Function _

python/dolfinx/plot.py:78–132

Create VTK mesh topology based on the degree-of-freedom coordinates. This function supports visualisation when the degree of the finite element space is different from the geometric degree of the mesh. Note: This function supports Lagrange elements (continuous and disco

(V: fem.FunctionSpace, entities=None)

@vtk_mesh.register
def _(V: fem.FunctionSpace, entities=None):  # type: ignore
    """Create VTK mesh topology based on the degree-of-freedom coordinates.

    This function supports visualisation when the degree of the finite
    element space is different from the geometric degree of the mesh.

    Note:
        This function supports Lagrange elements (continuous and
        discontinuous) only.

    Args:
        V: Mesh to extract data from.
        entities: Entities to extract. Extract all if ``None``.

    Returns:
        Topology, type for each cell, and geometry in VTK-ready format.
    """
    if V.ufl_element().family_name not in [
        "Discontinuous Lagrange",
        "Lagrange",
        "DQ",
        "Q",
        "DP",
        "P",
    ]:
        raise RuntimeError(
            "Can only create meshes from continuous or discontinuous Lagrange"
            "spaces, not {V.ufl_element().family_name}."
        )

    degree = V.ufl_element().degree
    if degree == 0:
        raise RuntimeError("Cannot create topology from cellwise constants.")

    # Use all local cells if not supplied
    msh = V.mesh
    tdim = msh.topology.dim
    if entities is None:
        entities = range(msh.topology.index_map(tdim).size_local)

    dofmap = V.dofmap
    num_dofs_per_cell = V.dofmap.dof_layout.num_dofs
    cell_type = msh.topology.cell_type
    perm = np.argsort(_cpp.io.perm_vtk(cell_type, num_dofs_per_cell))

    vtk_type = (
        _first_order_vtk[cell_type] if degree == 1 else _cpp.io.get_vtk_cell_type(cell_type, tdim)
    )
    cell_types = np.full(len(entities), vtk_type)

    topology = np.zeros((len(entities), num_dofs_per_cell + 1), dtype=np.int32)
    topology[:, 0] = num_dofs_per_cell
    dofmap_ = dofmap.list
    topology[:, 1:] = dofmap_[entities][:, perm]
    return topology.reshape(1, -1)[0], cell_types, V.tabulate_dof_coordinates()