docs: def _head_length(self, port):
          """Distance from the center of the port to the perpendicular waypoint"""
          if not port:
              return 0.
          parent_state_v = self.get_parent_state_v()
          if parent_state_v is port.parent:  # port of connection's parent state
              return port.port_size[1]
          return max(port.port_size[1] * 1.5, self._calc_line_width() / 1.3)