warp.mesh\_eval\_position
=========================

.. function:: warp._src.lang.mesh_eval_position(id: uint64, face: int32, bary_u: float32, bary_v: float32) -> vec3f

   .. hlist::
      :columns: 8

      * Kernel
      * Differentiable

   Evaluate the interpolated position on a face of the :class:`warp.Mesh` from barycentric coordinates.
   
   Linearly interpolates the face's three vertex positions: with the face's vertices ``v0``,
   ``v1``, ``v2``, returns ``v0 * bary_u + v1 * bary_v + v2 * (1 - bary_u - bary_v)``, in the
   mesh's local space. Use this to turn a ``face``/``u``/``v`` result from a mesh point or ray
   query back into a position.
   
   :param id: The mesh identifier
   :param face: The face (triangle) index
   :param bary_u: Barycentric weight of the face's first vertex
   :param bary_v: Barycentric weight of the face's second vertex
   
   :returns: The interpolated position, in the mesh's local space.
   
   .. rubric:: Example
   
   .. testcode::
   
       @wp.kernel
       def centroid(mesh_id: wp.uint64, out: wp.array[wp.vec3]):
           out[0] = wp.mesh_eval_position(mesh_id, 0, 1.0 / 3.0, 1.0 / 3.0)
   
       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)
       mesh = wp.Mesh(points=points, indices=indices)
   
       out = wp.zeros(1, dtype=wp.vec3)
       wp.launch(centroid, dim=1, inputs=[mesh.id], outputs=[out])
       p = out.numpy()[0]
       print(f"({p[0]:.3f}, {p[1]:.3f}, {p[2]:.3f})")
   
   .. testoutput::
   
       (0.333, 0.667, 0.000)