'Draws a line between the two points. Coordinates are given in
Postscript point coordinates (72 points per inch, (0, 0) is the lower
left corner of the page).'

def line(self, xy0, xy1):

    xy = (xy0 + xy1)
    self._fp_write(('%d    %d    %d    %d    Vl\n' % xy))
