FreeCAD 0.18.4 fails to build with vtk 9.0

[kkremitzki]

The state of VTK in Debian is actually a bit of a problem... something I was thinking I might have to jump into myself. Not surprised to see it not build, though.

[hobbes1069]

I asked the Fedora maintainer of VTK if there's some kind of porting guide due to the significance of the changes. Hopefully there's something.

[sgrogan]

So now I'm back in install hell... But at least it builds!

I'm not having much luck building master, so before I keep hitting my head against the wall, do we even know if it's compatible with VTK 9.0?

What changed?

I think VTK 9 is going to be tough. I don't see any activity yet upstream https://git.salome-platform.org/gitweb/ ... ;a=summary
Nor this fork https://github.com/LaughlinResearch/SMESH/issues which disables MED BTW.
For the Conda based builds we already use this fork already.
And of course FreeCAD's internal version.

[hobbes1069]

I pinged upstream about a porting guide...

https://discourse.vtk.org/t/vtk-9-0-0/3 ... chard_shaw

[hobbes1069]

So basically all the function names changed?

https://vtk.org/Wiki/VTK/API_Changes_8_2_0_to_9_0_0

They also moved from the old CMake module find method to using targets:

https://vtk.org/doc/nightly/html/md__ho ... c815a.html

https://lorensen.github.io/VTKExamples/site/

[wmayer]

I have merged right now a PR I was working on this week: https://github.com/FreeCAD/FreeCAD/pull/3606

FreeCAD master is now fully ported to Py 3.9's C API (not necessarily to changes of the Python modules), boost 1.73 and tons of deprecation warnings of Qt 5.14 but also some general C++ stuff are fixed now. PrzemoF have triggered a few builds for me to catch all the warnings: https://forum.freecadweb.org/viewtopic.php?f=10&t=47348

Btw: The used vtk version there was 8.2.0

[hobbes1069]

Ok, great! I'll play around with that. I did create a vtk_9.0 branch (haven't pushed it to my fork yet). I think I can help with the CMake part but the API changes will be beyond my time or abilities.

Thanks,
Richard

[wmayer]

Is there a vtk porting guide for V9.0 available somewhere?

There are a few API changes that affect the smesh code.

• The declaration of vtkCellLinks *vtkUnstructuredGrid::GetCellLinks() has changed to vtkAbstractCellLinks *vtkUnstructuredGrid::GetCellLinks().
  It looks like doing a static_cast is sufficient because this is what they did in their example code, too.
  https://gitlab.kitware.com/vtk/vtk/-/co ... 458e3bb56a
• The declaration of void vtkUnstructuredGrid::GetCellPoints(vtkIdType, vtkIdType&, vtkIdType* &) has changed to void vtkUnstructuredGrid::GetCellPoints(vtkIdType, vtkIdType&, vtkIdType const* &)
  Note the "const" in the third argument.
  Now, the problem is that in a few places in the smesh code the content of the third variable is modified after calling GetCellPoints(). But now this is not longer possible because it's declared as "const".
  See: https://gitlab.kitware.com/vtk/vtk/-/co ... 522df0b95f
  
  In the documentation about GetCellPoints() it's clearly said that the content of the third argument must not be changed afterwards:
  https://vtk.org/doc/nightly/html/classv ... f1916e75ca
  
  Examples how to do it with v9
  https://gitlab.kitware.com/vtk/vtk/-/co ... 6f1813a7bb
  https://gitlab.kitware.com/vtk/vtk/-/co ... e32f7af95b
  https://vtk.org/doc/nightly/html/classvtkCellArray.html

[hobbes1069]

Is there a vtk porting guide for V9.0 available somewhere?

The links I provided above is what I was pointed to when I asked that exact question on the vtk forums.

Thanks,
Richard

[hobbes1069]

In working on updating the cmake config for vtk 9.0 I'm running into some things I don't understand. I'm guessing they were historically needed but may not be anymore:

Code: Select all

        # if we use smesh we definitely also need vtk, no matter of external or internal smesh
        set (VTK_COMPONENTS
            CommonDataModel
            FiltersVerdict
            IOXML
            FiltersCore
            FiltersGeneral
            IOLegacy
            FiltersExtraction
            FiltersSources
            FiltersGeometry
        )
        
         # Modules used by FreeCAD on linux and windows only?
        if(UNIX OR WIN32)
            list(APPEND VTK_COMPONENTS IOMPIParallel ParallelMPI hdf5 FiltersParallelDIY2 RenderingCore InteractionStyle RenderingFreeType RenderingOpenGL2)
        endif()

followed by:

Code: Select all

       # Find if other modules are available
        foreach(_module ${VTK_COMPONENTS})
            list (FIND VTK_MODULES_ENABLED ${_module} _index)
            if (${_index} GREATER -1)
                list(APPEND AVAILABLE_VTK_COMPONENTS ${_module})
            endif()
        endforeach()

The vtk cmake config already provides ${VTK_AVAILABLE_COMPONENTS}. Additionally, I greped through the source for several of the components in the list and could not find any other instance of it being used anywhere.

Then the logic seems to be "we only require CommonCore, otherwise we figure out what's available and then require it" which doesn't make any sense...

Code: Select all

        # don't check VERSION 6 as this would exclude VERSION 7
        if(AVAILABLE_VTK_COMPONENTS)
            message(STATUS "VTK components: ${AVAILABLE_VTK_COMPONENTS}")
            find_package(VTK COMPONENTS ${AVAILABLE_VTK_COMPONENTS} REQUIRED NO_MODULE)
        else()
            message(STATUS "VTK components: not found or used")
            find_package(VTK REQUIRED NO_MODULE)
        endif()

I would think either these modules are a hard requirement, or an optional requirement for specific FreeCAD apps/modules, but I can't find any instance of that being the case in my limited searching.

Fow now I may completely separate the vtk < 9 logic until someone can explain this to me.

Thanks,
Richard