This is a subclass of GD::Polygon used to draw an arrow between two vertices.

GD::Arrow::Full draws a full arrow between two verticies.
  
                                  |\
           +----------------------+ \
  (X2, Y2) *                         * (X1, Y1)
           +----------------------+ /
                                  |/

GD::Arrow::RightHalf draws a half arrow between two verticies.
  
  (X2, Y2) *-------------------------* (X1, Y1)
           +----------------------+ /
                                  |/

GD::Arrow::LeftHalf draws a half arrow between two verticies.
                                    
                                  |\ 
           +----------------------+ \
  (X2, Y2) *-------------------------* (X1, Y1)

WWW: http://search.cpan.org/dist/GD-Arrow/