Name

    NV_robustness_video_memory_purge

Name Strings

    GL_NV_robustness_video_memory_purge
    GLX_NV_robustness_video_memory_purge
    EGL_NV_robustness_video_memory_purge

Contact

    Arthur Huillet, NVIDIA Corporation (ahuillet 'at' nvidia.com)

Contributors

    Arthur Huillet, NVIDIA Corporation
    Jeff Juliano, NVIDIA Corporation

Status

    Shipping.

Version

    Last Modified Date: May 26, 2016
    Revision:           5

Number

    Unassigned

Dependencies

    This extension is written against the ARB_robustness and 
    GLX_ARB_create_context extensions.

Overview

    Allow applications to be notified when video memory has been purged.

    The NVIDIA OpenGL driver architecture on Linux has a limitation:
    resources located in video memory are not persistent across certain
    events. VT switches, suspend/resume events, and mode switching
    events may erase the contents of video memory. Any resource that
    is located exclusively in video memory, such as framebuffer objects
    (FBOs), will be lost. As the OpenGL specification makes no mention
    of events where the video memory is allowed to be cleared, the
    driver attempts to hide this fact from the application, but cannot
    do it for all resources.

    This extension provides a way for applications to discover when video
    memory content has been lost, so that the application can re-populate
    the video memory content as necessary.

    This extension will have a limited lifespan, as planned architectural
    evolutions in the NVIDIA Linux driver stack will allow
    video memory to be persistent. Any driver that exposes this
    extension is a driver that considers video memory to be
    volatile. Once the driver stack has been improved, the extension
    will no longer be exposed.

New Procedures and Functions

    NONE

New Tokens

    Returned by GetGraphicsResetStatusARB, in addition to other tokens 
    defined in ARB_robustness:

        PURGED_CONTEXT_RESET_NV    0x92BB
    
    Accepted as an attribute name in the <*attrib_list> argument of
    glXCreateContextAttribsARB:
        
        GLX_GENERATE_RESET_ON_VIDEO_MEMORY_PURGE_NV 0x20F7

    Accepted as an attribute name in the <*attrib_list> argument of 
    eglCreateContext:
        
        EGL_GENERATE_RESET_ON_VIDEO_MEMORY_PURGE_NV 0x334C

Additions to Chapter 2 of the OpenGL 3.2 (Compatibility Profile)
Specification (OpenGL Operation)

    Modify subsection 2.6 "Graphics Reset Recovery". After:
        UNKNOWN_CONTEXT_RESET_ARB indicates a detected graphics reset 
        whose cause is unknown.

    add:
        PURGED_CONTEXT_RESET_NV indicates that video memory was purged
        in a mode switch event. In that case, the application can no 
        longer count on its resources' content being preserved, and must 
        delete and recreate all buffer objects including FBOs and all 
        textures bound to an FBO, transfer all relevant data again, 
        and re-render to FBOs. Using buffer objects, including FBOs, 
        that haven't been deleted and re-created is undefined behavior. 
        Other objects are unaffected.

        GetGraphicsResetStatusARB() needs to be called at least once 
        every frame, after a Flush(), Finish(), or buffer swapping call.

Additions to the GLX 1.4 Specification

    This extension modifies language specified in the
    GLX_ARB_create_context and GLX_ARB_create_context_profile
    extensions.

    Add a new paragraph to the description of glXCreateContextAttribsARB:

        The attribute name GLX_GENERATE_RESET_ON_VIDEO_MEMORY_PURGE_NV, 
        which defaults to GL_FALSE, can be specified as GL_TRUE. In this 
        case, a context reset notification will be generated when video 
        memory content has been lost. This will only take effect if the 
        attribute GLX_CONTEXT_RESET_NOTIFICATION_STRATEGY_ARB is set to 
        GLX_LOSE_CONTEXT_ON_RESET_ARB.

Additions to the EGL 1.5 Specification

    Modify the description of eglCreateContext. Add a new section:

        3.7.1.7 OpenGL reset notification for video memory purge events

        The attribute name EGL_GENERATE_RESET_ON_VIDEO_MEMORY_PURGE_NV, 
        which defaults to GL_FALSE, can be specified as GL_TRUE. In this 
        case, a context reset notification will be generated when video 
        memory content has been lost. This will only take effect if the 
        attribute EGL_CONTEXT_OPENGL_RESET_NOTIFICATION_STRATEGY is set 
        to EGL_LOSE_CONTEXT_ON_RESET.

Errors

    NONE

Issues

    (1) Does this extension allow an application to be sure that the
    rendered image is always perfect?

    Events that clear video memory happen asynchronously to OpenGL
    clients, so this extension does not guarantee perfect rendering.

    (2) Which NVIDIA drivers are affected?

    Not all NVIDIA drivers expose this extension, but all desktop Linux 
    drivers at the time of its publishing are affected by the issues it 
    addresses.

Example

    create_gl_context();
    create_resources();
    while (1) {
        update_world();
        if (GetGraphicsResetStatusARB() == PURGED_CONTEXT_RESET_NV) {
            delete_resources();
            create_resources();
        }
        render_frame();
    }

Revision History

    #1 April 1, 2016: Arthur Huillet
        - First draft.

    #2 April 2, 2016: Jeff Juliano
        - Reflow with line wrap, eliminate tabs.

    #3 April 5, 2016: Arthur Huillet
        - Rewrite as extension of ARB_robustness.

    #4 April 20, 2016: Arthur Huillet
        - Improve language.

    #5 May 26, 2016: Arthur Huillet
        - Add a context creation bit.