Added LightDismissOverlayLayer.InputPassThroughElement.

Which implements something similar to UWP's `FlyoutBase.OverlayInputPassThroughElement`. With this feature, `Menu`/`MenuItem` can use `IsLightDismissEnabled="True"` fixing #3965 for top-level menus.

src/Avalonia.Controls/Menu.cs

@@ -1,4 +1,5 @@
 using Avalonia.Controls.Platform;
+using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Interactivity;
@@ -16,6 +17,8 @@ namespace Avalonia.Controls
         private static readonly ITemplate<IPanel> DefaultPanel =
             new FuncTemplate<IPanel>(() => new StackPanel { Orientation = Orientation.Horizontal });
 
+        private LightDismissOverlayLayer? _overlay;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Menu"/> class.
         /// </summary>
@@ -45,6 +48,13 @@ namespace Avalonia.Controls
                 return;
             }
 
+            if (_overlay?.InputPassThroughElement == this)
+            {
+                _overlay.InputPassThroughElement = null;
+            }
+
+            _overlay = null;
+
             foreach (var i in ((IMenu)this).SubItems)
             {
                 i.Close();
@@ -68,6 +78,13 @@ namespace Avalonia.Controls
                 return;
             }
 
+            _overlay = LightDismissOverlayLayer.GetLightDismissOverlayLayer(this);
+
+            if (_overlay is object)
+            {
+                _overlay.InputPassThroughElement = this;
+            }
+
             IsOpen = true;
 
             RaiseEvent(new RoutedEventArgs

src/Avalonia.Controls/Primitives/LightDismissOverlayLayer.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Linq;
 using Avalonia.Controls.Templates;
+using Avalonia.Input;
+using Avalonia.Rendering;
 using Avalonia.Styling;
 using Avalonia.VisualTree;
 
@@ -11,8 +13,10 @@ namespace Avalonia.Controls.Primitives
     /// <summary>
     /// A layer that is used to dismiss a <see cref="Popup"/> when the user clicks outside.
     /// </summary>
-    public class LightDismissOverlayLayer : Border
+    public class LightDismissOverlayLayer : Border, ICustomHitTest
     {
+        public IInputElement? InputPassThroughElement { get; set; }
+
         /// <summary>
         /// Returns the light dismiss overlay for a specified visual.
         /// </summary>
@@ -37,5 +41,21 @@ namespace Avalonia.Controls.Primitives
 
             return manager?.LightDismissOverlayLayer;
         }
+
+        public bool HitTest(Point point)
+        {
+            if (InputPassThroughElement is object)
+            {
+                var p = point.Transform(this.TransformToVisual(VisualRoot)!.Value);
+                var hit = VisualRoot.GetVisualAt(p, x => x != this);
+
+                if (hit is object)
+                {
+                    return !InputPassThroughElement.IsVisualAncestorOf(hit);
+                }
+            }
+
+            return true;
+        }
     }
 }

src/Avalonia.Themes.Default/MenuItem.xaml

@@ -59,6 +59,7 @@
                   Grid.Column="4"/>
             <Popup Name="PART_Popup"
                    PlacementMode="Right"
+                   IsLightDismissEnabled="True"
                    IsOpen="{TemplateBinding IsSubMenuOpen, Mode=TwoWay}">
               <Border Background="{TemplateBinding Background}"
                       BorderBrush="{DynamicResource ThemeBorderMidBrush}"
@@ -107,6 +108,7 @@
               </ContentPresenter.DataTemplates>
             </ContentPresenter>
             <Popup Name="PART_Popup"
+                   IsLightDismissEnabled="True"
                    IsOpen="{TemplateBinding IsSubMenuOpen, Mode=TwoWay}">
               <Border Background="{TemplateBinding Background}"
                       BorderBrush="{DynamicResource ThemeBorderMidBrush}"

src/Avalonia.Themes.Fluent/MenuItem.xaml

@@ -108,8 +108,8 @@
             <Popup Name="PART_Popup"
                    WindowManagerAddShadowHint="True"
                    PlacementMode="Right"
-                   IsOpen="{TemplateBinding IsSubMenuOpen,
-                                            Mode=TwoWay}">
+                   IsLightDismissEnabled="True"
+                   IsOpen="{TemplateBinding IsSubMenuOpen, Mode=TwoWay}">
               <Border Background="{DynamicResource MenuFlyoutPresenterBackground}"
                       BorderBrush="{DynamicResource MenuFlyoutPresenterBorderBrush}"
                       BorderThickness="{DynamicResource MenuFlyoutPresenterBorderThemeThickness}"
@@ -154,6 +154,7 @@
             <Popup Name="PART_Popup"
                    WindowManagerAddShadowHint="False"
                    MinWidth="{Binding Bounds.Width, RelativeSource={RelativeSource TemplatedParent}}"
+                   IsLightDismissEnabled="True"
                    IsOpen="{TemplateBinding IsSubMenuOpen, Mode=TwoWay}">
               <Border Background="{DynamicResource MenuFlyoutPresenterBackground}"
                       BorderBrush="{DynamicResource MenuFlyoutPresenterBorderBrush}"

src/Avalonia.Visuals/Rendering/ICustomSimpleHitTest.cs

@@ -14,6 +14,17 @@ namespace Avalonia.Rendering
         bool HitTest(Point point);
     }
 
+    /// <summary>
+    /// Allows customization of hit-testing for all renderers.
+    /// </summary>
+    /// <remarks>
+    /// Note that this interface can only used to make a portion of a control non-hittable, it
+    /// cannot expand the hittable area of a control.
+    /// </remarks>
+    public interface ICustomHitTest : ICustomSimpleHitTest
+    {
+    }
+
     public static class CustomSimpleHitTestExtensions
     {
         public static bool HitTestCustom(this IVisual visual, Point point)

src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs

@@ -304,6 +304,12 @@ namespace Avalonia.Rendering.SceneGraph
                         clipped = !node.GeometryClip.FillContains(controlPoint.Value);
                     }
 
+                    if (!clipped && node.Visual is ICustomHitTest custom)
+                    {
+                        var controlPoint = _sceneRoot.Visual.TranslatePoint(_point, node.Visual);
+                        clipped = !custom.HitTest(controlPoint.Value);
+                    }
+
                     return !clipped;
                 }