warp.quat\_twist\_angle
=======================

.. function:: warp._src.lang.quat_twist_angle(axis: vec3f, q: quatf) -> float

   .. hlist::
      :columns: 8

      * Kernel
      * Differentiable

   Return the unsigned twist magnitude of ``q`` around ``axis``.
   
   This discards the sign of the twist, so rotations by ``+theta`` and
   ``-theta`` around ``axis`` return the same value. Use
   :func:`quat_twist_angle_signed` when the direction of rotation around
   ``axis`` matters.
   
   The result follows the quaternion branch supplied by ``q``. For
   canonicalized quaternions, the result is in ``[0, pi]``. Noncanonicalized
   inputs may return values in ``[0, 2*pi]``.
   
   :param axis: Twist axis. Expected to be normalized by the caller.
   :param q: Input quaternion.
   
   :returns: Unsigned twist angle in radians.
   :rtype: float