VTK Lagrange elements in 3D elements is not rendered correctly

MWE using dolfinx:

from mpi4py import MPI
import vedo
import numpy as np
import dolfinx
import dolfinx.io

mesh = dolfinx.UnitCubeMesh(MPI.COMM_WORLD, 1, 1, 1, dolfinx.cpp.mesh.CellType.hexahedron)
geo = mesh.geometry.x
num_cells = mesh.topology.index_map(mesh.topology.dim).size_local
topo = dolfinx.cpp.mesh.entities_to_geometry(mesh, mesh.topology.dim, np.arange(num_cells, dtype=np.int32), False)
perm_vtk = dolfinx.cpp.io.perm_vtk(mesh.topology.cell_type, topo.shape[1])
dolfin_to_vtk = np.zeros(topo.shape[1], dtype=np.int32)
for i in range(topo.shape[1]):
    dolfin_to_vtk[perm_vtk[i]] = i

dolfinx.io.VTKFile("mesh.pvd").write(mesh)
topo = topo[:, dolfin_to_vtk]
mesh_vedo = vedo.Mesh([geo, topo])
p = vedo.Plotter(shape=(1, 1), N=1, pos=(0, 0))
p.add(mesh_vedo)
p.show()
p.screenshot("mesh.png")
print(topo,"\n", geo)

yields:

[[1 4 6 2 0 5 7 3]]
 [[1. 0. 0.]
 [0. 0. 0.]
 [0. 1. 0.]
 [1. 1. 0.]
 [0. 0. 1.]
 [1. 0. 1.]
 [0. 1. 1.]
 [1. 1. 1.]]

and while the correponding VTU file contains;

<?xml version="1.0"?>
<VTKFile type="UnstructuredGrid"  version="0.1" >
<UnstructuredGrid>
<Piece  NumberOfPoints="8" NumberOfCells="1">
<Points>
<DataArray  type="Float64"  NumberOfComponents="3"  format="ascii">1 0 0  0 0 0  0 1 0  1 1 0  0 0 1  1 0 1  0 1 1  1 1 1  </DataArray>
</Points>
<Cells>
<DataArray  type="Int32"  Name="connectivity"  format="ascii">1 4 6 2 0 5 7 3  </DataArray>
<DataArray  type="Int32"  Name="offsets"  format="ascii">8 </DataArray>
<DataArray  type="Int8"  Name="types"  format="ascii">72 </DataArray>
</Cells>
</Piece>
</UnstructuredGrid>
</VTKFile>

Which is the same as the vedo mesh has, but yields

[jorgensd]

I forgot to add the PETSC_ARCH, i.e.

export  PETSC_ARCH="linux-gnu-real-32"
pip3  install vedo
# Install python components
pip3 install git+https://github.com/FEniCS/basix.git --upgrade && \
	pip3 install git+https://github.com/FEniCS/ufl.git --upgrade && \
	pip3 install git+https://github.com/FEniCS/ffcx.git --upgrade && \
	rm -rf /usr/local/include/dolfin /usr/local/include/dolfin.h

# Build C++ layer
git clone https://github.com/FEniCS/dolfinx.git && \
	 cd dolfinx/ && \
        git checkout  dokken/pyvista-demo && \
	 mkdir -p build && \
	 cd build && \
	 cmake -G Ninja -DCMAKE_BUILD_TYPE=Relase ../cpp/ && \
	 ninja -j3 install
source /usr/local/share/dolfinx/dolfinx.conf

cd ../python && \
pip3 -v install .

[jorgensd]

oh i haven’t thought about it! Not sure about quads, but for 3d it might be possible…

Let me know how you get along with things:) i’ve spent the day updating my dolfin-x tutorial after we removed matplotlib. When vedo is ready, Im ready to add it to some of the examples, such as: https://jorgensd.github.io/dolfinx-tutorial/chapter3/em.html or https://jorgensd.github.io/dolfinx-tutorial/chapter2/ns_code1.html Could also add a meshing demo with vedo if you have a good idea for an example application.