[Mesa-dev] GLX extension for vendor name lookup in libglvnd

Kyle Brenneman kbrenneman at nvidia.com
Wed Mar 9 19:53:37 UTC 2016

On 03/09/2016 12:21 PM, Adam Jackson wrote:
> On Wed, 2016-03-09 at 11:15 -0700, Kyle Brenneman wrote:
>> The current implementation of libglvnd uses a new X extension called
>> x11glvnd to look up a vendor name for each screen and to find a screen
>> number for a GLXDrawable.
>> But, Adam Jackson pointed out that a GLX extension could do the same job
>> more cleanly: Looking up a vendor name is just querying a per-screen
>> string, which GLXQueryServerString does. Looking up a screen number for
>> a drawable could work by adding a GLX_SCREEN attribute to the
>> GLXGetDrawableAttributes reply.
>> Based on that idea, I've written up a rough draft of a GLX extension
>> spec. Any comments, questions, or suggestions are welcome, of course.
> Argh, you beat me to it, I'd written almost exactly the same thing. I
> just an update to my serverstring branch on github implementing what
> I'd spec'd, details below...
Ah, sorry about that. I should have mentioned that I was working on it.
>> New Tokens
>>       Accepted by the  parameter of glXQueryServerString:
>>           GLX_VENDOR_NAMES_EXT    0x????
> Perhaps easier than getting an enum allocated here, I'd appended this
> string to the end of the response for GLX_VERSION, in the form
>      glvnd:<list>
> where list is comma-separated, since that part of the string is already
> "vendor-specific info".
That could work, although I would expect "vendor-specific info" to mean 
"random, arbitrary, and probably not machine-parsable". I'd be hesitant 
to try to impose a structure on something that's never had any structure 
> Agreed with your rationale in the Issues section. I'd also had:
>      1) Do we need to define the interaction with GLX_SGIX_pbuffer?
>         UNRESOLVED.  Xorg uses the same code paths for the 1.3 and
>         pbuffer versions of GetDrawableAttributes, but extra attributes
>         are probably harmless.
We probably don't need to -- as you say, extra attributes are likely 
harmless. I'd guess that any system that supports libglvnd is going to 
support at least GLX 1.3, so using glXQueryDrawable to look up the 
screen number seems reasonable.
>      2) Do we want to add GLX_SCREEN to the list of fbconfig attributes
>         as well?
>         UNRESOLVED.  glvnd does not need that information, but it would
>         be a natural orthogonality, and GLX_SGIX_fbconfig mentions it
>         though GLX 1.3 does not.
Possibly, but that wouldn't change the protocol at all. The screen 
number is included in the glXGetFBConfigs request, so it wouldn't make 
sense to add it to the reply as well. It would be up to the client to 
keep track of it instead.
> - ajax

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