[vtkusers] OpenGL2 using mesa

[Ken Martin]

You should not be getting that error.  Mesa should be providing at least a
3.2 context. That error is for cases when your OpenGL is not providing a
3.2 context.

I have no experience with Mesa on windows so I'm not sure how much of the
Window specific calls they have implemented. VTK with the OpenGL2 backend
makes use of newer wgl calls such as wglCreateContextAttributesARB. If mesa
has not provided that function then at runtime it will fall back on trying
to use an older context creation method that probably will return an old
context without the needed support and fail. We had this issue with OSMesa
and the Mesa folks were great and worked with us to add the method we
needed into newer releases.

I'l post something to the Mesa list and see if it rings a bell. I would bet
that is the issue.

On a different track, if you are doing software rendering and running into
issues with systems that don't have newer OpenGL support, could you use the
old OpenGL backend (by building VTK with VTK_RENDERING_BACKEND set to
OpenGL ? Would that solve the issue?


On Thu, Sep 29, 2016 at 8:22 AM, ianl <ilindsay at insigniamedical.co.uk>
wrote:

> Hi, I have now managed to get Mesa to build with LLVM 3.7.1 (yay!), thanks
> to
> this post:
> https://www.phoronix.com/forums/forum/linux-graphics-x-
> org-drivers/opengl-vulkan-mesa-gallium3d/883984-windows-
> binaries-for-mesa-12-llvmpipe-and-openswr
>
> Apparently LLVMipa seems to have been dropped in the newer releases - CMake
> does not even generate a project for it. This prevents Mesa from linking -
> not sure what is going on here. However, LLVM 3.7.1 does produce this
> library and Mesa goes on to build successfully with it.
>
> I have verified with glview that LLVMPipe is being used.
>
> However, I still have the warning (as expected from RobertS's post?), and I
> get a crash when I set the render window to off screen mode via
> SetOffScreenRendering(1). I have checked that I have called
> SetMultiSamples(0) on the render window.
>
> I expect the next thing you will tell me is that Mesa does not support
> offscreen rendering. I have seen mention of OSMesa (Off Screen Mesa?) in
> the
> VTK CMake config - is this worth pursuing?
>
> An interesting additional piece of information here is that the old build
> of
> VTK we were using (6.1) works fine (with off screen rendering) with the new
> Mesa opengl.dll built above (but slowly as you would expect).
>
> Any further ideas, or am I flogging a dead horse here?
>
>
>
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-- 
Ken Martin PhD
Chairman & CFO
Kitware Inc.
28 Corporate Drive
Clifton Park NY 12065
518 371 3971

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