extensions/EXT/EXT_shader_clock.txt

Name

    EXT_shader_clock

Name Strings

    GL_EXT_shader_clock

Contact

    Ashley Smith, Collabora <ashley.smith@collabora.com>

Contributors

    Ashley Smith, Collabora

    and contributors to the ARB_shader_clock spec,
    which provided the basis for this spec.

Notice

    Copyright (c) 2025 The Khronos Group Inc. Copyright terms at
        http://www.khronos.org/registry/speccopyright.html

Status

    Draft

Version

    Version 0.1, 2025/04/02

Number

    OpenGL ES Extension #348

Dependencies

    This extension is written against the OpenGL ES 3.1 specification.

Overview

    This extension is a port of GL_ARB_shader_clock to OpenGL ES. For the
    complete overview of this extension, refer to the "Overview" section of
    GL_ARB_shader_clock.

Differences from GL_ARB_shader_clock

    Append the EXT suffix to all new symbols.

    Renumber sections to match the OpenGL ES 3.1 Specification.

    Do not include GL_ARB_gpu_shader_int64 support and remove any references to
    the uint64 type.

New Procedures and Functions

    None.

New Tokens

    None.

IP Status

    None.

Modifications to the OpenGL Shading Language Specification, Version 4.60

    Including the following line in a shader can be used to control the
    language features described in this extension:

      #extension GL_EXT_shader_clock : <behavior>

    where <behavior> is as specified in section 3.3.

    New preprocessor #defines are added to the OpenGL Shading Language:

      #define GL_EXT_shader_clock               1

Additions to Chapter 8 of the OpenGL ES Shading Language Specification
(Built-in Functions)

    Add New Section 8.16, "Timing Functions"

    Syntax:

        uvec2 clock2x32EXT(void);

    clock2x32EXT() returns a value representing the current execution clock as
    seen by the shader processor encoded as a two-component vector of 32-bit
    unsigned integers with the first component containing the 32 least
    significant bits and the second component containing the 32 most significant
    bits. Time monotonically increments as the processor executes instructions.
    The returned time will wrap after it exceeds the maximum value representable
    in 64 bits. The units of time are not defined and need not be constant. Time
    is not guaranteed to be dynamically uniform across either a work group or a
    invocations of a single draw or dispatch. However time is guaranteed to be
    dynamically uniform across a single sub-group but only in a given shader
    stage (where sub-group is implementation dependent and may be just one
    invocation). The clock2x32EXT() functions serve as a code motion barriers.

Issues


Revision History

    Rev  Date        Author           Changes
    ---  ----------  --------------   ------------------------------------------
      1  2025/04/02  ashleysmithcol   Initial revision based on ARB_shader_clock