Re: Question about support for OpenGL 3.2 Core context

On 26 November 2015 at 11:37, Albert Freeman <[email protected]> wrote:
> On 25 November 2015 at 22:45, Ken Martin <[email protected]> wrote:
>>
>> Noob question incoming... I have an application that requests a 3.2 core
>> context from Mesa.  I tell folks to make sure they have mesa version 10.6.5
>> or later which I thought supported OpenGL 3.2.  Usually this works but now
>> and then I get users who's Mesa (including version 11) fails to provide a
>> 3.2 Core context. I tell them to set
>>
>> MESA_GL_VERSION_OVERRIDE=3.2
>>
>> and
>>
>> MESA_GLSL_VERSION_OVERRIDE=150 (or something like that)
>>
>> and it generally works. But I'm not sure why the original request for 3.2
>> Core is failing on some systems (drivers?).  Looking at
>>
>> http://mesamatrix.net/
>>
>> leads me to think that all drivers with a recent mesa should be fine with
>> 3.2 Core but obviously I am missing something. Do I need to be telling them
>> to use a specific driver? Is there a list of drivers that do not support 3.2
>> I should tell them to avoid? Anything else come to mind?
>>
>> I just want to try to provide a bit more help to folks to get them up and
>> running with Mesa and even better get our code to handle it automatically if
>> we could.
>>
>> Any pointers appreciated. The application is vtk.
>>
>> Thanks
>> Ken
>>
>>
>>
>>
>>
>>
>>
>> --
>> Ken Martin PhD
>> Chairman & CFO
>> Kitware Inc.
>> 28 Corporate Drive
>> Clifton Park NY 12065
>> 518 371 3971
>>
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> Not all mesa drivers support gl 3.2, e.g. the r300 gallium driver in
> the git mesa supports only glsl 1.20:
>         case PIPE_CAP_GLSL_FEATURE_LEVEL:
>             return 120;
>
> That website is based on gl3.txt. It does not list all drivers mesa
> supports (as gl3.txt dosen't). They are both only meant to be a rough
> guide. The svga driver apparently supports gl 3.3 and it isn't even
> mentioned in gl3.txt. So I think some of the vtk users have really old
> gpus that don't support gl 3.2. Some gl versions already have software
> emulated components for gl features not supported by the hardware on
> older gpus and some older gpus simply don't have support.
As those environment variables you use simply fake the gl version to
the application. If the application then uses say a gl 3.2 feature
that isn't supported by that driver, the behavior is undefined (e.g.
application can crash).
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