warp.volume\_sample\_grad\_index
================================

.. function:: warp._src.lang.volume_sample_grad_index(id: uint64, uvw: vec3f, sampling_mode: int32, voxel_data: Array[Any], background: Any, grad: Any) -> Any

   .. hlist::
      :columns: 8

      * Kernel
      * Differentiable

   Sample the volume given by ``id`` and its gradient at the volume local-space point ``uvw``.
   
   Values for allocated voxels are read from the ``voxel_data`` array, and ``background`` is used as the value of non-existing voxels.
   Interpolation should be :attr:`warp.Volume.CLOSEST` or :attr:`warp.Volume.LINEAR`.
   This function is available for both index grids and classical volumes.