undoredo.cpp

class UMoveObjectCommand: public USketchCommand {

private: 
  FString SketchObjectGuid;

  /* New transform in sketch-space */
  FTransform NewTransform;

public: 
  UMoveObjectCommand() {};

  void PostInitialize(FString SketchObjectGuid_, FTransform NewTransform_) {
    SketchObjectGuid = SketchObjectGuid_;
    NewTransform = NewTransform_;
  };

  USketchCommand * Execute(ASketchActor * SketchActor) {
    /* Effects */
    ASketchObjectActor * SketchObject = SketchActor->SketchObjects[SketchObjectGuid];
    FTransform OldTransform = SketchObject->GetTransform();
    SketchObject->SetActorRelativeTransform(NewTransform);

    /* Create undo command */
    UMoveObjectCommand * Command = NewObject <UMoveObjectCommand> ();
    Command->PostInitialize(SketchObjectGuid, OldTransform);
    return Command;
  };
};

class UCommandRunner: public UObject {

private: 
  TArray<USketchCommand *> UndoCommands;
  TArray<USketchCommand *> RedoCommands;

  int32 MaxUndo = 100;

public:
    UCommandRunner() {};

  void Undo(ASketchActor * SketchActor) {
    if (UndoCommands.Num() == 0) return;
    USketchCommand * UndoCommand = UndoCommands.Pop();
    USketchCommand * RedoCommand = UndoCommand->Execute(SketchActor);
    if (RedoCommand != nullptr) RedoCommands.Add(RedoCommand);
  };

  void Redo(ASketchActor * SketchActor) {
    if (RedoCommands.Num() == 0) return;
    USketchCommand * RedoCommand = RedoCommands.Pop();
    USketchCommand * UndoCommand = RedoCommand->Execute(SketchActor);
    if (UndoCommand != nullptr) UndoCommands.Add(UndoCommand);
  };

  void Execute(ASketchActor * SketchActor, USketchCommand * Command, bool bUndoable = true) {
    USketchCommand * UndoCommand = Command->Execute(SketchActor);
    if (UndoCommand != nullptr && bUndoable) {
      UndoCommands.Add(UndoCommand);

      if (UndoCommands.Num() > MaxUndo) UndoCommands.RemoveAt(0);
    }

    RedoCommands.Empty();
  };

  void ClearUndoRedo() {
    UndoCommands.Empty();
    RedoCommands.Empty();
  };
};