def points_to_pixels(self, points):
return points<EOL>
Convert points to display units

*points*
    a float or a numpy array of float

return points converted to pixels

You need to override this function (unless your backend
doesn't have a dpi, eg, postscript or svg).  Some imaging
systems assume some value for pixels per inch::

    points to pixels = points * pixels_per_inch/72.0 * dpi/72.0