xref: /third_party/openGLES/extensions/ARB/ARB_texture_multisample.txt (revision 5bd8dead)

Name

    ARB_texture_multisample

Name Strings

    GL_ARB_texture_multisample

Contact

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

Notice

    Copyright (c) 2009-2014 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 July 3, 2009.

Version

    Last Modified Date:         February 28, 2014
    Revision:                   12

Number

    ARB Extension #67

Dependencies

    This extension is written against the OpenGL 3.1 specification.

Overview

    This extension provides support for two new types of "multisample
    textures" - two-dimensional and two-dimensional array - as well as
    mechanisms to fetch a specific sample from such a texture in a shader,
    and to attach such textures to FBOs for rendering.

    This extension also includes the following functionality, first described
    in NV_explicit_multisample:

     * A query in the API to query the location of samples within the pixel

     * An explicit control for the multisample sample mask to augment the
       control provided by SampleCoverage

New Procedures and Functions

    void TexImage2DMultisample(enum target, sizei samples, enum internalformat,
                               sizei width, sizei height,
                               boolean fixedsamplelocations);

    void TexImage3DMultisample(enum target, sizei samples, enum internalformat,
                               sizei width, sizei height, sizei depth,
                               boolean fixedsamplelocations);

    void GetMultisamplefv(enum pname, uint index, float *val);

    void SampleMaski(uint index, bitfield mask);

New Tokens

    Accepted by the <pname> parameter of GetMultisamplefv:

        SAMPLE_POSITION                             0x8E50

    Accepted by the <cap> parameter of Enable, Disable, and IsEnabled, and by
    the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, and
    GetDoublev:

        SAMPLE_MASK                                 0x8E51

    Accepted by the <target> parameter of GetBooleani_v and
    GetIntegeri_v:

        SAMPLE_MASK_VALUE                           0x8E52

    Accepted by the <target> parameter of BindTexture and
    TexImage2DMultisample:

        TEXTURE_2D_MULTISAMPLE                      0x9100

    Accepted by the <target> parameter of TexImage2DMultisample:

        PROXY_TEXTURE_2D_MULTISAMPLE                0x9101

    Accepted by the <target> parameter of BindTexture and
    TexImage3DMultisample:

        TEXTURE_2D_MULTISAMPLE_ARRAY                0x9102

    Accepted by the <target> parameter of TexImage3DMultisample:

        PROXY_TEXTURE_2D_MULTISAMPLE_ARRAY          0x9103

    Accepted by the <pname> parameter of GetBooleanv, GetDoublev, GetIntegerv,
    and GetFloatv:

        MAX_SAMPLE_MASK_WORDS                       0x8E59
        MAX_COLOR_TEXTURE_SAMPLES                   0x910E
        MAX_DEPTH_TEXTURE_SAMPLES                   0x910F
        MAX_INTEGER_SAMPLES                         0x9110
        TEXTURE_BINDING_2D_MULTISAMPLE              0x9104
        TEXTURE_BINDING_2D_MULTISAMPLE_ARRAY        0x9105

    Accepted by the <pname> parameter of GetTexLevelParameter

        TEXTURE_SAMPLES                             0x9106
        TEXTURE_FIXED_SAMPLE_LOCATIONS              0x9107

    Returned by the <type> parameter of GetActiveUniform:

        SAMPLER_2D_MULTISAMPLE                      0x9108
        INT_SAMPLER_2D_MULTISAMPLE                  0x9109
        UNSIGNED_INT_SAMPLER_2D_MULTISAMPLE         0x910A
        SAMPLER_2D_MULTISAMPLE_ARRAY                0x910B
        INT_SAMPLER_2D_MULTISAMPLE_ARRAY            0x910C
        UNSIGNED_INT_SAMPLER_2D_MULTISAMPLE_ARRAY   0x910D

Additions to Chapter 2 of the OpenGL 3.1 Specification (OpenGL Operation)

    Add to table 2.9 "OpenGL Shading Language type tokens" page 56:

    Type Name Token                              Keyword
    -----------------------------------------    ------------
    SAMPLER_2D_MULTISAMPLE                       sampler2DMS
    SAMPLER_2D_MULTISAMPLE_ARRAY                 sampler2DMSArray
    INT_SAMPLER_2D_MULTISAMPLE_ARRAY             isampler2DMSArray
    UNSIGNED_INT_SAMPLER_2D_MULTISAMPLE          usampler2DMS
    UNSIGNED_INT_SAMPLER_2D_MULTISAMPLE_ARRAY    usampler2DMSArray

    Add to section 2.11.7, after subsection "Texel Fetches"

    Multisample Texel Fetches

    Multisample texel fetches are similar to standard texel fetches.
    Since multisample buffers can't have mipmaps, there is no LOD
    parameter. Instead, there is an integer parameter which selects the
    sample number to be fetched from the buffer. The number identifying
    the sample is the same as the value used to query the sample
    location using GetMultisamplefv. Multisample textures support only
    NEAREST filtering.

    Additionally, this fetch may only be performed on a multisample
    texture sampler. No other sample or fetch commands may be performed
    on a multisample texture sampler.

Additions to Chapter 3 of the OpenGL 3.1 Specification (Rasterization)

    (Insert into section 3.3.1, Multisampling after the discussion of
    the query for SAMPLES)

    The location of a given sample is queried with the command

        void GetMultisamplefv(enum pname, uint index, float *val);

    <pname> must be SAMPLE_POSITION and <index> corresponds to the
    sample for which the location should be returned. The sample
    location is returned as two floating point values in <val[0]> and
    <val[1]>, each between 0 and 1, corresponding to the <x> and <y>
    locations respectively in GL pixel space of that sample. (0.5, 0.5)
    thus corresponds to the pixel center. An INVALID_ENUM error is
    generated if <pname> is not SAMPLE_POSITION. An INVALID_VALUE error
    is generated if <index> is greater than or equal to the value of
    SAMPLES. If the multisample mode does not have fixed sample
    locations, the returned values may only reflect the locations of
    samples within some pixels.

    Modify Section 3.8.1, Texture Image Specification (p. 143)

    Add the two new targets to MAX_TEXTURE_SIZE description:

    In a similar fashion, the maximum allowable width of a texel array
    for a one or two-dimensional, one- or two-dimensional array,
    two-dimensional multisample, or two-dimensional multisample array
    texture, and the maximum allowable height of a two-dimensional,
    two-dimensional array, two- dimensional multisample, or
    two-dimensional multisample array texture, must be at least
    2^(k-lod)+2*b_t for image arrays of level 0 through k, where k is
    the log base 2 of MAX_TEXTURE_SIZE.

    (Insert new Section 3.8.4, Multisample Textures.  Renumber subsequent
    sections.)

    In addition to the texture types described in previous sections, two
    additional types of textures are supported. A multisample texture is
    similar to a two-dimensional or two-dimensional array texture,
    except it contains multiple samples per texel. Multisample textures
    do not have multiple image levels.

    The commands

        void TexImage2DMultisample(enum target, sizei samples,
                                   enum internalformat,
                                   sizei width, sizei height,
                                   boolean fixedsamplelocations);

        void TexImage3DMultisample(enum target, sizei samples,
                                   enum internalformat,
                                   sizei width, sizei height, sizei depth,
                                   boolean fixedsamplelocations);

    establish the data storage, format, dimensions, and number of
    samples of a multisample texture's image. For TexImage2DMultisample,
    <target> must be TEXTURE_2D_MULTISAMPLE or
    PROXY_TEXTURE_2D_MULTISAMPLE and for TexImage3DMultisample <target>
    must be TEXTURE_2D_MULTISAMPLE_ARRAY or
    PROXY_TEXTURE_2D_MULTISAMPLE_ARRAY. <width> and <height> are the
    dimensions in texels of the texture.

    <internalformat> must be color-renderable, depth-renderable, or
    stencil- renderable (as defined in section 4.4.4). The error
    INVALID_OPERATION may be generated if any of the following are true:

    * <internalformat> is a depth/stencil-renderable format and
      <samples> is greater than the value of MAX_DEPTH_TEXTURE_SAMPLES
    * <internalformat> is a color-renderable format and <samples> is
      greater than the value of MAX_COLOR_TEXTURE_SAMPLES
    * <internalformat> is a signed or unsigned integer format and
      <samples> is greater than the value of MAX_INTEGER_SAMPLES.

    If <fixedsamplelocations> is TRUE, the image will use identical
    sample locations and the same number of samples for all texels in
    the image, and the sample locations will not depend on the
    internalformat or size of the image. 

    An INVALID_VALUE error is generated by TexImage2DMultisample if <width>
    or <height> is greater than the value of MAX_TEXTURE_SIZE. An
    INVALID_VALUE error is generated by TexImage3DMultisample if <width>,
    <height>, or <depth> is greater than the value of MAX_3DTEXTURE_SIZE; An
    INVALID_VALUE error is generated if <samples> is greater than the value
    of MAX_SAMPLES. An OUT_OF_MEMORY error is generated if the GL is unable
    to create a texture level of the requested size.

    When a multisample texture is accessed in a shader, the access takes
    one vector of integers describing which texel to fetch and an
    integer corresponding to the sample numbers described in section
    3.3.1 describing which sample within the texel to fetch. No standard
    sampling instructions are allowed on the multisample texture
    targets.

    Modify Section 3.8.11, Texture Completeness (p. 154)

    (insert after first paragraph of section, p. 154)

    For multisample textures, a texture is complete if each dimension of
    the texture's level is positive.

    Modify Section 3.8.12, Texture State and Proxy State (p. 155)

    (insert into the first paragraph of the section, p. 155)

    ... the compressed flag set to FALSE, and a zero compressed size).
    Multisample textures contain an integer identifying the number of
    samples in each texel. The buffer texture target has associated an
    integer containing ...

    (add a new paragraph after the paragraph starting with "Proxy Arrays...")

    Proxy array for two-dimensional multisample and two-dimensional
    multisample array textures are operated on in the same way when
    TexImage2DMultisample is called with <target> specified as
    PROXY_TEXTURE_2D_MULTISAMPLE, or TexImage3DMultisample is called
    with <target> specified as PROXY_TEXTURE_2D_MULTISAMPLE_ARRAY.

    Modify Section 3.8.13, Texture Objects (p. 157)

    (modify first paragraphs of section, p. 157, simply adding
     references to multisample textures)

    In addition to the default textures TEXTURE_1D, TEXTURE_2D,
    TEXTURE_3D, TEXTURE_1D_ARRAY, TEXTURE_2D_ARRAY, TEXTURE_RECTANGLE,
    TEXTURE_BUFFER, TEXTURE_CUBE_MAP, TEXTURE_2D_MULTISAMPLE, and
    TEXTURE_2D_MULTISAMPLE_ARRAY, named one-, two-, and
    three-dimensional, one- and two-dimensional array, rectangular,
    buffer, cube map, two-dimensional multisample, and two- dimensional
    multisample array texture objects can be created and operated upon.
    The name space for texture objects is the unsigned integers, with
    zero reserved by the GL.

    ...

    In the initial state, TEXTURE_1D, TEXTURE_2D, TEXTURE_3D,
    TEXTURE_1D_ARRAY, TEXTURE_2D_ARRAY, TEXTURE_RECTANGLE,
    TEXTURE_BUFFER, TEXTURE_CUBE_MAP, TEXTURE_2D_MULTISAMPLE, and
    TEXTURE_2D_MULTISAMPLE_ARRAY have one-, two-, and three-dimensional,
    one- and two-dimensional array, rectangular, buffer, cube map,
    two-dimensional multisample, and two-dimensional multisample array
    texture state vectors respectively associated with them. In order
    that access to these initial textures not be lost, they are treated
    as texture objects all of whose names are 0. The initial one-, two-,
    three- dimensional, one- and two-dimensional array, rectangular,
    buffer, cube map, two-dimensional multisample, and two-dimensional
    multisample array texture is therefore operated upon, queried, and
    applied as TEXTURE_1D, TEXTURE_2D, TEXTURE_3D, TEXTURE_1D_ARRAY,
    TEXTURE_2D_ARRAY, TEXTURE_RECTANGLE, TEXTURE_BUFFER,
    TEXTURE_CUBE_MAP, TEXTURE_2D_MULTISAMPLE, and
    TEXTURE_2D_MULTISAMPLE_ARRAY respectively while 0 is bound to the
    corresponding targets.

    (modify second paragraph, p. 158)

    The texture object name space, including the initial one-, two-, and
    three-dimensional, one- and two-dimensional array, rectangular,
    buffer, cube map, two-dimensional multisample, and two-dimensional
    multisample array texture objects, is shared among all texture
    units. A texture object may be bound to more than one texture unit
    simultaneously. After a texture object is bound, any GL operations
    on that target object affect any other texture units to which the
    same texture object is bound.

Additions to Chapter 4 of the OpenGL 3.1 Specification (Per-Fragment
Operations and the Frame Buffer)

    Modify Section 4.1.3, Multisample Fragment Operations

    Modify the first paragraph to include SAMPLE_MASK and
    SAMPLE_MASK_VALUE on the list of values the coverage value is
    modified based on.

    Modify the discussion of SAMPLE_COVERAGE to start with "Next" instead of
    "Finally"

    Add after the discussion of SAMPLE_COVERAGE:

    Finally, if SAMPLE_MASK is enabled, the fragment coverage is ANDed
    with the coverage value SAMPLE_MASK_VALUE. The value of
    SAMPLE_MASK_VALUE is specified using

        void SampleMaski(GLuint index, GLbitfield mask);

    with <mask> set to the desired mask for <maskNumber>.
    SAMPLE_MASK_VALUE is queried by calling GetIntegeri_v with <pname>
    set to SAMPLE_MASK_VALUE and the index set to <maskNumber>. Bit B of
    mask M corresponds to sample 32*M+B as described in Section 3.3.1.
    The error INVALID_VALUE is generated if the mask word indexed is
    greater than or equal to MAX_SAMPLE_MASK_WORDS.

    Modify Section 4.4.2, Attaching Images to Framebuffer Objects, p. 203

    (the first paragraph of RenderbufferStorageMultisample p. 205)

    ... 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). ...

    (The second paragraph of "Required Renderbuffer Formats" p. 206):

    Implementations must support creation of renderbuffers in these
    required formats with up to the value of MAX_SAMPLES multisamples,
    with the exception that the signed and unsigned integer formats are
    required only to support creation of renderbuffers with up to the
    value of MAX_INTEGER_SAMPLES multisamples, which must be at least
    one.

    Modify the description of FrameBufferTextureARB in
    ARB_geometry_shader4, to allow multisample array textures with
    FramebufferTextureARB:

    If <texture> is the name of a three-dimensional texture, cube map
    texture, one- or two-dimensional array texture, or two-dimensional
    multisample array texture, the texture level attached to the
    framebuffer attachment point is an array of images, and the
    framebuffer attachment is considered layered.

    (At the end of p. 208, describing FrameBufferTexture*D)

    If <textarget> is TEXTURE_RECTANGLE, TEXTURE_2D_MULTISAMPLE, or
    TEXTURE_2D_MULTISAMPLE_ARRAY, then <level> must be zero.

    ...

    For FramebufferTexture2D, if <texture> is not zero, then <textarget>
    must be one of of TEXTURE_2D, TEXTURE_RECTANGLE,
    TEXTURE_CUBE_MAP_POSITIVE_X, TEXTURE_CUBE_MAP_POSITIVE_Y,
    TEXTURE_CUBE_MAP_POSITIVE_Z, TEXTURE_CUBE_MAP_NEGATIVE_X,
    TEXTURE_CUBE_MAP_NEGATIVE_Y, TEXTURE_CUBE_MAP_NEGATIVE_Z, or
    TEXTURE_2D_MULTISAMPLE.

    ...

    The command

        void FramebufferTextureLayer(enum target, enum attachment,
                                     uint texture, int level, int layer);

    operates identically to FramebufferTexture3D, except that it
    attaches a single layer of a three-dimensional, one- or
    two-dimensional array, or two-dimensional multisample array texture
    layer is an integer indicating the layer sample number, and is
    treated identically to the layer parameter in FramebufferTexture3D.
    The error INVALID_VALUE is generated if texture is non-zero and
    layer is negative. The error INVALID_OPERATION is generated if
    texture is non-zero and is not the name of a three dimensional, two-
    dimensional multisample array, or one-or two-dimensional array
    texture. Unlike FramebufferTexture3D, no textarget parameter is
    accepted. ...


    Modify Section 4.4.4, Framebuffer Completeness, p. 212

    (Modify the last bullet at the top of p. 215)

    - The value of RENDERBUFFER_SAMPLES is the same for all attached
      renderbuffers; the value of TEXTURE_SAMPLES is the same for all
      attached textures; and, if the attached images are a mix of
      renderbuffers and textures, the value of RENDERBUFFER_SAMPLES
      matches the value of TEXTURE_SAMPLES.

      { FRAMEBUFFER_INCOMPLETE_MULTISAMPLE }

    - The value of TEXTURE_FIXED_SAMPLE_LOCATIONS is the same for all
      attached textures; if the attached images are a mix of
      renderbuffers and textures, the value of
      TEXTURE_FIXED_SAMPLE_LOCATIONS must be TRUE for all attached
      textures.

      { FRAMEBUFFER_INCOMPLETE_MULTISAMPLE }

Additions to Chapter 6 of the OpenGL 3.1 Specification (State and
State Requests)

    Edit Section 6.1.3, p. 223 (Enumerated Queries)

    Add TEXTURE_2D_MULTISAMPLE, PROXY_TEXTURE_2D_MULTISAMPLE,
    TEXTURE_2D_MULTISAMPLE_ARRAY, and PROXY_TEXTURE_2D_MULTISAMPLE_ARRAY
    to the list of valid targets for GetTexLevelParameter{if}v.

Additions to the AGL/GLX/WGL Specifications

    None

GLX Protocol

    TBD

Errors

    The error INVALID_VALUE is generated by GetBooleani_v and
    GetIntegeri_v if <target> is SAMPLE_MASK_VALUE and <index> is greater
    than or equal to MAX_SAMPLE_MASK_WORDS.

    The error INVALID_VALUE is generated by SampleMaski if <index> is
    greater than or equal to MAX_SAMPLE_MASK_WORDS.

    The error INVALID_ENUM is generated by GetMultisamplefv if <pname>
    is not SAMPLE_POSITION.

    The error INVALID_VALUE is generated by GetMultisamplefv if <index> is
    greater than or equal to the value of SAMPLES.

    The error INVALID_OPERATION is generated by TexImage2DMultisample
    and TexImage3DMultisample if the number of samples exceeds the
    implementation dependent maximum for the given internal format.

    The error INVALID_VALUE is generated by TexImage2DMultisample
    TexImage3DMultisample if either <width> or <height> is greater than the
    value of MAX_TEXTURE_SIZE, or if <samples> is greater than the value of
    MAX_SAMPLES.

    The error INVALID_VALUE is generated by TexImage3DMultisample if
    <width>, <height>, or <depth> is greater than the value of
    MAX_3D_TEXTURE_SIZE, or if <samples> is greater than the value of
    MAX_SAMPLES.

    The error OUT_OF_MEMORY is generated by TexImage2DMultisample and
    TexImage3DMultisample if the GL is unable to create a texture level
    of the requested size.

    The error INVALID_OPERATION is generated by
    RenderbufferStorageMultisample if <internalformat> is a signed or
    unsigned integer format and <samples> is greater than the value of
    MAX_INTEGER_SAMPLES.

New State

    Get Value                       Get Command    Type    Initial Value
    ---------                       -----------    ----    -------------
    SAMPLE_MASK                     IsEnabled      B       FALSE
    SAMPLE_MASK_VALUE               GetIntegeri_v  nxZ+    ~0

    Where n is the number of sample mask words (the value of
    MAX_SAMPLE_MASK_WORDS) the implementation supports.

    (add to table 6.12, Texture State Per Texture Unit/Binding Point p. 250)

                                                               Initial
    Get Value                              Type    Get Command  Value  Description                 Sec.
    ------------------------------------   ----     ----------- ------- --------------------------- ------
    TEXTURE_BINDING_2D_MULTISAMPLE        32*xZ+   GetIntegerv    0    Texture object bound to     3.8.13
                                                                       TEXTURE_2D_MULTISAMPLE
    TEXTURE_BINDING_2D_MULTISAMPLE_ARRAY  32*xZ+   GetIntegerv    0    Texture object bound to     3.8.13
                                                                       TEXTURE_2D_MULTISAMPLE_ARRAY

    (add to table 6.14, Textures (state per texture image p. 252)

                                                                Initial
    Get Value                       Type  Get Command            Value  Description                 Sec.
    ----------------------          ----  -------------------   ------- --------------------------- ------
    TEXTURE_SAMPLES                  Z+   GetTexLevelParameter     0    Number of samples per texel 3.8.4
    TEXTURE_FIXED_SAMPLE_LOCATIONS   B    GetTexLevelParameter   TRUE   Whether the image uses a    3.8.4
                                                                        fixed sample pattern

    (add to table 6.41, Framebuffer dependent Values, p. 279)

                                                        Initial
    Get Value           Type        Get Command         Value           Description      Sec.
    ------------------  ----------  ------------------  --------------  ---------------  ------
    SAMPLE_POSITION     N*2*R[0,1]  GetMultisamplefv    implementation  Explicit sample  3.2.1
                                                        dependent       positions

    Where N is the number of samples (the value of SAMPLES) the framebuffer supports.

New Implementation Dependent State

                                                      Minimum
    Get Value                    Type    Get Command  Value   Description                   Sec.
    ---------                    ------- -----------  ------- ------------------------      ------
    MAX_SAMPLE_MASK_WORDS        Z+      GetIntegerv  1       maximum number of sample      4.1.3
                                                              mask words
    MAX_COLOR_TEXTURE_SAMPLES    Z+      GetIntegerv  1       maximum number of samples     4.1.3
                                                              in a color multisample
                                                              texture
    MAX_DEPTH_TEXTURE_SAMPLES    Z+      GetIntegerv  1       maximum number of samples     4.1.3
                                                              in a depth/stencil
                                                              multisample texture
    MAX_INTEGER_SAMPLES          Z+      GetIntegerv  1       Maximum number of samples     4.4.2
                                                              in integer format
                                                              multisample buffers

Modifications to the OpenGL Shading Language Specification, Version 1.40

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

      #extension GL_ARB_texture_multisample : <behavior>

    where <behavior> is as specified in section 3.3.

    A new preprocessor #define is added to the OpenGL Shading Language:

      #define GL_ARB_texture_multisample 1

    Add to section 3.6 "Keywords"

    The following new sampler types are added:

      sampler2DMS, isampler2DMS, usampler2DMS,
      sampler2DMSArray, isampler2DMSArray, usampler2DMSArray

    Add to section 4.1 "Basic Types"

    Add the following sampler type to the "Floating Point Sampler Types"
    table:

      sampler2DMS                handle for accessing a 2D multisample texture
      sampler2DMSArray           handle for accessing a 2D multisample array texture

    Add the following sampler type to the "Unsigned Integer Sampler
    Types" table:

      usampler2DMS               handle for accessing an unsigned integer 2D multisample texture
      usampler2DMSArray          handle for accessing an unsigned integer 2D multisample array texture

    Add the following sampler type to the "Integer Sampler Types" table:

      isampler2DMS               handle for accessing an integer 2D multisample texture
      isampler2DMSArray          handle for accessing an integer 2D multisample array texture

    Add to section 8.7 "Texture Lookup Functions"

    Add new functions to the set of allowed texture lookup functions:

    Syntax:

      gvec4 texelFetch(gsampler2DMS sampler, ivec2 P, int sample)
      gvec4 texelFetch(gsampler2DMSArray sampler, ivec3 P, int sample)

    Description:

      Use integer texture coordinate <P> to lookup a single sample
      <sample> on the texture bound to <sampler> as described in section
      2.11.7.1 of the OpenGL specification "Multisample Texel Fetches".

    Syntax:

      ivec2 textureSize(gsampler2DMS sampler)
      ivec3 textureSize(gsampler2DMSArray sampler)

    Description:

      Returns the dimensions, width and height of level 0 for the
      texture bound to <sampler>, as described in section 2.11.7.1 of
      the OpenGL specification section "Texture Size Query".

Examples

Issues

    (1) Do we need new "max size" queries for the new targets?

    RESOLVED: No. The existing MAX_TEXTURE_SIZE applies to 2D multisample
    textures, and MAX_3D_TEXTURE_SIZE to 3D multisample textures.

    (2) What commands may be used on multisample textures?

    RESOLVED: Multisample textures can be bound for rendering and texturing,
    but they cannot be loaded/read with SubImage commands (TexSubImage,
    CopyTexSubImage, GetTexImage), they don't support compressed formats,
    and they don't need TexParameters since they can only be fetched with
    texelFetchMultisample.

    (3) Should the new TexImage commands take an "int level" argument?

    RESOLVED: No. We can add new commands if/when we ever add mipmapped
    multisample textures.

    (4) GetMultisamplefv takes an index to support >32 samples, but
        NV_gpu_shader4_1's gl_SampleMask is only 32 bits. What gives?

    RESOLVED: This is gpu_shader4_1's problem, not ARB_texture_multisample's
    problem.

    (5) Should GLSL include a query to return the sample count of a
        texture, either as part of textureSizeMultisample or
        stand-alone?

    RESOLVED: No, there hasn't been a demand for it.

    (6) How does SAMPLE_POSITION interact with
        EXT_fragment_coord_conventions?

    RESOLVED: The SAMPLE_POSITION query is not in any way affected by
    the shader state added in EXT_fragment_coord_conventions. It is
    expected that the returned values will not actually be used within
    the shader, but rather to compute filter weights on the CPU, so
    whether the fragment coord is inverted or translated by 0.5 doesn't
    matter.

    (7) Should we use "TexImage3DMultisample" to make things look like
        regular 2D arrays, or just have TexImage2DArrayMultisample?

    RESOLVED: Leave it as is.

    (8) How should we deal with varying sample locations?

    RESOLVED: Allow the application to explicitly request fixed sample
    locations for when a texture will be used to do custom downsamples.
    When this is requested, the values returned by GetMultisamplefv will
    be valid for all texels in the image and can be used to construct
    elaborate filter kernels that can safely be used across the entire
    image.

    (9) Are depth multisample textures supported?

    RESOLVED: Some implementations may not support texturing from a
    multisample depth/stencil texture. In that case, they would export
    MAX_DEPTH_TEXTURE_SAMPLES = 1.

Revision History

    Rev.    Date    Author    Changes
    ----  --------  --------  -----------------------------------------------
    12    2/28/14   Jon Leech Add missing error for invalid <pname> to       
                              GetMultisamplefv, and change texture size
                              limits for TexImage3DMultisample to the value
                              of MAX_3D_TEXTURE_SIZE (Bugs 11134, 11135).
    11    9/23/13   Jon Leech Change type of <internalformat> argument to    
                              enum (Bug 10496).
    10    8/02/09   Jon Leech Reformat to 80 columns and assign ARB
                              extension number.
    9     7/23/09   groth     Update return of textureSize(gsampler2DMSarray)
    8     7/20/09   Jon Leech Assign enum values.
    7     6/26/09   groth     Update some language to correspond to gl3.2
    6     6/11/09   groth     Add new max queries to token section
    5     5/28/09   groth     Add MAX_INTEGER_SAMPLES query.
    4     5/22/09   jbolz     Add max sample queries.
    3     5/14/09   jbolz     Add allowance for not supporting multisample
                              depth textures.
    2     5/08/09   jbolz     Add allowance for varying sample locations,
                              and a mechanism to request fixed locations.
                              Resolve some issues.
    1     4/30/09   jbolz     First revision.