On 03/09/2016 12:53 PM, Kyle Brenneman wrote:
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 before.
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.
Oh, wait. Now that I think about it, GLX already provides a GLXFBConfig
to screen mapping in glXGetVisualFromFBConfig, and indirectly from
glXGetFBConfigs.
So, unless someone feels strongly otherwise, I think it would make the
most sense to leave glXGetFBConfigAttrib as it is.
- ajax
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