From 78abd6d4b588a2913441114219969085c34ce01b Mon Sep 17 00:00:00 2001
From: Emmanuel Hansen <emmausssss@gmail.com>
Date: Tue, 24 Jan 2023 20:03:02 +0000
Subject: [PATCH] Add IsScrollInertiaEnabled attached property to scrollviewer

---
 .../Pages/ScrollViewerPage.xaml               |  2 ++
 .../Pages/ScrollViewerPage.xaml.cs            |  8 +++++++
 .../ScrollGestureRecognizer.cs                | 24 +++++++++++++++++--
 src/Avalonia.Controls/ScrollViewer.cs         | 17 +++++++++++++
 .../Controls/ScrollViewer.xaml                |  3 ++-
 5 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/samples/ControlCatalog/Pages/ScrollViewerPage.xaml b/samples/ControlCatalog/Pages/ScrollViewerPage.xaml
index 1903e50ed7..5042d7823b 100644
--- a/samples/ControlCatalog/Pages/ScrollViewerPage.xaml
+++ b/samples/ControlCatalog/Pages/ScrollViewerPage.xaml
@@ -9,6 +9,7 @@
     <Grid ColumnDefinitions="Auto, *">
       <StackPanel Orientation="Vertical" Spacing="4">
         <ToggleSwitch IsChecked="{Binding AllowAutoHide}" Content="Allow auto hide" />
+        <ToggleSwitch IsChecked="{Binding EnableInertia}" Content="Enable Inertia" />
 
         <StackPanel Orientation="Vertical" Spacing="4">
           <TextBlock Text="Horizontal Scroll" />
@@ -24,6 +25,7 @@
       <ScrollViewer x:Name="ScrollViewer"
                     Grid.Column="1"
                     Width="400" Height="400"
+                    IsScrollInertiaEnabled="{Binding EnableInertia}"
                     AllowAutoHide="{Binding AllowAutoHide}"
                     HorizontalScrollBarVisibility="{Binding HorizontalScrollVisibility}"
                     VerticalScrollBarVisibility="{Binding VerticalScrollVisibility}">
diff --git a/samples/ControlCatalog/Pages/ScrollViewerPage.xaml.cs b/samples/ControlCatalog/Pages/ScrollViewerPage.xaml.cs
index dcd7a88a56..a097f1f951 100644
--- a/samples/ControlCatalog/Pages/ScrollViewerPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/ScrollViewerPage.xaml.cs
@@ -9,6 +9,7 @@ namespace ControlCatalog.Pages
     public class ScrollViewerPageViewModel : ViewModelBase
     {
         private bool _allowAutoHide;
+        private bool _enableInertia;
         private ScrollBarVisibility _horizontalScrollVisibility;
         private ScrollBarVisibility _verticalScrollVisibility;
 
@@ -25,6 +26,7 @@ namespace ControlCatalog.Pages
             HorizontalScrollVisibility = ScrollBarVisibility.Auto;
             VerticalScrollVisibility = ScrollBarVisibility.Auto;
             AllowAutoHide = true;
+            EnableInertia = true;
         }
 
         public bool AllowAutoHide
@@ -33,6 +35,12 @@ namespace ControlCatalog.Pages
             set => this.RaiseAndSetIfChanged(ref _allowAutoHide, value);
         }
 
+        public bool EnableInertia
+        {
+            get => _enableInertia;
+            set => this.RaiseAndSetIfChanged(ref _enableInertia, value);
+        }
+
         public ScrollBarVisibility HorizontalScrollVisibility
         {
             get => _horizontalScrollVisibility;
diff --git a/src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs b/src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs
index 790439245a..fdab2df0bf 100644
--- a/src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs
+++ b/src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs
@@ -23,7 +23,8 @@ namespace Avalonia.Input.GestureRecognizers
         // Movement per second
         private Vector _inertia;
         private ulong? _lastMoveTimestamp;
-        
+        private bool _isScrollInertiaEnabled;
+
         /// <summary>
         /// Defines the <see cref="CanHorizontallyScroll"/> property.
         /// </summary>
@@ -42,6 +43,15 @@ namespace Avalonia.Input.GestureRecognizers
                 o => o.CanVerticallyScroll,
                 (o, v) => o.CanVerticallyScroll = v);
 
+        /// <summary>
+        /// Defines the <see cref="IsScrollInertiaEnabled"/> property.
+        /// </summary>
+        public static readonly DirectProperty<ScrollGestureRecognizer, bool> IsScrollInertiaEnabledProperty =
+            AvaloniaProperty.RegisterDirect<ScrollGestureRecognizer, bool>(
+                nameof(IsScrollInertiaEnabled),
+                o => o.IsScrollInertiaEnabled,
+                (o, v) => o.IsScrollInertiaEnabled = v);
+
         /// <summary>
         /// Defines the <see cref="ScrollStartDistance"/> property.
         /// </summary>
@@ -68,6 +78,15 @@ namespace Avalonia.Input.GestureRecognizers
             get => _canVerticallyScroll;
             set => SetAndRaise(CanVerticallyScrollProperty, ref _canVerticallyScroll, value);
         }
+        
+        /// <summary>
+        /// Gets or sets whether the gesture should include inertia in it's behavior.
+        /// </summary>
+        public bool IsScrollInertiaEnabled
+        {
+            get => _isScrollInertiaEnabled;
+            set => SetAndRaise(IsScrollInertiaEnabledProperty, ref _isScrollInertiaEnabled, value);
+        }
 
         /// <summary>
         /// Gets or sets a value indicating the distance the pointer moves before scrolling is started
@@ -168,7 +187,8 @@ namespace Avalonia.Input.GestureRecognizers
                 if (_inertia == default
                     || e.Timestamp == 0
                     || _lastMoveTimestamp == 0
-                    || e.Timestamp - _lastMoveTimestamp > 200)
+                    || e.Timestamp - _lastMoveTimestamp > 200
+                    || !IsScrollInertiaEnabled)
                     EndGesture();
                 else
                 {
diff --git a/src/Avalonia.Controls/ScrollViewer.cs b/src/Avalonia.Controls/ScrollViewer.cs
index 503187e2d3..d16cd209c0 100644
--- a/src/Avalonia.Controls/ScrollViewer.cs
+++ b/src/Avalonia.Controls/ScrollViewer.cs
@@ -193,6 +193,14 @@ namespace Avalonia.Controls
                 nameof(IsScrollChainingEnabled),
                 defaultValue: true);
 
+        /// <summary>
+        /// Defines the <see cref="IsScrollInertiaEnabled"/> property.
+        /// </summary>
+        public static readonly AttachedProperty<bool> IsScrollInertiaEnabledProperty =
+            AvaloniaProperty.RegisterAttached<ScrollViewer, Control, bool>(
+                nameof(IsScrollInertiaEnabled),
+                defaultValue: true);
+
         /// <summary>
         /// Defines the <see cref="ScrollChanged"/> event.
         /// </summary>
@@ -444,6 +452,15 @@ namespace Avalonia.Controls
             set => SetValue(IsScrollChainingEnabledProperty, value);
         }
 
+        /// <summary>
+        /// Gets or sets whether scroll gestures should include inertia in their behavior and value.
+        /// </summary>
+        public bool IsScrollInertiaEnabled
+        {
+            get => GetValue(IsScrollInertiaEnabledProperty);
+            set => SetValue(IsScrollInertiaEnabledProperty, value);
+        }
+
         /// <summary>
         /// Scrolls the content up one line.
         /// </summary>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml b/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml
index 71df4d419f..15cd9428f3 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml
@@ -39,7 +39,8 @@
                                   IsScrollChainingEnabled="{TemplateBinding IsScrollChainingEnabled}">
             <ScrollContentPresenter.GestureRecognizers>
               <ScrollGestureRecognizer CanHorizontallyScroll="{TemplateBinding CanHorizontallyScroll}"
-                                       CanVerticallyScroll="{TemplateBinding CanVerticallyScroll}" />
+                                       CanVerticallyScroll="{TemplateBinding CanVerticallyScroll}"
+                                       IsScrollInertiaEnabled="{TemplateBinding IsScrollInertiaEnabled}"/>
             </ScrollContentPresenter.GestureRecognizers>
           </ScrollContentPresenter>
           <ScrollBar Name="PART_HorizontalScrollBar"