VTK EGL, OSMesa variants will soon be unnecessary in 9.4

[jspanchu]

Hi,

I'm a VTK developer and wanted to inform about an upcoming change which affects your build variants.

We're in the process of removing the need to compile VTK separately for GLX/OSMesa/EGL window system support starting from 9.4. I've announced the plans in our community discourse.vtk.org and the merge request is https://gitlab.kitware.com/vtk/vtk/-/merge_requests/11367.

The new change makes VTK able to compile support for all GLX, EGL and OSMesa on Linux in one build. There is also no need to have libegl/libosmesa installed at compile time. These libraries are instead loaded at runtime if necessary. The idea being that VTK will automatically fallback to libEGL/OSMesa if it fails to open an X window or fails to find a GPU capable of OpenGL.

On windows, the idea is to compile support for both Win32 OpenGL and OSMesa. Of course, it is the responsibility of the users to obtain and install libosmesa.dll.

I'm opening this so you can track changes and start a discussion.

[traversaro]

Thanks a lot, this is great!