Add IsBackdropAlwaysActive property to control backdrop behavior on focus loss

EleCho.WpfSuite.Helpers/Helpers/WindowOption.NativeMethods.cs

@@ -160,6 +160,7 @@ public enum DwmWindowAttribute
                 TEXT_COLOR,
                 VISIBLE_FRAME_BORDER_THICKNESS,
                 SYSTEMBACKDROP_TYPE,
+                SYSTEMBACKDROP_ALWAYS_ACTIVE,
                 LAST
             }
 

EleCho.WpfSuite.Helpers/Helpers/WindowOption.cs

@@ -89,6 +89,40 @@ public static void SetBackdrop(DependencyObject obj, WindowBackdrop value)
         }
 
 
+        /// <summary>
+        /// Get value of IsBackdropAlwaysActive property
+        /// </summary>
+        /// <param name="obj"></param>
+        /// <returns></returns>
+        /// <remarks>
+        /// This property controls whether the window backdrop (Mica/Acrylic) remains active when the window loses focus.
+        /// By default (false), Windows automatically deactivates the backdrop when the window is not focused.
+        /// When set to true, the backdrop will remain active even when the window loses focus.
+        /// This property is primarily designed for Window objects, but also supports Popup, ToolTip, ContextMenu, and MenuItem for consistency with other WindowOption properties.
+        /// </remarks>
+        [AttachedPropertyBrowsableForType(typeof(Window))]
+        public static bool GetIsBackdropAlwaysActive(DependencyObject obj)
+        {
+            return (bool)obj.GetValue(IsBackdropAlwaysActiveProperty);
+        }
+
+        /// <summary>
+        /// Set value of IsBackdropAlwaysActive property
+        /// </summary>
+        /// <param name="obj"></param>
+        /// <param name="value"></param>
+        /// <remarks>
+        /// This property controls whether the window backdrop (Mica/Acrylic) remains active when the window loses focus.
+        /// By default (false), Windows automatically deactivates the backdrop when the window is not focused.
+        /// When set to true, the backdrop will remain active even when the window loses focus.
+        /// This property is primarily designed for Window objects, but also supports Popup, ToolTip, ContextMenu, and MenuItem for consistency with other WindowOption properties.
+        /// </remarks>
+        public static void SetIsBackdropAlwaysActive(DependencyObject obj, bool value)
+        {
+            obj.SetValue(IsBackdropAlwaysActiveProperty, value);
+        }
+
+
         /// <summary>
         /// Get value of Corner property
         /// </summary>
@@ -398,6 +432,18 @@ public static void SetIsCaption(DependencyObject obj, bool value)
         public static readonly DependencyProperty BackdropProperty =
             DependencyProperty.RegisterAttached("Backdrop", typeof(WindowBackdrop), typeof(WindowOption), new FrameworkPropertyMetadata(WindowBackdrop.Auto, OnBackdropChanged));
 
+        /// <summary>
+        /// The DependencyProperty of IsBackdropAlwaysActive property
+        /// </summary>
+        /// <remarks>
+        /// Controls whether the window backdrop (Mica/Acrylic) remains active when the window loses focus.
+        /// Default value is false, meaning the backdrop will be deactivated when the window loses focus (standard Windows behavior).
+        /// When set to true, the backdrop will remain active even when the window is not focused.
+        /// This property requires Windows 11 Build 22621 or later.
+        /// </remarks>
+        public static readonly DependencyProperty IsBackdropAlwaysActiveProperty =
+            DependencyProperty.RegisterAttached("IsBackdropAlwaysActive", typeof(bool), typeof(WindowOption), new FrameworkPropertyMetadata(false, OnIsBackdropAlwaysActiveChanged));
+
         /// <summary>
         /// The DependencyProperty of Corner property
         /// </summary>
@@ -1010,6 +1056,54 @@ backdrop is not WindowBackdrop.Auto &&
             }
         }
 
+        private static void OnIsBackdropAlwaysActiveChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+        {
+            var isAlwaysActive = GetIsBackdropAlwaysActive(d);
+
+            if (GetWindowHwndSource(d) is HwndSource hwndSource)
+            {
+                ApplyIsBackdropAlwaysActive(hwndSource, isAlwaysActive);
+            }
+
+            // Always remove the event handler first to prevent duplicates
+            if (d is Window window)
+            {
+                window.SourceInitialized -= EventHandlerApplyIsBackdropAlwaysActive;
+                if (isAlwaysActive)
+                    window.SourceInitialized += EventHandlerApplyIsBackdropAlwaysActive;
+            }
+            else if (d is Popup popup)
+            {
+                popup.Opened -= EventHandlerApplyIsBackdropAlwaysActive;
+                if (isAlwaysActive)
+                    popup.Opened += EventHandlerApplyIsBackdropAlwaysActive;
+            }
+            else if (d is ToolTip toolTip)
+            {
+                toolTip.Opened -= EventHandlerApplyIsBackdropAlwaysActive;
+                if (isAlwaysActive)
+                    toolTip.Opened += EventHandlerApplyIsBackdropAlwaysActive;
+            }
+            else if (d is ContextMenu contextMenu)
+            {
+                contextMenu.Opened -= EventHandlerApplyIsBackdropAlwaysActive;
+                if (isAlwaysActive)
+                    contextMenu.Opened += EventHandlerApplyIsBackdropAlwaysActive;
+            }
+            else if (d is MenuItem menuItem)
+            {
+                menuItem.SubmenuOpened -= EventHandlerApplyIsBackdropAlwaysActive;
+                if (isAlwaysActive)
+                    menuItem.SubmenuOpened += EventHandlerApplyIsBackdropAlwaysActive;
+            }
+            else if (d is FrameworkElement element)
+            {
+                element.Loaded -= EventHandlerApplyIsBackdropAlwaysActive;
+                if (isAlwaysActive)
+                    element.Loaded += EventHandlerApplyIsBackdropAlwaysActive;
+            }
+        }
+
         private static void OnCornerChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             var corner = GetCorner(d);
@@ -1988,6 +2082,17 @@ private static unsafe void ApplyCorner(HwndSource hwndSource, WindowCorner corne
             DwmSetWindowAttribute(handle, DwmWindowAttribute.WINDOW_CORNER_PREFERENCE, (nint)(void*)&corner, (uint)sizeof(WindowCorner));
         }
 
+        private static unsafe void ApplyIsBackdropAlwaysActive(HwndSource hwndSource, bool isAlwaysActive)
+        {
+            // this api is only available on windows 11 22621
+            if (s_versionCurrentWindows < s_versionWindows11_22621)
+                return;
+
+            var handle = hwndSource.Handle;
+
+            DwmSetWindowAttribute(handle, DwmWindowAttribute.SYSTEMBACKDROP_ALWAYS_ACTIVE, (nint)(void*)&isAlwaysActive, (uint)sizeof(bool));
+        }
+
         private static unsafe void ApplyCaptionColor(HwndSource hwndSource, WindowOptionColor color)
         {
             // this api is only available on windows 11 22000
@@ -2423,6 +2528,13 @@ private static void EventHandlerApplyCorner(object? sender, EventArgs e)
                 ApplyCorner(hwndSource, GetCorner(d));
         }
 
+        private static void EventHandlerApplyIsBackdropAlwaysActive(object? sender, EventArgs e)
+        {
+            if (sender is DependencyObject d &&
+                GetWindowHwndSource(d) is HwndSource hwndSource)
+                ApplyIsBackdropAlwaysActive(hwndSource, GetIsBackdropAlwaysActive(d));
+        }
+
         private static void EventHandlerApplyCaptionColor(object? sender, EventArgs e)
         {
             if (sender is DependencyObject d &&

WpfTest/Tests/BackdropAlwaysActiveTestWindow.xaml

@@ -0,0 +1,69 @@
+<Window x:Class="WpfTest.Tests.BackdropAlwaysActiveTestWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:local="clr-namespace:WpfTest.Tests"
+        xmlns:ws="https://schemas.elecho.dev/wpfsuite"
+        mc:Ignorable="d"
+        Title="Backdrop Always Active Test" Height="400" Width="600"
+        Background="Transparent"
+        d:Background="White"
+        ws:WindowOption.Backdrop="Acrylic"
+        ws:WindowOption.IsBackdropAlwaysActive="True">
+
+    <WindowChrome.WindowChrome>
+        <WindowChrome CaptionHeight="45"
+                      GlassFrameThickness="-1"/>
+    </WindowChrome.WindowChrome>
+
+    <Grid>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto"/>
+            <RowDefinition Height="*"/>
+        </Grid.RowDefinitions>
+
+        <!-- Title Bar -->
+        <Grid Grid.Row="0" Height="45" Background="#20000000">
+            <TextBlock Text="Backdrop Always Active Test"
+                       VerticalAlignment="Center"
+                       HorizontalAlignment="Left"
+                       Margin="15,0,0,0"
+                       FontSize="14"
+                       FontWeight="SemiBold"/>
+        </Grid>
+
+        <!-- Content -->
+        <Grid Grid.Row="1" Margin="20">
+            <StackPanel VerticalAlignment="Center" HorizontalAlignment="Center">
+                <TextBlock Text="Test Instructions:"
+                           FontSize="18"
+                           FontWeight="Bold"
+                           Margin="0,0,0,15"/>
+
+                <TextBlock TextWrapping="Wrap"
+                           FontSize="14"
+                           MaxWidth="500"
+                           Margin="0,0,0,10">
+                    <Run Text="1. This window has"/>
+                    <Run Text="ws:WindowOption.IsBackdropAlwaysActive=&quot;True&quot;" FontWeight="Bold"/>
+                    <LineBreak/>
+                    <Run Text="2. Click another window to make this window lose focus"/>
+                    <LineBreak/>
+                    <Run Text="3. The Acrylic backdrop should"/>
+                    <Run Text="remain active" FontWeight="Bold"/>
+                    <Run Text="even when the window loses focus"/>
+                    <LineBreak/>
+                    <LineBreak/>
+                    <Run Text="Compare this with the standard behavior:"/>
+                </TextBlock>
+
+                <Button Content="Open Window Without Always Active"
+                        Click="OpenNormalWindow_Click"
+                        Padding="15,8"
+                        Margin="0,15,0,0"
+                        HorizontalAlignment="Center"/>
+            </StackPanel>
+        </Grid>
+    </Grid>
+</Window>

WpfTest/Tests/BackdropAlwaysActiveTestWindow.xaml.cs

@@ -0,0 +1,21 @@
+using System.Windows;
+
+namespace WpfTest.Tests
+{
+    /// <summary>
+    /// Interaction logic for BackdropAlwaysActiveTestWindow.xaml
+    /// </summary>
+    public partial class BackdropAlwaysActiveTestWindow : Window
+    {
+        public BackdropAlwaysActiveTestWindow()
+        {
+            InitializeComponent();
+        }
+
+        private void OpenNormalWindow_Click(object sender, RoutedEventArgs e)
+        {
+            var normalWindow = new BackdropNormalTestWindow();
+            normalWindow.Show();
+        }
+    }
+}

WpfTest/Tests/BackdropNormalTestWindow.xaml

@@ -0,0 +1,59 @@
+<Window x:Class="WpfTest.Tests.BackdropNormalTestWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:local="clr-namespace:WpfTest.Tests"
+        xmlns:ws="https://schemas.elecho.dev/wpfsuite"
+        mc:Ignorable="d"
+        Title="Normal Backdrop Test" Height="350" Width="500"
+        Background="Transparent"
+        d:Background="White"
+        ws:WindowOption.Backdrop="Acrylic">
+
+    <WindowChrome.WindowChrome>
+        <WindowChrome CaptionHeight="45"
+                      GlassFrameThickness="-1"/>
+    </WindowChrome.WindowChrome>
+
+    <Grid>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto"/>
+            <RowDefinition Height="*"/>
+        </Grid.RowDefinitions>
+
+        <!-- Title Bar -->
+        <Grid Grid.Row="0" Height="45" Background="#20000000">
+            <TextBlock Text="Normal Backdrop Test"
+                       VerticalAlignment="Center"
+                       HorizontalAlignment="Left"
+                       Margin="15,0,0,0"
+                       FontSize="14"
+                       FontWeight="SemiBold"/>
+        </Grid>
+
+        <!-- Content -->
+        <Grid Grid.Row="1" Margin="20">
+            <StackPanel VerticalAlignment="Center" HorizontalAlignment="Center">
+                <TextBlock Text="Normal Behavior Window"
+                           FontSize="18"
+                           FontWeight="Bold"
+                           Margin="0,0,0,15"/>
+
+                <TextBlock TextWrapping="Wrap"
+                           FontSize="14"
+                           MaxWidth="450"
+                           TextAlignment="Center">
+                    <Run Text="This window has"/>
+                    <Run Text="ws:WindowOption.IsBackdropAlwaysActive=&quot;False&quot;" FontWeight="Bold"/>
+                    <Run Text="(default behavior)"/>
+                    <LineBreak/>
+                    <LineBreak/>
+                    <Run Text="When this window loses focus, the Acrylic backdrop"/>
+                    <LineBreak/>
+                    <Run Text="will become inactive and turn gray-white."/>
+                </TextBlock>
+            </StackPanel>
+        </Grid>
+    </Grid>
+</Window>

WpfTest/Tests/BackdropNormalTestWindow.xaml.cs

@@ -0,0 +1,15 @@
+using System.Windows;
+
+namespace WpfTest.Tests
+{
+    /// <summary>
+    /// Interaction logic for BackdropNormalTestWindow.xaml
+    /// </summary>
+    public partial class BackdropNormalTestWindow : Window
+    {
+        public BackdropNormalTestWindow()
+        {
+            InitializeComponent();
+        }
+    }
+}

WpfTest/Tests/WindowCompositionTest.xaml

@@ -39,6 +39,15 @@
                         <ws:Button Content="Custom Acrylic Window" Command="{Binding OpenDarkCustomAcrylicWindowCommand}"/>
                     </ws:StackPanel>
                 </ws:GroupBox>
+
+                <ws:GroupBox Header="Backdrop Always Active"
+                             Padding="8">
+                    <ws:StackPanel Orientation="Horizontal"
+                               HorizontalAlignment="Left"
+                               Spacing="8">
+                        <ws:Button Content="Test Backdrop Always Active" Command="{Binding OpenBackdropAlwaysActiveTestWindowCommand}"/>
+                    </ws:StackPanel>
+                </ws:GroupBox>
             </ws:StackPanel>
         </Grid>
     </ws:ScrollViewer>

WpfTest/Tests/WindowCompositionTest.xaml.cs

@@ -75,5 +75,11 @@ public void OpenDarkCustomAcrylicWindow()
             window.Foreground = new SolidColorBrush(Color.FromRgb(214, 214, 214));
             window.Show();
         }
+
+        [RelayCommand]
+        public void OpenBackdropAlwaysActiveTestWindow()
+        {
+            new BackdropAlwaysActiveTestWindow().Show();
+        }
     }
 }