OSMesa has been removed

[Meakk]

Describe the bug It seems like OSMesa library has been removed from Mesa recent versions (starting from 25.1).
See https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33836

Let's decide what we should do with the osmesa backend:

• Continue supporting it as long as VTK has a OSMesa render window available
• Deprecate and remove osmesa backend in 4.0

In a comment, a dev suggest to use EGL with EGL_MESA_device_software instead. We should also find a way to let the user select software rasterizer with EGL somehow.

To Reproduce Steps to reproduce the behavior:

1. f3d example.glb --rendering-backend=osmesa

Expected behavior We should find a way to do software rendering on recent Mesa versions

System Information:

• OS: Linux with Mesa >= 25.1
• GPU and GPU driver:

Additional context https://www.reddit.com/r/EndeavourOS/comments/1ksq2to/libosmesaso8_missing_since_mesa_update/

[mwestphal]

not a F3D issue imo, we should keep the osmesa backend until we stop supporting a VTK version that supports it, so for quite some time.

Using EGL with mesa is as simple as installing mesa, nothing to do on F3D side.

[Meakk]

If we decide to keep the backend, we should at least document/recommend to not use it, and we should have a way to enable software rendering in EGL somehow.

[mwestphal]

If we decide to keep the backend, we should at least document/recommend to not use it, and we should have a way to enable software rendering in EGL somehow.

Its not F3D nor VTK responsability to enable software rendering in EGL, it depends on the libegl being used.

[mwestphal]

We also probably need to disable/remove TestSDKExternalWindowOSMesa