Plotting a quad mesh in pyvista produces a triangular mesh. A CG-1 space on a quad mesh properly shows a quad mesh, so it seems like this is in part hidden in dolfinx’s vtk_mesh implementation. Specifically, in the dispatched code for plotting meshes (and then the call to _cpp.io.extract_vtk_connectivity maybe?)
# dolfinx v0.9.0
from mpi4py import MPI
from dolfinx import mesh, fem, plot
import pyvista
domain = mesh.create_unit_square(MPI.COMM_WORLD, 10, 10, cell_type=mesh.CellType.quadrilateral)
CG1 = fem.functionspace(domain, ("Lagrange", 1, (domain.geometry.dim,)))
CG2 = fem.functionspace(domain, ("Lagrange", 2, (domain.geometry.dim,)))
def plot_mesh(plottable):
plotter = pyvista.Plotter()
grid = pyvista.UnstructuredGrid(*plot.vtk_mesh(plottable))
plotter.add_mesh(grid, show_edges=True)
plotter.show()
plot_mesh(domain) # Wrong
plot_mesh(CG1) # Correct
plot_mesh(CG2) # Wrong
Unfortunately CG-2 again renders as triangles, but that is somewhat understandable due to the added nodes. Is there anything I can do about this at this point?