feat(controls): Add setting border color + fix background extending inside FluentWindow (#1508)

* Add setting border color

* Update FluentWindow.cs

* Update FluentWindow.cs

It's actually SystemAccent used by Windows.

* Update UnsafeNativeMethods.cs

* Use border only when active, similar to WinUI

* Update UnsafeNativeMethods.cs

* Listen for theme changes

* Ensure desktop composition is enabled before changing WindowChrome

Author: Nuklon

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

@@ -4,7 +4,9 @@
 // All Rights Reserved.
 
 using System.Windows.Shell;
+using Wpf.Ui.Appearance;
 using Wpf.Ui.Interop;
+using Wpf.Ui.Win32;
 
 // ReSharper disable once CheckNamespace
 namespace Wpf.Ui.Controls;
@@ -82,6 +84,17 @@ public bool ExtendsContentIntoTitleBar
     public FluentWindow()
     {
         SetResourceReference(StyleProperty, typeof(FluentWindow));
+
+        if (Utilities.IsOSWindows11OrNewer)
+        {
+            ApplicationThemeManager.Changed += (_, _) =>
+            {
+                if (IsActive)
+                {
+                    UnsafeNativeMethods.ApplyBorderColor(this, ApplicationAccentColorManager.SystemAccent);
+                }
+            };
+        }
     }
 
     /// <summary>
@@ -103,12 +116,35 @@ static FluentWindow()
     protected override void OnSourceInitialized(EventArgs e)
     {
         OnCornerPreferenceChanged(default, WindowCornerPreference);
-        OnExtendsContentIntoTitleBarChanged(default, ExtendsContentIntoTitleBar);
+        OnExtendsContentIntoTitleBarChanged(false, ExtendsContentIntoTitleBar);
         OnBackdropTypeChanged(default, WindowBackdropType);
 
         base.OnSourceInitialized(e);
     }
 
+    /// <inheritdoc />
+    protected override void OnActivated(EventArgs e)
+    {
+        base.OnActivated(e);
+
+        if (Utilities.IsOSWindows11OrNewer)
+        {
+            UnsafeNativeMethods.ApplyBorderColor(this, ApplicationAccentColorManager.SystemAccent);
+        }
+    }
+
+    /// <inheritdoc />
+    protected override void OnDeactivated(EventArgs e)
+    {
+        base.OnDeactivated(e);
+
+        if (Utilities.IsOSWindows11OrNewer)
+        {
+            // DWMWA_COLOR_DEFAULT.
+            UnsafeNativeMethods.ApplyBorderColor(this, unchecked((int)0xFFFFFFFF));
+        }
+    }
+
     /// <summary>
     /// Private <see cref="WindowCornerPreference"/> property callback.
     /// </summary>
@@ -182,10 +218,11 @@ protected virtual void OnBackdropTypeChanged(WindowBackdropType oldValue, Window
             return;
         }
 
+        SetWindowChrome();
+
         if (newValue == WindowBackdropType.None)
         {
             _ = WindowBackdrop.RemoveBackdrop(this);
-
             return;
         }
 
@@ -233,20 +270,36 @@ protected virtual void OnExtendsContentIntoTitleBarChanged(bool oldValue, bool n
         // AllowsTransparency = true;
         SetCurrentValue(WindowStyleProperty, WindowStyle.SingleBorderWindow);
 
-        WindowChrome.SetWindowChrome(
-            this,
-            new WindowChrome
-            {
-                CaptionHeight = 0,
-                CornerRadius = default,
-                GlassFrameThickness = new Thickness(-1),
-                ResizeBorderThickness = ResizeMode == ResizeMode.NoResize ? default : new Thickness(4),
-                UseAeroCaptionButtons = false,
-            }
-        );
-
         // WindowStyleProperty.OverrideMetadata(typeof(FluentWindow), new FrameworkPropertyMetadata(WindowStyle.SingleBorderWindow));
         // AllowsTransparencyProperty.OverrideMetadata(typeof(FluentWindow), new FrameworkPropertyMetadata(false));
         _ = UnsafeNativeMethods.RemoveWindowTitlebarContents(this);
     }
+
+    /// <summary>
+    /// This virtual method is called when <see cref="WindowBackdropType"/> is changed.
+    /// </summary>
+    protected virtual void SetWindowChrome()
+    {
+        try
+        {
+            if (Utilities.IsCompositionEnabled)
+            {
+                WindowChrome.SetWindowChrome(
+                                          this,
+                                          new WindowChrome
+                                          {
+                                              CaptionHeight = 0,
+                                              CornerRadius = default,
+                                              GlassFrameThickness = WindowBackdropType == WindowBackdropType.None ? new Thickness(0.00001) : new Thickness(-1), // 0.00001 so there's no glass frame drawn around the window, but the border is still drawn.
+                                              ResizeBorderThickness = ResizeMode == ResizeMode.NoResize ? default : new Thickness(4),
+                                              UseAeroCaptionButtons = false,
+                                          }
+                                         );
+            }
+        }
+        catch (COMException)
+        {
+            // Ignored.
+        }
+    }
 }

src/Wpf.Ui/Interop/UnsafeNativeMethods.cs

@@ -49,15 +49,64 @@ public static bool ApplyWindowCornerPreference(IntPtr handle, WindowCornerPrefer
 
         int pvAttribute = (int)UnsafeReflection.Cast(cornerPreference);
 
-        // TODO: Validate HRESULT
-        _ = Dwmapi.DwmSetWindowAttribute(
+        return Dwmapi.DwmSetWindowAttribute(
             handle,
             Dwmapi.DWMWINDOWATTRIBUTE.DWMWA_WINDOW_CORNER_PREFERENCE,
             ref pvAttribute,
             Marshal.SizeOf(typeof(int))
-        );
+        ) == 0;
+    }
 
-        return true;
+    /// <summary>
+    /// Tries to apply the color of the border.
+    /// </summary>
+    /// <param name="window">The window.</param>
+    /// <param name="color">The color.</param>
+    /// <returns><see langword="true" /> if invocation of native Windows function succeeds.</returns>
+    public static bool ApplyBorderColor(Window window, Color color) =>
+        GetHandle(window, out IntPtr windowHandle)
+     && ApplyBorderColor(windowHandle, color);
+
+    /// <summary>
+    /// Tries to apply the color of the border.
+    /// </summary>
+    /// <param name="window">The window.</param>
+    /// <param name="color">The color.</param>
+    /// <returns><see langword="true" /> if invocation of native Windows function succeeds.</returns>
+    public static bool ApplyBorderColor(Window window, int color) =>
+        GetHandle(window, out IntPtr windowHandle)
+     && ApplyBorderColor(windowHandle, color);
+
+    /// <summary>
+    /// Tries to apply the color of the border.
+    /// </summary>
+    /// <param name="handle">The handle.</param>
+    /// <param name="color">The color.</param>
+    /// <returns><see langword="true"/> if invocation of native Windows function succeeds.</returns>
+    public static bool ApplyBorderColor(IntPtr handle, Color color)
+    {
+        return ApplyBorderColor(handle, (color.B << 16) | (color.G << 8) | color.R);
+    }
+
+    /// <summary>
+    /// Tries to apply the color of the border.
+    /// </summary>
+    /// <param name="handle">The handle.</param>
+    /// <param name="color">The color.</param>
+    /// <returns><see langword="true"/> if invocation of native Windows function succeeds.</returns>
+    public static bool ApplyBorderColor(IntPtr handle, int color)
+    {
+        if (handle == IntPtr.Zero)
+        {
+            return false;
+        }
+
+        if (!User32.IsWindow(handle))
+        {
+            return false;
+        }
+
+        return Dwmapi.DwmSetWindowAttribute(handle, Dwmapi.DWMWINDOWATTRIBUTE.DWMWA_BORDER_COLOR, ref color, sizeof(int)) == 0;
     }
 
     /// <summary>
@@ -93,10 +142,7 @@ public static bool RemoveWindowDarkMode(IntPtr handle)
             dwAttribute = Dwmapi.DWMWINDOWATTRIBUTE.DMWA_USE_IMMERSIVE_DARK_MODE_OLD;
         }
 
-        // TODO: Validate HRESULT
-        _ = Dwmapi.DwmSetWindowAttribute(handle, dwAttribute, ref pvAttribute, Marshal.SizeOf(typeof(int)));
-
-        return true;
+        return Dwmapi.DwmSetWindowAttribute(handle, dwAttribute, ref pvAttribute, Marshal.SizeOf(typeof(int))) == 0;
     }
 
     /// <summary>
@@ -132,10 +178,7 @@ public static bool ApplyWindowDarkMode(IntPtr handle)
             dwAttribute = Dwmapi.DWMWINDOWATTRIBUTE.DMWA_USE_IMMERSIVE_DARK_MODE_OLD;
         }
 
-        // TODO: Validate HRESULT
-        _ = Dwmapi.DwmSetWindowAttribute(handle, dwAttribute, ref pvAttribute, Marshal.SizeOf(typeof(int)));
-
-        return true;
+        return Dwmapi.DwmSetWindowAttribute(handle, dwAttribute, ref pvAttribute, Marshal.SizeOf(typeof(int))) == 0;
     }
 
     /// <summary>
@@ -214,15 +257,12 @@ public static bool ApplyWindowBackdrop(IntPtr handle, WindowBackdropType backgro
             return false;
         }
 
-        // TODO: Validate HRESULT
-        _ = Dwmapi.DwmSetWindowAttribute(
+        return Dwmapi.DwmSetWindowAttribute(
             handle,
             Dwmapi.DWMWINDOWATTRIBUTE.DWMWA_SYSTEMBACKDROP_TYPE,
             ref backdropPvAttribute,
             Marshal.SizeOf(typeof(int))
-        );
-
-        return true;
+        ) == 0;
     }
 
     /// <summary>
@@ -296,15 +336,12 @@ public static bool ApplyWindowLegacyMicaEffect(IntPtr handle)
     {
         var backdropPvAttribute = 0x1; // Enable
 
-        // TODO: Validate HRESULT
-        _ = Dwmapi.DwmSetWindowAttribute(
+        return Dwmapi.DwmSetWindowAttribute(
             handle,
             Dwmapi.DWMWINDOWATTRIBUTE.DWMWA_MICA_EFFECT,
             ref backdropPvAttribute,
             Marshal.SizeOf(typeof(int))
-        );
-
-        return true;
+        ) == 0;
     }
 
     /// <summary>