Building VTK for Arm64 with OpenGL ES

Support
1

Hello,

I am trying to build VTK on FriendlyDesktop (Ubuntu flavour) on my NanoPC-T4, and am running into a build error.

/home/pi/devel/PB-x64/Deps/vtk/GUISupport/Qt/QVTKOpenGLNativeWidget.cxx: In member function ‘virtual void QVTKOpenGLNativeWidget::paintGL()’:
/home/pi/devel/PB-x64/Deps/vtk/GUISupport/Qt/QVTKOpenGLNativeWidget.cxx:537:3: error: ‘QOpenGLFunctions_3_2_Core’ was not declared in this scope
   QOpenGLFunctions_3_2_Core* f =
   ^~~~~~~~~~~~~~~~~~~~~~~~~
/home/pi/devel/PB-x64/Deps/vtk/GUISupport/Qt/QVTKOpenGLNativeWidget.cxx:537:3: note: suggested alternative: ‘QOpenGLFunctionsPrivate’
   QOpenGLFunctions_3_2_Core* f =
   ^~~~~~~~~~~~~~~~~~~~~~~~~
   QOpenGLFunctionsPrivate
/home/pi/devel/PB-x64/Deps/vtk/GUISupport/Qt/QVTKOpenGLNativeWidget.cxx:537:30: error: ‘f’ was not declared in this scope
   QOpenGLFunctions_3_2_Core* f =
                              ^
/home/pi/devel/PB-x64/Deps/vtk/GUISupport/Qt/QVTKOpenGLNativeWidget.cxx:538:83: error: no matching function for call to ‘QOpenGLContext::versionFunctions<QOpenGLFunctions_3_2_Core>()’
     QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_3_2_Core>();
                                                                                   ^
In file included from /opt/qt-5.12.2/include/QtGui/QOpenGLContext:1:0,
                 from /home/pi/devel/PB-x64/Deps/vtk/GUISupport/Qt/QVTKOpenGLNativeWidget.cxx:20:

I have set the VTK_OPENGL_HAS_ES and VTK_OPENGL_HAS_EGL flags, and the appropriate libraries seem to be found.

I have built my own Qt with the -opengl es2 backend selected. Has anyone successfully built for arm64/opengl es?

2

So, exploring the code at it looks like QVTKOpenGLNativeWidget cannot be compiled with OpenGL ES, as the header for QOpenGLFunctions_3_2_Core has a guard against it. I am exploring some workarounds.

3

By removing QVTKOpenGLNativeWidget from my working copy and appropriate CMakeLists.txt changes I am able to build. This project is using CTK so hopefully it will still work with QVTKOpenGLWidget (which it should according to its CMakeLists.txt)

4

Some minor changes to QVTKOpenGLNativeWidget enable compilation of VTK. Specifically using QOpenGLExtraFunctions instead of QOpenGLFunctions_3_2_Core.

5

Hi Adam,

Thanks for your work. We do not test on Arm64 obviously but your contributions are welcome. Feel free to open a merge request so your changes can be integrated into VTK.

6

Of course, I know it’s not a normal use case, but I thought I’d explore it anyways.

QVTKOpenGLNativeWidget seems like an easy fix (if I understand the Qt OpenGL wrapping correctly), but QVTKGraphicsItem (via vtkOpenGLError) will be a bit harder to unravel. For now I’ve just disabled Module_vtkGUISupportQtOpenGL as I don’t need it (I think).