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Specifying the GL context version to request

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robertosfield
OSG Project Lead


Joined: 18 Mar 2009
Posts: 11152

PostPosted: Mon Aug 21, 2017 5:47 pm    Post subject:
Specifying the GL context version to request
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HI Sandro,

On 21 August 2017 at 18:16, Sandro Mani < (
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Sure. However I'm curious, how is the logic supposed to work under Windows, where support for specifying the GL version was already implemented? Wouldn't you hit the same issues on that platform also?


So far it's be a niche feature used by small number of developers on their specific applications/platform combinations.  Functionality in the OSG community gets developed on a need basis, so if the functionality isn't there yet then it's because few people have required it.  There are so many things one can do in real-time graphics one has to spend ones time on the most important issues one hits upon with your own applications.



 
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I see it as a constraint on osgEarth working with Intel drivers and recent GL versions and associate drivers.  What we are talking about is working around these constraints in the driver to provide to full osgEarth functionality across a wider range of hardware.  The first step has been to add the GL version functionality to OSG's GLX support. 


Whether we need to push any changes to osgEarth is something I'm not clear on, if the above export's now work with OSG master and osgEarth then I think we are most of the way to getting what is reasonable to expect.




Not that I want to be annoying or repetitive, but surely it's not ideal that osgEarth::Capabilities::Capabilities performs it's checks with a 1.0 context, even though you specify OSG_GL_CONTEXT_VERSION=4.0? Or am I missing something here?



Having the the OSG to worry about is enough for my little brain, I can't comment on the specifics of 3rd party software that builds upon it.  osgEarth has evolved alot over the years, the Capabilities functionality is something I'm not familiar with at all.  All I can say in general is that one would typically check for functionality supported by the driver once a graphics context has been created, if one did create a dummy context just testing functionality then you'd want to make sure it's created with the same settings as you create the final viewer windows. 

If osgEarth doesn't do this then it's something to take up with the osgEarth team,


Robert.

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Sandro Mani
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PostPosted: Mon Aug 21, 2017 5:51 pm    Post subject:
Specifying the GL context version to request
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Hi Robert
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Having the the OSG to worry about is enough for my little brain, I can't comment on the specifics of 3rd party software that builds upon it.  osgEarth has evolved alot over the years, the Capabilities functionality is something I'm not familiar with at all.  All I can say in general is that one would typically check for functionality supported by the driver once a graphics context has been created, if one did create a dummy context just testing functionality then you'd want to make sure it's created with the same settings as you create the final viewer windows. 

If osgEarth doesn't do this then it's something to take up with the osgEarth team,




That's a good enough answer for me, ultimately I just want to understand what needs to be fixed where. From your answer I gather that OSG should be okay now and that I'll take up the rest with osgEarth upstream.

Best,
Sandro

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robertosfield
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PostPosted: Tue Aug 22, 2017 7:19 am    Post subject:
Specifying the GL context version to request
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HI Sandro,

On 21 August 2017 at 18:50, Sandro Mani < (
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That's a good enough answer for me, ultimately I just want to understand what needs to be fixed where. From your answer I gather that OSG should be okay now and that I'll take up the rest with osgEarth upstream.



The change to use DisplaySettings::instance() by default in Triats is something I'm not comfortable with as it changes the behaviour which may catch some OSG users out, and if they did find problems they would be hard to diagnose.


For osgEarth it does sound like the Capabilities mechanism needs tightening up to make sure the same context, or at least type of context, is used for the viewer is used when when checking the driver capabilities.


From your description it looks like the Capabilties mechanism would work fine on drivers that don't have multiple behaviours, so link to a standard GL context and then you can query all the features/extensions just fine (this is how GL has traditionally worked over the years) but fails to handle newer GL drivers that allow for specific generations of functionality to be split i.e. you get a GL3.x context with no backwards compatibility or a GL1.x context with no forwards computability.


When expressed this way it shows that the GL core profile approach that the ARB took really fundamentally changes OpenGL, breaking one of it's greatest assets as programmer developing software that is long lived.  NVidia for sure have maintained the old way and remain easy to manage, but Apple and Intel/MESA have taken the opportunity for use non compatibility to break the old way of doing things, and breaking approaches like osgEarth::Capabilities.


Robert.




 

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