Name

    OES_texture_half_float
    OES_texture_float

Name Strings

    GL_OES_texture_half_float, GL_OES_texture_float

Contact

    Benj Lipchak, Apple (lipchak 'at' apple.com)

Notice

    Copyright (c) 2005-2013 The Khronos Group Inc. Copyright terms at
        http://www.khronos.org/registry/speccopyright.html

IP Status

    Please refer to the ARB_texture_float extension.

Status

    Ratified by the Khronos BOP, July 22, 2005.

Version

    Last Modified Date:  November 9, 2011

Number

    OpenGL ES Extension #36

Dependencies

    This extension is written against the OpenGL ES 2.0 Specification.

    OES_texture_3D affects the definition of this extension.

Overview

    These extensions add texture formats with 16- (aka half float) and 32-bit
    floating-point components.  The 32-bit floating-point components
    are in the standard IEEE float format.  The 16-bit floating-point
    components have 1 sign bit, 5 exponent bits, and 10 mantissa bits.
    Floating-point components are clamped to the limits of the range
    representable by their format.

    The OES_texture_half_float extension string indicates that the
    implementation supports 16-bit floating pt texture formats.

    The OES_texture_float extension string indicates that the 
    implementation supports 32-bit floating pt texture formats.

    Both these extensions only require NEAREST magnification filter and 
    NEAREST, and NEAREST_MIPMAP_NEAREST minification filters to be supported.

Issues

    1.  What should we do if magnification filter for a texture with half-float
        or float channels is set to LINEAR.

        RESOLUTION: The texture will be marked as incomplete.  
        Only the NEAREST filter is supported.  
        
        The cost of doing a LINEAR filter for these texture formats can be
        quite prohibitive.  There was a discussion on having the shader 
        generate code to do LINEAR filter by making individual texture calls with a 
        NEAREST filter but again the computational and memory b/w costs decided 
        against mandating this approach.  The decision was that this extension
        would only enable NEAREST magnification filter.  Support for LINEAR
        magnification filter would be done through a separate extension.

    2.  What should we do if minification filter is set to LINEAR or 
        LINEAR_MIPMAP_NEAREST, NEAREST_MIPMAP_LINEAR and LINEAR_MIPMAP_LINEAR.

        RESOLUTION: The texture will be marked as incomplete.  Only the NEAREST 
        and NEAREST_MIPMAP_NEAREST minification filters are supported.  

        This was decided for the same reasons given in issue #1.  The decision
        was that this extension would only enable NEAREST and NEAREST_MIPMAP_NEAREST
        minification filters, and the remaining OpenGL ES minification filters
        would be supported through a separate extension.
        
    3.  Should CopyTexImage2D, CopyTexSubImage{2D|3D} be supported for textures
        with half-float and float channels?
        
        RESOLUTION: No.

New Procedures and Functions

   None

New Tokens

    Accepted by the <type> parameter of TexImage2D,  TexSubImage2D, 
    TexImage3D, and TexSubImage3D

        HALF_FLOAT_OES                0x8D61
        FLOAT                         0x1406

Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL Operation)

    Add a new section called 16-Bit Floating-Point Numbers

    "A 16-bit floating-point number has a 1-bit sign (S), a 5-bit
    exponent (E), and a 10-bit mantissa (M).  The value of a 16-bit
    floating-point number is determined by the following:

        (-1)^S * 0.0,                        if E == 0 and M == 0,
        (-1)^S * 2^-14 * (M / 2^10),         if E == 0 and M != 0,
        (-1)^S * 2^(E-15) * (1 + M/2^10),    if 0 < E < 31,
        (-1)^S * INF,                        if E == 31 and M == 0, or
        NaN,                                 if E == 31 and M != 0,

    where

        S = floor((N mod 65536) / 32768),
        E = floor((N mod 32768) / 1024), and
        M = N mod 1024.

    Implementations are also allowed to use any of the following
    alternative encodings:

        (-1)^S * 0.0,                        if E == 0 and M != 0,
        (-1)^S * 2^(E-15) * (1 + M/2^10),    if E == 31 and M == 0, or
        (-1)^S * 2^(E-15) * (1 + M/2^10),    if E == 31 and M != 0,

    Any representable 16-bit floating-point value is legal as input
    to a GL command that accepts 16-bit floating-point data.  The
    result of providing a value that is not a floating-point number
    (such as infinity or NaN) to such a command is unspecified, but
    must not lead to GL interruption or termination.  Providing a
    denormalized number or negative zero to GL must yield predictable
    results."

    Add to Table 2.2, p. 12:

                Minimum
       GL Type  Bit Width  Description
       -------  ---------  -----------------------------------
       half     16         Half-precision floating-point value
                           encoded in an unsigned scalar

Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization)

    Add to Table 3.2, p. 62:

        type Parameter  Corresponding  Special
        Token Name      GL Data Type   Interpretation
        --------------  -------------  --------------
        HALF_FLOAT_OES  half           No
                           
    Modify first sentence of "Unpacking", p. 62: 
    
    "Data are taken from client memory as a sequence of one of the GL data
    types listed in Table 3.2. These elements are..."
                           
    Add to Table 3.4, p. 63:

        Format           Type            Bytes per Pixel
        ---------        --------------  ---------------
        RGBA             FLOAT           16
        RGB              FLOAT           12
        LUMINANCE_ALPHA  FLOAT           8
        LUMINANCE        FLOAT           4
        ALPHA            FLOAT           4
        RGBA             HALF_FLOAT_OES  8
        RGB              HALF_FLOAT_OES  6
        LUMINANCE_ALPHA  HALF_FLOAT_OES  4
        LUMINANCE        HALF_FLOAT_OES  2
        ALPHA            HALF_FLOAT_OES  2

    Modify fifth paragraph of 3.7.1 Texture Image Specification, p. 67:
    
    "The selected groups are processed as described in section 3.6.2, stopping
    after final expansion to RGBA. If the internal format of the texture is 
    fixed-point, components are clamped to [0,1]. Otherwise, values are not 
    modified."

Interactions with OES_texture_3D

    If OES_texture_3D is not supported, ignore references to TexImage3D and 
    TexSubImage3D.

Revision History

    04/29/2005    0.1    Original draft.
    06/29/2005    0.2    Added issues on why only NEAREST and 
                         NEAREST_MIPMAP_NEAREST filters are required.
    04/21/2006    0.3    Added TexSubImage2D and TexSubImage3D as
                         functions that take the new tokens.
    06/14/2006    0.4    CopyTexImage2D, CopyTexSubImag{2D|3D} are
                         not supported.
    07/26/2011    0.5    Fix several omissions discovered while writing
                         EXT_color_buffer_half_float.
    11/09/2011    0.6    Fix missing FLOAT entries in Table 3.4,
                         add interaction with OES_texture_3D.