feature<TextDiffView>: do NOT reset scroll offset after recompute diff with same change

src/ViewModels/DiffContext.cs

@@ -1,4 +1,5 @@
-using Avalonia.Threading;
+using Avalonia;
+using Avalonia.Threading;
 using CommunityToolkit.Mvvm.ComponentModel;
 using System.IO;
 using System.Threading.Tasks;
@@ -49,6 +50,11 @@ namespace SourceGit.ViewModels {
             private set => SetProperty(ref _content, value);
         }
 
+        public Vector SyncScrollOffset {
+            get => _syncScrollOffset;
+            set => SetProperty(ref _syncScrollOffset, value);
+        }
+
         public DiffContext(string repo, Models.DiffOption option) {
             _repo = repo;
             _option = option;
@@ -113,5 +119,6 @@ namespace SourceGit.ViewModels {
         private bool _isNoChange = false;
         private bool _isTextDiff = false;
         private object _content = null;
+        private Vector _syncScrollOffset = Vector.Zero;
     }
 }

src/ViewModels/TwoSideTextDiff.cs

@@ -4,11 +4,6 @@ using System.Collections.Generic;
 
 namespace SourceGit.ViewModels {
     public class TwoSideTextDiff : ObservableObject {
-        public Vector SyncScrollOffset {
-            get => _syncScrollOffset;
-            set => SetProperty(ref _syncScrollOffset, value);
-        }
-
         public string File { get; set; } = string.Empty;
         public List<Models.TextDiffLine> Old { get; set; } = new List<Models.TextDiffLine>();
         public List<Models.TextDiffLine> New { get; set; } = new List<Models.TextDiffLine>();
@@ -46,7 +41,5 @@ namespace SourceGit.ViewModels {
                 for (int i = 0; i < diff; i++) New.Add(new Models.TextDiffLine());
             }
         }
-
-        private Vector _syncScrollOffset;
     }
 }

src/ViewModels/WorkingCopy.cs

@@ -1,4 +1,5 @@
-using Avalonia.Controls;
+using Avalonia;
+using Avalonia.Controls;
 using Avalonia.Platform.Storage;
 using Avalonia.Threading;
 using CommunityToolkit.Mvvm.ComponentModel;
@@ -194,6 +195,9 @@ namespace SourceGit.ViewModels {
 
                 // Restore last selection states.
                 if (viewChange != null) {
+                    var scrollOffset = Vector.Zero;
+                    if (_detailContext is DiffContext old) scrollOffset = old.SyncScrollOffset;
+
                     if (lastSelectedIsUnstaged) {
                         SelectedUnstagedChange = viewChange;
                         SelectedUnstagedTreeNode = FileTreeNode.SelectByPath(_unstagedTree, viewFile);
@@ -201,6 +205,8 @@ namespace SourceGit.ViewModels {
                         SelectedStagedChange = viewChange;
                         SelectedStagedTreeNode = FileTreeNode.SelectByPath(_stagedTree, viewFile);
                     }
+
+                    if (_detailContext is DiffContext cur) cur.SyncScrollOffset = scrollOffset;
                 } else {
                     SelectedUnstagedChange = null;
                     SelectedUnstagedTreeNode = null;

src/Views/TextDiffView.axaml

@@ -18,13 +18,14 @@
                                    SecondaryFG="{DynamicResource Brush.FG2}"
                                    FontFamily="{StaticResource JetBrainsMono}"
                                    FontSize="12"
-                                   DiffData="{Binding}"/>
+                                   DiffData="{Binding}"
+                                   SyncScrollOffset="{Binding $parent[v:DiffView].DataContext.(vm:DiffContext).SyncScrollOffset, Mode=TwoWay}"/>
     </DataTemplate>
 
     <DataTemplate DataType="vm:TwoSideTextDiff">
       <Grid ColumnDefinitions="*,1,*">
         <v:SingleSideTextDiffPresenter Grid.Column="0"
-                                       SyncScrollOffset="{Binding SyncScrollOffset, Mode=TwoWay}"
+                                       SyncScrollOffset="{Binding $parent[v:DiffView].DataContext.(vm:DiffContext).SyncScrollOffset, Mode=TwoWay}"
                                        IsOld="True"
                                        HorizontalScrollBarVisibility="Auto"
                                        VerticalScrollBarVisibility="Auto"
@@ -39,7 +40,7 @@
         <Rectangle Grid.Column="1" Fill="{DynamicResource Brush.Border2}" Width="1" HorizontalAlignment="Center" VerticalAlignment="Stretch"/>
 
         <v:SingleSideTextDiffPresenter Grid.Column="2"
-                                       SyncScrollOffset="{Binding SyncScrollOffset, Mode=TwoWay}"
+                                       SyncScrollOffset="{Binding $parent[v:DiffView].DataContext.(vm:DiffContext).SyncScrollOffset, Mode=TwoWay}"
                                        IsOld="False"
                                        HorizontalScrollBarVisibility="Auto"
                                        VerticalScrollBarVisibility="Auto"

src/Views/TextDiffView.axaml.cs

@@ -188,6 +188,14 @@ namespace SourceGit.Views {
             set => SetValue(SecondaryFGProperty, value);
         }
 
+        public static readonly StyledProperty<Vector> SyncScrollOffsetProperty =
+            AvaloniaProperty.Register<SingleSideTextDiffPresenter, Vector>(nameof(SyncScrollOffset));
+
+        public Vector SyncScrollOffset {
+            get => GetValue(SyncScrollOffsetProperty);
+            set => SetValue(SyncScrollOffsetProperty, value);
+        }
+
         protected override Type StyleKeyOverride => typeof(TextEditor);
 
         public CombinedTextDiffPresenter() : base(new TextArea(), new TextDocument()) {
@@ -208,6 +216,7 @@ namespace SourceGit.Views {
             TextArea.TextView.BackgroundRenderers.Add(new LineBackgroundRenderer(this));
             TextArea.TextView.LineTransformers.Add(new LineStyleTransformer(this, SecondaryFG));
             TextArea.TextView.ContextRequested += OnTextViewContextRequested;
+            TextArea.TextView.ScrollOffsetChanged += OnTextViewScrollOffsetChanged;
 
             if (App.Current?.ActualThemeVariant == ThemeVariant.Dark) {
                 _registryOptions = new RegistryOptions(ThemeName.DarkPlus);
@@ -226,6 +235,7 @@ namespace SourceGit.Views {
             TextArea.TextView.BackgroundRenderers.Clear();
             TextArea.TextView.LineTransformers.Clear();
             TextArea.TextView.ContextRequested -= OnTextViewContextRequested;
+            TextArea.TextView.ScrollOffsetChanged -= OnTextViewScrollOffsetChanged;
             _registryOptions = null;
             _textMate.Dispose();
             _textMate = null;
@@ -255,6 +265,10 @@ namespace SourceGit.Views {
             e.Handled = true;
         }
 
+        private void OnTextViewScrollOffsetChanged(object sender, EventArgs e) {
+            SyncScrollOffset = TextArea.TextView.ScrollOffset;
+        }
+
         protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change) {
             base.OnPropertyChanged(change);
 
@@ -270,6 +284,11 @@ namespace SourceGit.Views {
                 } else {
                     Text = string.Empty;
                 }
+            } else if (change.Property == SyncScrollOffsetProperty) {
+                if (TextArea.TextView.ScrollOffset != SyncScrollOffset) {
+                    IScrollable scrollable = TextArea.TextView;
+                    scrollable.Offset = SyncScrollOffset;
+                }
             } else if (change.Property.Name == "ActualThemeVariant" && change.NewValue != null && _textMate != null) {
                 if (App.Current?.ActualThemeVariant == ThemeVariant.Dark) {
                     _textMate.SetTheme(_registryOptions.LoadTheme(ThemeName.DarkPlus));