code: void setSweepY(double y, double x) {
  		// _ASSERT(m_sweep_y != y || m_sweep_x != x);
  		m_sweep_y = y;
  		m_sweep_x = x;
  		m_prev_1 = -1;
  		m_prev_2 = -1;
  		m_vertex_1 = -1;
  		m_vertex_2 = -1;
  	}
docs: Sets new sweep line position.