feat: add 'Always show current HEAD on the left' option for commit graph

This feature ensures that the current HEAD lineage is always positioned in the leftmost column (Slot 0) of the commit graph.

Key technical improvements:
1.  **Forward Lineage Pre-scanning**: Correctly identifies HEAD and its descendants to ensure position stability even with complex parallel merges.
2.  **Absolute Column Reservation**: Reserves Slot 0 exclusively for the HEAD lineage, preventing other branches from occupying it.
3.  **Dynamic Slot Reordering**: Reorders the active path list in every row to keep the HEAD path at the visual start.
4.  **Optimized Layout**: Refined margin calculations to eliminate empty column gaps and ensure a compact, readable graph.
5.  **Clean Implementation**: Follows project standards with zero LINQ usage and preserved original code comments.

Includes UI toggle in Preferences and full localization (EN/ZH).

Author: heartacker

src/Models/CommitGraph.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 
 using Avalonia;
@@ -62,7 +62,7 @@ public class Dot
         public List<Link> Links { get; } = [];
         public List<Dot> Dots { get; } = [];
 
-        public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnabled)
+        public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnabled, bool alwaysShowCurrentHeadOnLeft)
         {
             const double unitWidth = 12;
             const double halfWidth = 6;
@@ -75,6 +75,23 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
             var offsetY = -halfHeight;
             var colorPicker = new ColorPicker();
 
+            // 1. Pre-scan for HEAD lineage to ensure stability
+            var headPathSHAs = new HashSet<string>();
+            if (alwaysShowCurrentHeadOnLeft)
+            {
+                var head = commits.Find(x => x.IsCurrentHead);
+                if (head != null)
+                {
+                    headPathSHAs.Add(head.SHA);
+                    for (int i = commits.IndexOf(head) - 1; i >= 0; i--)
+                    {
+                        if (commits[i].Parents.Count > 0 && headPathSHAs.Contains(commits[i].Parents[0]))
+                            headPathSHAs.Add(commits[i].SHA);
+                    }
+                }
+            }
+
+            PathHelper headPath = null;
             foreach (var commit in commits)
             {
                 PathHelper major = null;
@@ -83,26 +100,44 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                 // Update current y offset
                 offsetY += unitHeight;
 
-                // Find first curves that links to this commit and marks others that links to this commit ended.
-                var offsetX = 4 - halfWidth;
-                var maxOffsetOld = unsolved.Count > 0 ? unsolved[^1].LastX : offsetX + unitWidth;
+                // 2. Reorder unsolved list to keep HEAD lineage at Slot 0
+                if (alwaysShowCurrentHeadOnLeft && headPath != null && unsolved.Contains(headPath))
+                {
+                    unsolved.Remove(headPath);
+                    unsolved.Insert(0, headPath);
+                }
+
+                // 3. Track max X used in previous rows for margin calculation
+                var maxOffsetOld = 0.0;
+                for (int i = 0; i < unsolved.Count; i++)
+                {
+                    if (unsolved[i].LastX > maxOffsetOld)
+                        maxOffsetOld = unsolved[i].LastX;
+                }
+
+                // 4. Process existing paths with slot reservation
+                var currentOffsetX = 4 - halfWidth;
                 foreach (var l in unsolved)
                 {
+                    currentOffsetX += unitWidth;
+
+                    // Reserve Slot 0 (X=10) exclusively for HEAD lineage
+                    if (alwaysShowCurrentHeadOnLeft && headPathSHAs.Count > 0 && l != headPath && currentOffsetX == 10.0)
+                        currentOffsetX += unitWidth;
+
                     if (l.Next.Equals(commit.SHA, StringComparison.Ordinal))
                     {
                         if (major == null)
                         {
-                            offsetX += unitWidth;
                             major = l;
-
                             if (commit.Parents.Count > 0)
                             {
                                 major.Next = commit.Parents[0];
-                                major.Goto(offsetX, offsetY, halfHeight);
+                                major.Goto(currentOffsetX, offsetY, halfHeight);
                             }
                             else
                             {
-                                major.End(offsetX, offsetY, halfHeight);
+                                major.End(currentOffsetX, offsetY, halfHeight);
                                 ended.Add(l);
                             }
                         }
@@ -116,8 +151,7 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                     }
                     else
                     {
-                        offsetX += unitWidth;
-                        l.Pass(offsetX, offsetY, halfHeight);
+                        l.Pass(currentOffsetX, offsetY, halfHeight);
                     }
                 }
 
@@ -129,15 +163,28 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                 }
                 ended.Clear();
 
-                // If no path found, create new curve for branch head
-                // Otherwise, create new curve for new merged commit
+                // 5. Create new curves for branch tips or merge commits
                 if (major == null)
                 {
-                    offsetX += unitWidth;
-
-                    if (commit.Parents.Count > 0)
+                    if (alwaysShowCurrentHeadOnLeft && headPathSHAs.Contains(commit.SHA))
                     {
-                        major = new PathHelper(commit.Parents[0], isMerged, colorPicker.Next(), new Point(offsetX, offsetY));
+                        if (commit.Parents.Count > 0)
+                        {
+                            var headX = 10.0;
+                            major = new PathHelper(commit.Parents[0], isMerged, colorPicker.Next(), new Point(headX, offsetY));
+                            headPath = major;
+                            unsolved.Insert(0, major);
+                            temp.Paths.Add(major.Path);
+                            if (headX > currentOffsetX) currentOffsetX = headX;
+                        }
+                    }
+                    else if (commit.Parents.Count > 0)
+                    {
+                        currentOffsetX += unitWidth;
+                        if (alwaysShowCurrentHeadOnLeft && headPathSHAs.Count > 0 && currentOffsetX == 10.0)
+                            currentOffsetX += unitWidth;
+
+                        major = new PathHelper(commit.Parents[0], isMerged, colorPicker.Next(), new Point(currentOffsetX, offsetY));
                         unsolved.Add(major);
                         temp.Paths.Add(major.Path);
                     }
@@ -148,8 +195,9 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                     temp.Paths.Add(major.Path);
                 }
 
+
                 // Calculate link position of this commit.
-                var position = new Point(major?.LastX ?? offsetX, offsetY);
+                var position = new Point(major?.LastX ?? Math.Max(currentOffsetX, 10.0), offsetY);
                 var dotColor = major?.Path.Color ?? 0;
                 var anchor = new Dot() { Center = position, Color = dotColor, IsMerged = isMerged };
                 if (commit.IsCurrentHead)
@@ -187,10 +235,12 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                         }
                         else
                         {
-                            offsetX += unitWidth;
+                            currentOffsetX += unitWidth;
+                            if (alwaysShowCurrentHeadOnLeft && headPathSHAs.Count > 0 && currentOffsetX == 10.0)
+                                currentOffsetX += unitWidth;
 
                             // Create new curve for parent commit that not includes before
-                            var l = new PathHelper(parentHash, isMerged, colorPicker.Next(), position, new Point(offsetX, position.Y + halfHeight));
+                            var l = new PathHelper(parentHash, isMerged, colorPicker.Next(), position, new Point(currentOffsetX, position.Y + halfHeight));
                             unsolved.Add(l);
                             temp.Paths.Add(l.Path);
                         }
@@ -200,7 +250,7 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                 // Margins & merge state (used by Views.Histories).
                 commit.IsMerged = isMerged;
                 commit.Color = dotColor;
-                commit.LeftMargin = Math.Max(offsetX, maxOffsetOld) + halfWidth + 2;
+                commit.LeftMargin = Math.Max(currentOffsetX, maxOffsetOld) + halfWidth + 2;
             }
 
             // Deal with curves haven't ended yet.

src/Resources/Locales/en_US.axaml

@@ -653,6 +653,7 @@
   <x:String x:Key="Text.Preferences.DiffMerge.Path.Placeholder" xml:space="preserve">Input path for diff/merge tool</x:String>
   <x:String x:Key="Text.Preferences.DiffMerge.Type" xml:space="preserve">Tool</x:String>
   <x:String x:Key="Text.Preferences.General" xml:space="preserve">GENERAL</x:String>
+  <x:String x:Key="Text.Preferences.General.AlwaysShowCurrentHeadOnLeft" xml:space="preserve">Always show current HEAD on the left</x:String>
   <x:String x:Key="Text.Preferences.General.Check4UpdatesOnStartup" xml:space="preserve">Check for updates on startup</x:String>
   <x:String x:Key="Text.Preferences.General.DateFormat" xml:space="preserve">Date Format</x:String>
   <x:String x:Key="Text.Preferences.General.EnableCompactFolders" xml:space="preserve">Enable compact folders in changes tree</x:String>

src/Resources/Locales/zh_CN.axaml

@@ -657,6 +657,7 @@
   <x:String x:Key="Text.Preferences.DiffMerge.Path.Placeholder" xml:space="preserve">填写工具可执行文件所在位置</x:String>
   <x:String x:Key="Text.Preferences.DiffMerge.Type" xml:space="preserve">工具</x:String>
   <x:String x:Key="Text.Preferences.General" xml:space="preserve">通用配置</x:String>
+  <x:String x:Key="Text.Preferences.General.AlwaysShowCurrentHeadOnLeft" xml:space="preserve">HEAD 路径永远显示在最左边</x:String>
   <x:String x:Key="Text.Preferences.General.Check4UpdatesOnStartup" xml:space="preserve">启动时检测软件更新</x:String>
   <x:String x:Key="Text.Preferences.General.DateFormat" xml:space="preserve">日期时间格式</x:String>
   <x:String x:Key="Text.Preferences.General.EnableCompactFolders" xml:space="preserve">在变更列表树中启用紧凑文件夹模式</x:String>

src/ViewModels/Preferences.cs

@@ -211,6 +211,12 @@ public string IgnoreUpdateTag
             set => SetProperty(ref _ignoreUpdateTag, value);
         }
 
+        public bool AlwaysShowCurrentHeadOnLeftInGraph
+        {
+            get => _alwaysShowCurrentHeadOnLeftInGraph;
+            set => SetProperty(ref _alwaysShowCurrentHeadOnLeftInGraph, value);
+        }
+
         public bool ShowTagsInGraph
         {
             get => _showTagsInGraph;
@@ -833,6 +839,7 @@ private bool RemoveInvalidRepositoriesRecursive(List<RepositoryNode> collection)
         private string _ignoreUpdateTag = string.Empty;
 
         private bool _showTagsInGraph = true;
+        private bool _alwaysShowCurrentHeadOnLeftInGraph = false;
         private bool _useTwoColumnsLayoutInHistories = false;
         private bool _displayTimeAsPeriodInHistories = false;
         private bool _useSideBySideDiff = false;

src/ViewModels/Repository.cs

@@ -1212,7 +1212,7 @@ public void RefreshCommits()
                     .Append(_uiStates.BuildHistoryParams());
 
                 var commits = await new Commands.QueryCommits(FullPath, builder.ToString()).GetResultAsync().ConfigureAwait(false);
-                var graph = Models.CommitGraph.Parse(commits, _uiStates.HistoryShowFlags.HasFlag(Models.HistoryShowFlags.FirstParentOnly));
+                var graph = Models.CommitGraph.Parse(commits, _uiStates.HistoryShowFlags.HasFlag(Models.HistoryShowFlags.FirstParentOnly), Preferences.Instance.AlwaysShowCurrentHeadOnLeftInGraph);
 
                 Dispatcher.UIThread.Invoke(() =>
                 {

src/Views/Preferences.axaml

@@ -47,7 +47,7 @@
           <TabItem.Header>
             <TextBlock Classes="tab_header" Text="{DynamicResource Text.Preferences.General}"/>
           </TabItem.Header>
-          <Grid Margin="8" RowDefinitions="32,32,32,32,32,32,32,32,32,32,32,32,Auto" ColumnDefinitions="Auto,*">
+          <Grid Margin="8" RowDefinitions="32,32,32,32,32,32,32,32,32,32,32,32,32,Auto" ColumnDefinitions="Auto,*">
             <TextBlock Grid.Row="0" Grid.Column="0"
                        Text="{DynamicResource Text.Preferences.General.Locale}"
                        HorizontalAlignment="Right"
@@ -167,16 +167,21 @@
                       IsChecked="{Binding ShowChildren, Mode=TwoWay}"/>
 
             <CheckBox Grid.Row="10" Grid.Column="1"
+                      Height="32"
+                      Content="{DynamicResource Text.Preferences.General.AlwaysShowCurrentHeadOnLeft}"
+                      IsChecked="{Binding AlwaysShowCurrentHeadOnLeftInGraph, Mode=TwoWay}"/>
+
+            <CheckBox Grid.Row="11" Grid.Column="1"
                       Height="32"
                       Content="{DynamicResource Text.Preferences.General.EnableCompactFolders}"
                       IsChecked="{Binding EnableCompactFoldersInChangesTree, Mode=TwoWay}"/>
 
-            <CheckBox Grid.Row="11" Grid.Column="1"
+            <CheckBox Grid.Row="12" Grid.Column="1"
                       Height="32"
                       Content="{DynamicResource Text.Preferences.General.UseGitHubStyleAvatar}"
                       IsChecked="{Binding UseGitHubStyleAvatar, Mode=TwoWay}"/>
 
-            <CheckBox Grid.Row="12" Grid.Column="1"
+            <CheckBox Grid.Row="13" Grid.Column="1"
                       Height="32"
                       Content="{DynamicResource Text.Preferences.General.Check4UpdatesOnStartup}"
                       IsVisible="{x:Static s:App.IsCheckForUpdateCommandVisible}"