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

[Kyle Brenneman]

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.

-Kyle


Name

     EXT_libglvnd

Name Strings

     GLX_EXT_libglvnd

Contact

     Kyle Brenneman, NVIDIA, kbrenneman at nvidia.com

Contributors

     Kyle Brenneman
     Adam Jackson

Status

     XXX - Not complete yet

Version

     Last Modified Date: March 8, 2016
     Revision: 1

Number

     ???

Dependencies

     GLX version 1.3 is required.

     This specification is written against the wording of the GLX 1.4
     Specification.

Overview

     This extension allows the vendor-neutral GLX client library, 
libglvnd, to
     determine which vendor-specific driver is needed to support a given GLX
     drawable or X11 screen.

     This GLX extension is not intended to be used directly by applications.
     Instead, it is intended to be used by the GLX client library.

IP Status

     No known IP claims.

New Procedures and Functions

     None

New Types

     None

New Tokens

     Accepted by the <name> parameter of glXQueryServerString:

         GLX_VENDOR_NAMES_EXT    0x????

Additions to Chapter 3 of the GLX 1.4 Specification
(Functions and Errors)

     [Modify Section 3.3.2, GLX Versioning]

     [Replace the 2nd sentence of the 5th paragraph with the following]

     "The possible values for <name> and the format of the strings is 
the same
     as for glXGetClientString. <name> may also be GLX_VENDOR_NAMES_EXT."

     [Add the following paragraph to the end of the section]

     "If <name> is GLX_VENDOR_NAMES_EXT, then the returned string is a
     space-separated sequence of vendor names. The names are in order of
     preference, with the most preferred vendor first."


     [Modify Section 3.3.6, Querying Attributes]

     [Replace the 2nd sentence of the 1st paragraph with the following]

     "<attribute> must be set to one of GLX_WIDTH, GLX_HEIGHT,
     GLX_PRESERVED_CONTENTS, GLX_LARGEST_PBUFFER, GLX_FBCONFIG_ID, or
     GLX_SCREEN"

     [Add the following paragraph just before the last of the section]

     "If <attribute> is GLX_SCREEN, then <value> will be the screen 
number that
     the drawable was created on."

GLX Protocol

     This extension does not add any new requests. The 
GLX_VENDOR_NAMES_EXT enum
     is used with the existing glXQueryServerString request, and 
GLX_SCREEN is
     added to the attributes in the glXGetDrawableAttributes reply.

Errors

     None

Issues
     1)  Should GLX_VENDOR_NAMES_EXT contain a single vendor name or a 
list of
         names?

         Allowing multiple names would allow for multiple client-side 
drivers
         that work with a single server-side driver. With only a single 
name,
         selecting between multiple client drivers would require some 
form of
         additional configuration.

     2)  How are vendor names defined and interpreted?

         The vendor names for a screen are defined based on the server's GLX
         implementation. Typically, a server will simply send the name 
of the
         driver that controls the screen.

         The GLX client library is responsible for translating the 
vendor name
         to a vendor library name. The details of the translation are 
part of
         the interface between the vendor library and the GLX client 
library,
         and so is not defined in this specification.

     3)  What order should the vendor names be returned in?

         The GLX client library will try to load and use each vendor 
name, in
         the order that the server lists them. It will stop when it 
finds the
         first vendor that works.

Revision History

     1. 8 March 2016
         - Initial draft.