Add feature to split vocal part at playhead cursor

OpenUtau/Strings/Strings.axaml

@@ -11,6 +11,7 @@
   <system:String x:Key="context.part.merge">Merge parts</system:String>
   <system:String x:Key="context.part.rename">Rename part</system:String>
   <system:String x:Key="context.part.replaceaudio">Reselect audio file</system:String>
+  <system:String x:Key="context.part.split">Split part at playhead</system:String>
   <system:String x:Key="context.part.transcribe">Transcribe audio to create a note part</system:String>
   <system:String x:Key="context.part.transcribing">Transcribing</system:String>
   <system:String x:Key="context.pitch.easein">Ease in</system:String>
@@ -44,6 +45,9 @@ OpenUtau aims to be an open source editing environment for UTAU community, with
   <system:String x:Key="dialogs.installdll.message">Installing </system:String>
   <system:String x:Key="dialogs.merge.caption">Merging Parts</system:String>
   <system:String x:Key="dialogs.merge.multitracks">Parts on different tracks cannot be merged.</system:String>
+  <system:String x:Key="dialogs.splitpart.caption">Splitting Part</system:String>
+  <system:String x:Key="dialogs.splitpart.intheway">There are one or more note(s) overlapping with the playhead.
+Do you want to continue by splitting at the nearest position after current playhead with no notes in the way?</system:String>
   <system:String x:Key="dialogs.messagebox.cancel">Cancel</system:String>
   <system:String x:Key="dialogs.messagebox.copy">Copy error to clipboard</system:String>
   <system:String x:Key="dialogs.messagebox.no">No</system:String>

OpenUtau/ViewModels/MainWindowViewModel.cs

@@ -25,6 +25,7 @@ public class PartsContextMenuArgs {
         public ReactiveCommand<UPart, Unit>? PartReplaceAudioCommand { get; set; }
         public ReactiveCommand<UPart, Unit>? PartTranscribeCommand { get; set; }
         public ReactiveCommand<UPart, Unit>? PartMergeCommand { get; set; }
+        public ReactiveCommand<UPart, Unit>? PartSplitCommand { get; set; }
     }
 
     public class RecentFileInfo {

OpenUtau/Views/MainWindow.axaml

@@ -370,6 +370,10 @@
                           IsVisible="{Binding IsVoicePart}"
                           Command="{Binding PartMergeCommand}"
                           CommandParameter="{Binding Part}"/>
+                <MenuItem Header="{DynamicResource context.part.split}"
+                          IsVisible="{Binding IsVoicePart}"
+                          Command="{Binding PartSplitCommand}"
+                          CommandParameter="{Binding Part}"/>
               </ContextMenu>
             </c:PartsCanvas.ContextMenu>
           </c:PartsCanvas>

OpenUtau/Views/MainWindow.axaml.cs

@@ -49,6 +49,7 @@ public partial class MainWindow : Window, ICmdSubscriber {
         private readonly ReactiveCommand<UPart, Unit> PartReplaceAudioCommand;
         private readonly ReactiveCommand<UPart, Unit> PartTranscribeCommand;
         private readonly ReactiveCommand<UPart, Unit> PartMergeCommand;
+        private readonly ReactiveCommand<UPart, Unit> PartSplitCommand;
 
         public MainWindow() {
             Log.Information("Creating main window.");
@@ -82,6 +83,7 @@ public MainWindow() {
             PartReplaceAudioCommand = ReactiveCommand.Create<UPart>(part => ReplaceAudio(part));
             PartTranscribeCommand = ReactiveCommand.Create<UPart>(part => Transcribe(part));
             PartMergeCommand = ReactiveCommand.Create<UPart>(part => MergePart(part));
+            PartSplitCommand = ReactiveCommand.Create<UPart>(async part =>  await SplitPart(part));
 
             AddHandler(DragDrop.DropEvent, OnDrop);
 
@@ -1081,6 +1083,7 @@ public void PartsCanvasPointerPressed(object sender, PointerPressedEventArgs arg
                             PartRenameCommand = PartRenameCommand,
                             PartTranscribeCommand = PartTranscribeCommand,
                             PartMergeCommand = PartMergeCommand,
+                            PartSplitCommand = PartSplitCommand
                         };
                         shouldOpenPartsContextMenu = true;
                     }
@@ -1369,7 +1372,69 @@ void MergePart(UPart part) {
             DocManager.Inst.ExecuteCmd(new AddPartCommand(DocManager.Inst.Project, mergedPart));
             DocManager.Inst.EndUndoGroup();
         }
+        async Task SplitPart(UPart part) {
+            int tick = DocManager.Inst.playPosTick;
+            if (part.position >= tick || part.End <= tick) return;
+            if (part is not UVoicePart vp) return;
+            var notesInTheWay = vp.notes.Where(n => (n.position < tick - vp.position) && (n.End > tick - vp.position));
+            if (notesInTheWay.Any()) {
+                var res = await MessageBox.Show(
+                    this,
+                    ThemeManager.GetString("dialogs.splitpart.intheway"),
+                    ThemeManager.GetString("dialogs.splitpart.caption"),
+                    MessageBox.MessageBoxButtons.YesNo);
+                if (res == MessageBox.MessageBoxResult.No) { return; }
+                do {
+                    tick = vp.position + notesInTheWay.Max(n => n.End);
+                    notesInTheWay = vp.notes.Where(n => (n.position < tick - vp.position) && (n.End > tick - vp.position));
+                } while (notesInTheWay.Any());
+            }
+
+            static SortedSet<UNote> GetNotes(IEnumerable<UNote> notes, int relTick, bool after) => after
+                ? [.. notes.Where(n => n.position >= relTick).Select(n => { var m = n.Clone(); m.position -= relTick; return m; })]
+                : [.. notes.Where(n => n.position < relTick).Select(n => n.Clone())];
+            static List<UCurve> GetCurves(IEnumerable<UCurve> curves, int relTick, bool after) =>
+                curves.Select(c => {
+                    var cloned = c.Clone();
+                    var zipped = cloned.xs.Zip(cloned.ys, (x, y) => (x, y));
+                    var filtered = after
+                        ? zipped.Where(z => z.x >= relTick).Select(z => (x: z.x - relTick, z.y))
+                        : zipped.Where(z => z.x < relTick);
+                    cloned.xs = [.. filtered.Select(z => z.x)];
+                    cloned.ys = [.. filtered.Select(z => z.y)];
+                    return cloned;
+                }).ToList();
+
+            var notesAfter = GetNotes(vp.notes, tick - vp.position, after: true);
+            var notesBefore = GetNotes(vp.notes, tick - vp.position, after: false);
+            var curvesAfter = GetCurves(vp.curves, tick - vp.position, after: true);
+            var curvesBefore = GetCurves(vp.curves, tick - vp.position, after: false);
+
+            var firstPart = new UVoicePart {
+                name = vp.name + "-1",
+                comment = vp.comment,
+                trackNo = vp.trackNo,
+                position = vp.position,
+                notes = notesBefore,
+                curves = curvesBefore,
+                Duration = tick - vp.position
+            };
+            var secondPart = new UVoicePart {
+                name = vp.name + "-2",
+                comment = vp.comment,
+                trackNo = vp.trackNo,
+                position = tick,
+                notes = notesAfter,
+                curves = curvesAfter,
+                Duration = vp.End - tick
+            };
 
+            DocManager.Inst.StartUndoGroup();
+            DocManager.Inst.ExecuteCmd(new RemovePartCommand(DocManager.Inst.Project, vp));
+            DocManager.Inst.ExecuteCmd(new AddPartCommand(DocManager.Inst.Project, firstPart));
+            DocManager.Inst.ExecuteCmd(new AddPartCommand(DocManager.Inst.Project, secondPart));
+            DocManager.Inst.EndUndoGroup();
+        }
         public async void OnWelcomeRecent(object sender, PointerPressedEventArgs args) {
             if (sender is StackPanel panel &&
                 panel.DataContext is RecentFileInfo fileInfo) {