Avoid exceptions when getting a position from a PointerEventArgs

src/Avalonia.Base/Input/PointerEventArgs.cs

@@ -3,14 +3,14 @@
 using Avalonia.Input.Raw;
 using Avalonia.Interactivity;
 using Avalonia.Metadata;
-using Avalonia.VisualTree;
+using Avalonia.Rendering;
 
 namespace Avalonia.Input
 {
     public class PointerEventArgs : RoutedEventArgs, IKeyModifiersEventArgs
     {
-        private readonly Visual? _rootVisual;
-        private readonly Point _rootVisualPosition;
+        private readonly IPresentationSource? _eventPresentationSource; // the original observer of the event
+        private readonly Point _presentationSourcePosition;
         private readonly PointerPointProperties _properties;
         private readonly Lazy<IReadOnlyList<RawPointerPoint>?>? _previousPoints;
 
@@ -24,8 +24,8 @@ public PointerEventArgs(RoutedEvent? routedEvent,
            : base(routedEvent)
         {
             Source = source;
-            _rootVisual = rootVisual;
-            _rootVisualPosition = rootVisualPosition;
+            _eventPresentationSource = rootVisual?.PresentationSource;
+            _presentationSourcePosition = rootVisualPosition;
             _properties = properties;
             Pointer = pointer;
             Timestamp = timestamp;
@@ -76,31 +76,33 @@ private set
 
         private Point GetPosition(Point pt, Visual? relativeTo)
         {
-            if (_rootVisual == null)
-                return default;
             if (relativeTo == null)
                 return pt;
+            if (_eventPresentationSource == null || relativeTo?.PresentationSource?.RootVisual == null)
+                return default;
 
-            // If the visual the user passed in, is not connected to the same visual root
-            // (i.e. they called it for a control inside a popup.
-            if (!ReferenceEquals(_rootVisual, relativeTo.VisualRoot) && relativeTo.VisualRoot is { })
+            if (relativeTo.PresentationSource != _eventPresentationSource)
             {
-                // Convert to absolute screen coordinates.
-                var screenPt = _rootVisual.PointToScreen(pt);
-
-                // Convert to client co-ordinates of the visual inside the other visual root.
-                return relativeTo.PointToClient(screenPt);
+                if (_eventPresentationSource.PointToScreen(pt) is { } screenPt &&
+                    relativeTo.PresentationSource.PointToClient(screenPt) is { } targetClientPt)
+                {
+                    pt = targetClientPt;
+                }
+                else
+                {
+                    return default;
+                }
             }
 
-            return pt * _rootVisual.TransformToVisual(relativeTo) ?? default;
+            return relativeTo.PresentationSource.RootVisual.TranslatePoint(pt, relativeTo) ?? default;
         }
 
         /// <summary>
         /// Gets the pointer position relative to a control.
         /// </summary>
         /// <param name="relativeTo">The visual whose coordinate system to use. Pass null for toplevel coordinate system</param>
         /// <returns>The pointer position in the control's coordinates.</returns>
-        public Point GetPosition(Visual? relativeTo) => GetPosition(_rootVisualPosition, relativeTo);
+        public Point GetPosition(Visual? relativeTo) => GetPosition(_presentationSourcePosition, relativeTo);
 
         /// <summary>
         /// Returns the PointerPoint associated with the current event
@@ -117,7 +119,7 @@ public PointerPoint GetCurrentPoint(Visual? relativeTo)
         /// <returns></returns>
         public IReadOnlyList<PointerPoint> GetIntermediatePoints(Visual? relativeTo)
         {
-            var previousPoints = _previousPoints?.Value;            
+            var previousPoints = _previousPoints?.Value;
             if (previousPoints == null || previousPoints.Count == 0)
                 return new[] { GetCurrentPoint(relativeTo) };
             var points = new PointerPoint[previousPoints.Count + 1];
@@ -145,7 +147,7 @@ public void PreventGestureRecognition()
         /// </summary>
         public PointerPointProperties Properties => _properties;
     }
-    
+
     public enum MouseButton
     {
         None,

src/Avalonia.Base/Rendering/IPresentationSource.cs

@@ -41,6 +41,6 @@ public interface IPresentationSource
     /// </summary>
     internal Size ClientSize { get; }
 
-    internal PixelPoint PointToScreen(Point point);
-    internal Point PointToClient(PixelPoint point);
+    internal PixelPoint? PointToScreen(Point point);
+    internal Point? PointToClient(PixelPoint point);
 }

src/Avalonia.Base/VisualExtensions.cs

@@ -14,12 +14,13 @@ public static class VisualExtensions
         /// <param name="visual">The visual.</param>
         /// <param name="point">The point in screen coordinates.</param>
         /// <returns>The point in client coordinates.</returns>
+        /// <exception cref="ArgumentException">Thown when <paramref name="visual"/> does not belong to a visual tree.</exception>
         public static Point PointToClient(this Visual visual, PixelPoint point)
         {
             var source = visual.PresentationSource;
             var root = source?.RootVisual ??
-                       throw new ArgumentException("Control does not belong to a visual tree.", nameof(visual));
-            var rootPoint = source.PointToClient(point);
+                       throw new ArgumentException("Visual does not belong to a visual tree.", nameof(visual));
+            var rootPoint = source.PointToClient(point) ?? default;
             return root.TranslatePoint(rootPoint, visual)!.Value;
         }
 
@@ -29,13 +30,14 @@ public static Point PointToClient(this Visual visual, PixelPoint point)
         /// <param name="visual">The visual.</param>
         /// <param name="point">The point in client coordinates.</param>
         /// <returns>The point in screen coordinates.</returns>
+        /// <exception cref="ArgumentException">Thown when <paramref name="visual"/> does not belong to a visual tree.</exception>
         public static PixelPoint PointToScreen(this Visual visual, Point point)
         {
             var source = visual.PresentationSource;
             var root = source?.RootVisual ??
-                       throw new ArgumentException("Control does not belong to a visual tree.", nameof(visual));
+                       throw new ArgumentException("Visual does not belong to a visual tree.", nameof(visual));
             var p = visual.TranslatePoint(point, root);
-            return source.PointToScreen(p!.Value);
+            return source.PointToScreen(p!.Value) ?? default;
         }
 
         /// <summary>

src/Avalonia.Controls/PresentationSource/PresentationSource.RenderRoot.cs

@@ -23,9 +23,9 @@ public void SceneInvalidated(object? sender, SceneInvalidatedEventArgs sceneInva
         _pointerOverPreProcessor?.SceneInvalidated(sceneInvalidatedEventArgs.DirtyRect);
     }
 
-    public PixelPoint PointToScreen(Point point) => PlatformImpl?.PointToScreen(point) ?? default;
+    public PixelPoint? PointToScreen(Point point) => PlatformImpl?.PointToScreen(point);
 
-    public Point PointToClient(PixelPoint point) => PlatformImpl?.PointToClient(point) ?? default;
+    public Point? PointToClient(PixelPoint point) => PlatformImpl?.PointToClient(point);
 
     private void HandleScalingChanged(double scaling)
         => RenderScaling = LayoutHelper.ValidateScaling(scaling);

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

@@ -1,4 +1,6 @@
-using Avalonia.Controls;
+using System;
+using Avalonia.Controls;
+using Avalonia.Headless;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.Media;
@@ -128,6 +130,74 @@ public void GetPosition_Should_Respect_Control_RenderTransform()
             Assert.Equal(new Point(1, 11), result);
         }
 
+        private IDisposable SetupCrossTreePositionRequest(PixelPoint topLevelPosition, out PointerEventArgs pointerEvent, out Control elementA, out Control elementB)
+        {
+            var app = UnitTestApplication.Start(new TestServices(
+                inputManager: new InputManager(),
+                renderInterface: new HeadlessPlatformRenderInterface()));
+
+            var renderer = new Mock<IHitTester>();
+            var deviceMock = CreatePointerDeviceMock();
+            var impl1 = CreateTopLevelImplMock();
+            // Mocked position: topLevelPosition
+            impl1.Setup(w => w.PointToScreen(default)).Returns<Point>(p => (PixelPoint.FromPoint(p, 1) + topLevelPosition));
+
+            elementA = new Border();
+            PointerEventArgs? moveEventArgs = null;
+
+            elementA.PointerMoved += (s, e) => moveEventArgs = e;
+            var root1 = CreateInputRoot(impl1.Object, elementA, renderer.Object);
+
+            SetMove(deviceMock, root1.InputRoot, elementA);
+            impl1.Object.Input!(CreateRawPointerMovedArgs(deviceMock.Object, root1));
+
+            Assert.NotNull(moveEventArgs);
+            pointerEvent = moveEventArgs;
+
+            var impl2 = CreateTopLevelImplMock();
+            // Mocked position: topLevelPosition * 2
+            impl2.Setup(w => w.PointToClient(default)).Returns<PixelPoint>(p => (p - topLevelPosition - topLevelPosition).ToPoint(1));
+
+            elementB = new Border();
+            var root2 = CreateInputRoot(impl2.Object, elementB, renderer.Object);
+
+            return app;
+        }
+
+        [Fact]
+        public void GetPosition_Should_Support_Cross_Tree_Requests()
+        {
+            var topLevelOffset = new PixelPoint(5, 0);
+            using (SetupCrossTreePositionRequest(topLevelOffset, out var pointerEvent, out _, out var elementB))
+            {
+                Assert.Equal(topLevelOffset.ToPoint(1), pointerEvent.GetPosition(elementB));
+            }
+        }
+
+        [Fact]
+        public void GetPosition_Should_Return_Default_When_Cross_Tree_Source_Closed()
+        {
+            var topLevelOffset = new PixelPoint(5, 0);
+            using (SetupCrossTreePositionRequest(topLevelOffset, out var pointerEvent, out var elementA, out var elementB))
+            {
+                ((PresentationSource)elementA.PresentationSource!).Dispose();
+
+                Assert.Equal(default, pointerEvent.GetPosition(elementB));
+            }
+        }
+
+        [Fact]
+        public void GetPosition_Should_Return_Default_When_Cross_Tree_Target_Closed()
+        {
+            var topLevelOffset = new PixelPoint(5, 0);
+            using (SetupCrossTreePositionRequest(topLevelOffset, out var pointerEvent, out _, out var elementB))
+            {
+                ((PresentationSource)elementB.PresentationSource!).Dispose();
+
+                Assert.Equal(default, pointerEvent.GetPosition(elementB));
+            }
+        }
+
         [Fact]
         public void Mouse_Pointer_Should_Set_Focus_On_Pointer_Pressed()
         {

tests/Avalonia.RenderTests/TestRenderRoot.cs

@@ -67,9 +67,9 @@ public void Invalidate(Rect rect)
         {
         }
 
-        public Point PointToClient(PixelPoint point) => point.ToPoint(RenderScaling);
+        public Point? PointToClient(PixelPoint point) => point.ToPoint(RenderScaling);
 
-        public PixelPoint PointToScreen(Point point) => PixelPoint.FromPoint(point, RenderScaling);
+        public PixelPoint? PointToScreen(Point point) => PixelPoint.FromPoint(point, RenderScaling);
 
         public IFocusManager? FocusManager { get; }
         public IPlatformSettings? PlatformSettings { get; }

tests/Avalonia.UnitTests/TestRoot.cs

@@ -113,9 +113,9 @@ public void Invalidate(Rect rect)
         {
         }
 
-        public Point PointToClient(PixelPoint p) => p.ToPoint(1);
+        public Point? PointToClient(PixelPoint p) => p.ToPoint(1);
 
-        public PixelPoint PointToScreen(Point p) => PixelPoint.FromPoint(p, 1);
+        public PixelPoint? PointToScreen(Point p) => PixelPoint.FromPoint(p, 1);
 
 
         public void RegisterChildrenNames()