Name

    EXT_texture

Name Strings

    GL_EXT_texture

Version

    $Date: 1996/04/05 19:17:03 $ $Revision: 1.21 $

Number

    4

Dependencies

    None

Overview

    The original intention of this extension was simply to support various
    numeric resolutions of color components in texture images.  While it
    accomplishes this, it also accomplishes a larger task, that of
    formalizing the notion of an internal format for images, corresponding
    to the external format that already existed for image data in host
    memory.  This notion of an internal image format will be used
    extensively in later extensions, especially those concerned with pixel
    manipulation.

    The idea of an internal format is simple: rather than treating a
    retained image as having 1, 2, 3, or 4 components, treat it as though
    it has a specific format, such as LUMINANCE_ALPHA, or just ALPHA.  Then
    define the semantics of the use of internal images with these formats in
    a consistent way.  Because texture mapping is already defined in GL, the
    semantics for internal-format images were chosen to match those of the 1,
    2, 3, and 4 component internal images that already existed.  The new
    semantics are a superset of the old ones, however, so this extension
    adds capabilities to GL, as well as allowing internal resolutions to be
    specified.

    This extension also defines a robust method for applications to
    determine what combinations of texture dimensions and resolutions are
    supported by an implementation.  It also introduces a new texture
    environment: REPLACE_EXT.

New Procedures and Functions

    None

New Tokens

    Accepted by the <components> parameter of TexImage1D and TexImage2D:

        ALPHA4_EXT                       0x803B
        ALPHA8_EXT                       0x803C
        ALPHA12_EXT                      0x803D
        ALPHA16_EXT                      0x803E
        LUMINANCE4_EXT                   0x803F
        LUMINANCE8_EXT                   0x8040
        LUMINANCE12_EXT                  0x8041
        LUMINANCE16_EXT                  0x8042
        LUMINANCE4_ALPHA4_EXT            0x8043
        LUMINANCE6_ALPHA2_EXT            0x8044
        LUMINANCE8_ALPHA8_EXT            0x8045
        LUMINANCE12_ALPHA4_EXT           0x8046
        LUMINANCE12_ALPHA12_EXT          0x8047
        LUMINANCE16_ALPHA16_EXT          0x8048
        INTENSITY_EXT                    0x8049
        INTENSITY4_EXT                   0x804A
        INTENSITY8_EXT                   0x804B
        INTENSITY12_EXT                  0x804C
        INTENSITY16_EXT                  0x804D
        RGB2_EXT                         0x804E
        RGB4_EXT                         0x804F
        RGB5_EXT                         0x8050
        RGB8_EXT                         0x8051
        RGB10_EXT                        0x8052
        RGB12_EXT                        0x8053
        RGB16_EXT                        0x8054
        RGBA2_EXT                        0x8055
        RGBA4_EXT                        0x8056
        RGB5_A1_EXT                      0x8057
        RGBA8_EXT                        0x8058
        RGB10_A2_EXT                     0x8059
        RGBA12_EXT                       0x805A
        RGBA16_EXT                       0x805B

    Accepted by the <pname> parameters of GetTexLevelParameteriv and
    GetTexLevelParameterfv:

        TEXTURE_RED_SIZE_EXT             0x805C
        TEXTURE_GREEN_SIZE_EXT           0x805D
        TEXTURE_BLUE_SIZE_EXT            0x805E
        TEXTURE_ALPHA_SIZE_EXT           0x805F
        TEXTURE_LUMINANCE_SIZE_EXT       0x8060
        TEXTURE_INTENSITY_SIZE_EXT       0x8061

    Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv, and
    TexEnvfi when the <pname> parameter value is
    GL_TEXTURE_ENV_MODE

        REPLACE_EXT                      0x8062

    Accepted by the <target> parameters of TexImage1D,
    GetTexLevelParameteriv, and GetTexLevelParameterfv:

        PROXY_TEXTURE_1D_EXT             0x8063

    Accepted by the <target> parameters of TexImage2D,
    GetTexLevelParameteriv, and GetTexLevelParameterfv:

        PROXY_TEXTURE_2D_EXT             0x8064

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

    A new error token value, TEXTURE_TOO_LARGE_EXT, is defined and added to
    table 2.3:

                                                                           Offending
                                                                           command
        Error                   Description                                ignored?
        -----                   -----------                                ---------
        INVALID_ENUM            enum argument out of range                 Yes
        INVALID_VALUE           Numeric argument out of range              Yes
        INVALID_OPERATION       Operation illegal in current state         Yes
        STACK_OVERFLOW          Command would cause a stack overflow       Yes
        STACK_UNDERFLOW         Command would cause a stack underflow      Yes
        TEXTURE_TOO_LARGE_EXT   The specified texture is too large         Yes
        OUT_OF_MEMORY           Not enough memory left to execute command  Unknown

        Table 2.3: Summary of GL errors

     and defined as follows:

        TEXTURE_TOO_LARGE_EXT            0x8065

Additions to Chapter 3 of the GL Specification (Rasterization)

    Many additional values can be specified for the <components> parameter
    of TexImage1D and TexImage2D.  The GL Specification indicates (in
    section 3.8) that only values 1, 2, 3, and 4 can be specified.  This
    extension defines semantics for the currently existing tokens ALPHA,
    RGB, RGBA, LUMINANCE, and LUMINANCE_ALPHA, and also defines semantics
    for many new tokens.  Each of the new tokens (except INTENSITY_EXT)
    indicates a desired storage resolution, as well as a base format.  These
    tokens are:

                                                                Red     Green   Blue    Alpha   Luminance   Intensity
        Token name                      Base format             Bits    Bits    Bits    Bits    Bits        Bits
        ----------                      -----------             ----    ----    ----    ----    ----        ----

        ALPHA4_EXT                      ALPHA                                             4
        ALPHA8_EXT                      ALPHA                                             8
        ALPHA12_EXT                     ALPHA                                            12
        ALPHA16_EXT                     ALPHA                                            16
        LUMINANCE4_EXT                  LUMINANCE                                                 4
        LUMINANCE8_EXT                  LUMINANCE                                                 8
        LUMINANCE12_EXT                 LUMINANCE                                                12
        LUMINANCE16_EXT                 LUMINANCE                                                16
        LUMINANCE4_ALPHA4_EXT           LUMINANCE_ALPHA                                   4       4
        LUMINANCE6_ALPHA2_EXT           LUMINANCE_ALPHA                                   2       6
        LUMINANCE8_ALPHA8_EXT           LUMINANCE_ALPHA                                   8       8
        LUMINANCE12_ALPHA4_EXT          LUMINANCE_ALPHA                                   4      12
        LUMINANCE12_ALPHA12_EXT         LUMINANCE_ALPHA                                  12      12
        LUMINANCE16_ALPHA16_EXT         LUMINANCE_ALPHA                                  16      16
        INTENSITY_EXT                   INTENSITY_EXT                                                        ?
        INTENSITY4_EXT                  INTENSITY_EXT                                                        4
        INTENSITY8_EXT                  INTENSITY_EXT                                                        8
        INTENSITY12_EXT                 INTENSITY_EXT                                                       12
        INTENSITY16_EXT                 INTENSITY_EXT                                                       16
        RGB2_EXT                        RGB                       2       2       2                
        RGB4_EXT                        RGB                       4       4       4                
        RGB5_EXT                        RGB                       5       5       5                
        RGB8_EXT                        RGB                       8       8       8                
        RGB10_EXT                       RGB                      10      10      10                
        RGB12_EXT                       RGB                      12      12      12                
        RGB16_EXT                       RGB                      16      16      16                
        RGBA2_EXT                       RGBA                      2       2       2       2        
        RGBA4_EXT                       RGBA                      4       4       4       4        
        RGB5_A1_EXT                     RGBA                      5       5       5       1        
        RGBA8_EXT                       RGBA                      8       8       8       8        
        RGB10_A2_EXT                    RGBA                     10      10      10       2        
        RGBA12_EXT                      RGBA                     12      12      12      12        
        RGBA16_EXT                      RGBA                     16      16      16      16        

    All implementations of this extension support the base formats ALPHA,
    LUMINANCE, LUMINANCE_ALPHA, RGB, and RGBA.  All implementations also
    accept all the tokens in the table above, but may not allocate storage
    exactly equal to that indicated in the table.  Instead, storage is
    allocated to best match the resolutions in the table.  The determination
    of best match is left to the implementation.  Storage allocation for the
    base formats (as well as for formats "1", "2", "3", and "4") is an
    implementation dependent compromise of component resolution,
    performance, image size, and memory availability.
    
    It is acceptable for an implementation to vary its allocation of
    internal component resolution based on any TexImage1D or TexImage2D
    parameter, but the allocation must not be a function of any other
    factor, and cannot be changed once it is established.  In particular,
    allocations must be invariant -- the same allocation must be made each
    time a texture image is specified with the same parameter values.
    Provision is made for an application to determine what component
    resolutions are available without having to fully specify the texture
    (see below).

    A set of mipmap arrays is incomplete (see the Mipmapping section of the
    GL Specification) if different internal formats are specified for arrays
    in the set, even if the resulting formats of the arrays are identical.
    An implementation can, however, report different component precisions
    for the arrays in the set, even if all were specified with the same
    internal format.  (The set of arrays will be complete in this case.)

    The assignments of texture component values from color components
    "extracted" from the incoming image (see the discussion in section 3.8
    of the GL Specification) are defined by this new version of Table 3.6:

        Base Internal Format    red     green   blue    alpha   luminance       intensity
        --------------------    ---     -----   ----    -----   ---------       ---------

        ALPHA                                           A
        LUMINANCE                                               R
        LUMINANCE_ALPHA                                 A       R
        INTENSITY_EXT                                                           R
        RGB                     R       G       B
        RGBA                    R       G       B       A

        Table 3.6: Correspondence of texture components to extracted
        R, G, B, and A values.

    Texture components are assigned to Rt, Gt, Bt, and At.
    Table 3.8 (Texture functions) refers to these components.
    The assignments are defined by the following table:

                                Texture Environment
                                -------------------

        Base Texture Format     Rt      Gt      Bt      At
        -------------------     --      --      --      --

        LUMINANCE               Lt      Lt      Lt      x

        ALPHA                   x       x       x       At

        INTENSITY_EXT           It      It      It      It

        LUMINANCE_ALPHA         Lt      Lt      Lt      At

        RGB                     Rt      Gt      Bt      x

        RGBA                    Rt      Gt      Bt      At

        Table ??: Mapping of Texture Components to Rt, Gt, Bt, At.

    Where there appears an "x", the assignment is "don't care", since
    that component is not used by the texture environment.

    This extension redefines the application of a texture to the color
    components of a fragment.  In particular, a new texture environment, REPLACE,
    and two new texture formats, ALPHA and INTENSITY_EXT, are included.
    Table 3.8 (Texture functions) of the GL
    Specification is replaced by the following table:

                                Texture Environment
                                -------------------

        Base Texture Format     REPLACE         MODULATE        BLEND                           DECAL
        -------------------     -------         --------        -----                           -----

        LUMINANCE               Rv =    Rt      Rv = Rf * Rt    Rv = Rf * (1-Rt) + Rc * Rt      undefined
                                Gv =    Gt      Gv = Gf * Gt    Gv = Gf * (1-Gt) + Gc * Gt
                                Bv =    Bt      Bv = Bf * Bt    Bv = Bf * (1-Bt) + Bc * Bt
                                Av = Af         Av = Af         Av = Af

        ALPHA                   Rv = Rf         Rv = Rf         Rv = Rf                         undefined
                                Gv = Gf         Gv = Gf         Gv = Gf
                                Bv = Bf         Bv = Bf         Bv = Bf
                                Av =    At      Av = Af * At    Av = Af * At

        INTENSITY_EXT           Rv =    Rt      Rv = Rf * Rt    Rv = Rf * (1-Rt) + Rc * Rt      undefined
                                Gv =    Gt      Gv = Gf * Gt    Gv = Gf * (1-Gt) + Gc * Gt
                                Bv =    Bt      Bv = Bf * Bt    Bv = Bf * (1-Bt) + Bc * Bt
                                Av =    At      Av = Af * At    Av = Af * (1-At) + Ac * At

        LUMINANCE_ALPHA         Rv =    Rt      Rv = Rf * Rt    Rv = Rf * (1-Rt) + Rc * Rt      undefined
                                Gv =    Gt      Gv = Gf * Gt    Gv = Gf * (1-Gt) + Gc * Gt
                                Bv =    Bt      Bv = Bf * Bt    Bv = Bf * (1-Bt) + Bc * Bt
                                Av =    At      Av = Af * At    Av = Af * At

        RGB                     Rv =    Rt      Rv = Rf * Rt    Rv = Rf * (1-Rt) + Rc * Rt      Rv =    Rt
                                Gv =    Gt      Gv = Gf * Gt    Gv = Gf * (1-Gt) + Gc * Gt      Gv =    Gt
                                Bv =    Bt      Bv = Bf * Bt    Bv = Bf * (1-Bt) + Bc * Bt      Bv =    Bt
                                Av = Af         Av = Af         Av = Af                         Av = Af

        RGBA                    Rv =    Rt      Rv = Rf * Rt    Rv = Rf * (1-Rt) + Rc * Rt      Rv = Rf * (1-At) + Rt * At
                                Gv =    Gt      Gv = Gf * Gt    Gv = Gf * (1-Gt) + Gc * Gt      Gv = Gf * (1-At) + Gt * At
                                Bv =    Bt      Bv = Bf * Bt    Bv = Bf * (1-Bt) + Bc * Bt      Bv = Bf * (1-At) + Bt * At
                                Av =    At      Av = Af * At    Av = Af * At                    Av = Af

        Table 3.8: Texture functions.

    Finally, for backward compatibility, the semantics of <components>
    values 1, 2, 3, and 4 are identical to those of LUMINANCE,
    LUMINANCE_ALPHA, RGB, and RGBA respectively.  The one exception is that
    the token values for 1, 2, 3, and 4 are not the same as the token values
    LUMINANCE, LUMINANCE_ALPHA, RGB, and RGBA.

    Query support
    -------------

    Alternate sets of partial per-level texture state are defined for
    the proxy textures PROXY_TEXTURE_1D_EXT and PROXY_TEXTURE_2D_EXT.
    Specifically, TEXTURE_WIDTH, TEXTURE_HEIGHT, TEXTURE_BORDER,
    TEXTURE_COMPONENTS, TEXTURE_RED_SIZE_EXT, TEXTURE_GREEN_SIZE_EXT,
    TEXTURE_BLUE_SIZE_EXT, TEXTURE_ALPHA_SIZE_EXT,
    TEXTURE_LUMINANCE_SIZE_EXT, and TEXTURE_INTENSITY_SIZE_EXT are
    maintained for proxy textures.  When TexImage2D is called with
    <target> set to PROXY_TEXTURE_2D_EXT, these proxy state values are
    always recomputed and updated, even if the texture is too large to
    actually be used.  If the texture is too large, all of these state
    variables are set to zero.  If the texture could be accommodated
    by TexImage2D called with <target> TEXTURE_2D, these values are
    set as though TEXTURE_2D were being defined.  All of these state
    value can be queried with GetTexLevelParameteriv or
    GetTexLevelParameterfv with <target> set to PROXY_TEXTURE_2D_EXT.
    Calling TexImage2D with <target> PROXY_TEXTURE_2D_EXT has no
    effect on the actual 2-dimensional texture or its state.

    To determine the maximum array size for a mipmap texture, specify and
    query the proxy texture at the highest level that accurately reflects the
    aspect ratio of the desired level zero array.

    There is no image associated with PROXY_TEXTURE_2D_EXT.  Therefore
    PROXY_TEXTURE_2D_EXT cannot be used as a texture, and its image must
    never be queried using GetTexImage.  (The error INVALID_ENUM results if
    this is attempted.)  Likewise, there is no nonlevel-related state
    associated with a proxy texture, so calling GetTexParameteriv or
    GetTexParameterfv with <target> PROXY_TEXTURE_2D_EXT results in the
    error INVALID_ENUM.

    The proxy 1-dimensional texture behaves identically to the proxy
    2-dimensional texture, except that its state does not include
    TEXTURE_HEIGHT.

Additions to Chapter 4 of the GL Specification (Per-Fragment Operations
and the Framebuffer)

    None

Additions to Chapter 5 of the GL Specification (Special Functions)

    TexImage1D with a proxy target and TexImage2D with a proxy target
    are not included in display lists, but are instead executed
    immediately.

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

    GetTexLevelParameteriv, when called with <pname> TEXTURE_COMPONENTS,
    returns the value of the <components> state variable as specified by the
    application.  This remains true even if the actual internal format
    matches that of another token.

    GetTexLevelParameteriv, when called with <pname> TEXTURE_RED_SIZE_EXT,
    TEXTURE_GREEN_SIZE_EXT, TEXTURE_BLUE_SIZE_EXT, TEXTURE_ALPHA_SIZE_EXT,
    TEXTURE_LUMINANCE_SIZE_EXT, or TEXTURE_INTENSITY_SIZE_EXT returns the
    actual number of bits of internal storage for red, green, blue, alpha,
    luminance, or intensity.  This value may not match the value of the
    specified internal format.

    GetTexImage continues to operate as though ReadPixels were called with
    the texture image as the framebuffer.  The assignments of texture
    component values to the initial R, G, B, and A values of the read-back
    texel (prior to PixelTransfer and PixelStorage operations) are:

        Base Internal Format    R               G       B       A
        --------------------    -               -       -       -

        ALPHA                   0.0             0.0     0.0     alpha
        LUMINANCE               luminance       0.0     0.0     0.0                                             
        LUMINANCE_ALPHA         luminance       0.0     0.0     alpha
        INTENSITY_EXT           intensity       0.0     0.0     0.0
        RGB                     red             green   blue    0.0
        RGBA                    red             green   blue    alpha

Additions to the GLX Specification

    None

GLX Protocol

    None

Dependencies on EXT_abgr

    Token ABGR_EXT cannot be used to specify internal texture image formats.

Errors

    The GL Specification requires that INVALID_VALUE be generated if any
    texture dimension is specified less than zero, greater than
    MAX_TEXTURE_SIZE, or with a value that cannot be represented as 2**k +
    2*border, for some integer k.  This extension eliminates the requirement
    that all dimensions be specified less than or equal to MAX_TEXTURE_SIZE,
    and replaces it with a new error token and error condition.
    INVALID_VALUE is generated if any texture dimension is specified less
    than zero, or with a value that cannot be represented as 2**k + 2*border.
    TEXTURE_TOO_LARGE_EXT is generated if the texture is too large to be
    accommodated, for whatever reason.  An implementation must specify
    MAX_TEXTURE_SIZE such that TEXTURE_TOO_LARGE_EXT is never generated if
    all the dimensions of the texture are less than or equal to
    MAX_TEXTURE_SIZE.  Also, TEXTURE_TOO_LARGE_EXT is never generated when
    the target is a proxy texture, such as PROXY_TEXTURE_1D_EXT or
    PROXY_TEXTURE_2D_EXT.

    This change to the error semantics does not require that the major
    revision level be incremented, because the GL Specification allows for
    changes to error semantics (Section 2.5).

New State

                                                                                        Initial
    Get Value                           Get Command             Type                    Value   Attrib
    ---------                           -----------             ----                    ------- ------
    TEXTURE_RED_SIZE_EXT                GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -
    TEXTURE_GREEN_SIZE_EXT              GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -
    TEXTURE_BLUE_SIZE_EXT               GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -
    TEXTURE_ALPHA_SIZE_EXT              GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -
    TEXTURE_LUMINANCE_SIZE_EXT          GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -
    TEXTURE_INTENSITY_SIZE_EXT          GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -

    TEXTURE                             GetTexImage             2 x 1 x levels x I      null       -
    TEXTURE_WIDTH                       GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -
    TEXTURE_HEIGHT                      GetTexLevelParameteriv  1 x 2 x levels x Z+     0          -
    TEXTURE_BORDER                      GetTexLevelParameteriv  2 x 2 x levels x Z+     0          -
    TEXTURE_COMPONENTS                  GetTexLevelParameteriv  2 x 2 x levels x Z42    1          -

New Implementation Dependent State

    None