def rotate(self, theta):
a = np.cos(theta)<EOL>b = np.sin(theta)<EOL>rotate_mtx = np.array(<EOL>[[a, -b, <NUM_LIT:0.0>], [b, a, <NUM_LIT:0.0>], [<NUM_LIT:0.0>, <NUM_LIT:0.0>, <NUM_LIT:1.0>]],<EOL>np.float_)<EOL>self._mtx = np.dot(rotate_mtx, self._mtx)<EOL>self.invalidate()<EOL>return self<EOL>
Add a rotation (in radians) to this transform in place.

Returns *self*, so this method can easily be chained with more
calls to :meth:`rotate`, :meth:`rotate_deg`, :meth:`translate`
and :meth:`scale`.