public StateInteractive add_corner(PlaPointFloat p_location){
  PlaPointInt location=snap_to_restriction(p_location.round());
  corner_list.add(location);
  i_brd.repaint();
  actlog_add_corner(p_location);
  return this;
}

public StateInteractive add_corner ( PlaPointFloat p_location ) { PlaPointInt location = snap_to_restriction ( p_location . round ( ) ) ; corner_list . add ( location ) ; i_brd . repaint ( ) ; actlog_add_corner ( p_location ) ; return this ; }
adds a corner to the polygon of the item under construction
