warp.volume\_lookup\_index
==========================

.. function:: warp._src.lang.volume_lookup_index(id: uint64, i: int32, j: int32, k: int32) -> int32

   .. hlist::
      :columns: 8

      * Kernel
      * Python

   Return the linear index associated with integer index-space coordinates ``i``, ``j``, ``k``.
   
   This function is not differentiable.
   
   :param id: The ``id`` of a :class:`warp.Volume`.
   :param i: Voxel coordinate along the first index-space axis.
   :param j: Voxel coordinate along the second index-space axis.
   :param k: Voxel coordinate along the third index-space axis.
   
   :returns: The voxel's linear index in ``[0, volume_voxel_count(id))``, or ``-1`` when the coordinate
             is not indexable. Guard against ``-1`` before gathering from a per-voxel array.
   
   .. rubric:: Example
   
   .. testcode::
   
       @wp.kernel
       def lookup_index(vid: wp.uint64, out: wp.array[wp.int32]):
           out[0] = wp.volume_lookup_index(vid, 1, 0, 0)
   
       voxels = wp.array([[0, 0, 0], [1, 0, 0]], dtype=wp.vec3i)
       volume = wp.Volume.allocate_by_voxels(voxels, voxel_size=1.0)
       out = wp.zeros(1, dtype=wp.int32)
       wp.launch(lookup_index, dim=1, inputs=[volume.id], outputs=[out])
       print(int(out.numpy()[0]))
   
   .. testoutput::
   
       1