public mxRectangle processChanges(List<mxUndoableChange> changes,boolean invalidate,boolean ignoreDirty){
  return processChanges(changes,invalidate,ignoreDirty,null);
}

public mxRectangle processChanges ( List < mxUndoableChange > changes , boolean invalidate , boolean ignoreDirty ) { return processChanges ( changes , invalidate , ignoreDirty , null ) ; }
processes the changes and returns the minimal rectangle to be repainted in the buffer . a return value of null means no repaint is required .
