warp.bvh\_get\_group\_root
==========================

.. function:: warp._src.lang.bvh_get_group_root(id: uint64, group: int32) -> int

   .. hlist::
      :columns: 8

      * Kernel

   Get the root of a group in a BVH.
   
   :param id: The BVH identifier
   :param group: The group identifier
   
   :returns:
   
             The root node index for the specified group. If the group does not exist, returns ``-1``
                 (sentinel for the BVH global root). Pass ``-1`` to BVH queries to traverse from the global root.
   
   .. rubric:: Example
   
   .. testcode::
   
       @wp.kernel
       def query_group(bvh_id: wp.uint64, lowers: wp.array[wp.vec3], uppers: wp.array[wp.vec3],
                       lo: wp.vec3, hi: wp.vec3, centers: wp.array[wp.vec3]):
           root = wp.bvh_get_group_root(bvh_id, 1)  # restrict the query to group 1
           query = wp.bvh_query_aabb(bvh_id, lo, hi, root)
           item = int(0)
           while wp.bvh_query_next(query, item):
               centers[item] = 0.5 * (lowers[item] + uppers[item])
   
       lowers = wp.array([[0, 0, 0], [2, 0, 0], [4, 0, 0]], dtype=wp.vec3)
       uppers = wp.array([[1, 1, 1], [3, 1, 1], [5, 1, 1]], dtype=wp.vec3)
       groups = wp.array([0, 0, 1], dtype=wp.int32)  # one group index per box (box 2 is alone in group 1)
       bvh = wp.Bvh(lowers=lowers, uppers=uppers, groups=groups)
   
       centers = wp.zeros(3, dtype=wp.vec3)
       wp.launch(query_group, dim=1, inputs=[bvh.id, lowers, uppers, wp.vec3(-1.0, -1.0, -1.0), wp.vec3(6.0, 6.0, 6.0)], outputs=[centers])
       print(centers.numpy().tolist())
   
   .. testoutput::
   
       [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0], [4.5, 0.5, 0.5]]