Implement Win32Properties.WindowCornerPreference (#21615)

* Implement Win32Properties.WindowCornerPreference

* Add corner preference to ControlCatalog

* Update API suppressions

api/Avalonia.nupkg.xml

@@ -97,4 +97,16 @@
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.OpenGL.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.OpenGL.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0006</DiagnosticId>
+    <Target>M:Avalonia.Controls.Platform.IWin32OptionsTopLevelImpl.SetWindowCornerPreference(Avalonia.Controls.Win32Properties.WindowCornerPreference)</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Controls.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0006</DiagnosticId>
+    <Target>M:Avalonia.Controls.Platform.IWin32OptionsTopLevelImpl.SetWindowCornerPreference(Avalonia.Controls.Win32Properties.WindowCornerPreference)</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Controls.dll</Right>
+  </Suppression>
 </Suppressions>

samples/ControlCatalog/MainWindow.xaml

@@ -12,6 +12,7 @@
         CanResize="{Binding CanResize}"
         CanMinimize="{Binding CanMinimize}"
         CanMaximize="{Binding CanMaximize}"
+        Win32Properties.WindowCornerPreference="{Binding Win32WindowCornerPreference}"
         x:Class="ControlCatalog.MainWindow" WindowState="{Binding WindowState, Mode=TwoWay}"
         x:DataType="vm:MainWindowViewModel">
   <NativeMenu.Menu>

samples/ControlCatalog/Pages/WindowCustomizationsPage.xaml

@@ -42,6 +42,19 @@
                 IsChecked="{Binding CanMaximize}"
                 IsEnabled="{Binding CanResize}" />
 
+      <DockPanel>
+
+        <Label Content="Corner Preference (Windows 11+): "
+               Margin="4"
+               DockPanel.Dock="Left" />
+
+        <ComboBox ItemsSource="{Binding Win32WindowCornerPreferences}"
+                  SelectedItem="{Binding Win32WindowCornerPreference, Mode=TwoWay}"
+                  HorizontalAlignment="Left"
+                  MinWidth="220" />
+
+      </DockPanel>
+
     </StackPanel>
 
     <StackPanel Spacing="10" Margin="25" IsEnabled="{OnFormFactor false, Mobile=true}">

samples/ControlCatalog/ViewModels/MainWindowViewModel.cs

@@ -122,7 +122,6 @@ namespace ControlCatalog.ViewModels
             set { RaiseAndSetIfChanged(ref _selectedDecorationIndex, value); }
         }
 
-
         public MiniCommand AboutCommand { get; }
 
         public MiniCommand ExitCommand { get; }
@@ -138,5 +137,14 @@ namespace ControlCatalog.ViewModels
             get => _validatedDateExample;
             set => RaiseAndSetIfChanged(ref _validatedDateExample, value);
         }
+
+        public Win32Properties.WindowCornerPreference[] Win32WindowCornerPreferences { get; } =
+            Enum.GetValues<Win32Properties.WindowCornerPreference>();
+
+        public Win32Properties.WindowCornerPreference Win32WindowCornerPreference
+        {
+            get;
+            set { RaiseAndSetIfChanged(ref field, value); }
+        }
     }
 }

src/Avalonia.Controls/Platform/IWin32OptionsTopLevelImpl.cs

@@ -1,9 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using Avalonia.Metadata;
+using Avalonia.Metadata;
 using Avalonia.Platform;
 using static Avalonia.Controls.Win32Properties;
 
@@ -21,5 +16,11 @@ namespace Avalonia.Controls.Platform
         /// Gets or sets a custom callback for the window's WndProc
         /// </summary>
         public CustomWndProcHookCallback? WndProcHookCallback { get; set; }
+
+        /// <summary>
+        /// Sets a window corner preference for the window.
+        /// </summary>
+        /// <param name="preference">The value to set.</param>
+        public void SetWindowCornerPreference(WindowCornerPreference preference);
     }
 }

src/Avalonia.Controls/Platform/Win32Properties.cs

@@ -17,9 +17,38 @@ namespace Avalonia.Controls
     /// </summary>
     public static class Win32Properties
     {
+        /// <summary>
+        /// Defines the <c>NonClientHitTestResult</c> attached property.
+        /// </summary>
+        public static readonly AttachedProperty<Win32HitTestValue> NonClientHitTestResultProperty =
+            AvaloniaProperty.RegisterAttached<Visual, Win32HitTestValue>(
+                "NonClientHitTestResult",
+                typeof(Win32Properties),
+                inherits: true,
+                defaultValue: Win32HitTestValue.Client);
+
+        /// <summary>
+        /// Defines the <c>WindowCornerPreferenceProperty</c> attached property.
+        /// </summary>
+        public static readonly AttachedProperty<WindowCornerPreference> WindowCornerPreferenceProperty =
+            AvaloniaProperty.RegisterAttached<Window, WindowCornerPreference>(
+                "WindowCornerPreference",
+                typeof(Win32Properties),
+                defaultValue: WindowCornerPreference.Default,
+                validate: ValidateWindowCornerPreference);
+
         public delegate (uint style, uint exStyle) CustomWindowStylesCallback(uint style, uint exStyle);
         public delegate IntPtr CustomWndProcHookCallback(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam, ref bool handled);
 
+        static Win32Properties()
+        {
+            WindowCornerPreferenceProperty.Changed.AddClassHandler<Window>((window, e) =>
+            {
+                if (window.PlatformImpl is IWin32OptionsTopLevelImpl toplevelImpl)
+                    toplevelImpl.SetWindowCornerPreference(e.GetNewValue<WindowCornerPreference>());
+            });
+        }
+
         /// <summary>
         /// Adds a callback to set the window's style.
         /// </summary>
@@ -72,16 +101,48 @@ namespace Avalonia.Controls
             }
         }
 
-        public static readonly AttachedProperty<Win32HitTestValue> NonClientHitTestResultProperty =
-            AvaloniaProperty.RegisterAttached<Visual, Win32HitTestValue>(
-                "NonClientHitTestResult",
-                typeof(Win32Properties),
-                inherits: true,
-                defaultValue: Win32HitTestValue.Client);
+        /// <summary>
+        /// Sets the value of the <c>NonClientHitTestResult</c> attached property on the specified visual.
+        /// </summary>
+        /// <param name="obj">The visual.</param>
+        /// <param name="value">The value to set.</param>
+        public static void SetNonClientHitTestResult(Visual obj, Win32HitTestValue value)
+            => obj.SetValue(NonClientHitTestResultProperty, value);
+
+        /// <summary>
+        /// Gets the value of the <c>NonClientHitTestResult</c> attached property on the specified visual.
+        /// </summary>
+        /// <param name="obj">The visual.</param>
+        /// <returns>The hit test value for <paramref name="obj"/>.</returns>
+        public static Win32HitTestValue GetNonClientHitTestResult(Visual obj)
+            => obj.GetValue(NonClientHitTestResultProperty);
+
+        /// <summary>
+        /// Sets the value of the <c>WindowCornerPreference</c> attached property on the specified window.
+        /// </summary>
+        /// <param name="window">The window.</param>
+        /// <param name="value">The value to set.</param>
+        /// <remarks>
+        /// This value is supported starting with Windows 11 Build 22000.
+        /// It is ignored on earlier Windows versions.
+        /// </remarks>
+        public static void SetWindowCornerPreference(Window window, WindowCornerPreference value)
+            => window.SetValue(WindowCornerPreferenceProperty, value);
+
+        /// <summary>
+        /// Gets the value of the <c>WindowCornerPreference</c> attached property on the specified window.
+        /// </summary>
+        /// <param name="window">The window.</param>
+        /// <returns>The window corner preference for <paramref name="window"/>.</returns>
+        public static WindowCornerPreference GetWindowCornerPreference(Window window)
+            => window.GetValue(WindowCornerPreferenceProperty);
 
-        public static void SetNonClientHitTestResult(Visual obj, Win32HitTestValue value) => obj.SetValue(NonClientHitTestResultProperty, value);
-        public static Win32HitTestValue GetNonClientHitTestResult(Visual obj) => obj.GetValue(NonClientHitTestResultProperty);
+        private static bool ValidateWindowCornerPreference(WindowCornerPreference preference)
+            => preference is >= WindowCornerPreference.Default and <= WindowCornerPreference.RoundSmall;
 
+        /// <summary>
+        /// Represents a hit test value for a visual.
+        /// </summary>
         public enum Win32HitTestValue
         {
             Nowhere = 0,
@@ -99,5 +160,23 @@ namespace Avalonia.Controls
             BottomRight = 17,
             Close = 20,
         }
+
+        /// <summary>
+        /// Represents the rounded corner preference for a window.
+        /// </summary>
+        public enum WindowCornerPreference
+        {
+            /// <summary>Let the system decide when to round window corners.</summary>
+            Default = 0,
+
+            /// <summary>Never round window corners.</summary>
+            DoNotRound = 1,
+
+            /// <summary>Round the corners, if appropriate.</summary>
+            Round = 2,
+
+            /// <summary>Round the corners if appropriate, with a small radius.</summary>
+            RoundSmall = 3
+        }
     }
 }

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -108,6 +108,7 @@ namespace Avalonia.Win32
         internal bool _ignoreWmChar;
         private WindowTransparencyLevel _transparencyLevel;
         private readonly WindowTransparencyLevel _defaultTransparencyLevel;
+        private WindowCornerPreference _cornerPreference;
 
         private const int MaxPointerHistorySize = 512;
         private static readonly PooledList<RawPointerPoint> s_intermediatePointsPooledList = new();
@@ -1197,6 +1198,18 @@ namespace Avalonia.Win32
             return margins;
         }
 
+        private void UpdateWindowCornerPreference()
+        {
+            if (!OperatingSystem.IsWindowsVersionAtLeast(10, 0, 22000))
+                return;
+
+            unsafe
+            {
+                var preference = (int)_cornerPreference;
+                DwmSetWindowAttribute(_hwnd, (int)DwmWindowAttribute.DWMWA_WINDOW_CORNER_PREFERENCE, &preference, sizeof(int));
+            }
+        }
+
         private void ExtendClientArea()
         {
             if (!_shown)
@@ -1219,10 +1232,6 @@ namespace Avalonia.Win32
 
                 // Make sure that Windows still paints the non-client area so we get native borders and shadows.
                 SetNCRenderingPolicy(DwmNCRenderingPolicy.DWMNCRP_ENABLED);
-
-                // On Windows 11 21H2 and later, corners are configurable.
-                if (OperatingSystem.IsWindowsVersionAtLeast(10, 0, 22000))
-                    SetWindowCornerPreference(DwmWindowCornerPreference.DWMWCP_ROUND);
             }
             else
             {
@@ -1231,16 +1240,7 @@ namespace Avalonia.Win32
 
                 _extendedMargins = new Thickness();
 
-                if (OperatingSystem.IsWindowsVersionAtLeast(10, 0, 22000))
-                    SetWindowCornerPreference(DwmWindowCornerPreference.DWMWCP_DEFAULT);
-
                 SetNCRenderingPolicy(DwmNCRenderingPolicy.DWMNCRP_USEWINDOWSTYLE);
-
-                unsafe
-                {
-                    int cornerPreference = (int)DwmWindowCornerPreference.DWMWCP_DEFAULT;
-                    DwmSetWindowAttribute(_hwnd, (int)DwmWindowAttribute.DWMWA_WINDOW_CORNER_PREFERENCE, &cornerPreference, sizeof(int));
-                }
             }
 
             if (!_isClientAreaExtended)
@@ -1262,9 +1262,6 @@ namespace Avalonia.Win32
             ExtendClientAreaToDecorationsChanged?.Invoke(_isClientAreaExtended);
         }
 
-        private unsafe void SetWindowCornerPreference(DwmWindowCornerPreference value)
-            => DwmSetWindowAttribute(_hwnd, (int)DwmWindowAttribute.DWMWA_WINDOW_CORNER_PREFERENCE, &value, sizeof(int));
-
         private unsafe void SetNCRenderingPolicy(DwmNCRenderingPolicy value)
             => DwmSetWindowAttribute(_hwnd, (int)DwmWindowAttribute.DWMWA_NCRENDERING_POLICY, &value, sizeof(int));
 
@@ -1615,6 +1612,12 @@ namespace Avalonia.Win32
             ExtendClientArea();
         }
 
+        public void SetWindowCornerPreference(WindowCornerPreference preference)
+        {
+            _cornerPreference = preference;
+            UpdateWindowCornerPreference();
+        }
+
         /// <inheritdoc/>
         public bool IsClientAreaExtendedToDecorations => _isClientAreaExtended;