This tutorial is part of viskex.

Plot boundaries mesh sets of a 2D firedrake mesh

import firedrake

import viskex

import common_firedrake as common  # isort: skip

Generate meshes of the unit square by dividing each edge of the square in 6 segments, using either a triangular or quadrangular mesh.

square_tria = firedrake.UnitSquareMesh(6, 6, quadrilateral=False, diagonal="right")
square_quad = firedrake.UnitSquareMesh(6, 6, quadrilateral=True, diagonal="right")

Mark boundaries according to the $(x, y)$ position of the vertices of the mesh:

• if $x > 0$ and $x \leq \frac{1}{3}$, assign boundary mesh tag equal to $1$;
• if $x \geq \frac{2}{3}$ and $x < 1$, assign boundary mesh tag equal to $2$;
• if $x = 0$, assign boundary mesh tag equal to $3$;
• if $x = 1$, assign boundary mesh tag equal to $4$;
• otherwise, leave the boundary mesh tag unassigned.

square_tria_with_boundaries = common.mark_boundaries(square_tria)
square_quad_with_boundaries = common.mark_boundaries(square_quad)

We plot the resulting boundaries.

viskex.firedrake.plot_mesh_sets(square_tria_with_boundaries, 1, "boundaries")

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

viskex.firedrake.plot_mesh_sets(square_quad_with_boundaries, 1, "boundaries")

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

We can also plot all boundaries which belong to the mesh set $4$ (first and second plot), $2$ (third and fourth plot) or both (fifth and sixth plot), which will be displayed with colors. The rest of the mesh facets are still included in the plot, but are colored in gray.

viskex.firedrake.plot_mesh_sets(
    square_quad_with_boundaries, 1, "boundaries_4", viskex.utils.values_in([4]))

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

viskex.firedrake.plot_mesh_sets(
    square_quad_with_boundaries, 1, "boundaries_4", viskex.utils.values_in([4]))

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

viskex.firedrake.plot_mesh_sets(
    square_quad_with_boundaries, 1, "boundaries_2", viskex.utils.values_in([2]))

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

viskex.firedrake.plot_mesh_sets(
    square_quad_with_boundaries, 1, "boundaries_2", viskex.utils.values_in([2]))

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

viskex.firedrake.plot_mesh_sets(
    square_quad_with_boundaries, 1, "boundaries_24", viskex.utils.values_in([2, 4]))

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

viskex.firedrake.plot_mesh_sets(
    square_quad_with_boundaries, 1, "boundaries_24", viskex.utils.values_in([2, 4]))

error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

The mesh sets are stored as part of the firedrake mesh object. If the mesh sets get removed, all cells will be displayed in gray in the plot.

square_tria.topology_dm.removeLabel(firedrake.cython.dmcommon.FACE_SETS_LABEL)
square_quad.topology_dm.removeLabel(firedrake.cython.dmcommon.FACE_SETS_LABEL)

viskex.firedrake.plot_mesh_sets(square_tria, 1, "boundaries")

/home/firedrake/firedrake/lib/python3.12/site-packages/pyvista/plotting/mapper.py:669: RuntimeWarning: All-NaN axis encountered
  clim = [np.nanmin(scalars), np.nanmax(scalars)]
error: XDG_RUNTIME_DIR is invalid or not set in the environment.
MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

viskex.firedrake.plot_mesh_sets(square_quad, 1, "boundaries")

/home/firedrake/firedrake/lib/python3.12/site-packages/pyvista/plotting/mapper.py:669: RuntimeWarning: All-NaN axis encountered
  clim = [np.nanmin(scalars), np.nanmax(scalars)]

error: XDG_RUNTIME_DIR is invalid or not set in the environment.

MESA: error: ZINK: failed to choose pdev
glx: failed to create drisw screen

What's next?

• next step: plot a scalar field
• repeat this step with dolfinx