Fix ICustomHitTest

src/Avalonia.Visuals/Rendering/ICustomSimpleHitTest.cs

@@ -11,16 +11,13 @@ namespace Avalonia.Rendering
     /// </summary>
     public interface ICustomSimpleHitTest
     {
+        /// <param name="point">The point to hit test in global coordinate space.</param>
         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
     {
     }

src/Avalonia.Visuals/Rendering/ImmediateRenderer.cs

@@ -225,7 +225,7 @@ private static Rect GetTransformedBounds(IVisual visual)
 
             if (filter?.Invoke(visual) != false)
             {
-                bool containsPoint = false;
+                bool containsPoint;
 
                 if (visual is ICustomSimpleHitTest custom)
                 {

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

@@ -256,7 +256,8 @@ public bool MoveNext()
 
                     if (childCount == 0 || wasVisited)
                     {
-                        if ((wasVisited || FilterAndClip(node, ref clip)) && node.HitTest(_point))
+                        if ((wasVisited || FilterAndClip(node, ref clip)) &&
+                            (node.Visual is ICustomSimpleHitTest custom ? custom.HitTest(_point) : node.HitTest(_point)))
                         {
                             _current = node.Visual;
 
@@ -311,8 +312,7 @@ private bool FilterAndClip(IVisualNode node, ref Rect? clip)
 
                     if (!clipped && node.Visual is ICustomHitTest custom)
                     {
-                        var controlPoint = _sceneRoot.Visual.TranslatePoint(_point, node.Visual);
-                        clipped = !custom.HitTest(controlPoint.Value);
+                        clipped = !custom.HitTest(_point);
                     }
 
                     return !clipped;

tests/Avalonia.Visuals.UnitTests/Rendering/CustomHitTestBorder.cs

@@ -0,0 +1,17 @@
+using Avalonia.Controls;
+using Avalonia.Media;
+using Avalonia.Rendering;
+
+namespace Avalonia.Visuals.UnitTests.Rendering
+{
+    internal class CustomHitTestBorder : Border, ICustomHitTest
+    {
+        public bool HitTest(Point point)
+        {
+            // Move hit testing window halfway to the left
+            return Bounds
+                .WithX(Bounds.X - Bounds.Width / 2)  
+                .Contains(point);
+        }
+    }
+}

tests/Avalonia.Visuals.UnitTests/Rendering/DeferredRendererTests_HitTesting.cs

@@ -1,6 +1,9 @@
-using System.Linq;
+using System;
+using System.Linq;
 using Avalonia.Controls;
 using Avalonia.Controls.Presenters;
+using Avalonia.Controls.Shapes;
+using Avalonia.Input;
 using Avalonia.Layout;
 using Avalonia.Media;
 using Avalonia.Platform;
@@ -9,8 +12,6 @@
 using Avalonia.VisualTree;
 using Moq;
 using Xunit;
-using System;
-using Avalonia.Controls.Shapes;
 
 namespace Avalonia.Visuals.UnitTests.Rendering
 {
@@ -501,6 +502,42 @@ public void HitTest_Should_Respect_Geometry_Clip()
             }
         }
 
+        [Fact]
+        public void HitTest_Should_Accommodate_ICustomHitTest()
+        {
+            using (TestApplication())
+            {
+                Border border;
+
+                var root = new TestRoot
+                {
+                    Width = 300,
+                    Height = 200,
+                    Child = border = new CustomHitTestBorder
+                    {
+                        Width = 100,
+                        Height = 100,
+                        Background = Brushes.Red,
+                        HorizontalAlignment = HorizontalAlignment.Center,
+                        VerticalAlignment = VerticalAlignment.Center
+                    }
+                }; 
+
+                root.Renderer = new DeferredRenderer(root, null);
+                root.Measure(Size.Infinity);
+                root.Arrange(new Rect(root.DesiredSize));
+
+                var result = root.Renderer.HitTest(new Point(75, 100), root, null);
+                Assert.Equal(new[] { border }, result);
+
+                result = root.Renderer.HitTest(new Point(125, 100), root, null);
+                Assert.Equal(new[] { border }, result);
+
+                result = root.Renderer.HitTest(new Point(175, 100), root, null);
+                Assert.Empty(result);
+            }
+        }
+
         private IDisposable TestApplication()
         {
             return UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);

tests/Avalonia.Visuals.UnitTests/Rendering/ImmediateRendererTests_HitTesting.cs

@@ -413,6 +413,43 @@ public void HitTest_Should_Not_Find_Control_Outside_Scroll_Viewport()
             }
         }
 
+        [Fact]
+        public void HitTest_Should_Accommodate_ICustomHitTest()
+        {
+            using (TestApplication())
+            {
+                Border border;
+
+                var root = new TestRoot
+                {
+                    Width = 300,
+                    Height = 200,
+                    Child = border = new CustomHitTestBorder
+                    {
+                        Width = 100,
+                        Height = 100,
+                        Background = Brushes.Red,
+                        HorizontalAlignment = HorizontalAlignment.Center,
+                        VerticalAlignment = VerticalAlignment.Center
+                    }
+                };
+
+                root.Renderer = new ImmediateRenderer(root);
+                root.Measure(Size.Infinity);
+                root.Arrange(new Rect(root.DesiredSize));
+                root.Renderer.Paint(new Rect(root.ClientSize));
+
+                var result = root.Renderer.HitTest(new Point(75, 100), root, null).First();
+                Assert.Equal(border, result);
+
+                result = root.Renderer.HitTest(new Point(125, 100), root, null).First();
+                Assert.Equal(border, result);
+
+                result = root.Renderer.HitTest(new Point(175, 100), root, null).First();
+                Assert.Equal(root, result);
+            }
+        }
+
         private IDisposable TestApplication()
         {
             return UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);