extensions/EXT/EXT_shader_image_load_formatted.txt

Name

    EXT_shader_image_load_formatted

Name Strings

    GL_EXT_shader_image_load_formatted

Contact

    Jeff Bolz, NVIDIA Corporation (jbolz 'at' nvidia.com)
    Pat Brown, NVIDIA Corporation (pbrown 'at' nvidia.com)

Contributors

Status

    Complete.

Version

    Last Modified Date:         March 11, 2014
    Revision:                   1

Number

    OpenGL Extension #449

Dependencies

    This extension is written against the OpenGL 4.3 specification
    (Compatibility Profile).

    This extension is written against version 4.30 of the OpenGL
    Shading Language Specification.

    This extension interacts with GL_NV_bindless_texture.

    This extension interacts with GL_EXT_shader_image_load_store and
    NV_gpu_program5.

Overview

    ARB_shader_image_load_store (and OpenGL 4.2) added support for
    random access load and store from/to texture images, but due to 
    hardware limitations, loads were required to declare the image
    format in the shader source. This extension relaxes that 
    requirement, and the return values from imageLoad can be format-
    converted based on the format of the image binding.

New Procedures and Functions

    None.

New Tokens

    None.

Additions to Chapter 8 of the OpenGL 4.3 (Compatibility Profile) Specification
(Rasterization)

    Modify Section 8.25 Texture Image Loads and Stores, p. 284

    (modify the bullet describing the format layout mismatch)

    - the format layout qualifier for an image variable used for an image load 
      (if specified) or atomic operation does not match the format of the image 
      unit, according to table 8.33; or

    (modify the first paragraph on p. 285)

    Image variables used for shader loads, stores, and atomics may be declared 
    with a format layout qualifier. If the format layout qualifier is present, 
    then the format must match the format of the associated image unit, as 
    enumerated in table 8.33, otherwise the access is considered to involve a 
    format mismatch, as described above. Image variables used for atomics must 
    be declared with a format layout qualifier. Image variables used only for
    loads and stores may be declared without a format layout qualifier, in which
    case the format of the image is inferred from the associated image unit.


New Implementation Dependent State

    None.

New State

    None.

Additions to the AGL/GLX/WGL Specifications

    None.

GLX Protocol

    None.
    
Modifications to the OpenGL Shading Language Specification, Version 4.30


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

      #extension GL_EXT_shader_image_load_formatted : <behavior>

    where <behavior> is as specified in section 3.3.

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

      #define GL_EXT_shader_image_load_formatted    1


    Modify Section 4.4.6.2 Format Layout Qualifiers (p. 71)
    
    (modify the second paragraph on p.71)
    
    Any image variable used for image atomic operations must specify a format 
    layout qualifier; it is a compile-time error to pass an image uniform 
    variable or function parameter declared without a format layout qualifier 
    to an image atomic function.

    Delete the last paragraph on p.71: (Uniforms not qualified with <writeonly> 
    must have a format layout qualifier. ...)


Errors



Dependencies on NV_bindless_texture

    When an image variable uses a bindless image handle, the format of the
    image is inferred from the handle rather than "from the associated image 
    unit".

Dependencies on EXT_shader_image_load_store and NV_gpu_program5

    Modify Section 2.X.4, Program Execution Environment

      Instr-      Modifiers 
      uction  V  F I C S H D  Out Inputs    Description
      ------- -- - - - - - -  --- --------  --------------------------------
      LOADIM  50 X X X X - F  v   vs,i      image load

    (Add to "Section 2.X.6, Program Options" of the NV_gpu_program4 extension,
    as extended by NV_gpu_program5:)

      + Formatted Image Loads (EXT_shader_image_load_formatted)

      If a program specifies the "EXT_shader_image_load_formatted" option, it 
      may use the "F", "U", or "S" data types with the "LOADIM" opcodes to 
      perform formatted image load operations.

    Modify Section 2.X.8.Z, (LOADIM:  Image Load)

    LOADIM supports an optional base data type (formatted) or storage modifier 
    (unformatted).  Formatted image loads operate as described in Section 8.25. 
    Unformatted image loads are treated as invalid unless the storage modifier 
    matches the image unit format, as described in Table X.3.  The base data 
    type of the result vector is derived from the storage modifier. The single 
    operand is always interpreted as a signed integer vector.

          Class      Supported Modifers
          -------    -------------------
          4x32       F32X4, S32X4, U32X4
          2x32       F32X2, S32X2, U32X2
          1x32       F32,   S32,   U32
          1x16              S16,   U16
          1x8               S8,    U8

      Table X.3, Supported Storage Modifiers.  Unformatted image operations
      are considered invalid unless the storage modifier is compatible with
      the "Class" entry for the image unit format, as described in Table
      8.33.


Issues


Revision History

    Rev.    Date    Author    Changes
    ----  --------  --------  -----------------------------------------------
     1    01/28/14  jbolz     Internal revisions.