feature: add new graph-highlighting option "Selected Commits (only first-parent)" (#2646)

* Refactor: move relevant code to new method Histories.RecalculateMergeState()
* Reduce redundant code in RecalculateMergeState()
* Reduce redundant highlighting-code by modifying if-conditions
* Highlight first parent separately for "extra" commits
* The remaining parents are covered further down (under condition '!firstParentOnlyEnabled').
* This is made in prep for upcoming work on adding a new highlighting option.
* Add new graph-highlight option "Selected Commits (only first-parent)"

Author: goran-w

src/Models/CommitGraph.cs

@@ -13,6 +13,7 @@ public enum CommitGraphHighlighting
         All = 0,
         CurrentBranchOnly,
         SelectedCommitsOnly,
+        SelectedCommitsOnlyFirstParent,
         CurrentBranchAndSelectedCommits,
     }
 
@@ -70,7 +71,7 @@ public class Dot
         public List<Link> Links { get; } = [];
         public List<Dot> Dots { get; } = [];
 
-        public static CommitGraph Generate(List<Commit> commits, bool recalculateMergeState, bool firstParentOnlyEnabled, CommitGraphHighlighting highlighting, HashSet<string> highlightExtraCommits)
+        public static CommitGraph Generate(List<Commit> commits, bool firstParentOnlyEnabled, CommitGraphHighlighting highlighting, HashSet<string> highlightExtraCommits)
         {
             const double unitWidth = 12;
             const double halfWidth = 6;
@@ -82,29 +83,11 @@ public static CommitGraph Generate(List<Commit> commits, bool recalculateMergeSt
             var ended = new List<PathHelper>();
             var offsetY = -halfHeight;
             var colorPicker = new ColorPicker();
-            var merged = new HashSet<string>();
 
             foreach (var commit in commits)
             {
                 PathHelper major = null;
 
-                // Update merge state of this commit.
-                if (recalculateMergeState)
-                {
-                    if (commit.IsMerged)
-                    {
-                        merged.Remove(commit.SHA);
-                        foreach (var p in commit.Parents)
-                            merged.Add(p);
-                    }
-                    else if (merged.Remove(commit.SHA))
-                    {
-                        commit.IsMerged = true;
-                        foreach (var p in commit.Parents)
-                            merged.Add(p);
-                    }
-                }
-
                 // Update current y offset
                 offsetY += unitHeight;
 
@@ -164,31 +147,23 @@ public static CommitGraph Generate(List<Commit> commits, bool recalculateMergeSt
                     {
                         isHighlighted = true;
                     }
-                    else if (highlighting == CommitGraphHighlighting.CurrentBranchOnly)
+
+                    if (!isHighlighted &&
+                        (highlighting == CommitGraphHighlighting.CurrentBranchOnly ||
+                         highlighting == CommitGraphHighlighting.CurrentBranchAndSelectedCommits))
                     {
                         isHighlighted = commit.IsMerged;
                     }
-                    else if (highlighting == CommitGraphHighlighting.SelectedCommitsOnly)
+
+                    if (!isHighlighted &&
+                        (highlighting == CommitGraphHighlighting.SelectedCommitsOnly ||
+                         highlighting == CommitGraphHighlighting.SelectedCommitsOnlyFirstParent ||
+                         highlighting == CommitGraphHighlighting.CurrentBranchAndSelectedCommits))
                     {
                         isHighlighted = highlightExtraCommits.Remove(commit.SHA);
-                        if (isHighlighted)
-                        {
-                            foreach (var p in commit.Parents)
-                                highlightExtraCommits.Add(p);
-                        }
-                    }
-                    else
-                    {
-                        if (commit.IsMerged)
-                        {
-                            isHighlighted = true;
-                        }
-                        else if (highlightExtraCommits.Remove(commit.SHA))
-                        {
-                            isHighlighted = true;
-                            foreach (var p in commit.Parents)
-                                highlightExtraCommits.Add(p);
-                        }
+                        // Highlight first parent, other parents are dealt with later
+                        if (isHighlighted && commit.Parents.Count > 0)
+                            highlightExtraCommits.Add(commit.Parents[0]);
                     }
                 }
                 commit.IsHighlightedInGraph = isHighlighted;
@@ -227,6 +202,9 @@ public static CommitGraph Generate(List<Commit> commits, bool recalculateMergeSt
                 // Deal with other parents (the first parent has been processed)
                 if (!firstParentOnlyEnabled)
                 {
+                    if (highlighting == CommitGraphHighlighting.SelectedCommitsOnlyFirstParent)
+                        isHighlighted = false;
+
                     for (int j = 1; j < commit.Parents.Count; j++)
                     {
                         var parentHash = commit.Parents[j];

src/Resources/Locales/en_US.axaml

@@ -518,6 +518,7 @@
   <x:String x:Key="Text.Histories.HighlightsInGraph.CurrentBranchOnly" xml:space="preserve">Current Branch Only</x:String>
   <x:String x:Key="Text.Histories.HighlightsInGraph.CurrentBranchAndSelectedCommits" xml:space="preserve">Current Branch &amp; Selected Commits</x:String>
   <x:String x:Key="Text.Histories.HighlightsInGraph.SelectedCommitsOnly" xml:space="preserve">Selected Commits Only</x:String>
+  <x:String x:Key="Text.Histories.HighlightsInGraph.SelectedCommitsOnlyFirstParent" xml:space="preserve">Selected Commits (only first-parent)</x:String>
   <x:String x:Key="Text.Histories.Selected" xml:space="preserve">SELECTED {0} COMMITS</x:String>
   <x:String x:Key="Text.Histories.ShowColumns" xml:space="preserve">SHOW COLUMNS</x:String>
   <x:String x:Key="Text.Histories.Tips" xml:space="preserve">Hold 'Ctrl' or 'Shift' to select multiple commits.</x:String>

src/ViewModels/Histories.cs

@@ -75,7 +75,8 @@ public List<Models.Commit> Commits
             get => _commits;
             set
             {
-                GenerateGraph(value, true);
+                RecalculateMergeState(value);
+                GenerateGraph(value);
                 if (SetProperty(ref _commits, value))
                     PostCommitsChanged();
             }
@@ -510,7 +511,24 @@ private void PostSelectedCommitsChanged()
                 GenerateGraph(_commits);
         }
 
-        private void GenerateGraph(List<Models.Commit> commits, bool commitsChanged = false)
+        private void RecalculateMergeState(List<Models.Commit> commits)
+        {
+            var merged = new HashSet<string>();
+
+            foreach (var commit in commits)
+            {
+                if (merged.Remove(commit.SHA))
+                    commit.IsMerged = true;
+
+                if (commit.IsMerged)
+                {
+                    foreach (var p in commit.Parents)
+                        merged.Add(p);
+                }
+            }
+        }
+
+        private void GenerateGraph(List<Models.Commit> commits)
         {
             var firstParentOnly = _repo.UIStates.HistoryShowFlags.HasFlag(Models.HistoryShowFlags.FirstParentOnly);
             var highlighting = _repo.UIStates.GraphHighlighting;
@@ -522,7 +540,7 @@ private void GenerateGraph(List<Models.Commit> commits, bool commitsChanged = fa
                     extraHeads.Add(c.SHA);
             }
 
-            Graph = Models.CommitGraph.Generate(commits, commitsChanged, firstParentOnly, highlighting, extraHeads);
+            Graph = Models.CommitGraph.Generate(commits, firstParentOnly, highlighting, extraHeads);
         }
 
         private Repository _repo = null;

src/Views/Repository.axaml.cs

@@ -487,6 +487,16 @@ private void OnOpenAdvancedHistoriesOption(object sender, RoutedEventArgs e)
                     ev.Handled = true;
                 };
 
+                var selectedCommitsOnlyFirstParent = new MenuItem();
+                selectedCommitsOnlyFirstParent.Header = App.Text("Histories.HighlightsInGraph.SelectedCommitsOnlyFirstParent");
+                if (histories.GraphHighlighting == Models.CommitGraphHighlighting.SelectedCommitsOnlyFirstParent)
+                    selectedCommitsOnlyFirstParent.Icon = this.CreateMenuIcon("Icons.Check");
+                selectedCommitsOnlyFirstParent.Click += (_, ev) =>
+                {
+                    histories.GraphHighlighting = Models.CommitGraphHighlighting.SelectedCommitsOnlyFirstParent;
+                    ev.Handled = true;
+                };
+
                 var currentBranchAndSelectedCommits = new MenuItem();
                 currentBranchAndSelectedCommits.Header = App.Text("Histories.HighlightsInGraph.CurrentBranchAndSelectedCommits");
                 if (histories.GraphHighlighting == Models.CommitGraphHighlighting.CurrentBranchAndSelectedCommits)
@@ -516,6 +526,7 @@ private void OnOpenAdvancedHistoriesOption(object sender, RoutedEventArgs e)
                 menu.Items.Add(all);
                 menu.Items.Add(currentBranchOnly);
                 menu.Items.Add(selectedCommitsOnly);
+                menu.Items.Add(selectedCommitsOnlyFirstParent);
                 menu.Items.Add(currentBranchAndSelectedCommits);
                 menu.Open(button);
             }