first_row = text.get_n_lines()-visible_rows-static_cast<unsigned>(value);
if(first_row!=old_first_row)
signal_scroll_position_changed.emit(first_row);
first_row = text.get_n_lines()-visible_rows-static_cast<unsigned>(value);
if(first_row!=old_first_row)
signal_scroll_position_changed.emit(first_row);