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GL_EXT_texture
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.
None
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
Implementation Support
List of OpenGL implementations supporting the GL_EXT_texture extension
Original File
Original text file for the GL_EXT_texture extension
Page generated on Sun Nov 20 18:37:22 2005