[Paraview] Paraview v5.0.0-RC1 with OpenGL2 backend not running using OSMESA v10.5.5

[Utkarsh Ayachit]

Frank,

First of all, thanks for all your exhausting testing, it's greatly appreciated!

* OSMesa and MESA_GL_VERSION_OVERRIDE

Communicating with the Mesa team, we learnt that
MESA_GL_VERSION_OVERRIDE is a bad idea since it doesnt' really create
the specified OpenGL context. Thus if anything tries to use features
from the specific OpenGL version, the rendering would crash and burn.
Working with Brian Paul from the Mesa team, Ken recently pushed a fix
to VTK (after the RC2) that uses new OSMesa API to create the correct
OpenGL context. This new OSMesa API will appear in Mesa 11.2, however.
Earlier version can be patched using the "alpha" patch that Brian
provided us (attached).

* Classic v/s llvm

Your observation is indeed correct. llvmpipe is the way to go for
software rendering. On my builds, classic mesa was painstakingly slow
for rendering even small geometries.

* Issues with LIC

Another correct observation. There are a few regressions in the new
implementation for SurfaceLIC. Realistically, we  may not be able to
address these before the 5.0 release. If you're using SurfaceLIC
heavily, I'd suggest building ParaView 5.0 with the older OpenGL
backend (or sticking with 4.4) for the interim.

* OSMesa + SWR

While currently I am not sure openswr+osmesa builds are possible, I
wouldn't be surprised if that on the roadmap. I am going to try to
contact the OpenSWR team to see if they have any thoughts on that.

Utkarsh
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