def place(self, center, radius):
self._radius = float(radius)<EOL>self._center[<NUM_LIT:0>] = center[<NUM_LIT:0>]<EOL>self._center[<NUM_LIT:1>] = center[<NUM_LIT:1>]<EOL>
Place Arcball, e.g. when window size changes.

        center : sequence[2]
            Window coordinates of trackball center.
        radius : float
            Radius of trackball in window coordinates.