extensions/ARB/ARB_internalformat_query.txt

Name

    ARB_internalformat_query

Name Strings

    GL_ARB_internalformat_query

Contact

    Jan-Harald Fredriksen (jan-harald.fredriksen 'at' arm.com)
    Daniel Koch (daniel 'at' transgaming 'dot' com)

Contributors

    Bruce Merry, ARM
    Daniel Koch, Transgaming
    Acorn Pooley, NVIDIA
    Christophe Riccio, Imagination Technologies

Notice

    Copyright (c) 2011-2013 The Khronos Group Inc. Copyright terms at
        http://www.khronos.org/registry/speccopyright.html

Specification Update Policy

    Khronos-approved extension specifications are updated in response to
    issues and bugs prioritized by the Khronos OpenGL 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

Status

    Complete. Approved by the ARB on 2011/06/20.
    Approved by the Khronos Promoters on 2011/07/29.

Version

    Last Modified Date: June 13, 2011
    Revision: 7

Number

    ARB Extension #112

Dependencies

    OpenGL 3.0 or ARB_framebuffer_object is required.

    This extension is written against the OpenGL 4.1 (Core Profile)
    Specification (July 25, 2010).

    ARB_texture_multisample affects the definition of this extension.

Overview

    OpenGL 4.1 has a number of queries to indicate the maximum number of
    samples available for different formats. These give a coarse-grained
    query mechanism e.g. an implementation can expose different sample
    counts for integer and floating-point formats, but not for different
    floating-point formats. There is also no convenient way for the user
    to determine the granularity of sample counts available, only the
    maximum.

    This extension adds a query mechanism that allows the user to
    determine which sample counts are available for a specific internal
    format.

IP Status

    No known IP claims.

New Procedures and Functions

    void GetInternalformativ(enum target, enum internalformat,
                             enum pname, sizei bufSize, int *params);

New Types

    None.

New Tokens

    Accepted by the <target> parameter of GetInternalformativ:

        RENDERBUFFER
        TEXTURE_2D_MULTISAMPLE
        TEXTURE_2D_MULTISAMPLE_ARRAY

    Accepted by the <pname> parameter of GetInternalformativ:

        SAMPLES
        NUM_SAMPLE_COUNTS                          0x9380

Additions to Chapter 2 of the OpenGL 4.1 (Core Profile) Specification
(OpenGL Operation)

    None.

Additions to Chapter 3 of the OpenGL 4.1 (Core Profile) Specification
(Rasterization)

    In section 3.8.6 (Multisample Textures), replace the bulleted
    list of error conditions (for exceeding MAX_*_SAMPLES) and the
    preceeding sentence with:

        "The error INVALID_OPERATION will be generated if <samples> is
        greater than the maximum number of samples supported for this
        <target> and <internalformat>, which can be determined by
        calling GetInternalformativ with a <pname> of SAMPLES (see
        section 6.X)."

    In the following paragraph, remove "or if samples is greater
    than MAX_SAMPLES".

Additions to Chapter 4 of the OpenGL 4.1 (Core Profile) Specification
(Per-Fragment Operations and the Frame Buffer)

    In section 4.4.2 (Attaching Images to Framebuffer Objects), under
    the description of RenderbufferStorageMultisample:

    Replace

        "If either <width> or <height> is greater than the value of
        MAX_RENDERBUFFER_SIZE, or if <samples> is greater than the value
        of MAX_SAMPLES, then the error INVALID_VALUE is generated. If
        <internalformat> is a signed or unsigned integer format and
        <samples> is greater than the value of MAX_INTEGER_SAMPLES, then
        the error INVALID_OPERATION is generated (see ``Required
        Renderbuffer Formats'' below)."

    with

        "If either <width> or <height> is greater than the value of
        MAX_RENDERBUFFER_SIZE then the error INVALID_VALUE is
        generated. If <samples> is greater than the maximum number of
        samples supported for <internalformat> then the error
        INVALID_OPERATION is generated (see GetInternalformativ in
        section 6.X)."

Additions to Chapter 5 of the OpenGL 4.1 (Compatibility Profile)
Specification (Special Functions)

    Add GetInternalformativ to the list of commands not included in
    display lists.

Additions to Chapter 6 of the OpenGL 4.1 (Core Profile) Specification
(State and State Requests)

    Add a new section 6.1.X "Internalformat queries"

    Information about implementation-dependent support for internal
    formats can be queried with the command

    void GetInternalformativ(enum target, enum internalformat,
                             enum pname, sizei bufSize, int *params);

    <internalformat> must be color-renderable, depth-renderable or
    stencil-renderable (as defined in section 4.4.4).

    <target> indicates the usage of the <internalformat>, and must be
    one of RENDERBUFFER, TEXTURE_2D_MULTISAMPLE, or
    TEXTURE_2D_MULTISAMPLE_ARRAY, corresponding to usage as a
    renderbuffer, 2D multisample texture, or 2D multisample array
    texture.

    No more than <bufSize> integers will be written into <params>. If
    more data are available, they will be ignored and no error will be
    generated.

    <pname> indicates the information to query, and is one of the
    following:

    - SAMPLES: The sample counts supported for this <format> and
      <target> are written into <params>, in descending order. Only
      positive values are returned.
    - NUM_SAMPLE_COUNTS: The number of sample counts that would be
      returned by querying SAMPLES is returned in <params>.

    Note that querying SAMPLES with a <bufSize> of 1 will return just
    the maximum supported number of samples for this format.

    The maximum value in SAMPLES is guaranteed to be at least the lowest
    of the following:
    - The value of GetIntegerv(MAX_INTEGER_SAMPLES), if <internalformat>
      is a signed or unsigned integer format.
    - The value of GetIntegerv(MAX_DEPTH_TEXTURE_SAMPLES), if
      <internalformat> is a depth/stencil-renderable format and <target>
      is TEXTURE_2D_MULTISAMPLE or TEXTURE_2D_MULTISAMPLE_ARRAY.
    - The value of GetIntegerv(MAX_COLOR_TEXTURE_SAMPLES), if
      <internalformat> is a color-renderable format and <target> is
      TEXTURE_2D_MULTISAMPLE or TEXTURE_2D_MULTISAMPLE_ARRAY.
    - The value of GetIntegerv(MAX_SAMPLES).

Additions to Appendix A of the OpenGL 4.1 (Core Profile) Specification
(Invariance)

    None.

Additions to Appendix D of the OpenGL 4.1 (Core Profile) Specification
(Shared Objects and Multiple Contexts)

    None.

GLX Protocol

    XXX - TODO.

Dependencies on ARB_texture_multisample

    If OpenGL 3.2 or ARB_texture_multisample is not supported, then
    TEXTURE_2D_MULTISAMPLE and TEXTURE_2D_MULTISAMPLE_ARRAY are not
    supported <target> parameters to GetInternalformativ.

Dependencies on OpenGL ES

    If implemented on OpenGL ES (together with an extension adding
    RenderbufferStorageMultisample), then this extension behaves as
    specified, except:

    - Ignore all references to multisample textures and display lists.
    - Ignore all references to MAX_COLOR_TEXTURE_SAMPLES,
      MAX_DEPTH_TEXTURE_SAMPLES, MAX_INTEGER_SAMPLES and MAX_SAMPLES.

Errors

    If the <internalformat> parameter to GetInternalformativ is not
    color-, depth- or stencil-renderable, then an INVALID_ENUM error is
    generated.

    If the <target> parameter to GetInternalformativ is not one of
    TEXTURE_2D_MULTISAMPLE, TEXTURE_2D_MULTISAMPLE_ARRAY or RENDERBUFFER
    then an INVALID_ENUM error is generated.

    If the <pname> parameter to GetInternalformativ is not SAMPLES
    or NUM_SAMPLE_COUNTS, then an INVALID_ENUM error is generated.

    If the <bufSize> parameter to GetInternalformativ is negative,
    then an INVALID_VALUE error is generated.

    If the <samples> parameter to TexImage2DMultisample,
    TexImage3DMultisample or RenderbufferStorageMultisample is greater
    than the maximum number of samples supported for the target and
    internalformat, an INVALID_OPERATION error is generated.

    An INVALID_VALUE error is no longer generated if the <samples>
    argument to TexImage2DMultisample, TexImage3DMultisample or
    RenderbufferStorageMultisample is greater than the value of
    GetIntegerv(MAX_SAMPLES).

New State

    None.

New Implementation Dependent State

    Changes to table 6.52, p. 393 (Implementation Dependent Values)

                                                                Minimum
    Get Value                  Type    Get Command              Value    Description                            Sec.
    ---------                  ----    -----------              -------  ------------------------------------   -----
    MAX_DEPTH_TEXTURE_SAMPLES  Z+      GetIntegerv               1       Maximum number of samples supported    6.1.X
                                                                         for all depth/stencil formats in a
                                                                         multisample texture
    MAX_COLOR_TEXTURE_SAMPLES  Z+      GetIntegerv               1       Maximum number of samples supported    6.1.X
                                                                         for all color formats in a
                                                                         multisample texture
    MAX_INTEGER_SAMPLES        Z+      GetIntegerv               1       Maximum number of samples supported    6.1.X
                                                                         for all integer format multisample
                                                                         buffers

    (only the description and section numbers change)

    Changes to table 6.54, p. 395 (Framebuffer Dependent Values)

                                                                Minimum
    Get Value                  Type    Get Command              Value    Description                            Sec.
    ---------                  ----    -----------              -------  ------------------------------------   -----
    MAX_SAMPLES                Z+      GetIntegerv               4       Maximum number of samples supported    6.1.X
                                                                         for all non-integer formats

    (only the description and section number change - note this query should
    probably be in table 6.52 to start with)

    Add new table 6.X Internalformat-specific Implementation Dependent Values after 6.52

                                                                Minimum
    Get Value                  Type    Get Command              Value    Description                            Sec.
    ---------                  ----    -----------              -------  ------------------------------------   -----
    SAMPLES                    0*xZ+   GetInternalformativ       fn1     Supported sample counts                6.X
    NUM_SAMPLE_COUNTS          Z+      GetInternalformativ       1       Number of supported sample counts      6.X

    fn1: see section 6.X.

Sample Code

    To determine all the sample counts available for a specific
    renderbuffer format:

    GLint *samples;
    GLint samples_length, i;

    glGetInternalformativ(GL_RENDERBUFFER, format,
                          GL_NUM_SAMPLE_COUNTS, 1, &samples_length);
    samples = malloc(samples_length * sizeof(GLint));
    glGetInternalformativ(GL_RENDERBUFFER, format,
                          GL_SAMPLES, samples_length, samples);
    for (i = 0; i < samples_length; i++)
    {
        printf("Format %#x supports %d samples\n", samples[i]);
    }

    To determine the maximum sample count available for a specific
    renderbuffer format:

    GLint max_samples;
    glGetInternalformativ(GL_RENDERBUFFER, format,
                          GL_SAMPLES, 1, &max_samples);

Conformance Tests

    1. Test each of the error conditions described in Errors.

    2. For each format that is not color-, depth- or stencil-renderable
    (if any), test that INVALID_ENUM is generated if passed to
    GetInternalformativ (e.g. LUMINANCE_ALPHA).

    3. Call GetInternalformativ for each <pname> in turn with a
    <bufSize> of zero; check that <params> is not modified and that no
    error results.

    4. For each color-, depth- or stencil-renderable format and each
    target:
       4.1. Query NUM_SAMPLE_COUNTS and verify that it is greater than
       zero.
       4.2. Query SAMPLES, using a larger-than-necessary buffer, and
       check that only NUM_SAMPLE_COUNTS values are written.
       4.3. Check that the values returned by SAMPLES are all positive
       and strictly decreasing.
       4.4. Query MAX_SAMPLES and check that it matches the first value
       returned by SAMPLES.
       4.5. Check that MAX_SAMPLES is at least the lower bound computed
       from MAX_SAMPLES, MAX_INTEGER_SAMPLES, MAX_COLOR_TEXTURE_SAMPLES
       and MAX_DEPTH_TEXTURE_SAMPLES.
       4.6. Check that MAX_SAMPLE_MASK_WORDS is at least
       ceil(MAX_SAMPLES / 32).

Issues

    1) Should we have the MAX_SAMPLES query as well as the SAMPLES
    query? It's syntactic sugar (since you can just take the largest
    value in the SAMPLES array), but very convenient sugar since you
    don't have to allocate a dynamically-sized array. It also simplifies
    the specification.

    RESOLVED: no, we don't need it. Passing a <bufSize> of 1 when
    querying SAMPLES gives the same effect.

    2) Should we explicitly include 0 in the list of sample counts
    (meaning "not multisampled")? It might allow one to indicate that certain
    formats are flat-out unsupported with certain targets but supported with
    others.

    RESOLVED: no, we would rather layer on a separate <pname> later.

    3) For multisample textures, is a per-target query too fine-grained?
    Should the <target> just be TEXTURE instead of
    TEXTURE_2D_MULTISAMPLE[_ARRAY]?

    RESOLVED: Keep the per-target query as it may useful to distinguish
    results for some future values of <pname>.

    4) What should the new command be called?

    RESOLVED: GetInternalformativ

    GetInternalformativ is potentially confusing, but consistent with
    GL precedent such as GetQueryiv (which returns information such as
    the number of bits supported for a specific query target).

    5) What should the query of the number of samples counts be called?

    RESOLVED: NUM_SAMPLE_COUNTS

    The original proposal was NUM_SAMPLES, which is consistent with
    NUM_COMPRESSED_TEXTURE_FORMATS. However, it's confusing because what
    is being queried is not the number of samples (whereas
    NUM_COMPRESSED_TEXTURE_FORMATS is the number of compressed texture
    formats). NUM_SAMPLE_COUNTS is also consistent with the
    NUM_COMPRESSED_TEXTURE_FORMATS precedent and the description of this
    value.

    Another proposal was SAMPLES_LENGTH, but this is misleading
    because in OpenGL LENGTH is only used for string length.

    6) What should GetIntegerv(MAX_INTEGER_SAMPLES) and similar queries
    return (excluding MAX_SAMPLES - see next issue)?

    Discussion: there are (at least) two options:

    A. Querying MAX_INTEGER_SAMPLES returns a count that is guaranteed
    to be supported for all integer formats, but some integer formats
    may support more samples and the existing errors are relaxed to
    allow this.

    B. Require that all integer formats support the same maximum number
    of samples, and GetInternalformativ becomes an alternative
    interface to the same set of limits.

    RESOLVED: option A.

    7) What should GetIntegerv(MAX_SAMPLES) return?

    In OpenGL 4.1, MAX_SAMPLES serves two purposes.
    A. An upper bound on the number of samples supported for any format.
    This manifests in INVALID_VALUE errors when trying to use more than
    this number.
    B. A number of samples that is guaranteed to be supported for all
    formats that don't fall into certain classes (such as integer
    formats).

    Backwards compatibility would suggest that it should return option
    B in future, although this leaves no way to determine the maximum
    number of samples supported for any format unless a new query is
    introduced.

    RESOLVED: option B.

    8) Does this extension make the MAX_SAMPLES query unnecessary?

    RESOLVED: MAX_SAMPLES will need to be retained in API versions where
    it already exists (for backwards compatibilities), but there is no
    need to add it as this query provides more accurate information and
    it is expected that shipping hardware will support different numbers
    of samples for different formats.

    9) Can we query additional properties supported for an internal format
    in addition to multisample-related information with this API?

    RESOLVED: DEFERRED. Yes this API is suitable for that, but the
    specification is left for a layered extension.

    Other possible <pnames> include:
      MAX_WIDTH
        - maximum width of object
      MAX_HEIGHT
        - maximum height of object
      MAX_DEPTH
        - maximum depth/# of layers of object
      MAX_COMBINED_SIZE
        - maximum size of object (w*h*d) (due to implementation-specific
          limitations)
      FRAMEBUFFER_RENDERABLE
        - can be rendered to via FBO attachment
      FRAMEBUFFER_RENDERABLE_BLEND
        - can be rendered to via FBO attachment when blending is enabled
      MIPMAPS
        - more than one mipmap can be supported
      GENERATE_MIPMAPS
        - is generate mipmaps supported
      READPIXEL
        - framebuffers with this internal format can be read directly with
          an appropriate format/type by ReadPixels
      FILTER_LINEAR
        - can the MIN/MAG filter be set to LINEAR values? Are filters other
          than NEAREST supported?
      SRGB_READ
        - texture reads from this internalformat occur in SRGB colorspace
      SRGB_WRITE
        - framebuffers with this internalformat can be rendered to with
          FRAMEBUFFER_SRGB enabled
      SRGB_DECODE
        - textures of this format support toggling TEXTURE_SRGB_DECODE
          (ie EXT_texture_sRGB_decode)
      VERTEX_TEXTURE
        - textures with this internalformat can be sampled from vertex shaders
      TESS_CONTROL_TEXTURE
        - textures with this internalformat can be sampled from tessellation
          control shaders
      TESS_EVALUATION_TEXTURE
        - textures with this internalformat can be sampled from tessellation
          evaluation shaders
      GEOMETRY_TEXTURE
        - textures with this internalformat can be sampled from geometry shaders
      FRAGMENT_TEXTURE
        - textures with this internalformat can be sampled from fragment shaders
      TEXTURE_SHADOW
        - textures with this internalformat support shadow samplers
      TEXTURE_GATHER
        - textures with this internalformat support texture gather operations
      TEXTURE_GATHER_SHADOW
        - textures with this internalformat support texture gather operations
          with shadow samplers
      SHADER_IMAGE_LOAD
        - textures with this internalformat support image load operations
          from shaders
      SHADER_IMAGE_STORE
        - textures with this internalformat support image store operations
          from shaders
      SHADER_IMAGE_ATOMIC
        - textures with this internalformat support atomic memory operations
          from shaders
      FORMAT_SUPPORTED
        - the requested internal format is known and supported for at least
          some subset of the possible operations
      ACTUAL_INTERNALFORMAT
        - the actual internalformat used by the implementation when the
          specified internalformat is requested
      PERFORMANCE_HINT
        - an indication that this format will or may operate at reduced
          performance in some cases (should this be a bitfield, array,
          or a specific bit on each of the other queries?)

    Possible values for some of the above pnames:
        - HARDWARE (or SUPPORTED), SOFTWARE (or CAVEAT), UNSUPPORTED.

    Additional Values for <target> that would be valid for
      TEXTURE_1D
      TEXTURE_1D_ARRAY
      TEXTURE_2D
      TEXTURE_2D_ARRAY
      TEXTURE_3D
      TEXTURE_CUBE_MAP
      TEXTURE_CUBE_MAP_ARRAY
      TEXTURE_RECTANGLE
      TEXTURE_BUFFER
    Could also consider meta targets such as:
      ALL
      ANY
      TEXTURE


    10) Is the <target> parameter required?  If so, should it be the first or
    second parameter?

    RESOLVED:
    a) Yes. It is possible that in some implementations and for some of the possible
    uses of this query, that the results will depend on the texture target.
    b) First parameter. All other entry points that take a <target> have it as the
    first parameter.

Revision History

    Revision 7, 2011/06/13 dgkoch
      - recast as ARB extension

    Revision 6, 2011/05/19 dgkoch
      - resolved issue 3, 9 per F2F.

    Revision 5, 2011/05/16 dgkoch
      - resolved issue 10 per F2F. Keep target; as the first parameter.
      - fix extension name
      - updates to Issue 9

    Revision 4, 2011/05/11 dgkoch
      - also fix the formal paramter in the New Functions area
      - updates to issue 9, added issue 10

    Revision 3, 2011/05/05 dgkoch
      - rename the formal parameter from 'format' to 'internalformat'
        to match the spec body.
      - changed SAMPLES_LENGTH to NUM_SAMPLE_COUNTS
      - added issue 9

    Revision 2, 2011/04/21 bmerry
      - Fix typo InternalFormat -> Internalformat
      - Removed per-format MAX_SAMPLES query
      - Marked issues 1, 2, and 4-7 as resolved

    Revision 1, 2011/04/13 bmerry
      - First draft.