fix(controls): Fix ClearType when using None backdrop

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

@@ -3,7 +3,6 @@
 // Copyright (C) Leszek Pomianowski and WPF UI Contributors.
 // All Rights Reserved.
 
-using System.Runtime.InteropServices;
 using System.Windows.Shell;
 using Wpf.Ui.Appearance;
 using Wpf.Ui.Interop;
@@ -295,26 +294,33 @@ protected virtual void SetWindowChrome()
     {
         try
         {
-            if (Utilities.IsCompositionEnabled)
+            bool canSetBorderMargins = Utilities.IsOSWindows11_24H2OrNewer;
+
+            Thickness glassFrameThickness = WindowBackdropType switch
+            {
+                WindowBackdropType.None when canSetBorderMargins => new Thickness(0),
+                WindowBackdropType.None => new Thickness(1),
+                _ => new Thickness(-1)
+            };
+
+            WindowChrome.SetWindowChrome(
+                                         this,
+                                         new WindowChrome
+                                         {
+                                             CaptionHeight = 0,
+                                             CornerRadius = default,
+                                             GlassFrameThickness = glassFrameThickness,
+                                             ResizeBorderThickness = ResizeMode == ResizeMode.NoResize ? default : new Thickness(4),
+                                             UseAeroCaptionButtons = false
+                                         }
+                                        );
+
+            if (canSetBorderMargins && WindowBackdropType == WindowBackdropType.None)
             {
-                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,
-                    }
-                );
+                UnsafeNativeMethods.SetBorderMargins(this, new Thickness(1));
             }
         }
-        catch (COMException)
+        catch
         {
             // Ignored.
         }

src/Wpf.Ui/Interop/UnsafeNativeMethods.cs

@@ -257,6 +257,29 @@ public static bool RemoveWindowTitlebarContents(IntPtr handle)
         return result.ToInt64() > 0;
     }
 
+    public static void SetBorderMargins(Window window, Thickness thickness)
+    {
+        if (GetHandle(window, out IntPtr windowHandle))
+        {
+            FRAME_MARGIN frameMargin = new()
+            {
+                bottom = (short)thickness.Bottom,
+                left = (short)thickness.Left,
+                top = (short)thickness.Top,
+                right = (short)thickness.Right
+            };
+
+            unsafe
+            {
+                PInvoke.DwmSetWindowAttribute(
+                                              new HWND(windowHandle),
+                                              DWMWINDOWATTRIBUTE.DWMWA_BORDER_MARGINS,
+                                              &frameMargin,
+                                              (uint)sizeof(FRAME_MARGIN));
+            }
+        }
+    }
+
     /// <summary>
     /// Tries to get currently selected Window accent color.
     /// </summary>

src/Wpf.Ui/NativeMethods.txt

@@ -32,4 +32,5 @@ HTMINBUTTON
 HTNOWHERE
 HTRIGHT*
 HTSYSMENU
-HTTOP*
+HTTOP*
+FRAME_MARGIN

src/Wpf.Ui/Win32/Utilities.cs

@@ -60,22 +60,22 @@ internal sealed class Utilities
     /// <summary>
     /// Gets a value indicating whether the operating system version is greater than or equal to 10.0* (build 10240).
     /// </summary>
-    public static bool IsOSWindows10OrNewer => _osVersion.Build >= 10240;
+    public static bool IsOSWindows10OrNewer => _osVersion is { Major: >= 10, Build: >= 10240 };
 
     /// <summary>
     /// Gets a value indicating whether the operating system version is greater than or equal to 10.0* (build 22000).
     /// </summary>
-    public static bool IsOSWindows11OrNewer => _osVersion.Build >= 22000;
+    public static bool IsOSWindows11OrNewer => _osVersion is { Major: >= 10, Build: >= 22000 };
 
     /// <summary>
-    /// Gets a value indicating whether the operating system version is greater than or equal to 10.0* (build 22523).
+    /// Gets a value indicating whether the operating system version is greater than or equal to 10.0* (build 26100).
     /// </summary>
-    public static bool IsOSWindows11Insider1OrNewer => _osVersion.Build >= 22523;
+    public static bool IsOSWindows11_24H2OrNewer => _osVersion is { Major: >= 10, Build: >= 26100 };
 
     /// <summary>
-    /// Gets a value indicating whether the operating system version is greater than or equal to 10.0* (build 22557).
+    /// Gets a value indicating whether the operating system version is greater than or equal to 10.0* (build 22523).
     /// </summary>
-    public static bool IsOSWindows11Insider2OrNewer => _osVersion.Build >= 22557;
+    public static bool IsOSWindows11Insider1OrNewer => _osVersion is { Major: >= 10, Build: >= 22523 };
 
     /// <summary>
     /// Gets a value indicating whether Desktop Window Manager (DWM) composition is enabled.