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Name Strings
Daniel Koch, TransGaming, Inc.
Jon Leech, Khronos
Daniel Koch, TransGaming, Inc. (daniel 'at'
Copyright (c) 2008-2013 The Khronos Group Inc. Copyright terms at
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
Approved by the ARB on July 11, 2008
Last Modified Date: May 28, 2009
Author Revision: 6
ARB Extension #53
OpenGL 1.1 is required.
This extension is written against the OpenGL 2.1 Specification.
EXT_texture_integer affects the definition of this extension.
ARB_texture_float affects the definition of this extension.
EXT_packed_depth_stencil affects the definition of this extension.
This extension interacts with ARB_framebuffer_object and
This extension is subsumed by OpenGL 3.0.
Historically one- and two- component textures have been specified in OpenGL
using the intensity, luminance or luminance-alpha (I/L/LA) formats.
With the advent of programmable shaders and render-to-texture capabilites
these legacy formats carry some historical artifacts which are no longer
For example, when sampling from such textures, the luminance values
are replicated across the color components, and the intensity values are
replicated across both the color and alpha components. This is no
longer necessary with programmable shaders.
It is also desirable to be able to render to one- and two-
component format textures using capabilities such as framebuffer
objects (FBO), but rendering to I/L/LA formats is under-specified
(specifically how to map R/G/B/A values to I/L/A texture channels).
This extension adds new base internal formats for the one-component RED
and two-component RG (red green) texture formats as well as sized
internal formats for fixed-point, floating-point and pure integer texture
formats. The new texure formats can be used for texturing as well
as for rendering into with framebuffer objects.
IP Status
No known IP claims.
New Tokens
Accepted by the <internalFormat> parameter of TexImage1D, TexImage2D,
TexImage3D, CopyTexImage1D, and CopyTexImage2D:
R8 0x8229
R16 0x822A
RG8 0x822B
RG16 0x822C
R16F 0x822D
R32F 0x822E
RG16F 0x822F
RG32F 0x8230
R8I 0x8231
R8UI 0x8232
R16I 0x8233
R16UI 0x8234
R32I 0x8235
R32UI 0x8236
RG8I 0x8237
RG8UI 0x8238
RG16I 0x8239
RG16UI 0x823A
RG32I 0x823B
RG32UI 0x823C
RED 0x1903
RG 0x8227
Accepted by the <format> parameter of TexImage1D, TexImage2D,
TexImage3D, TexSubImage1D, TexSubImage2D, TexSubImage3D,
and ReadPixels:
RG 0x8227
Accepted by the <format> parameter of DrawPixels:
RG 0x8227
Accepted by the <param> parameter of the TexParameter{if}*
functions when <pname> is DEPTH_TEXTURE_MODE:
RED 0x1903
Accepted by the <format> parameter of GetTexImage:
RG 0x8227
New Procedures and Functions
Additions to Chapter 2 of the OpenGL 2.1 Specification (OpenGL Operation)
Additions to Chapter 3 of the OpenGL 2.1 Specification (Rasterization)
Modify section 3.6.3 "Pixel Transfer Modes", the "Color Table Specification"
subsection and in the third paragraph of the definition of ColorTable modify
the last sentence to read:
"internalformat must be one of the formats in table 3.15 or table 3.16,
with the exception of the RED, RG and DEPTH_COMPONENT base and sized
internal formats."
(Add the following to Table 3.6: "DrawPixels and ReadPixels formats",
as modified by EXT_texture_integer)
Format Name Element Meaning and Order Target Buffer
----------- ------------------------- -------------
RG R, G Color
(Add the following to Table 3.15: "Conversion from RGBA and depth
pixel components to internal texture, table, or filter components")
Base Internal Format RGBA and Depth Values Internal Components
-------------------- --------------------- -------------------
(Add the following to Table 3.16: "Correspondence of sized internal
formats to base internal formats, and desired component resolutions
for each sized internal format", as modified by ARB_texture_float and
Sized Base R G B A L I D
Internal Format Internal Format bits bits bits bits bits bits bits
--------------- --------------- ---- ---- ---- ---- ---- ---- ----
R8 RED 8
R16 RED 16
RG8 RG 8 8
RG16 RG 16 16
R16F RED f16
R32F RED f32
RG16F RG f16 f16
RG32F RG f32 f32
R8I RED i8
R8UI RED ui8
R16I RED i16
R16UI RED ui16
R32I RED i32
R32UI RED ui32
RG8I RG i8 i8
RG8UI RG ui8 ui8
RG16I RG i16 i16
RG16UI RG ui16 ui16
RG32I RG i32 i32
RG32UI RG ui32 ui32
(Add the following to Table 3.17: "Generic and specific compressed
internal formats")
Compressed Internal Format Base Internal Format Type
-------------------------- -------------------- ---------
(Modify Table 3.18: "Texure parameters and their values")
Add RED to the "Legal Values" column for the row containing the
definition of DEPTH_TEXTURE_MODE.
Modify the first sentence of section 3.8.5 "Depth Component Textures"
(as modified by EXT_packed_depth_stencil or ARB_framebuffer_object) to read:
"Depth textures and the depth components of depth/stencil textures can
be treated as RED, LUMINANCE, INTENSITY or ALPHA textures during texture
filtering and application."
(Add the following to Table 3.20: "Correspondence of filtered texture
components to texture source components.")
Texture Base Texture source color
Internal Format C_s A_s
--------------- ------------- ------
RED (R_t, 0, 0) 1
RG (R_t, G_t, 0) 1
(Modify Table 3.21: "Texture functions REPLACE, MODULATE and DECAL.")
Add RED and RG to the "Texture Base Internal Format" column for the
row which defines the behaviour for RGB (or 3).
(Modify Table 3.22: "Texture functions BLEND and ADD.")
Add RED and RG to the "Texture Base Internal Format" column for the
row which defines the behaviour for RGB (or 3).
Modify Section 3.8.14 "Texture Comparision Modes", the "Depth Texture
Comparision Mode" subsection, and change the second to last paragraph
to read:
"The resulting r is assigned to R_t, L_t, I_t, or A_t if the value of the
Additions to Chapter 4 of the OpenGL 2.1 Specification (Per-Fragment Operations
and the Framebuffer)
In section 4.3.2 "Reading Pixels" the subsection "Obtaining Pixels from
the framebuffer", modify the first sentence of the 3rd paragraph in the
definition of ReadBuffer to read:
"If the GL is in RGBA mode, and format is one of RED, GREEN, BLUE, ALPHA,
green, blue, and alpha values are obtained from the selected buffer at
each pixel location."
In subsection "Placement in Pixel Pack Buffer or Client Memory," modify
the second to last sentence to read:
"Likewise if the format is RG, LUMINANCE_ALPHA, RGB, BGR, only the
corresponding two or three elements are written."
In section 4.4.4 "Framebuffer Completeness" as added by
EXT_framebuffer_object or ARB_framebuffer_object, modify the first bullet
point and add RED and RG to the list of base internal formats which
are color-renderable.
Additions to Chapter 5 of the OpenGL 2.1 Specification (Special Functions)
Additions to Chapter 6 of the OpenGL 2.1 Specification (State and State Requests)
Modify section 6.1.4 "Texture Queries". Change the second sentence of the
second paragraph to read:
"Calling GetTexImage with a color format (one of RED, GREEN, BLUE, ALPHA,
*_INTEGER variants) when the base internal format of the texture image is
not a color format; with a format of DEPTH_COMPONENT when the base internal
format is not DEPTH_COMPONENT or DEPTH_STENCIL; with a format of
DEPTH_STENCIL when the base internal format is not DEPTH_STENCIL; with an
*_INTEGER format when the base internal format is not one of the integral
types; or with non-integer format when the base internal is an integral
type, causes the error INVALID_OPERATION."
(Add the following to Table 6.1: "Texture, table, and filter return values")
Base Internal Format R G B A
-------------------- ---- ----- --- ---
RED R_i 0 0 1
RG R_i G_i 0 1
Dependencies on EXT_packed_depth_stencil
If EXT_packed_depth_stencil is not supported then delete any reference to
depth/stencil textures (unless ARB_framebuffer_objects is supported).
Dependencies on EXT_framebuffer_object
If EXT_framebuffer_object is not supported then delete any reference to
framebuffer objects (unless ARB_framebuffer_objects is supported).
Dependencies on ARB_framebuffer_object
If ARB_framebuffer_object is not supported:
* delete any reference to depth/stencil textures
(unless EXT_packed_depth_stencil is supported).
* delete any reference to framebuffer objects
(unless EXT_framebuffer_object is supported).
Dependencies on EXT_texture_integer
If EXT_texture_integer is not supported:
* delete any reference to the R*I*, R*UI* and *INTEGER* formats.
Dependencies on ARB_texture_float
If ARB_texture_float is not supported:
* delete any reference to the R*F* formats.
1) What should this extension be called? ARB_rg_formats, ARB_rg_texture,
ARB_texture_rg, etc
DECIDED. Using ARB_texture_rg.
2) Why use RED token used instead of just "R"?
a) there is already some precedent for using RED for single-component
b) the "R" token is already used for texcoord generation, and it is
less confusing if we don't reuse it.
3) Why use RG instead of REDGREEN?
The list {RED, RG, RGB, RGBA} is more visually appealing than
4) Why don't the new tokens and entry points in this extension have
"ARB" suffixes like other ARB extensions?
RESOLVED: Unlike most ARB extensions, this is a strict subset of
functionality already approved in OpenGL 3.0. This extension
exists only to support that functionality on older hardware that
cannot implement a full OpenGL 3.0 driver. Since there are no
possible behavior changes between the ARB extension and core
features, source code compatibility is improved by not using
suffixes on the extension.
5) What are the default values for the unspecified channels if you sampled
from an R or RG texture? Is it (r,0,0,1) or (r,1,1,1).
CLARIFICATION: As per OpenGL defaults as specified in Table 3.20
(as modified by this extension) the default values for unspecified
components are (r,0,0,1). Note that this does differ from D3D where
unspecified values would be filled in as (r,1,1,1).
6) Are the RG formats accepted by the imaging subset of functions?
RESOLUTION: NO. This extension does not add RG support to the functions
defined in the imaging subset (that is: [Get]Color[Sub]Table,
[Get]ConvolutionFilter, [Get]SeparableFilter, GetHistogram, GetMinMax)
as it is felt that there is little benefit in doing so. This could be
added as a separate extension if desired.
Revision History
#6 May 28, 2008, jleech
- Remove extraneous *_INTEGER formats from table 6.1
#5 April 8, 2008, dgkoch
- Address issues raised in Bug 4163
- clarify that RG_INTEGER is not allowed for DrawPixels
- added issue 6) and clarify that support for RED and RG formats
is not added to the imaging subset
- GetTexImage supports RG (but no conversion)
#4 November 14, 2008, dgkoch
- marked issue 1) as resolved.
- add issue 5) as clarification
- Better compatibility with GL 3.0 spec
- allow unsized RED and RG formats as internal formats (Bug 4161)
- add enums for COMPRESSED_RED/RG and allow as internal formats (Bug 4162)
#3 August 7, 2008, jleech
- Remove ARB suffixes.
#2 June 9, 2008, dgkoch
- add COMPRESSED_RED/RG generic formats.
- add CopyTexImage1/2D to list of functions accepting the new
#1 June 8, 2008, dgkoch
- initial version extracted from GL3 core.