def fillRoundRect(self, x, y, w, h, r, color=None, aa=False):
md.fill_round_rect(self.set, x, y, w, h, r, color, aa)<EOL>
Draw a rounded rectangle with top-left corner at (x, y), width w,
height h, and corner radius r

:param aa: if True, use Bresenham's algorithm for line drawing;
    otherwise use Xiaolin Wu's algorithm