Optional RAW-ZLIB compression

[flabowski]

Hi! I added support for VTK’s built-in XML zlib compression for appended VTU output via format='raw-zlib' (optional CMake flag VTKFORTRAN_USE_ZLIB). zlib compression reduces file size quite a bit for our cases (compared to base64 or uncompressed raw), ParaView or Pyvista can read these files directly. I used Cursor, but the changes are straightforward and work fine for me.

[szaghi]

@flabowski Thank you very much!

[szaghi]

@flabowski Do you think that your zlib approach can also be used for the others XML formats aside VTU? I have not yet read your implementation, but if you think it is possible, I will study it carefully, and I will apply sistematically to all outputs.

[flabowski]

Yes, zlib compression isn not VTU specific in principle. It should work for any XML output that uses appended/raw data. I’ve only tested it with VTU though.
The CI failure looks like the runner isn’t linking against zlib ('compress2' and 'compressBound' are undefined). I did not add madler/zlib as a submodule because I did not want to force the dependency on everyone. Could zlib be installed on the CI runner (e.g. Ubuntu zlib1g-dev) so find_package(ZLIB) works?

[szaghi]

Yes, zlib compression isn not VTU specific in principle. It should work for any XML output that uses appended/raw data. I’ve only tested it with VTU though. The CI failure looks like the runner isn’t linking against zlib ('compress2' and 'compressBound' are undefined). I did not add madler/zlib as a submodule because I did not want to force the dependency on everyone. Could zlib be installed on the CI runner (e.g. Ubuntu zlib1g-dev) so find_package(ZLIB) works?

Very soon, I will address all issues (CI, ship a zlib compiled for CI, add a compressor to all outputs). I already use zlib for other projects involving HDF5; it is just a matter of grabbing the CI things from those projects.

Thank you again