Merge branch 'development' into feature/4.0

src/Wpf.Ui/Appearance/WindowBackgroundManager.cs

@@ -100,6 +100,7 @@ WindowBackdropType backdrop
         }
 
         _ = WindowBackdrop.ApplyBackdrop(window, backdrop);
+
         if (applicationTheme is ApplicationTheme.Dark)
         {
             ApplyDarkThemeToWindow(window);
@@ -109,6 +110,8 @@ WindowBackdropType backdrop
             RemoveDarkThemeFromWindow(window);
         }
 
+        _ = WindowBackdrop.RemoveTitlebarBackground(window);
+
         foreach (object? subWindow in window.OwnedWindows)
         {
             if (subWindow is Window windowSubWindow)
@@ -123,6 +126,8 @@ WindowBackdropType backdrop
                 {
                     RemoveDarkThemeFromWindow(windowSubWindow);
                 }
+
+                _ = WindowBackdrop.RemoveTitlebarBackground(window);
             }
         }
     }

src/Wpf.Ui/Controls/FluentWindow/FluentWindow.cs

@@ -199,6 +199,8 @@ protected virtual void OnBackdropTypeChanged(WindowBackdropType oldValue, Window
         if (WindowBackdrop.IsSupported(newValue) && WindowBackdrop.RemoveBackground(this))
         {
             _ = WindowBackdrop.ApplyBackdrop(this, newValue);
+
+            _ = WindowBackdrop.RemoveTitlebarBackground(this);
         }
     }
 

src/Wpf.Ui/Controls/Window/WindowBackdrop.cs

@@ -38,7 +38,7 @@ public static bool IsSupported(WindowBackdropType backdropType)
     /// <param name="window">The window to which the backdrop effect will be applied.</param>
     /// <param name="backdropType">The type of backdrop effect to apply. Determines the visual appearance of the window's backdrop.</param>
     /// <returns><see langword="true"/> if the operation was successful; otherwise, <see langword="false"/>.</returns>
-    public static bool ApplyBackdrop(System.Windows.Window window, WindowBackdropType backdropType)
+    public static bool ApplyBackdrop(System.Windows.Window? window, WindowBackdropType backdropType)
     {
         if (window is null)
         {
@@ -216,6 +216,40 @@ public static bool RemoveBackground(System.Windows.Window? window)
         return true;
     }
 
+    public static bool RemoveTitlebarBackground(System.Windows.Window? window)
+    {
+        if (window is null)
+        {
+            return false;
+        }
+
+        IntPtr windowHandle = new WindowInteropHelper(window).Handle;
+
+        if (windowHandle == IntPtr.Zero)
+        {
+            return false;
+        }
+
+        HwndSource? windowSource = HwndSource.FromHwnd(windowHandle);
+
+        // Remove background from client area
+        if (windowSource?.Handle != IntPtr.Zero && windowSource?.CompositionTarget != null)
+        {
+            // NOTE: https://learn.microsoft.com/en-us/windows/win32/api/dwmapi/ne-dwmapi-dwmwindowattribute
+            // Specifying DWMWA_COLOR_DEFAULT (value 0xFFFFFFFF) for the color will reset the window back to using the system's default behavior for the caption color.
+            uint titlebarPvAttribute = 0xFFFFFFFE;
+
+            Dwmapi.DwmSetWindowAttribute(
+                windowSource.Handle,
+                Dwmapi.DWMWINDOWATTRIBUTE.DWMWA_CAPTION_COLOR,
+                ref titlebarPvAttribute,
+                Marshal.SizeOf(typeof(uint))
+            );
+        }
+
+        return true;
+    }
+
     private static bool ApplyDwmwWindowAttrubute(IntPtr hWnd, Dwmapi.DWMSBT dwmSbt)
     {
         if (hWnd == IntPtr.Zero)
@@ -228,7 +262,7 @@ private static bool ApplyDwmwWindowAttrubute(IntPtr hWnd, Dwmapi.DWMSBT dwmSbt)
             return false;
         }
 
-        var backdropPvAttribute = (int)dwmSbt;
+        int backdropPvAttribute = (int)dwmSbt;
 
         var dwmApiResult = Dwmapi.DwmSetWindowAttribute(
             hWnd,

src/Wpf.Ui/Interop/Dwmapi.cs

@@ -619,6 +619,22 @@ public static extern int DwmSetWindowAttribute(
         [In] int cbAttribute
     );
 
+    /// <summary>
+    /// Sets the value of Desktop Window Manager (DWM) non-client rendering attributes for a window.
+    /// </summary>
+    /// <param name="hWnd">The handle to the window for which the attribute value is to be set.</param>
+    /// <param name="dwAttribute">A flag describing which value to set, specified as a value of the DWMWINDOWATTRIBUTE enumeration.</param>
+    /// <param name="pvAttribute">A pointer to an object containing the attribute value to set.</param>
+    /// <param name="cbAttribute">The size, in bytes, of the attribute value being set via the <c>pvAttribute</c> parameter.</param>
+    /// <returns>If the function succeeds, it returns <c>S_OK</c>. Otherwise, it returns an <c>HRESULT</c> error code.</returns>
+    [DllImport(Libraries.Dwmapi)]
+    public static extern int DwmSetWindowAttribute(
+        [In] IntPtr hWnd,
+        [In] DWMWINDOWATTRIBUTE dwAttribute,
+        [In] ref uint pvAttribute,
+        [In] int cbAttribute
+    );
+
     /// <summary>
     /// Retrieves the current value of a specified Desktop Window Manager (DWM) attribute applied to a window. For programming guidance, and code examples, see Controlling non-client region rendering.
     /// </summary>