public override void Do()
 {
     if (m_replace)
     {
         m_currentTileSelection.Clear();
     }
     m_currentTileSelection.Merge(m_newTileSelection);
 }
 public override void Undo()
 {
     m_currentTileSelection.Clear();
     m_currentTileSelection.Merge(m_oldTileSelection);
 }