xref: /third_party/openGLES/extensions/EXT/GLX_EXT_libglvnd.txt

Name

    EXT_libglvnd

Name Strings

    GLX_EXT_libglvnd

Contact

    Kyle Brenneman, NVIDIA, kbrenneman at nvidia.com

Contributors

    Kyle Brenneman
    Adam Jackson
    Andy Ritger
    Robert Morell
    Arthur Huillet
    Martin Peres

Status

    Complete

Version

    Last Modified Date: March 8, 2016
    Revision: 1

Number

    OpenGL Extension #482

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    0x20F6

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?

        RESOLVED: Allow a list of names.

        Allowing multiple names would allow for multiple client-side
        vendor libraries 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.

        For example, some vendors may have both a proprietary
        client-side vendor library and an open source vendor library
        that work with the same server-side driver. In that case, the
        server would return the names for both of the vendor libraries.
        The client would then try loading each vendor library as
        described below in Issue 3.

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

        RESOLVED: If there are multiple vendor names, then the client
        should use the names earlier in the list in preference to names
        later in the list.

        Specifically, 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.

    3)  How are vendor names defined and interpreted?

        RESOLVED: 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 are not defined in this specification.

    4)  Does the vendor name list need a new enum? Could it be appended
        to the GLX_VENDOR string instead?

        RESOLVED: Use a new enum. The vendor-specific part of the
        GLX_VENDOR string is by definition arbitrary, even if in
        practice every most if not all GLX implementatinos leave it
        blank.

        In addition, using a new enum also makes parsing the string much
        easier. The client can simply pass the unmodified string to
        strtok or strtok_r.

    5)  Do we need to define the interaction with GLX_SGIX_pbuffer?

        RESOLVED. No. Any client or server that implements this
        extension will already support GLX 1.3, so using
        glXQueryDrawable to look up a screen number is sufficient.

        There's no harm if a server includes a GLX_SCREEN attribute in
        its GetDrawableAttributesSGIX reply, so a server is still free
        to use the same codepath for GetDrawableAttributesSGIX and
        glXGetDrawableAttributes.

    6)  Do we want to add GLX_SCREEN to the list of fbconfig attributes
        as well?

        RESOLVED: No. Adding GLX_SCREEN to glXGetFBConfigAttrib would be
        redundant, because a client can already find the screen number
        for a GLXFBConfig using glXGetVisualFromFBConfig and indirectly
        using glXGetFBConfigs.

Revision History

    1. 8 March 2016
        - Initial draft.