Bezier.py

        #        ) / 6
        #
        #     = P0*(-t + 1)**3/6 + P1*(3*t**3 - 6*t**2 + 4)/6 + P2*(-3*t**3 + 3*t**2 + 3*t + 1)/6 + P3*t**3/6

        return (self._p0/6 + 2*self._p1/3 + self._p2/6 +
                (-self._p0/2 + self._p2/2)*t +
                (self._p0/2 - self._p1 + self._p2/2)*t**2 +
                (-self._p0/6 + self._p1/2 - self._p2/2 + self._p3/6)*t**3)