWND, const RECT, winrt::TerminalApp::LaunchMode& launchMode)> pfn) noexcept;
 
-    void UpdateTheme(const winrt::Windows::UI::Xaml::ElementTheme& requestedTheme);
-
 #pragma region IUiaWindow
     void ChangeViewport(const SMALL_RECT /*NewWindow*/)
     {