[vtkusers] Future OSMesa

[Kevin H. Hobbs]

For some time now my dashboard builds which use Mesa for software GL and
OSMesa for offscreen rendering have had failing tests related to
offscreen rendering.

After a long conversation on the Mesa developers list I've learned that
OSMesa can no longer be linked together with GL.

I have patched Mesa on two of my dashboard builds (murron and bubbles)
to link the osmesa.c code directly into GL. I tell cmake to use the
patched GL library for both Gl and OSMesa. This seems to work well for
VTK and ParaView but I don't really view it as a long term solution.

Does anybody here have some advice for what I should do?

The long story is :
  1. Mesa stopped building cleanly with the make linux-x86-64 target due
to a mismatch in drm headers.
  2. The autoconf build could disable the unnecessary parts of the
build, but added -fvisibility=hidden to the build flags.
  3. With all of Mesa's internal functions hidden OSMesa could no longer
depend on accessing these symbols with GL.
  4. All of Mesa's internals and the GL API functions were then linked
directly into OSMesa. (This is the case for both the old style make
targets and for the autoconf build.)
  5. This produced an OSMesa that is independent of GL, but caused the
transition from GL being required by OSMesa to GL being in conflict with
OSMesa.


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