Name

    ARB_copy_image

Name Strings

    GL_ARB_copy_image

Contact

    Michael Gold, NVIDIA Corporation (gold 'at' nvidia.com)
    Graham Sellers, AMD (graham.sellers 'at' amd.com)

Contributors

    Jeff Bolz, NVIDIA Corporation (jbolz 'at' nvidia.com)
    James Jones, NVIDIA Corporation (jajones 'at' nvidia.com)
    Joe Kain, NVIDIA Corporation (jkain 'at' nvidia.com)
    Benjamin Morris, NVIDIA Corporation (bmorris 'at' nvidia.com)
    Michael Morrison, NVIDIA Corporation (mmorrison 'at' nvidia.com)
    Aaron Plattner, NVIDIA Corporation (aplattner 'at' nvidia.com)
    Mathias Schott, NVIDIA Corporation (mschott 'at' nvidia.com)
    Thomas Volk, NVIDIA Corporation (tvolk 'at' nvidia.com)
    Eric Werness, NVIDIA Corporation (ewerness 'at' nvidia.com)
    Daniel Koch, TransGaming Inc. (daniel 'at' transgaming.com)

Notice

    Copyright (c) 2012-2013 The Khronos Group Inc. Copyright terms at
        http://www.khronos.org/registry/speccopyright.html

Status

    Complete.
    Approved by the ARB on 2012/06/12.

Version

    Last Modified Date:         May 10, 2012
    Revision:                   3

Number

    ARB Extension #123

Dependencies

    OpenGL 1.1 is required.

    The extension is written against the OpenGL 4.2 (Core Profile) Specification.

    This extension interacts with OpenGL 4.3 and ARB_texture_view.

    This extension interacts with the Compatibility Profile.

    This extension interacts with EXT_texture_compression_s3tc.

    This extension interacts with OpenGL 3.0 and ARB_texture_compression_rgtc.

    This extension interacts with OpenGL 4.2 and ARB_texture_compression_bptc.

Overview

    This extension enables efficient image data transfer between image
    objects (i.e. textures and renderbuffers) without the need to bind
    the objects or otherwise configure the rendering pipeline.

    This is accomplised by adding a new entry-point CopyImageSubData,
    which takes a named source and destination.

    CopyImageSubData does not perform general-purpose conversions
    such as scaling, resizing, blending, color-space, or format 
    conversions. It should be considered to operate in a manner 
    similar to a CPU memcpy, but using the GPU for the copy.

    CopyImageSubData supports copies between images with different
    internal formats, if the formats are compatible for TextureViews.

    CopyImageSubData also supports copying between compressed and
    uncompressed images if the compressed block / uncompressed texel
    sizes are the same.

New Procedures and Functions

    void CopyImageSubData(
        uint srcName, enum srcTarget, int srcLevel,
        int srcX, int srcY, int srcZ,
        uint dstName, enum dstTarget, int dstLevel,
        int dstX, int dstY, int dstZ,
        sizei srcWidth, sizei srcHeight, sizei srcDepth);

New Tokens

    None

Additions to Chapter 4 of the OpenGL 4.2 (Core Profile) Specification (Per-Fragment
Operations and the Frame Buffer)

    Append to section 4.3.2 (Copying Pixels):

    The function

        void CopyImageSubData(
            uint srcName, enum srcTarget, int srcLevel,
            int srcX, int srcY, int srcZ,
            uint dstName, enum dstTarget, int dstLevel,
            int dstX, int dstY, int dstZ,
            sizei srcWidth, sizei srcHeight, sizei srcDepth);

    may be used to copy a region of texel data between two image
    objects.  An image object may be either a texture or a
    renderbuffer.

    CopyImageSubData does not perform general-purpose conversions
    such as scaling, resizing, blending, color-space, or format 
    conversions. It should be considered to operate in a manner 
    similar to a CPU memcpy. CopyImageSubData can copy between 
    images with different internal formats, provided
    the formats are compatible. 

    CopyImageSubData also allows copying between certain 
    types of compressed and uncompressed internal formats as detailed
    in Table 4.X.1. This copy does not perform on-the-fly compression
    or decompression. When copying from an uncompressed internal format
    to a compressed internal format, each texel of uncompressed data
    becomes a single block of compressed data. When copying from a
    compressed internal format to an uncompressed internal format,
    a block of compressed data becomes a single texel of uncompressed
    data. The texel size of the uncompressed format must be the same
    size the block size of the compressed formats. Thus it is permitted
    to copy between a 128-bit uncompressed format and a compressed
    format which uses 8-bit 4x4 blocks, or between a 64-bit uncompressed
    format and a compressed format which uses 4-bit 4x4 blocks.
    INVALID_OPERATION is generated if the texel size of
    the uncompressed image is not equal to the block size of the
    compressed image.

    The source object is identified by <srcName> and <srcTarget>.
    Similarly the destination object is identified by <dstName> and
    <dstTarget>.  The interpretation of the name depends on the value
    of the corresponding target parameter.  If the target parameter is
    RENDERBUFFER, the name is interpreted as the name of a
    renderbuffer object.  If the target parameter is a texture target,
    the name is interpreted as a texture object.  All non-proxy
    texture targets are accepted, with the exception of TEXTURE_BUFFER
    and the cubemap face selectors described in table 3.17. 
    INVALID_ENUM is generated if either target is not RENDERBUFFER
    or a valid non-proxy texture target, or is TEXTURE_BUFFER, or is one
    of the cubemap face selectors described in table 3.17, or if the
    target does not match the type of the object. INVALID_OPERATION
    is generated if either object is a texture and the texture is
    not complete (as defined in section 3.9.14), if the source and 
    destination internal formats are not compatible (see below), 
    or if the number of samples do not match.  
    INVALID_VALUE is generated if either name does not correspond to a
    valid renderbuffer or texture object according to the corresponding
    target parameter.

    <srcLevel> and <dstLevel> identify the source and destination
    level of detail.  For textures, this must be a valid level of
    detail in the texture object.  For renderbuffers, this value must
    be zero. INVALID_VALUE is generated if the specified level is not
    a valid level for the image.

    <srcX>, <srcY>, and <srcZ> specify the lower left texel
    coordinates of a <srcWidth>-wide by <srcHeight>-high by 
    <srcDepth>-deep rectangular subregion of the source texel array.  
    (Compatibility Only: Negative values
    of <srcX>, <srcY>, and <srcZ> correspond to the coordinates of
    border texels, addressed as in figure 3.10.)  Similarly, <dstX>,
    <dstY> and <dstZ> specify the coordinates of a subregion of the
    destination texel array.  The source and destination subregions
    must be contained entirely within the specified level of the
    corresponding image objects. 
    The dimensions are always specified in texels, even for compressed
    texture formats. But it should be noted that if only one of the
    source and destination textures is compressed then the number of
    texels touched in the compressed image will be a factor of the
    block size larger than in the uncompressed image.
    INVALID_VALUE is generated if the
    dimensions of the either subregion exceeds the boundaries of the
    corresponding image object, or if the image format is compressed
    and the dimensions of the subregion fail to meet the alignment
    constraints of the format.

    Slices of a TEXTURE_1D_ARRAY, TEXTURE_2D_ARRAY, TEXTURE_CUBE_MAP_ARRAY
    TEXTURE_3D and faces of TEXTURE_CUBE_MAP are all compatible provided 
    they share a compatible internal format, and multiple slices or faces
    may be copied between these objects with a single call by specifying the
    starting slice with <srcZ> and <dstZ>, and the number of slices to
    be copied with <srcDepth>.  Cubemap textures always have six faces
    which are selected by a zero-based face index, according to the
    order specified in table 3.17.

    For the purposes of CopyImageSubData, two internal formats
    are considered compatible if any of the following conditions are
    met:
     * the formats are the same,
     * the formats are considered compatible according to the 
       compatibility rules used for texture views as defined in 
       section 3.9.X. In particular, if both internal formats are listed
       in the same entry of Table 3.X.2, they are considered compatible, or
     * one format is compressed and the other is uncompressed and
       Table 4.X.1 lists the two formats in the same row.
    If the formats are not compatible INVALID_OPERATION is generated.

    ------------------------------------------------------------------------
    | Texel / | Uncompressed         |                                     |
    | Block   | internal format      | Compressed internal format          |
    | size    |                      |                                     | 
    ------------------------------------------------------------------------
    | 128-bit | RGBA32UI,            | COMPRESSED_RGBA_S3TC_DXT3_EXT,      |
    |         | RGBA32I,             | COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT,|
    |         | RGBA32F              | COMPRESSED_RGBA_S3TC_DXT5_EXT,      |
    |         |                      | COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT,|
    |         |                      | COMPRESSED_RG_RGTC2,                |
    |         |                      | COMPRESSED_SIGNED_RG_RGTC2,         |
    |         |                      | COMPRESSED_RGBA_BPTC_UNORM,         |
    |         |                      | COMPRESSED_SRGB_ALPHA_BPTC_UNORM,   |
    |         |                      | COMPRESSED_RGB_BPTC_SIGNED_FLOAT,   |
    |         |                      | COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT  |
    ------------------------------------------------------------------------
    | 64-bit  | RGBA16F, RG32F,      | COMPRESSED_RGB_S3TC_DXT1_EXT,       |
    |         | RGBA16UI, RG32UI,    | COMPRESSED_SRGB_S3TC_DXT1_EXT,      |
    |         | RGBA16I, RG32I,      | COMPRESSED_RGBA_S3TC_DXT1_EXT,      |
    |         | RGBA16, RGBA16_SNORM | COMPRESSED_SRGB_ALPHA_S3TC_DXT1_EXT,|
    |         |                      | COMPRESSED_RED_RGTC1,               |
    |         |                      | COMPRESSED_SIGNED_RED_RGTC1         |
    ------------------------------------------------------------------------

        Table 4.X.1: Compatible internal formats for copying between
        compressed and uncompressed internal formats with CopyImageSubData.
        Formats in the same row can be copied between each other.


Dependencies on OpenGL 4.3 and ARB_texture_view:

    If OpenGL 4.3 or later and ARB_texture_view are not supported,
    any references to view-compatible image formats should be removed.

Dependencies on the Compatibility Profile:

    If the Compatibility Profile is not supported, remove any 
    references to negative values for the source dimensions and
    to border texels.

Dependencies on EXT_texture_compression_s3tc:

    If EXT_texture_compression_s3tc is not supported, remove any
    references to S3TC compressed texture formats.

Dependencies on OpenGL 3.0 and ARB_texture_compression_rgtc:

    If OpenGL 3.0 or later, and ARB_texture_compression_rgtc is not
    supported, remove any references to the RGTC compressed texture
    formats.

Dependencies on OpenGL 4.2 and ARB_texture_compression_bptc:

    If OpenGL 4.2 or later, and ARB_texture_compression_bptc is not
    supported, remove any references to the PBTC compressed texture
    formats.
    
Errors

    CopyImageSubData may fail with any of the following errors:

    INVALID_ENUM is generated
     * if either <srcTarget> or <dstTarget> 
      - is not RENDERBUFFER or a valid non-proxy texture target
      - is TEXTURE_BUFFER, or
      - is one of the cubemap face selectors described in table 3.17,
     * if the target does not match the type of the object.

    INVALID_OPERATION is generated
     * if either object is a texture and the texture is not complete,
     * if the source and destination formats are not compatible,
     * if the source and destination number of samples do not match,
     * if one image is compressed and the other is uncompressed and the
       block size of compressed image is not equal to the texel size
       of the compressed image.

    INVALID_VALUE is generated
     * if either <srcName> or <dstName> does not correspond to a valid
       renderbuffer or texture object according to the corresponding
       target parameter, or
     * if the specified level is not a valid level for the image, or
     * if the dimensions of the either subregion exceeds the boundaries 
       of the corresponding image object, or
     * if the image format is compressed and the dimensions of the
       subregion fail to meet the alignment constraints of the format.

Sample Code

    TBD

Issues

    1) Should there be a single function for all image types, or
       "per-dimensional" functions?

       RESOLVED:  A single function can support all image types.  Not only are
       per-dimensional functions an unnecessary convenience, they also
       restrict some of the flexibility offered by this extension,
       e.g. copying a slice of data between a 2D and a 3D image.

    2) Should the extension support "deep copies", i.e. multiple slices of
       a 3D texture, a 2D array texture, or a cubemap?

       RESOLVED: Yes, there may be performance advantages in copying a multiple
       slices in a single call.

    3) Should renderbuffers be supported by the same function as textures?

       RESOLVED: Yes, there is no fundamental difference between the two object
       classes, and allowing them to be used interchangeably has the
       advantage of allowing data transfers between them.

    4) Is the "target" parameter necessary?

       RESOLVED: Yes, given the current object model and texture API, there are
       two obvious applications of the target parameter:

           1) Allows the selection of a single cubemap face.
           2) Differentiate between TEXTURE and RENDERBUFFER targets.

    5) Should the target TEXTURE_CUBE_MAP be supported, and with what
       behavior?

       RESOLVED: Given the resolution of issue 7, this is moot.  The
        TEXTURE_CUBE_MAP token is the only way to access a cubemap.
    
    6) Should the "extra" parameters for a given dimension be ignored, or
       should there be required values?
    
        Resolved.
    
        All parameters are required to have sensible values, for the
        simple reason that future extensions may give meaning to these
        values.  For dimensions which are currently superfluous, the
        offset must be zero and the size must be one, e.g. if the target
        is TEXTURE_2D, z must be 0 and depth must be 1.
    
    7) Should the per-face cubemap targets be accepted at all?  Why not
       use Z as the selector?

        Resolved.

        The existing per-face targets effectively define the face order:

           face_index = face_target - TEXTURE_CUBE_MAP_POSITIVE_X;

        Therefore it makes sense to generalize a cubemap as an array of
        size 6, and use the Z parameter to select the face(s).

    8) How is this extension different from NV_copy_image?

        RESOLVED: This extension does not include the WGL/GLX windowing-
        layer copy functions. This extension adds the ability to copy
        between images which have different formats where the formats 
        are compatible for texture views. This extension adds the ability
        to copy between uncompressed and compressed images if the texel
        and block sizes are the same.

    9) Please explain copying between compressed and uncompressed images.
       Is the copy doing compression/decompression on the fly?

       DISCUSSION. The CopyImageSubData does NOT provide any on-the-fly
       compression, decompression, or even any format conversions.
       Instead, it provides the ability for an application to implement
       it's own compressor in a shader by constructing the blocks and
       writing them out as texels and then copying them to a compressed
       texture so that it can in turn be used for sampling.

    (10) Is copying from/to images with ETC2/EAC compressed texture formats
         defined?

    RESOLVED: Only when the source and destination formats are identical,
    because texture view classes for ETC2/EAC are not defined (see issue 13
    of the ARB_texture_view specification).

Revision History

    Rev.    Date       Author    Changes
    ----  --------     --------  -----------------------------------------
     1    04/26/2012   gsellers  Initial revision based on NV_copy_image.
     2    05/08/2012   dgkoch    Update some references for 4.2 spec
                                 Allow copies between view-compatible images.
                                 Allow copies between compressed/uncompressed images.
                                 Clarify errors, updated overview.
     3    05/10/2012   dgkoch    Clarify dimensions refer to texels in the src image.
                                 Re-order/reflow text to make it read better.
                                 Add mention of TEXTURE_CUBE_MAP_ARRAY.
     4    10/08/2013   Jon Leech Add issue 10 discussing why copying 
                                 involving conversions between ETC2/EAC
                                 compressed formats is not supported (Bug
                                 11011).