OES_EGL_image_external

GL_OES_EGL_image_external

Acorn Pooley
David Garcia
Bruce Merry
Aske Simon Christensen
Mark Callow
Tom Olson
Jon Leech
Maurice Ribble

Acorn Pooley, NVIDIA Corporation (apooley 'at' nvidia.com)

Copyright (c) 2009-2013 The Khronos Group Inc. Copyright terms at
    http://www.khronos.org/registry/speccopyright.html

Khronos-approved extension specifications are updated in response to
issues and bugs prioritized by the Khronos OpenGL ES Working Group. For
extensions which have been promoted to a core Specification, fixes will
first appear in the latest version of that core Specification, and will
eventually be backported to the extension document. This policy is
described in more detail at
    https://www.khronos.org/registry/OpenGL/docs/update_policy.php

Ratified by Khronos Promoters, 10 December 2010
Approved by the OpenGL ES Working Group, 15 September 2010

April 6, 2018 (version 25)

OpenGL ES Extension #87

Requires OpenGL ES 1.1 or OpenGL ES 2.0.

Requires EGL 1.2

Requires either the EGL_KHR_image_base or the EGL_KHR_image extension

This extension is written based on the wording of the OpenGL ES 2.0
specification, the OpenGL ES Shading Language version 1.0, and the
EGL_KHR_image_base extension.  On an OpenGL ES 2.0 implementation, ignore
sections which are added only to the OpenGL ES 1.1 specification.

This extension is also written based on the wording of the OpenGL ES 1.1
specification.  On an OpenGL ES 1.X implementation, ignore sections which
are added only to the OpenGL ES 2.0 or OpenGL ES Shading Language
specification.  Also ignore all mention of MAX_VERTEX_TEXTURE_IMAGE_UNITS,
and MAX_COMBINED_TEXTURE_IMAGE_UNITS.

This extension borrows concepts and function names from the
GL_OES_EGL_image extension.  This extension is compatible with, but does
not require, the GL_OES_EGL_image extension.

This extension provides a mechanism for creating EGLImage texture targets
from EGLImages.  This extension defines a new texture target,
TEXTURE_EXTERNAL_OES.  This texture target can only be specified using an
EGLImage.  There is no support for most of the functions that manipulate
other texture targets (e.g. you cannot use gl*Tex*Image*() functions with
TEXTURE_EXTERNAL_OES).  Also, TEXTURE_EXTERNAL_OES targets never have more
than a single LOD level.  Because of these restrictions, it is possible to
bind EGLImages which have internal formats not otherwise supported by
OpenGL ES.  For example some implementations may allow EGLImages with
planar or interleaved YUV data to be GLES texture target siblings.  It is
up to the implementation exactly what formats are accepted.

Please see the EGL_OES_image_base specification for a list of terms
used by this specification.

/*
 * GLeglImageOES is an opaque handle to an EGLImage
 * Note: GLeglImageOES is also defined in GL_OES_EGL_image
 */
typedef void* GLeglImageOES;

/* (OpenGL ES 2.x only)
 * New sampler type allowed by the OpenGL ES Shading Language when
 *      #extension GL_OES_EGL_image_external
 * is used.
 */
samplerExternalOES

/* Note: EGLImageTargetTexture2DOES is also defined in GL_OES_EGL_image */
void EGLImageTargetTexture2DOES(enum target, eglImageOES image)

 Accepted as a target in the <target> parameter of BindTexture and
 EGLImageTargetTexture2DOES:

    TEXTURE_EXTERNAL_OES                                0x8D65

(OpenGL ES 2.x only) Returned in the <type> parameter of GetActiveUniform:
    SAMPLER_EXTERNAL_OES                                0x8D66

Accepted as the <pname> parameter of GetBooleanv, GetIntegerv,
GetFloatv, and GetFixedv:
    TEXTURE_BINDING_EXTERNAL_OES                        0x8D67

Accepted as <value> in GetTexParameter*() queries:
    REQUIRED_TEXTURE_IMAGE_UNITS_OES                    0x8D68

- For OpenGL ES 2.0 add a new section: "3.7.14 External Textures," which
follows section "3.7.13 Texture Objects."  For OpenGL ES 1.1 add a new
section after section "3.7.11 Texture Objects."

    "3.7.14 External Textures

    External textures cannot be used with TexImage2D, TexSubImage2D,
    CompressedTexImage2D, CompressedTexSubImage2D, CopyTexImage2D, or
    CopyTexSubImage2D, and an INVALID_ENUM error will be generated if this
    is attempted.  Their default min filter is LINEAR.  It is an
    INVALID_ENUM error to set the min filter value to anything other than
    LINEAR or NEAREST.  The default s and t wrap modes are CLAMP_TO_EDGE
    and it is an INVALID_ENUM error to set the wrap mode to any other
    value.  (For OpenGL ES 1.x only: The texture parameter GENERATE_MIPMAP
    is always FALSE, and setting it to any other value generates an
    INVALID_ENUM error.  (For OpenGL ES 2.x only: Calling GenerateMipmaps
    with <target> set to TEXTURE_EXTERNAL_OES results in an INVALID_ENUM.)

    The command

        void EGLImageTargetTexture2DOES(enum target, eglImageOES image);

    with <target> set to TEXTURE_EXTERNAL_OES defines the currently bound
    external texture object to be a target sibling of <image>.  The width,
    height, format, type, internalformat, border, and image data are all
    determined based on the specified eglImageOES <image>.  Any sibling
    previously associated with this external texture object is deleted.

    A EGLImageTargetTexture2DOES() call with <target> set to
    TEXTURE_EXTERNAL_OES will not modify the pixel data values in the
    EGLImage.

    <image> must be the handle of a valid EGLImage resource, cast into the
    type eglImageOES.

    Assuming no errors are generated in EGLImageTargetTexture2DOES, the
    newly specified texture object will be an EGLImage target of the
    specified eglImageOES.

    If the GL is unable to specify a texture object using the supplied
    eglImageOES <image> (if, for example, <image> refers to a multisampled
    eglImageOES), the error INVALID_OPERATION is generated.

    If <target> is not TEXTURE_EXTERNAL_OES, the error INVALID_ENUM is
    generated.  (Note: if GL_OES_EGL_image is supported then <target> may
    also be TEXTURE_2D).

    Sampling an external texture which is not associated with any EGLImage
    sibling will return a sample value of (0,0,0,1).

    Each TEXTURE_EXTERNAL_OES texture object may require up to 3 texture
    image units for each texture unit to which it is bound.  The number of
    texture image units required by a bound texture object can be queried
    using GetTexParameteriv() with <target> set to the texture target in
    question, <value> set to REQUIRED_TEXTURE_IMAGE_UNITS_OES, and
    ActiveTexture set to the texture unit to which the texture object is
    bound.  When <target> is set to TEXTURE_EXTERNAL_OES this value will
    be between 1 and 3 (inclusive).  For other valid texture targets this
    value will always be 1.  Note that, when a TEXTURE_EXTERNAL_OES
    texture object is bound, the number of texture image units required by
    a single texture unit may be 1, 2, or 3, while for other texture
    objects each texture unit requires exactly 1 texture image unit.

    (For OpenGL ES 1.x only) DrawArrays and DrawElements will fail and
    generate an INVALID_OPERATION error if the number of texture image
    units required is greater than the number available.  The number of
    required texture image units is equal to the sum of the requirements
    for each enabled texture unit.  For each texture unit the requirement
    is the value returned by GetTexParameteriv() when <value> is set to
    REQUIRED_TEXTURE_IMAGE_UNITS_OES, <target> is set to the target which
    is enabled, and ActiveTexture has been set to the texture unit in
    question.

    (For OpenGL ES 2.x only) DrawArrays and DrawElements will fail and
    generate an INVALID_OPERATION error if the number of texture image
    units required is greater than the number available.  The number of
    required texture image units for each stage (fragment or vertex) is
    equal to the sum of the requirements for each sampler referenced by
    the stage.  A sampler is considered referenced if its location
    (returned by GetUniformLocation) is not -1.  For each referenced
    sampler the requirement is the value returned by GetTexParameteriv()
    when <value> is set to REQUIRED_TEXTURE_IMAGE_UNITS_OES, <target> is
    set to the target corresponding to the sampler type, and ActiveTexture
    has been set to the texture unit corresponding to the value of the
    sampler uniform.  The condition can be detected by calling Validate.

    (For OpenGL ES 2.x only) A shader that uses external texture samplers
    may require some number of hidden uniform variables to implement the
    conversion from YUV to RGB, and this may reduce the amount of space
    available for uniforms defined by the shader program.  This may cause
    a shader program which was working to stop working when a different
    external texture is used (i.e. when Uniform1i or BindTexture is
    called).  If there are not enough uniforms available then calls to
    DrawArrays or DrawElements will fail and generate an INVALID_OPERATION
    error.  This condition can be detected by calling ValidateProgram.

    Sampling an external texture which has been modified since it was
    bound will return samples which may correspond to image values either
    before, during, or after the modification.  Binding (or re-binding if
    already bound) an external texture by calling BindTexture after all
    modifications are complete guarantees that sampling done in future
    draw calls will return values corresponding to the values in the
    buffer at or after the time that BindTexture is called.  (Note that
    calling BindTexture after calling commands that modify the EGLImage
    may not be sufficient to ensure that the modifications are complete;
    additional synchronization (for example eglWaitAPI, eglWaitNative,
    glFinish, vgFinish, or eglWaitSyncKHR, etc) may be required following
    the call initiating modifications, to ensure they have taken effect on
    the texture, before the call to BindTexture is made.)

    Sampling an external texture will return an RGBA vector in the same
    colorspace as the source image.  If the source image is stored in YUV
    (or some other basis) then the YUV values will be transformed to RGB
    values. (But these RGB values will be in the same colorspace as the
    original image.  Colorspace here includes the linear or non-linear
    encoding of the samples. For example, if the original image is in the
    sRGB color space then the RGB value returned by the sampler will also
    be sRGB, and if the original image is stored in ITU-R Rec. 601 YV12
    then the RGB value returned by the sampler will be an RGB value in the
    ITU-R Rec. 601 colorspace.) The parameters of the transformation
    from one basis (e.g.  YUV) to RGB (color conversion matrix, sampling
    offsets, etc) are taken from the EGLImage which is associated with the
    external texture.  The implementation may choose to do this
    transformation when the external texture is sampled, when the external
    texture is bound, or any other time so long as the effect is the same.
    It is undefined whether texture filtering occurs before or after the
    transformation to RGB.

    If the EGLImage associated with the external texture contains alpha
    values then the value of the alpha component returned is taken from
    the image; otherwise the alpha component is 1.0.

- In the subsection "Uniform Variables" paragraph 13, last sentence, add

    "SAMPLER_EXTERNAL_OES"
to the list of types that can be returned.

- In the subsection "Validation", add to the bullet points in the second
  paragraph:

    "- the number of texture image units required is greater than
       the number available (see REQUIRED_TEXTURE_IMAGE_UNITS_OES,
       MAX_COMBINED_TEXTURE_IMAGE_UNITS, MAX_VERTEX_TEXTURE_IMAGE_UNITS,
       and MAX_TEXTURE_IMAGE_UNITS).

    - the number of uniforms required to implement the shader program is
       greater than the number available."

- Add to the end of the section a new paragraph:

        "When <target> is TEXTURE_EXTERNAL_OES only NEAREST and LINEAR are
    accepted as TEXTURE_MIN_FILTER, only CLAMP_TO_EDGE is accepted as
    TEXTURE_WRAP_S and TEXTURE_WRAP_T, and only FALSE is accepted as
    GENERATE_MIPMAP.  Attempting to set other values for
    TEXTURE_MIN_FILTER, TEXTURE_WRAP_S, TEXTURE_WRAP_T, or GENERATE_MIPMAP
    will result in an INVALID_ENUM error.

- Add to the end of the section a new paragraph:

        "When <target> is TEXTURE_EXTERNAL_OES only NEAREST and LINEAR are
    accepted as TEXTURE_MIN_FILTER and only CLAMP_TO_EDGE is accepted as
    TEXTURE_WRAP_S and TEXTURE_WRAP_T.  Attempting to set other values for
    TEXTURE_MIN_FILTER, TEXTURE_WRAP_S, or TEXTURE_WRAP_T will result in
    an INVALID_ENUM error.

- Add an additional sentence at the end of the section:

        "In the initial state of a TEXTURE_EXTERNAL_OES texture object,
    the value assigned to TEXTURE_MIN_FILTER and TEXTURE_MAG_FILTER is
    LINEAR, and the s and t wrap modes are both set to
    CLAMP_TO_EDGE."

- Add two additional paragraphs to the end of the section:

        "When <target> is set to TEXTURE_EXTERNAL_OES, GenerateMipmap
    always fails and generates an INVALID_ENUM error."

- Modify this section as follows: (changed lines marked with *, and added
  lines are marked with +)

- Modify this section as follows: (changed lines marked with *, and added
  lines are marked with +)

- Replace the first sentence of the first paragraph with:

        "Texturing is enabled or disabled using the generic Enable and
    Disable commands, with the symbolic constant TEXTURE_2D or
    TEXTURE_EXTERNAL_OES to enable or disable texturing with the
    TEXTURE_2D or TEXTURE_EXTERNAL_OES texture target, respectively.  If
    TEXTURE_EXTERNAL_OES is enabled it takes precedence over TEXTURE_2D,
    TEXTURE_CUBE_MAP_OES, TEXTURE_RECTANGLE_ARB, and
    TEXTURE_RECTANGLE_NV."

- Add to the end of the last paragraph of the subsection "Texture Access"

    "The REQUIRED_TEXTURE_IMAGE_UNITS_OES parameter can change based on the
    number of external textures which are currently bound (see section
    3.7.14)."

- Change:
    "...TEXTURE_2D..."
  to
    "...TEXTURE_2D or TEXTURE_EXTERNAL..."
  in the last paragraph.

- Change:
    "...TEXTURE_2D or TEXTURE_CUBE_MAP..."
  to
    "...TEXTURE_2D, TEXTURE_CUBE_MAP, or TEXTURE_EXTERNAL..."
  in the second paragraph.

- Add to "Table 6.13 Textures (state per texture unit and binding point)"

    +-------------------+-------+-------------+-------+------------------+
    | TEXTURE_BINDING_- | 8*xZ+ | GetIntegerv | 0     | Texture object   |
    |   EXTERNAL_OES    |       |             |       | bound to         |
    |                   |       |             |       | TEXTURE_-        |
    |                   |       |             |       |    EXTERNAL_OES  |
    +-------------------+-------+-------------+-------+------------------+
    | TEXTURE_-         | 2*xB  | IsEnabled   | False | True if external |
    |   EXTERNAL_OES    |       |             |       | texturing is     |
    |                   |       |             |       | enabled          |
    +-------------------+-------+-------------+---+----------------------+

- Add to "Table 6.14 Textures (state per texture object)"

    +--------------------+-------+-----------------+---+----------------+
    | REQUIRED_TEXTURE_- | n*xZ3 | GetTexParameter | 1 | Number of      |
    |   IMAGE_UNITS_OES  |       |                 |   | texture image  |
    |                    |       |                 |   | units required |
    |                    |       |                 |   |    by texture  |
    +--------------------+-------+-----------------+---+----------------+

- Add to "Table 6.7 Textures (state per texture unit and binding point)"

    +-------------------+-------+-------------+-------+------------------+
    | TEXTURE_BINDING_- | 8*xZ+ | GetIntegerv | 0     | Texture object   |
    |   EXTERNAL_OES    |       |             |       | bound to         |
    |                   |       |             |       | TEXTURE_-        |
    |                   |       |             |       |    EXTERNAL_OES  |
    +-------------------+-------+-------------+-------+------------------+

- Add to "Table 6.8 Textures (state per texture object)"

    +--------------------+-------+-----------------+---+----------------+
    | REQUIRED_TEXTURE_- | n*xZ3 | GetTexParameter | 1 | Number of      |
    |   IMAGE_UNITS_OES  |       |                 |   | texture image  |
    |                    |       |                 |   | units required |
    |                    |       |                 |   |    by texture  |
    +--------------------+-------+-----------------+---+----------------+

- Add to the list of keywords:

    "samplerExternalOES"

- Add to the list of basic types:

    "samplerExternalOES   a handle for accessing an external texture"

- Add to the list of "vertex language has the following predeclared
globally scoped default precision statements:"

    "precision lowp samplerExternalOES;"

- Add to the list of "fragment language has the following predeclared
globally scoped default precision statements:"

    "precision lowp samplerExternalOES;"

- Add to the table the following sampler functions:

    "vec4 texture2D(
                samplerExternalOES sampler,
                vec2 coord)
    vec4 texture2DProj(
                samplerExternalOES sampler,
                vec3 coord)
    vec4 texture2DProj(
                samplerExternalOES sampler,
                vec4 coord)"

- Add to token list:

    "SAMPLEREXTERNAL"

- Add following "type_specifier_no_prec:"

    "SAMPLEREXTERNAL"

- Change the first sentence of the last paragraph to

    "Part of the storage may be reserved by an implementation for its own
    use e.g. for computation of transcendental functions or conversion of
    external textures."

1.  What happens when GenerateMipmaps() is called with <target> set to
    TEXTURE_EXTERNAL_OES?

    Possible options:

    A) Fail (INVALID_ENUM)
    B) Generate the mipmaps and copy them into the TEXTURE_2D target.

    Option B could be useful and should not be difficult to implement.
    What happens when the texture is NPOT and GenerateMipmaps() is called?

    Ben Bowman and David Garcia have indicated they prefer A.  No other
    strong opinions yet.

    RESOLVED: A (fail)

2.  Should the wrap mode of an external texture be allowed to be anything
    other than CLAMP_TO_EDGE?

    RESOLVED: no

3.  What about portability problems introduced by allowing implementation-
    dependent failures?

    This is the same issue described in Issue 14 of the
    EGL_OES_image specification.  Like the resolution for that issue,
    this specification should include some minimum requirements, but
    leave the larger portability problem unresolved at the moment.

    RESOLVED: This and other (EGL_KHR_image_uses and EGL_KHR_il_image)
    extensions attempt to minimize this problem by allowing EGL to pick
    EGLImage attributes which will work in various situations.  However it
    is not possible to guarantee that every usecase will work on every
    platform.

4.  Should EGLImageTargetTexture2DOES result in undefined pixel data,
    as with calls to eglCreateImageOES?

    See also issue 4 of GL_OES_EGL_image

    Comment from Aske:
    In the description for EGLImageTargetTexture2DOES, it says: "As a
    result of this operation all pixel data in <image> will become
    undefined." Why is this? I would imagine one would want to take an
    existing EGL image containing image data and bind it as an external
    texture, possibly multiple times, to use it for rendering. I have read
    through issue 4 of OES_EGL_image, and it seems the concern here is
    what happens when the image is (potentially) modified from OpenGL ES.
    Since external images cannot be modified from OpenGL ES, I would guess
    the same issues do not apply here.

    Comment from Acorn:
    Another potential issue is that the memory for the EGLImage may
    have to be reallocated in order to be compatible with GLES (e.g. GLES
    may have more strict alignment or other requirements).  However, the
    implementation can fail (or do a copy) if this is the case.  If the
    EGL_KHR_image_uses extension is used to specify that the EGLImage will
    be used as a GLES external texture then this should not be an issue
    because EGL will be able to allocate the memory correctly in the first
    place.

    RESOLVED: pixel data will not become undefined when
    EGLImageTargetTexture2DOES() is used with an external texture target.

5.  What happens if the texture is bound while the associated EGLImage is
    being modified.

    Some implementations may need to color convert the data
    after it has been generated.  A solution to this is to state that the
    texels become undefined if the external texture is bound while the
    underlying texels are modified.  This way any color conversion can be
    done (e.g. to a second buffer) when the texture is bound.

    Options:
    A) require the texture be unbound while the EGLImage is being modified
    B) Require the texture to be bound (or re-bound if already bound)
        between modification and use (i.e. after modification and before
        used as a texture).
    C) No requirement.

    RESOLVED: B

6.  How can current generation hardware support planar YUV EGLImage formats?

    GLES 2.0 hardware can perform color conversion by inserting
    extra instructions into the shader program.  However, planar textures
    require 2 or 3 surfaces to be read in order to sample a single texture.
    One solution is to increase the number of texture image units required
    by a texture object which is associated with such an EGLImage.

    RESOLVED: allow the implementation to set the number of texture
    image units required by each texture object.  Allow the app to query
    this with REQUIRED_TEXTURE_IMAGE_UNITS_OES.  Have drawing commands
    fail (INVALID_OPERATION) when the number of texture image units
    required by all enabled/referenced texture units exceeds the
    implementation limit (which can be queried with
    MAX_COMBINED_TEXTURE_IMAGE_UNITS, MAX_VERTEX_TEXTURE_IMAGE_UNITS, and
    MAX_TEXTURE_IMAGE_UNITS)

    See also issue 10.

7.  Should there be new texture sampling functions for samplerExternalOES
    or is it OK to use the existing 2D sampler functions.

    RESOLVED: Use existing 2D sampler functions.

8.  If an EGLImage associated with an external texture does not contain an
    alpha channel, should the alpha be 1 or undefined.

    From an app point of view, 1 probably makes more sense.
    However, if the texture is in a RGBA format and there is garbage in
    the A channel, it may be difficult for implementations to return 1.
    An implementation may have to recompile the shader to force the alpha
    channel to 1.

    RESOLVED: alpha is defined to be 1 in this case.

9.  How should the color conversion be described.

    Options:

    A) State that the color values are transformed to a linear colorspace
    and represented as RGB values in that space.  This may be difficult
    for implementations since it may require nonlinear transformations
    (e.g. gamma decoding).  It is also problematic because usually many
    more bits are required to represent a value in a linear colorspace
    than in a gamma encoded colorspace.

    B) State that the color is transformed to RGB but in the same
    colorspace as the source image (i.e. no gamma encode or decode).

    RESOLVED: Option B.

10. How does the implementation indicate which texture samplers and/or
    texture units are not available when one or more external textures are
    bound.

    See discussion on GLES email list around Feb 23 with
    subject "RE: [OpenGL-ES] IL/ES interaction: YUV texture extension
    proposal"

    Proposals:

    A) The MAX_COMBINED_TEXTURE_IMAGE_UNITS,
    MAX_VERTEX_TEXTURE_IMAGE_UNITS, and MAX_TEXTURE_IMAGE_UNITS parameters
    change to reflect the current state.

    B) New queries AVAILABLE_COMBINED_TEXTURE_IMAGE_UNITS,
    AVAILABLE_VERTEX_TEXTURE_IMAGE_UNITS, and
    AVAILABLE_TEXTURE_IMAGE_UNITS indicate current state, while
    MAX_COMBINED_TEXTURE_IMAGE_UNITS, MAX_VERTEX_TEXTURE_IMAGE_UNITS, and
    MAX_TEXTURE_IMAGE_UNITS remain constant and indicate the state when no
    external textures are bound.

    C) Query for number of required texture image units per texture
    object.  Draw calls fail with INVALID_OPERATION if the current
    requirements for texture image units exceeds the number available.

    RESOLVED: C

11. What happens when glUniform1i() sets a sampler to a value that is
    larger than the number of available texture units?

    NOTE: This issue no longer affects this extension.  See issue 10 for
    different issue related to texture *image* units.

    This is really a GLES2 spec issue.  See
        khronos bug 3702
        https://cvs.khronos.org/bugzilla/show_bug.cgi?id=3702
        http://www.khronos.org/members/login/list_archives/arb-glsl/
                                                      0705/msg00010.html
        http://www.khronos.org/members/login/list_archives/opengl_es/
                                                      0902/msg00148.html

    RESOLVED: The issue is not resolved, but it no longer applies
    directly to this extension.  Further discussion should be in bug 3702.

12. What happens at draw time when the current state requires more texture
    units than the implementation can support?

    RESOLVED:  The precedent, from (desktop) OpenGL, is to fail in
    glValidate, and to fail in any draw call with an INVALID_OPERATION
    error.  Behavior described in this extension will match that
    precedent.

13. How can this be conformance tested?

    In the native code, add a function which takes as a
    parameter an array of pixels.  The function returns an EGLImage which
    contains the pixels in some unspecified format.  A test can call this
    function, call glEGLImageTargetTexture2DOES() to associate it with an
    external texture, and render using this texture, and read back the
    framebuffer to confirm that the result is the expected result.

    Note1: since the format is unknown and unknowable, possibly only the
    high bit of each component (RGB) should be tested.  It may be
    sufficient to pass a single pixel (or single bit for each of R, G, an
    B) and then create the EGLImage with every pixel in the image set to
    that same value.

    Note2: It might be a good idea to have an extra parameter, int index,
    which allows the function to be implemented several different ways.
    The test could be run several times, with index set to 0, 1, 2, ...
    until the function returns EGL_NO_IMAGE.  This way the function could
    generate EGLImages with various formats.  For example when index is 0
    it could call OMX IL to generate a YUV planar EGLImage, when index is
    1 it could call OMX AL to generate a YUV interleaved EGLImage, and
    when index is 2 it could call into VG to generate an RGB EGLImage.
    The meaning of each index would be up to the implementation.  A simple
    implementation might return an EGLImage when index=0 and return
    EGL_NO_IMAGE otherwise.

    Additional suggestion from Jon Leech:
    The suggested conformance test in issue 13 is intentionally so vague
    on precision (1 bit/component) that the conversion language seems even
    less meaningful. The RGB bits that come out of texture sampling would
    need have almost no relationship to what went in. ISTM the supplier of
    the EGLImage knows the precision of it, and that information could be
    provided to the test to put on tighter constraints.

    RESOLVED: As described above.

14. Can the number of uniforms required by a shader change when switching
    from one external texture to another, and therefore cause the shader
    to fail?  For example, imagine a program does this:
        glLinkProgram(prog); // successful link
        sampler = glGetUniformLocation(prog, "myExtSampler");
        glUniform1i(sampler, 1);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_EXTERNAL, myTex1_rgb);
        glDrawArrays(); // draw successfully

        glBindTexture(GL_TEXTURE_EXTERNAL, myTex2_yuv);
        glDrawArrays();  // Can this fail???
    Is it acceptable for an implementation to fail the second
    glDrawArrays() call because myTex2_yuv is a yuv image and requires
    more uniforms to implement a color conversion matrix than myTex1_rgb
    which is an rgb image and does not require any conversion matrix?

    Note that this situation will only occur on implementation which will
    recompile the shader based on the color conversion required.

    Options:

    A) No, the implementation is not allowed to fail.  When the program is
    linked the implementation must verify that there are enough uniforms
    to implement the program for any flavor of external texture.  If the
    implementation does not provide enough uniforms for the program to
    work with any external texture that the implementation supports, then
    the implementation must fail at link time.

    B) Yes, the implementation may fail in glDrawArrays or glDrawElements
    if the number of uniforms required by the program exceeds those
    available.  This means that a call to glUniform1i() or glBindTexture()
    can cause a shader program that used to work to stop working.  (Note
    that this is possible anyway since the new external texture may use
    more texture image units than the old external texture (independent of
    the number of uniforms). But that can be detected by the application
    by querying REQUIRED_TEXTURE_IMAGE_UNITS_OES)

    RESOLVED: choice B.

15. How should filtering of non-RGB formats be specified.

    Options:

    A) filtering occurs before transformation to RGB.
    B) filtering occurs after transformation to RGB.
    C) undefined (up to the implementation)

    RESOLVED: C

If either EGL 1.1 or the EGL_OES_image extension is not supported, all
discussion of EGLImages should be ignored, and any calls to
EGLImageTargetTexture2DOES should generate the error INVALID_OPERATION.

If GL_OES_EGL_image is supported then change the text in both extensions
to allow either TEXTURE_2D or TEXTURE_EXTERNAL_OES to be passed as the
<target> parameter to EGLImageTargetTexture2DOES().  When <target> is
TEXTURE_2D, behavior of EGLImageTargetTexture2DOES() is as described in
the GL_OES_EGL_image spec.  When <target> is TEXTURE_EXTERNAL_OES,
behavior of EGLImageTargetTexture2DOES() is as described in this spec.

#25 - (April 6, 2018) H1Gdev
    Fix typo.
#24 - (April 23, 2015) Jon Leech)
    - Fix typo EGLImageTargetTexImage2DOES -> EGLImageTargetTexture2DOES
      (Bug 8114). Improve description of supported queries for new
      tokens (Bug 8118).
#23 - (July 19, 2012) Acorn Pooley
    - fix extension name from OES_EGL_image_external to
       GL_OES_EGL_image_external
#22 - (Dec 17, 2010) Acorn Pooley
    status to ratified.
#21 - (Sept. 29, 2010) Maurice Ribble
    Update token numbers and updated status to approved.
#20 - (April 2, 2009) Acorn Pooley
    Rename GL_OES_egl_image_external to GL_OES_EGL_image_external to be
    consistant with GL_OES_EGL_image.
#19 - (March 31, 2009) Acorn Pooley
    Minor fixes
#18 - (March 30, 2009) Acorn Pooley
    Fix inconsistancy
#17 - (March 25, 2009) Acorn Pooley
    Resolved issue 4 (and some others)
#16 - (March 16, 2009) Acorn Pooley
    Augment issue 13
#15 - (March 13, 2009) Acorn Pooley
    fix dependancy section
    resolve issue 14 and fix text
#14 - (March 9, 2009) Acorn Pooley
    Fix colorspace comments.  Issue 9 is resolved.
#13 - (March 6, 2009) Acorn Pooley
    Mark issue 6, 10, and 11 resolved.
    Add issue 15.
#12 - (March 4, 2009) Acorn Pooley
    Fix wording of uniform stuff.
#11 - (March 4, 2009) Acorn Pooley
    Add issues 13, 14.
    Add comments about extra uniforms required by external texture
    samplers.
    Allow external textures to work with default object 0.
    Correct colorspace language.
#10 - (March 3, 2009) Acorn Pooley
    Remove stale reference to MAX_TEXTURE_IMAGE_UNITS.  Add fix to OpenGL
    ES 2.0 section 2.10.5 (from bruce).  Add contributors. Clarify
    "texture unit" vs "texture image unit".  Fix typos.
#9 - (February 26, 2009) Acorn Pooley
    Clarify sync further.  Add issue 12.  Change "too many texture units"
    behavior.
#8 - (February 26, 2009) Acorn Pooley
    Clarify sync requirements (i.e. that EGLImage does not do sync)
#7 - (February 25, 2009) Acorn Pooley
    Relax binding requirement - see issue 5
#6 - (February 25, 2009) Acorn Pooley
    Add TEXTURE_BINDING_EXTERNAL_OES.  Add texture state notes.  Modify
    colorspace conversion to be a linear function.
#5 - (February 24, 2009) Acorn Pooley
    Disable GenerateMipmaps.  Add issues 10 & 11.
#4 - (February 23, 2009) Acorn Pooley
    Modify the "Texture Parameters" section in ES 1 and 2 specs
#3 - (February 20, 2009) Acorn Pooley
    Clarify the reduction in number of texture units.
#2 - (February 20, 2009) Acorn Pooley
    Fix some errors.  replace textureExternal* sampler functions with
    existing sampler2D* functions.  Add issue 7,8,9.  Fix spelling.
#1 - (February 9, 2009) Original draft