Merge pull request #9751 from AvaloniaUI/gestures

Add Pinch Gestures and improved other gesture recognizers

samples/ControlCatalog/MainView.xaml

@@ -92,6 +92,9 @@
       <TabItem Header="Flyouts">
         <pages:FlyoutsPage />
       </TabItem>
+      <TabItem Header="Gestures">
+        <pages:GesturePage />
+      </TabItem>
       <TabItem Header="Image"
                ScrollViewer.HorizontalScrollBarVisibility="Disabled"
                ScrollViewer.VerticalScrollBarVisibility="Disabled">

samples/ControlCatalog/Pages/GesturePage.cs

@@ -0,0 +1,212 @@
+using System;
+using System.Numerics;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.LogicalTree;
+using Avalonia.Markup.Xaml;
+using Avalonia.Rendering.Composition;
+
+namespace ControlCatalog.Pages
+{
+    public class GesturePage : UserControl
+    {
+        private bool _isInit;
+        private float _currentScale;
+
+        public GesturePage()
+        {
+            this.InitializeComponent();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+
+        protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+        {
+            base.OnAttachedToVisualTree(e);
+
+            if(_isInit)
+            {
+                return;
+            }
+
+            _isInit = true;
+
+            SetPullHandlers(this.Find<Border>("TopPullZone"), false);
+            SetPullHandlers(this.Find<Border>("BottomPullZone"), true);
+            SetPullHandlers(this.Find<Border>("RightPullZone"), true);
+            SetPullHandlers(this.Find<Border>("LeftPullZone"), false);
+
+            var image = this.Find<Image>("PinchImage");
+            SetPinchHandlers(image);
+
+            var reset = this.Find<Button>("ResetButton");
+
+            reset!.Click += (s, e) =>
+            {
+                var compositionVisual = ElementComposition.GetElementVisual(image);
+
+                if(compositionVisual!= null)
+                {
+                    _currentScale = 1;
+                    compositionVisual.Scale = new Vector3(1,1,1);
+                    image.InvalidateMeasure();
+                }
+            };
+                
+        }
+
+        private void SetPinchHandlers(Control? control)
+        {
+            if (control == null)
+            {
+                return;
+            }
+
+            _currentScale = 1;
+            Vector3 currentOffset = default;
+            bool isZooming = false;
+
+            CompositionVisual? compositionVisual = null;
+
+            void InitComposition(Control visual)
+            {
+                if (compositionVisual != null)
+                {
+                    return;
+                }
+
+                compositionVisual = ElementComposition.GetElementVisual(visual);
+            }
+
+            control.LayoutUpdated += (s, e) =>
+            {
+                InitComposition(control!);
+                if (compositionVisual != null)
+                {
+                    compositionVisual.Scale = new(_currentScale, _currentScale, 1);
+
+                    if(currentOffset == default)
+                    {
+                        currentOffset = compositionVisual.Offset;
+                    }
+                }
+            };
+
+            control.AddHandler(Gestures.PinchEvent, (s, e) =>
+            {
+                InitComposition(control!);
+
+                isZooming = true;
+
+                if(compositionVisual != null)
+                {
+                    var scale = _currentScale * (float)e.Scale;
+
+                    compositionVisual.Scale = new(scale, scale, 1);
+                }
+            });
+
+            control.AddHandler(Gestures.PinchEndedEvent, (s, e) =>
+            {
+                InitComposition(control!);
+
+                isZooming = false;
+
+                if (compositionVisual != null)
+                {
+                    _currentScale = compositionVisual.Scale.X;
+                }
+            });
+
+            control.AddHandler(Gestures.ScrollGestureEvent, (s, e) =>
+            {
+                InitComposition(control!);
+
+                if (compositionVisual != null && !isZooming)
+                {
+                    currentOffset -= new Vector3((float)e.Delta.X, (float)e.Delta.Y, 0);
+
+                    compositionVisual.Offset = currentOffset;
+                }
+            });
+        }
+
+        private void SetPullHandlers(Control? control, bool inverse)
+        {
+            if (control == null)
+            {
+                return;
+            }
+
+            var ball = control.FindLogicalDescendantOfType<Border>();
+
+            Vector3 defaultOffset = default;
+
+            CompositionVisual? ballCompositionVisual = null;
+
+            if (ball != null)
+            {
+                InitComposition(ball);
+            }
+            else
+            {
+                return;
+            }
+
+            control.LayoutUpdated += (s, e) =>
+            {
+                InitComposition(ball!);
+                if (ballCompositionVisual != null)
+                {
+                    defaultOffset = ballCompositionVisual.Offset;
+                }
+            };
+
+            control.AddHandler(Gestures.PullGestureEvent, (s, e) =>
+            {
+                Vector3 center = new((float)control.Bounds.Center.X, (float)control.Bounds.Center.Y, 0);
+                InitComposition(ball!);
+                if (ballCompositionVisual != null)
+                {
+                    ballCompositionVisual.Offset = defaultOffset + new System.Numerics.Vector3((float)e.Delta.X * 0.4f, (float)e.Delta.Y * 0.4f, 0) * (inverse ? -1 : 1);
+                }
+            });
+
+            control.AddHandler(Gestures.PullGestureEndedEvent, (s, e) =>
+            {
+                InitComposition(ball!);
+                if (ballCompositionVisual != null)
+                {
+                    ballCompositionVisual.Offset = defaultOffset;
+                }
+            });
+
+            void InitComposition(Control control)
+            {
+                if (ballCompositionVisual != null)
+                {
+                    return;
+                }
+
+                ballCompositionVisual = ElementComposition.GetElementVisual(ball);
+
+                if (ballCompositionVisual != null)
+                {
+                    var offsetAnimation = ballCompositionVisual.Compositor.CreateVector3KeyFrameAnimation();
+                    offsetAnimation.Target = "Offset";
+                    offsetAnimation.InsertExpressionKeyFrame(1.0f, "this.FinalValue");
+                    offsetAnimation.Duration = TimeSpan.FromMilliseconds(100);
+
+                    var implicitAnimations = ballCompositionVisual.Compositor.CreateImplicitAnimationCollection();
+                    implicitAnimations["Offset"] = offsetAnimation;
+
+                    ballCompositionVisual.ImplicitAnimations = implicitAnimations;
+                }
+            }
+        }
+    }
+}

samples/ControlCatalog/Pages/GesturePage.xaml

@@ -0,0 +1,117 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             d:DesignHeight="800"
+             d:DesignWidth="400"
+             x:Class="ControlCatalog.Pages.GesturePage">
+  <StackPanel Orientation="Vertical"
+              Spacing="4">
+    <TextBlock FontWeight="Bold"
+               FontSize="18"
+               Margin="5">Pull Gexture (Touch / Pen)</TextBlock>
+    <TextBlock Margin="5">Pull from colored rectangles</TextBlock>
+    <Border>
+      <DockPanel HorizontalAlignment="Stretch"
+                 ClipToBounds="True"
+                 Margin="5"
+                 Height="200">
+        <Border DockPanel.Dock="Top"
+                Margin="2"
+                Name="TopPullZone"
+                Background="Transparent"
+                BorderBrush="Red"
+                HorizontalAlignment="Stretch"
+                Height="50"
+                BorderThickness="1">
+          <Border.GestureRecognizers>
+            <PullGestureRecognizer PullDirection="TopToBottom"/>
+          </Border.GestureRecognizers>
+          <Border Width="10"
+                  Height="10"
+                  HorizontalAlignment="Center"
+                  VerticalAlignment="Center"
+                  CornerRadius="5"
+                  Name="TopBall"
+                  Background="Green"/>
+        </Border>
+        <Border DockPanel.Dock="Bottom"
+                BorderBrush="Green"
+                Margin="2"
+                Background="Transparent"
+                Name="BottomPullZone"
+                HorizontalAlignment="Stretch"
+                Height="50"
+                BorderThickness="1">
+          <Border.GestureRecognizers>
+            <PullGestureRecognizer PullDirection="BottomToTop"/>
+          </Border.GestureRecognizers>
+          <Border Width="10"
+                  Name="BottomBall"
+                  HorizontalAlignment="Center"
+                  VerticalAlignment="Center"
+                  Height="10"
+                  CornerRadius="5"
+                  Background="Green"/>
+        </Border>
+        <Border DockPanel.Dock="Right"
+                Margin="2"
+                Background="Transparent"
+                Name="RightPullZone"
+                BorderBrush="Blue"
+                HorizontalAlignment="Right"
+                VerticalAlignment="Stretch"
+                Width="50"
+                BorderThickness="1">
+          <Border.GestureRecognizers>
+            <PullGestureRecognizer PullDirection="RightToLeft"/>
+          </Border.GestureRecognizers>
+          <Border Width="10"
+                  Height="10"
+                  Name="RightBall"
+                  HorizontalAlignment="Center"
+                  VerticalAlignment="Center"
+                  CornerRadius="5"
+                  Background="Green"/>
+
+        </Border>
+        <Border DockPanel.Dock="Left"
+                Margin="2"
+                Background="Transparent"
+                Name="LeftPullZone"
+                BorderBrush="Orange"
+                HorizontalAlignment="Left"
+                VerticalAlignment="Stretch"
+                Width="50"
+                BorderThickness="1">
+          <Border.GestureRecognizers>
+            <PullGestureRecognizer PullDirection="LeftToRight"/>
+          </Border.GestureRecognizers>
+          <Border Width="10"
+                  Height="10"
+                  Name="LeftBall"
+                  HorizontalAlignment="Center"
+                  VerticalAlignment="Center"
+                  CornerRadius="5"
+                  Background="Green"/>
+
+        </Border>
+      </DockPanel>
+    </Border>
+
+    <TextBlock FontWeight="Bold"
+               FontSize="18"
+               Margin="5">Pinch/Zoom Gexture (Multi Touch)</TextBlock>
+    <Border ClipToBounds="True">
+      <Image Stretch="UniformToFill"
+             Margin="5"
+             Name="PinchImage"
+             Source="/Assets/delicate-arch-896885_640.jpg">
+        <Image.GestureRecognizers>
+          <PinchGestureRecognizer/>
+          <ScrollGestureRecognizer CanHorizontallyScroll="True" CanVerticallyScroll="True"/>
+        </Image.GestureRecognizers>
+      </Image>
+    </Border>
+    <Button HorizontalAlignment="Center" Name="ResetButton">Reset</Button>
+  </StackPanel>
+</UserControl>

src/Avalonia.Base/Input/GestureRecognizers/PinchGestureRecognizer.cs

@@ -0,0 +1,128 @@
+using Avalonia.Input.GestureRecognizers;
+
+namespace Avalonia.Input
+{
+    public class PinchGestureRecognizer : StyledElement, IGestureRecognizer
+    {
+        private IInputElement? _target;
+        private IGestureRecognizerActionsDispatcher? _actions;
+        private float _initialDistance;
+        private IPointer? _firstContact;
+        private Point _firstPoint;
+        private IPointer? _secondContact;
+        private Point _secondPoint;
+        private Point _origin;
+
+        public void Initialize(IInputElement target, IGestureRecognizerActionsDispatcher actions)
+        {
+            _target = target;
+            _actions = actions;
+        }
+
+        private void OnPointerPressed(object? sender, PointerPressedEventArgs e)
+        {
+            PointerPressed(e);
+        }
+
+        private void OnPointerReleased(object? sender, PointerReleasedEventArgs e)
+        {
+            PointerReleased(e);
+        }
+
+        public void PointerCaptureLost(IPointer pointer)
+        {
+            RemoveContact(pointer);
+        }
+
+        public void PointerMoved(PointerEventArgs e)
+        {
+            if (_target != null && _target is Visual visual)
+            {
+                if(_firstContact == e.Pointer)
+                {
+                    _firstPoint = e.GetPosition(visual);
+                }
+                else if (_secondContact == e.Pointer)
+                {
+                    _secondPoint = e.GetPosition(visual);
+                }
+                else
+                {
+                    return;
+                }
+
+                if (_firstContact != null && _secondContact != null)
+                {
+                    var distance = GetDistance(_firstPoint, _secondPoint);
+
+                    var scale = distance / _initialDistance;
+
+                    _target?.RaiseEvent(new PinchEventArgs(scale, _origin));
+                }
+            }
+        }
+
+        public void PointerPressed(PointerPressedEventArgs e)
+        {
+            if (_target != null && _target is Visual visual && (e.Pointer.Type == PointerType.Touch || e.Pointer.Type == PointerType.Pen))
+            {
+                if (_firstContact == null)
+                {
+                    _firstContact = e.Pointer;
+                    _firstPoint = e.GetPosition(visual);
+
+                    return;
+                }
+                else if (_secondContact == null && _firstContact != e.Pointer)
+                {
+                    _secondContact = e.Pointer;
+                    _secondPoint = e.GetPosition(visual);
+                }
+                else
+                {
+                    return;
+                }
+
+                if (_firstContact != null && _secondContact != null)
+                {
+                    _initialDistance = GetDistance(_firstPoint, _secondPoint);
+
+                    _origin = new Point((_firstPoint.X + _secondPoint.X) / 2.0f, (_firstPoint.Y + _secondPoint.Y) / 2.0f);
+
+                    _actions!.Capture(_firstContact, this);
+                    _actions!.Capture(_secondContact, this);
+                }
+            }
+        }
+
+        public void PointerReleased(PointerReleasedEventArgs e)
+        {
+            RemoveContact(e.Pointer);
+        }
+
+        private void RemoveContact(IPointer pointer)
+        {
+            if (_firstContact == pointer || _secondContact == pointer)
+            {
+                if (_secondContact == pointer)
+                {
+                    _secondContact = null;
+                }
+
+                if (_firstContact == pointer)
+                {
+                    _firstContact = _secondContact;
+
+                    _secondContact = null;
+                }
+                _target?.RaiseEvent(new PinchEndedEventArgs());
+            }
+        }
+
+        private float GetDistance(Point a, Point b)
+        {
+            var length = _secondPoint - _firstPoint;
+            return (float)new Vector(length.X, length.Y).Length;
+        }
+    }
+}

src/Avalonia.Base/Input/GestureRecognizers/PullGestureRecognizer.cs

@@ -1,15 +1,19 @@
-using Avalonia.Input.GestureRecognizers;
+using System;
+using Avalonia.Input.GestureRecognizers;
 
 namespace Avalonia.Input
 {
     public class PullGestureRecognizer : StyledElement, IGestureRecognizer
     {
+        internal static int MinPullDetectionSize = 50;
+
         private IInputElement? _target;
         private IGestureRecognizerActionsDispatcher? _actions;
         private Point _initialPosition;
         private int _gestureId;
         private IPointer? _tracking;
         private PullDirection _pullDirection;
+        private bool _pullInProgress;
 
         /// <summary>
         /// Defines the <see cref="PullDirection"/> property.
@@ -31,23 +35,12 @@ namespace Avalonia.Input
             PullDirection = pullDirection;
         }
 
+        public PullGestureRecognizer() { }
+
         public void Initialize(IInputElement target, IGestureRecognizerActionsDispatcher actions)
         {
             _target = target;
             _actions = actions;
-
-            _target?.AddHandler(InputElement.PointerPressedEvent, OnPointerPressed, Interactivity.RoutingStrategies.Tunnel | Interactivity.RoutingStrategies.Bubble);
-            _target?.AddHandler(InputElement.PointerReleasedEvent, OnPointerReleased, Interactivity.RoutingStrategies.Tunnel | Interactivity.RoutingStrategies.Bubble);
-        }
-
-        private void OnPointerPressed(object? sender, PointerPressedEventArgs e)
-        {
-            PointerPressed(e);
-        }
-
-        private void OnPointerReleased(object? sender, PointerReleasedEventArgs e)
-        {
-            PointerReleased(e);
         }
 
         public void PointerCaptureLost(IPointer pointer)
@@ -94,6 +87,7 @@ namespace Avalonia.Input
                         break;
                 }
 
+                _pullInProgress = true;
                 _target?.RaiseEvent(new PullGestureEventArgs(_gestureId, delta, PullDirection));
             }
         }
@@ -111,16 +105,16 @@ namespace Avalonia.Input
                 switch (PullDirection)
                 {
                     case PullDirection.TopToBottom:
-                        canPull = position.Y < bounds.Height * 0.1;
+                        canPull = position.Y < Math.Max(MinPullDetectionSize, bounds.Height * 0.1);
                         break;
                     case PullDirection.BottomToTop:
-                        canPull = position.Y > bounds.Height - (bounds.Height * 0.1);
+                        canPull = position.Y > Math.Min(bounds.Height - MinPullDetectionSize, bounds.Height - (bounds.Height * 0.1));
                         break;
                     case PullDirection.LeftToRight:
-                        canPull = position.X < bounds.Width * 0.1;
+                        canPull = position.X < Math.Max(MinPullDetectionSize, bounds.Width * 0.1);
                         break;
                     case PullDirection.RightToLeft:
-                        canPull = position.X > bounds.Width - (bounds.Width * 0.1);
+                        canPull = position.X > Math.Min(bounds.Width - MinPullDetectionSize, bounds.Width - (bounds.Width * 0.1));
                         break;
                 }
 
@@ -135,7 +129,7 @@ namespace Avalonia.Input
 
         public void PointerReleased(PointerReleasedEventArgs e)
         {
-            if (_tracking == e.Pointer)
+            if (_tracking == e.Pointer && _pullInProgress)
             {
                 EndPull();
             }
@@ -145,6 +139,7 @@ namespace Avalonia.Input
         {
             _tracking = null;
             _initialPosition = default;
+            _pullInProgress = false;
 
             _target?.RaiseEvent(new PullGestureEndedEventArgs(_gestureId, PullDirection));
         }

src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs

@@ -16,6 +16,7 @@ namespace Avalonia.Input.GestureRecognizers
         private bool _canHorizontallyScroll;
         private bool _canVerticallyScroll;
         private int _gestureId;
+        private int _scrollStartDistance = 30;
         
         // Movement per second
         private Vector _inertia;
@@ -38,6 +39,15 @@ namespace Avalonia.Input.GestureRecognizers
                 nameof(CanVerticallyScroll),
                 o => o.CanVerticallyScroll,
                 (o, v) => o.CanVerticallyScroll = v);
+
+        /// <summary>
+        /// Defines the <see cref="ScrollStartDistance"/> property.
+        /// </summary>
+        public static readonly DirectProperty<ScrollGestureRecognizer, int> ScrollStartDistanceProperty =
+            AvaloniaProperty.RegisterDirect<ScrollGestureRecognizer, int>(
+                nameof(ScrollStartDistance),
+                o => o.ScrollStartDistance,
+                (o, v) => o.ScrollStartDistance = v);
         
         /// <summary>
         /// Gets or sets a value indicating whether the content can be scrolled horizontally.
@@ -56,6 +66,15 @@ namespace Avalonia.Input.GestureRecognizers
             get => _canVerticallyScroll;
             set => SetAndRaise(CanVerticallyScrollProperty, ref _canVerticallyScroll, value);
         }
+
+        /// <summary>
+        /// Gets or sets a value indicating the distance the pointer moves before scrolling is started
+        /// </summary>
+        public int ScrollStartDistance
+        {
+            get => _scrollStartDistance;
+            set => SetAndRaise(ScrollStartDistanceProperty, ref _scrollStartDistance, value);
+        }
         
 
         public void Initialize(IInputElement target, IGestureRecognizerActionsDispatcher actions)
@@ -75,9 +94,6 @@ namespace Avalonia.Input.GestureRecognizers
                 _trackedRootPoint = e.GetPosition((Visual?)_target);
             }
         }
-
-        // Arbitrary chosen value, probably need to move that to platform settings or something
-        private const double ScrollStartDistance = 30;
         
         // Pixels per second speed that is considered to be the stop of inertial scroll
         private const double InertialScrollSpeedEnd = 5;

src/Avalonia.Base/Input/Gestures.cs

@@ -46,6 +46,14 @@ namespace Avalonia.Input
         private static readonly WeakReference<object?> s_lastPress = new WeakReference<object?>(null);
         private static Point s_lastPressPoint;
 
+        public static readonly RoutedEvent<PinchEventArgs> PinchEvent =
+            RoutedEvent.Register<PinchEventArgs>(
+                "PinchEvent", RoutingStrategies.Bubble, typeof(Gestures));
+
+        public static readonly RoutedEvent<PinchEndedEventArgs> PinchEndedEvent =
+            RoutedEvent.Register<PinchEndedEventArgs>(
+                "PinchEndedEvent", RoutingStrategies.Bubble, typeof(Gestures));
+
         public static readonly RoutedEvent<PullGestureEventArgs> PullGestureEvent =
             RoutedEvent.Register<PullGestureEventArgs>(
                 "PullGesture", RoutingStrategies.Bubble, typeof(Gestures));

src/Avalonia.Base/Input/PinchEventArgs.cs

@@ -0,0 +1,24 @@
+using Avalonia.Interactivity;
+
+namespace Avalonia.Input
+{
+    public class PinchEventArgs : RoutedEventArgs
+    {
+        public PinchEventArgs(double scale, Point scaleOrigin) :  base(Gestures.PinchEvent)
+        {
+            Scale = scale;
+            ScaleOrigin = scaleOrigin;
+        }
+
+        public double Scale { get; } = 1;
+
+        public Point ScaleOrigin { get; }
+    }
+
+    public class PinchEndedEventArgs : RoutedEventArgs
+    {
+        public PinchEndedEventArgs() :  base(Gestures.PinchEndedEvent)
+        {
+        }
+    }
+}

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

@@ -1,6 +1,8 @@
 using System.Collections.Generic;
 using Avalonia.Controls;
 using Avalonia.Input;
+using Avalonia.Input.GestureRecognizers;
+using Avalonia.Media;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -201,5 +203,101 @@ namespace Avalonia.Base.UnitTests.Input
             border.AddHandler(Gestures.TappedEvent, (s, e) => result.Add("bt"));
             border.AddHandler(Gestures.DoubleTappedEvent, (s, e) => result.Add("bdt"));
         }
+
+        [Fact]
+        public void Pinched_Should_Not_Be_Raised_For_Same_Pointer()
+        {
+            var touch = new TouchTestHelper();
+
+            Border border = new Border()
+            {
+                Width = 100,
+                Height = 100,
+                Background = new SolidColorBrush(Colors.Red)
+            };
+            border.GestureRecognizers.Add(new PinchGestureRecognizer());
+            var decorator = new Decorator
+            {
+                Child = border
+            };
+            var raised = false;
+
+            decorator.AddHandler(Gestures.PinchEvent, (s, e) => raised = true);
+
+            var firstPoint = new Point(5, 5);
+            var secondPoint = new Point(10, 10);
+
+            touch.Down(border, position: firstPoint);
+            touch.Down(border, position: secondPoint);
+            touch.Down(border, position: new Point(20, 20));
+
+            Assert.False(raised);
+        }
+
+        [Fact]
+        public void Pinched_Should_Be_Raised_For_Two_Pointers_Moving()
+        {
+            Border border = new Border()
+            {
+                Width = 100,
+                Height = 100,
+                Background = new SolidColorBrush(Colors.Red)
+            };
+            border.GestureRecognizers.Add(new PinchGestureRecognizer());
+            var decorator = new Decorator
+            {
+                Child = border
+            };
+            var raised = false;
+
+            decorator.AddHandler(Gestures.PinchEvent, (s, e) => raised = true);
+
+            var firstPoint = new Point(5, 5);
+            var secondPoint = new Point(10, 10);
+
+            var firstTouch = new TouchTestHelper();
+            var secondTouch = new TouchTestHelper();
+
+            firstTouch.Down(border, position: firstPoint);
+            secondTouch.Down(border, position: secondPoint);
+            secondTouch.Move(border, position: new Point(20, 20));
+
+            Assert.True(raised);
+        }
+
+        [Fact]
+        public void Scrolling_Should_Start_After_Start_Distance_Is_Exceded()
+        {
+            Border border = new Border()
+            {
+                Width = 100,
+                Height = 100,
+                Background = new SolidColorBrush(Colors.Red)
+            };
+            border.GestureRecognizers.Add(new ScrollGestureRecognizer()
+            {
+                CanHorizontallyScroll = true,
+                CanVerticallyScroll = true,
+                ScrollStartDistance = 50
+            });
+            var decorator = new Decorator
+            {
+                Child = border
+            };
+            var raised = false;
+
+            decorator.AddHandler(Gestures.ScrollGestureEvent, (s, e) => raised = true);
+
+            var firstTouch = new TouchTestHelper();
+
+            firstTouch.Down(border, position: new Point(5, 5));
+            firstTouch.Move(border, position: new Point(20, 20));
+
+            Assert.False(raised);
+
+            firstTouch.Move(border, position: new Point(70, 20));
+
+            Assert.True(raised);
+        }
     }
 }

tests/Avalonia.UnitTests/TouchTestHelper.cs

@@ -0,0 +1,53 @@
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.VisualTree;
+
+namespace Avalonia.UnitTests
+{
+    public class TouchTestHelper
+    {
+        private readonly Pointer _pointer = new Pointer(Pointer.GetNextFreeId(), PointerType.Touch, true);
+        private ulong _nextStamp = 1;
+        private ulong Timestamp() => _nextStamp++;
+        public IInputElement Captured => _pointer.Captured;
+
+        public void Down(Interactive target, Point position = default, KeyModifiers modifiers = default)
+        {
+            Down(target, target, position, modifiers);
+        }
+
+        public void Down(Interactive target, Interactive source, Point position = default, KeyModifiers modifiers = default)
+        {
+            _pointer.Capture((IInputElement)target);
+            source.RaiseEvent(new PointerPressedEventArgs(source, _pointer, (Visual)source, position, Timestamp(), PointerPointProperties.None,
+                modifiers));
+        }
+
+        public void Move(Interactive target, in Point position, KeyModifiers modifiers = default) => Move(target, target, position, modifiers);
+
+        public void Move(Interactive target, Interactive source, in Point position, KeyModifiers modifiers = default)
+        {
+            target.RaiseEvent(new PointerEventArgs(InputElement.PointerMovedEvent, source, _pointer, (Visual)target, position,
+                Timestamp(), PointerPointProperties.None, modifiers));
+        }
+
+        public void Up(Interactive target, Point position = default, KeyModifiers modifiers = default)
+            => Up(target, target, position, modifiers);
+
+        public void Up(Interactive target, Interactive source, Point position = default, KeyModifiers modifiers = default)
+        {
+            source.RaiseEvent(new PointerReleasedEventArgs(source, _pointer, (Visual)target, position, Timestamp(), PointerPointProperties.None,
+                modifiers, MouseButton.None));
+            _pointer.Capture(null);
+        }
+
+        public void Tap(Interactive target, Point position = default,  KeyModifiers modifiers = default)
+            => Tap(target, target, position, modifiers);
+
+        public void Tap(Interactive target, Interactive source, Point position = default, KeyModifiers modifiers = default)
+        {
+            Down(target, source, position, modifiers);
+            Up(target, source, position, modifiers);
+        }
+    }
+}