Fighting Game · Guides & deep dives

Sequencer Undo Redo

and an action request.

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Task: TODOS.phase-72.72.15.2.7

The sequencer undo/redo surface is a V2Editor TimelineVisualizer history model for editor operations that mutate a sequence. It records before/after sequence snapshots, exposes deterministic undo and redo stacks, preserves the active track and keyframe selection, and clears stale redo history when a new edit is pushed after an undo.

Runtime API#

  • Panel spec: FV2SequencerUndoRedoPanelSpec
  • Snapshot: FV2SequencerUndoRedoSnapshot
  • Request: FV2SequencerUndoRedoRequest
  • State: FV2SequencerUndoRedoState
  • Result: FV2SequencerUndoRedoResult
  • Issue enum: EV2SequencerUndoRedoIssueType

ApplySequencerUndoRedoRequest accepts a current FV2SequencerUndoRedoState and an action request. Push requests append a validated snapshot to the undo stack, apply the after-sequence, clear the redo stack, and enforce the configured history capacity. Undo requests pop from the undo stack, apply the before-sequence, and move the snapshot to redo. Redo requests pop from redo, apply the after-sequence, and restore the snapshot to undo. Clear requests remove both stacks without changing the current sequence.

Behavior#

  • The panel spec targets TimelineVisualizer, uses icon controls, and exposes a visible history stack.
  • Operation snapshots cover track management, keyframe editing, curve editing, and recording-driven edits. Timeline playback is represented in the enum for editor surfaces that snapshot playback-affecting sequence mutations.
  • Each snapshot stores SequenceBefore, SequenceAfter, operation id, action description, frame number, selected track, and selected keyframes.
  • New push operations invalidate stale redo entries so later edits cannot replay an obsolete branch.
  • History capacity trims the oldest undo snapshots once MaxHistory is exceeded.
  • Validation reports invalid state, invalid request, sequence mismatch, missing operation id, missing undo snapshot, and missing redo snapshot issues.

The default QA fixture uses Seq.DataModel.CouncilIntro, operation Op.Track.AddVisibility, max history 64, and a property-track add operation to prove that the applied sequence changes across push, undo, and redo.

QA Inventory#

  • Panel controls: verify undo, redo, icon-button mode, history stack, and operation coverage flags.
  • Push: verify track/keyframe/curve/recording operation coverage, after-sequence application, undo stack append, redo invalidation, and selection preservation.
  • Undo: verify before-sequence restoration, undo stack pop, redo stack append, and bUndoApplied state.
  • Redo: verify after-sequence restoration, redo stack pop, undo stack append, and bRedoApplied state.
  • Off-path: reject empty undo, empty redo, missing operation id, mismatched sequence ids, invalid state, and over-capacity history.

js_repl Playwright interaction was unavailable in this session and the affected surface is Unreal editor data rather than browser-rendered UI, so verification is through UE editor automation and contract gates.

Verification#

  • python3 V2/ue/Tools/check-v2-sequencer-undo-redo.py
  • V2.Editor.Sequencer.UndoRedo
  • python3 V2/ue/Tools/check-v2-editor-module.py
  • python3 V2/ue/Tools/check-v2-ci-workflow.py