extensions/EXT/GLX_EXT_context_priority.txt

Name

    EXT_context_priority

Name Strings

    GLX_EXT_context_priority

Contributors

    Adam Jackson, Red Hat

    Cloned from EGL_IMG_context_priority, whose contributors included:

    Ben Bowman, Imagination Techonologies
    Graham Connor, Imagination Techonologies

Contacts

    Adam Jackson <ajax@redhat.com>

Status

    Complete

Version

    Version 2, 10 April 2019

Number

    OpenGL Extension #535

Dependencies

    Requires GLX_ARB_create_context.

    This extension is written against the text of the GLX 1.4 specification.

Overview

    This extension allows a GLXContext to be created with a priority
    hint. It is possible that an implementation will not honour the
    hint, especially if there are constraints on the number of high
    priority contexts available in the system, or system policy limits
    access to high priority contexts to appropriate system privilege
    level. A query is provided to find the real priority level assigned
    to the context after creation.

New Types

    None

New Procedures and Functions

    None

New Tokens

    New attributes accepted by the <attrib_list> argument of
    glXCreateContextAttribsARB:

        GLX_CONTEXT_PRIORITY_LEVEL_EXT          0x3100

    New attribute values accepted in the <attrib_list> argument
    of glXCreateContextAttribsARB:

        GLX_CONTEXT_PRIORITY_HIGH_EXT           0x3101
        GLX_CONTEXT_PRIORITY_MEDIUM_EXT         0x3102
        GLX_CONTEXT_PRIORITY_LOW_EXT            0x3103

Additions to the GLX_ARB_create_context specification

    Add to the text of attributes supported by glXCreateContextAttribsARB:

        "GLX_CONTEXT_PRIORITY_LEVEL_EXT determines the priority level of
        the context to be created. This attribute is a hint, as an
        implementation may not support multiple contexts at some
        priority levels and system policy may limit access to high
        priority contexts to appropriate system privilege level. The
        default value for GLX_CONTEXT_PRIORITY_LEVEL_EXT is
        GLX_CONTEXT_PRIORITY_MEDIUM_EXT."

Additions to the GLX 1.4 specification

    To Table 3.5 "Context attributes" add the row:

    Attribute                       Type    Description
    GLX_CONTEXT_PRIORITY_LEVEL_EXT  int     Context priority level

Issues

    Refer to the issues in EGL_IMG_context_priority for further background.

    1) What enumerant values should we use here?

    RESOLVED: Reuse the enums from EGL_IMG_context_priority. The window
    system binding APIs have trended towards sharing enumerant space. The
    range is not otherwise assigned for GLX, and Imagination have consented
    to its reuse in GLX.

Revision History

    Version 2, 10 April 2019 (Adam Jackson)
    - Resolve enumerant issue.

    Version 1, 20 February 2019 (Adam Jackson)
    - Clone from EGL_IMG_context_priority