'Draw the axis line.
1) transform the path to the display coordinate.
2) extend the path to make a room for arrow
3) update the path of the FancyArrowPatch.
4) draw'

def draw(self, renderer):

    path_in_disp = self._line_transform.transform_path(self._line_path)
    mutation_size = self.get_mutation_scale()
    extented_path = self._extend_path(path_in_disp, mutation_size=mutation_size)
    self._path_original = extented_path
    FancyArrowPatch.draw(self, renderer)
