Improve timeline undo performance

[ddennedy]

This pull request significantly improves the undo/redo system for timeline editing commands by making undo operations more efficient and context-aware. The changes focus on capturing only the affected tracks or clips for undo, rather than restoring entire tracks unnecessarily. This results in faster, more reliable undos and better user experience. Additionally, command descriptions are now copied to UndoHelper to show on a progress dialogs when things are slow. Things are usually slow on big projects especially when Ripple All Tracks is on.

Undo/Redo System Improvements

• Most timeline commands now call m_undoHelper.recordBeforeState() with a set of affected track indices, instead of always restoring whole tracks. This enables more efficient, fine-grained undo operations.

• For commands that can affect multiple tracks (such as ripple edits or move/align commands), logic was added to determine the precise scope of affected tracks and fall back to whole-track restores only when necessary (e.g., ripple-all-tracks is enabled).

---

Here's the complete picture of every timeline command's undo strategy on the branch now.

Fine-grained (fast per-clip undo — no RestoreTracks)

Use UndoHelper with NoHints/SkipXML:

Command	Notes
AppendCommand	NoHints
OverwriteCommand	NoHints (snapshots the replaced/split span)
LiftCommand	NoHints (snapshots lifted clip)
RemoveCommand	NoHints when not ripple-all
MergeCommand	NoHints
SplitCommand	NoHints (snapshots split clip)
InsertCommand	NoHints when not ripple-all (snapshots split clip)
AddTransitionCommand	NoHints when not ripple-all (snapshots mixed clips)
TrimClipInCommand	NoHints when not ripple
TrimClipOutCommand	SkipXML when not ripple
UpdateCommand	NoHints
DetachAudioCommand	NoHints
ReplaceCommand	NoHints

Still RestoreTracks (whole-track rebuild)

These are the genuinely track-wide or cross-track cases where fine-grained doesn't apply:

Command	When	Why it needs it
MoveClipCommand	always	can move across tracks / reorder
RemoveTrackCommand	always	the whole track is cleared
AlignClipsCommand	always	repositions many clips (lift+overwrite loop)
InsertCommand	ripple-all-tracks	shifts clips on other tracks
RemoveCommand	ripple-all-tracks	shifts other tracks
AddTransitionCommand	ripple-all-tracks	shifts other tracks
TrimClipInCommand	ripple	ripple shifts the track (and others if ripple-all)

Don't use UndoHelper at all (own inverse logic)

GroupCommand, UngroupCommand, NameTrackCommand, MuteTrackCommand, HideTrackCommand, CompositeTrackCommand, LockTrackCommand, FadeInCommand, FadeOutCommand, TrimTransitionInCommand, TrimTransitionOutCommand, ResizeTransitionCommand, AddTransitionByTrimInCommand, AddTransitionByTrimOutCommand, RemoveTransitionByTrimInCommand, RemoveTransitionByTrimOutCommand, AddTrackCommand, InsertTrackCommand, MoveTrackCommand, ChangeBlendModeCommand, ChangeTransitionPropertyCommand, ApplyFiltersCommand, ChangeGainCommand.

---

Progress Dialog

• All timeline commands now propagate their undo/redo text label via m_undoHelper.setText(text()) to show descriptions in the progress dialogs.

Improved Undo Data Capture

• For commands that split, overwrite, or otherwise modify clips, the system now snapshots only the affected clips’ XML, enabling cheap and accurate restoration without parsing the entire track.

Refactoring for Move/Align Commands

• The MoveClipCommand and AlignClipsCommand now defer the call to recordBeforeState() until the redo step, after the set of affected clips/tracks is known, further optimizing the undo scope.

[Copilot]

Pull request overview

Optimizes timeline undo/redo by limiting snapshots to affected tracks or clips and batching History dock operations.

Changes:

• Adds fine-grained snapshot and restoration strategies.
• Batches multi-step History operations and defers expensive refreshes.
• Adds progress reporting and XML-call instrumentation.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/shotcut_mlt_properties.h	Adds temporary serializable UUID property.
src/models/multitrackmodel.h	Declares bulk-update state and API.
src/models/multitrackmodel.cpp	Implements deferred updates and refreshes.
src/mltcontroller.h	Exposes XML-call instrumentation.
src/mltcontroller.cpp	Counts XML serialization calls.
src/mainwindow.cpp	Installs the specialized History view.
src/docks/timelinedock.h	Adds deferred selection state.
src/docks/timelinedock.cpp	Defers validation and scopes trim snapshots.
src/docks/historyundoview.h	Declares bulk-aware History view.
src/docks/historyundoview.cpp	Brackets History interactions as bulk updates.
src/dialogs/longuitask.h	Increases progress-dialog responsiveness.
src/commands/undohelper.h	Defines scoped snapshot strategies.
src/commands/undohelper.cpp	Implements fine-grained and whole-track restoration.
src/commands/timelinecommands.h	Adds move-command track scoping.
src/commands/timelinecommands.cpp	Applies scoped undo capture across commands.
src/CMakeLists.txt	Builds the new History view.

Suppressed comments (1)

src/commands/timelinecommands.cpp:1153

• TrimClipOutCommand also never calls setText() on its helper. If its fine-grained undo falls back to restoreAffectedTracks(), the progress dialog therefore displays the incomplete label Undo . Propagate the command text when creating or injecting the trim helper.

        m_undoHelper.reset(new UndoHelper(m_model));
        if (!m_ripple)
            m_undoHelper->setHints(UndoHelper::SkipXML);
        m_undoHelper->recordBeforeState(m_rippleAllTracks ? QSet<int>() : QSet<int>{m_trackIndex});

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated no new comments.

Suppressed comments (1)

src/docks/historyundoview.cpp:45

• Every key press in the History view enters a bulk update, including keys such as Shift or an unhandled character that do not change the undo-stack index. endBulkUpdate() nevertheless always calls MLT.refreshConsumer() and emits bulkUpdateFinished(), so these no-op keys trigger an expensive timeline refresh. Restrict bulk updates to index-changing navigation, or track whether the stack index changed and skip the final flush when no command was replayed.

    m_model->beginBulkUpdate();
    QUndoView::keyPressEvent(event);
    m_model->endBulkUpdate();