warp.mesh\_get\_velocity
========================

.. function:: warp._src.lang.mesh_get_velocity(id: uint64, index: int32) -> vec3f

   .. hlist::
      :columns: 8

      * Kernel

   Look up the velocity of a face's vertex in the :class:`warp.Mesh`.
   
   Like :func:`mesh_get_point`, ``index`` is a *face-vertex index* in ``[0, 3 * number_of_faces)``;
   returns the velocity of the vertex referenced there, i.e. ``velocities[indices[index]]``.
   Requires the mesh to have been constructed with a ``velocities`` array; returns a zero vector
   otherwise.
   
   :param id: The mesh identifier
   :param index: A face-vertex index, in ``[0, 3 * number_of_faces)``
   
   :returns: The referenced vertex's velocity, or a zero vector if the mesh has no velocities.
   
   .. rubric:: Example
   
   .. testcode::
   
       @wp.kernel
       def slot0(mesh_id: wp.uint64, out: wp.array[wp.vec3]):
           out[0] = wp.mesh_get_velocity(mesh_id, 0)
   
       points = wp.array([[0,0,0],[1,0,0],[1,1,0],[0,1,0],[0,0,1],[1,0,1],[1,1,1],[0,1,1]], dtype=wp.vec3)
       indices = wp.array([0,3,2, 0,2,1,  4,5,6, 4,6,7,  0,1,5, 0,5,4,
                           2,3,7, 2,7,6,  0,4,7, 0,7,3,  1,2,6, 1,6,5], dtype=wp.int32)
       velocities = wp.array(np.tile([0.0, 0.0, 1.0], (8, 1)), dtype=wp.vec3)
       mesh = wp.Mesh(points=points, indices=indices, velocities=velocities)
   
       out = wp.zeros(1, dtype=wp.vec3)
       wp.launch(slot0, dim=1, inputs=[mesh.id], outputs=[out])
       print(out.numpy()[0])
   
   .. testoutput::
   
       [0. 0. 1.]