    # File lib/prawn/graphics.rb, line 257
        def rounded_vertex(radius, *points)
          x0,y0,x1,y1,x2,y2 = points.flatten
          radial_point_1 = point_on_line(radius, points[0], points[1])
          bezier_point_1 = point_on_line((radius - radius*KAPPA), points[0], points[1] )
          radial_point_2 = point_on_line(radius, points[2], points[1])
          bezier_point_2 = point_on_line((radius - radius*KAPPA), points[2], points[1])
          line_to(radial_point_1)
          curve_to(radial_point_2, :bounds => [bezier_point_1, bezier_point_2])
        end