Use _effective_ capturer (which can be recognizer) for PlatformCapture (#22076)

src/Avalonia.Base/Input/Pointer.cs

@@ -58,9 +58,7 @@ namespace Avalonia.Input
 
         private void CaptureLostCore(CaptureSource source)
         {
-            if (Captured != null)
-                CaptureCore(null, source);
-            CaptureGestureRecognizerCore(null);
+            CaptureCore(null, null, source);
             IsGestureRecognitionSkipped = false;
         }
 
@@ -69,6 +67,8 @@ namespace Avalonia.Input
             Capture(control, CaptureSource.Explicit);
         }
 
+        private IInputElement? EffectiveCapturer => this.CapturedGestureRecognizer?.Target ?? Captured;
+
         internal void Capture(IInputElement? control, CaptureSource source)
         {
             if (_disposed)
@@ -77,16 +77,21 @@ namespace Avalonia.Input
                 return;
             }
 
-            CaptureCore(control, source);
+            CaptureCore(control, null, source);
         }
 
-        private void CaptureCore(IInputElement? control, CaptureSource source)
+        private void CaptureCore(
+            IInputElement? control,
+            GestureRecognizer? gestureRecognizer,
+            CaptureSource source)
         {
             var oldCapture = Captured;
+            var oldGestureRecognizer = CapturedGestureRecognizer;
             var oldSource = CaptureSource;
+            var oldEffectiveCapturer = EffectiveCapturer;
 
             // If a handler marks Implicit capture as handled, we still want them to have another chance if the element is captured explicitly.
-            if (oldCapture == control && oldSource == source)
+            if (oldCapture == control && oldGestureRecognizer == gestureRecognizer && oldSource == source)
                 return;
 
             var oldVisual = oldCapture as Visual;
@@ -110,12 +115,17 @@ namespace Avalonia.Input
 
             if (oldVisual != null)
                 oldVisual.DetachedFromVisualTree -= OnCaptureDetached;
+
+            if (oldGestureRecognizer != gestureRecognizer)
+                oldGestureRecognizer?.PointerCaptureLostInternal(this);
+
             Captured = control;
+            CapturedGestureRecognizer = gestureRecognizer;
             CaptureSource = source;
 
             // However, we still want to notify the platform only if the captured element actually changed.
-            if (oldCapture != control && source != CaptureSource.Platform)
-                PlatformCapture(control);
+            if (oldEffectiveCapturer != EffectiveCapturer && source != CaptureSource.Platform)
+                PlatformCapture(EffectiveCapturer);
 
             if (oldVisual != null)
                 foreach (var notifyTarget in oldVisual.GetSelfAndVisualAncestors().OfType<IInputElement>())
@@ -128,9 +138,6 @@ namespace Avalonia.Input
             if (newVisual != null)
                 newVisual.DetachedFromVisualTree += OnCaptureDetached;
 
-            if (Captured != null)
-                CaptureGestureRecognizer(null);
-
             if (Captured == null && CapturedGestureRecognizer == null)
             {
                 IsGestureRecognitionSkipped = false;
@@ -199,22 +206,7 @@ namespace Avalonia.Input
                 return;
             }
 
-            CaptureGestureRecognizerCore(gestureRecognizer);
-        }
-
-        private void CaptureGestureRecognizerCore(GestureRecognizer? gestureRecognizer)
-        {
-            if (CapturedGestureRecognizer != gestureRecognizer)
-            {
-                CapturedGestureRecognizer?.PointerCaptureLostInternal(this);
-            }
-
-            CapturedGestureRecognizer = gestureRecognizer;
-
-            if (gestureRecognizer != null)
-            {
-                Capture(null);
-            }
+            CaptureCore(null, gestureRecognizer, CaptureSource.Explicit);
         }
     }
 }

tests/Avalonia.Base.UnitTests/Input/PointerTests.cs

@@ -2,6 +2,7 @@ using System.Collections.Generic;
 using System.Linq;
 using Avalonia.Controls;
 using Avalonia.Input;
+using Avalonia.Input.GestureRecognizers;
 using Avalonia.UnitTests;
 using Avalonia.VisualTree;
 using Xunit;
@@ -54,6 +55,37 @@ namespace Avalonia.Base.UnitTests.Input
             Assert.Equal(2, pointer.PlatformCaptureCalled);
         }
 
+        [Fact]
+        public void Gesture_Recognizer_Capture_Should_Keep_Platform_Capture_On_Same_Target()
+        {
+            var pointer = new TestPointer(Pointer.GetNextFreeId(), PointerType.Mouse, true);
+            var target = new Border();
+            var recognizer = new TestGestureRecognizer { Target = target };
+
+            pointer.Capture(target, CaptureSource.Implicit);
+            recognizer.CapturePointer(pointer);
+
+            Assert.Null(pointer.Captured);
+            Assert.Same(recognizer, pointer.CapturedGestureRecognizer);
+            Assert.Equal([target], pointer.PlatformCaptures);
+        }
+
+        [Fact]
+        public void Gesture_Recognizer_Capture_Should_Move_Platform_Capture_To_Target()
+        {
+            var pointer = new TestPointer(Pointer.GetNextFreeId(), PointerType.Mouse, true);
+            var initialCapture = new Border();
+            var target = new Border { Child = initialCapture };
+            var recognizer = new TestGestureRecognizer { Target = target };
+
+            pointer.Capture(initialCapture, CaptureSource.Implicit);
+            recognizer.CapturePointer(pointer);
+
+            Assert.Null(pointer.Captured);
+            Assert.Same(recognizer, pointer.CapturedGestureRecognizer);
+            Assert.Equal([initialCapture, target], pointer.PlatformCaptures);
+        }
+
         [Fact]
         public void Capture_Explicit_ShouldNotify_After_Implicit()
         {
@@ -109,5 +141,26 @@ namespace Avalonia.Base.UnitTests.Input
 
             Assert.Equal(2, pointer.PlatformCaptureCalled);
         }
+
+        private sealed class TestGestureRecognizer : GestureRecognizer
+        {
+            public void CapturePointer(IPointer pointer) => Capture(pointer);
+
+            protected override void PointerPressed(PointerPressedEventArgs e)
+            {
+            }
+
+            protected override void PointerReleased(PointerReleasedEventArgs e)
+            {
+            }
+
+            protected override void PointerMoved(PointerEventArgs e)
+            {
+            }
+
+            protected override void PointerCaptureLost(IPointer pointer)
+            {
+            }
+        }
     }
 }

tests/Avalonia.Base.UnitTests/Input/PointerTestsBase.cs

@@ -1,5 +1,6 @@
 #nullable enable
 using System;
+using System.Collections.Generic;
 using Avalonia.Controls;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
@@ -17,12 +18,14 @@ public abstract class PointerTestsBase : ScopedTestBase
     protected class TestPointer : Pointer
     {
         internal int PlatformCaptureCalled = 0;
+        internal List<IInputElement?> PlatformCaptures { get; } = new();
 
         internal TestPointer(int id, PointerType type, bool isPrimary) : base(id, type, isPrimary) { }
 
         protected override void PlatformCapture(IInputElement? element)
         {
             PlatformCaptureCalled++;
+            PlatformCaptures.Add(element);
         }
     }