Prefer window content over underlay in chrome hit testing (#21177)

* Add unit tests for decoration hit testing

* Fix chrome hit testing

* macOS: handle TitleBar element role

src/Avalonia.Controls/PresentationSource/PresentationSource.cs

@@ -144,14 +144,7 @@ internal partial class PresentationSource : IPresentationSource, IInputRoot, IDi
 
     WindowDecorationsElementRole? IInputRoot.HitTestChromeElement(Point point)
     {
-        // Check all visuals at the point (not just topmost) because chrome elements
-        // may be in the underlay layer which sits below the TopLevel in the visual tree.
-        foreach (var visual in RootVisual.GetVisualsAt(point, ChromeHitTestFilter))
-        {
-            var role = GetChromeRoleFromVisual(visual);
-            if (role != null)
-                return role;
-        }
-        return null;
+        var visual = RootVisual.GetVisualAt(point, ChromeHitTestFilter);
+        return GetChromeRoleFromVisual(visual);
     }
 }

src/Avalonia.Native/WindowImpl.cs

@@ -1,5 +1,6 @@
 using System;
 using Avalonia.Controls;
+using Avalonia.Controls.Chrome;
 using Avalonia.Controls.Platform;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
@@ -154,7 +155,7 @@ namespace Avalonia.Native
                                 return true;
                             });
 
-                    if(visual == null)
+                    if (visual == null || WindowDecorationProperties.GetElementRole(visual) == WindowDecorationsElementRole.TitleBar)
                     {
                         if (_doubleClickHelper.IsDoubleClick(e.Timestamp, e.Position))
                         {

tests/Avalonia.Controls.UnitTests/PresentationSourceTests.cs

@@ -0,0 +1,147 @@
+using System;
+using Avalonia.Controls.Chrome;
+using Avalonia.Controls.Platform;
+using Avalonia.Controls.Templates;
+using Avalonia.Input;
+using Avalonia.Markup.Xaml.Templates;
+using Avalonia.Media;
+using Avalonia.Styling;
+using Avalonia.Threading;
+using Avalonia.UnitTests;
+using Avalonia.VisualTree;
+using Xunit;
+
+namespace Avalonia.Controls.UnitTests;
+
+public sealed class PresentationSourceTests : ScopedTestBase
+{
+    [Fact]
+    public void ChromeHitTest_Prefers_Overlay_Over_Content()
+    {
+        var overlay = new Border
+        {
+            Background = Brushes.Red,
+            [WindowDecorationProperties.ElementRoleProperty] = WindowDecorationsElementRole.TitleBar
+        };
+
+        var content = new Border
+        {
+            Background = Brushes.Blue
+        };
+
+        DoChromeHitTest(
+            underlay: null,
+            content: content,
+            overlay: overlay,
+            expectedChromeVisual: overlay,
+            expectedRole: WindowDecorationsElementRole.TitleBar);
+    }
+
+    [Fact]
+    public void ChromeHitTest_Prefers_Content_Over_Underlay()
+    {
+        var underlay = new Border
+        {
+            Background = Brushes.Red,
+            [WindowDecorationProperties.ElementRoleProperty] = WindowDecorationsElementRole.TitleBar
+        };
+
+        var content = new Border
+        {
+            Background = Brushes.Blue
+        };
+
+        DoChromeHitTest(
+            underlay: underlay,
+            content: content,
+            overlay: null,
+            expectedChromeVisual: content,
+            expectedRole: null);
+    }
+
+    private static void DoChromeHitTest(
+        Control? underlay,
+        Control? content,
+        Control? overlay,
+        Visual? expectedChromeVisual,
+        WindowDecorationsElementRole? expectedRole)
+    {
+        const double width = 100;
+        const double height = 100;
+
+        if (underlay is not null)
+        {
+            underlay.Width = width;
+            underlay.Height = height;
+        }
+
+        if (content is not null)
+        {
+            content.Width = width;
+            content.Height = height;
+        }
+
+        if (overlay is not null)
+        {
+            overlay.Width = width;
+            overlay.Height = height;
+        }
+
+        using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+        var decorations = new WindowDrawnDecorationsContent
+        {
+            Underlay = underlay,
+            Overlay = overlay
+        };
+
+        Application.Current!.Resources.Add(typeof(WindowDrawnDecorations), CreateDecorationsTheme(decorations));
+
+        var renderTimer = new CompositorTestServices.ManualRenderTimer();
+        var compositor = RendererMocks.CreateDummyCompositor(renderTimer);
+        var windowImpl = MockWindowingPlatform.CreateWindowMock(width, height, compositor);
+        windowImpl.Setup(w => w.IsClientAreaExtendedToDecorations).Returns(true);
+        windowImpl.Setup(w => w.RequestedDrawnDecorations).Returns(PlatformRequestedDrawnDecoration.TitleBar);
+        windowImpl.Setup(w => w.NeedsManagedDecorations).Returns(true);
+
+        var window = new Window(windowImpl.Object)
+        {
+            WindowDecorations = WindowDecorations.Full,
+            ExtendClientAreaToDecorationsHint = true,
+            Content = content
+        };
+
+        window.Show();
+
+        Dispatcher.CurrentDispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+        renderTimer.TriggerTick();
+        Dispatcher.CurrentDispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+
+        var hitTestPoint = new Point(width / 2, height / 2);
+
+        var clientVisual = window.GetVisualAt(hitTestPoint);
+        Assert.Same(window.Content, clientVisual);
+
+        var chromeVisual = window.PresentationSource.RootVisual.GetVisualAt(hitTestPoint);
+        Assert.Same(expectedChromeVisual, chromeVisual);
+
+        var chromeRole = ((IInputRoot)window.PresentationSource).HitTestChromeElement(hitTestPoint);
+        Assert.Equal(expectedRole, chromeRole);
+    }
+
+    private static ControlTheme CreateDecorationsTheme(WindowDrawnDecorationsContent content)
+    {
+        var template = new WindowDrawnDecorationsTemplate
+        {
+            Content = (IServiceProvider? _) => new TemplateResult<WindowDrawnDecorationsContent>(content, new NameScope())
+        };
+
+        return new ControlTheme(typeof(WindowDrawnDecorations))
+        {
+            Setters =
+            {
+                new Setter(WindowDrawnDecorations.TemplateProperty, template)
+            }
+        };
+    }
+}

tests/Avalonia.UnitTests/MockWindowingPlatform.cs

@@ -22,13 +22,13 @@ namespace Avalonia.UnitTests
             _popupImpl = popupImpl;
         }
 
-        public static Mock<IWindowImpl> CreateWindowMock(double initialWidth = 800, double initialHeight = 600)
+        public static Mock<IWindowImpl> CreateWindowMock(double initialWidth = 800, double initialHeight = 600, Compositor? compositor = null)
         {
             var windowImpl = new Mock<IWindowImpl>();
             var clientSize = new Size(initialWidth,  initialHeight);
 
             windowImpl.SetupAllProperties();
-            var compositor = RendererMocks.CreateDummyCompositor();
+            compositor ??= RendererMocks.CreateDummyCompositor();
             windowImpl.Setup(x => x.Compositor).Returns(compositor);
             windowImpl.Setup(x => x.ClientSize).Returns(() => clientSize);
             windowImpl.Setup(x => x.MaxAutoSizeHint).Returns(s_screenSize);

tests/Avalonia.UnitTests/RendererMocks.cs

@@ -16,8 +16,8 @@ namespace Avalonia.UnitTests
             return renderer;
         }
 
-        public static Compositor CreateDummyCompositor() =>
-            new(RenderLoop.FromTimer(new CompositorTestServices.ManualRenderTimer()), null, false,
+        public static Compositor CreateDummyCompositor(IRenderTimer? renderTimer = null) =>
+            new(RenderLoop.FromTimer(renderTimer ?? new CompositorTestServices.ManualRenderTimer()), null, false,
                 new CompositionCommitScheduler(), true, Dispatcher.UIThread);
 
         class CompositionCommitScheduler : ICompositorScheduler