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

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

   .. hlist::
      :columns: 8

      * Kernel
      * Differentiable

   Return the twist magnitude of ``q`` around ``axis``.
   
   This returns an unsigned twist magnitude. For canonicalized quaternions
   (for example from :func:`quat_from_axis_angle` with angles in ``(-pi, pi)``),
   both ``+theta`` and ``-theta`` map to ``|theta|``.
   
   :param axis: Twist axis (expected to be normalized).
   :param q: Input quaternion.
   
   :returns: Twist angle in radians in ``[0, pi]`` for canonicalized inputs.
   :rtype: float