'Get the font for text instance t, cacheing for efficiency'

def _get_agg_font(self, prop):

    fname = findfont(prop)
    font = get_font(fname, hinting_factor=rcParams[u'text.hinting_factor'])
    font.clear()
    size = prop.get_size_in_points()
    font.set_size(size, self.dpi)
    return font
