Name
ARB_texture_env_combine
Name Strings
GL_ARB_texture_env_combine
Contact
Bimal Poddar, Intel (bimal.poddar 'at' intel.com)
Michael Gold, NVIDIA (gold 'at' nvidia.com)
Tom Frisinger, AMD (tom.frisinger 'at' amd.com)
Rick Hammerstone, AMD (rick.hammerstone 'at' amd.com)
Status
Complete. Approved by ARB on February 16, 2001.
Version
Last modified date: 2006/11/04
Number
ARB Extension #17
Dependencies
This extension is written against the OpenGL 1.2.1 Specification.
OpenGL 1.1 and ARB_multitexture are required for this extension.
Overview
New texture environment function COMBINE_ARB allows programmable
texture combiner operations, including:
REPLACE Arg0
MODULATE Arg0 * Arg1
ADD Arg0 + Arg1
ADD_SIGNED_ARB Arg0 + Arg1 - 0.5
SUBTRACT_ARB Arg0 - Arg1
INTERPOLATE_ARB Arg0 * (Arg2) + Arg1 * (1-Arg2)
where Arg0, Arg1 and Arg2 are derived from
PRIMARY_COLOR_ARB primary color of incoming fragment
TEXTURE texture color of corresponding texture unit
CONSTANT_ARB texture environment constant color
PREVIOUS_ARB result of previous texture environment; on
texture unit 0, this maps to PRIMARY_COLOR_ARB
In addition, the result may be scaled by 1.0, 2.0 or 4.0.
Issues
1. Should the explicit bias be removed in favor of an implcit bias as
part of a ADD_SIGNED_ARB function?
- RESOLVED: Yes. This pre-scale bias is a special case and will
be treated as such.
2. Should the primary color of the incoming fragment be available to
all texture environments? Currently it is only available to the
texture environment of texture unit 0.
- RESOLVED: Yes. PRIMARY_COLOR_ARB has been added as an input
source.
3. Should textures from other texture units be allowed as sources?
- RESOLVED: NO. Even though this adds a lot of flexibility that
folks can use today, there is not enough support amonst the
ARB participants to add it to the base spec.
4. All of the 1.2 modes except BLEND can be expressed in terms of
this extension. Should texture color be allowed as a source for
Arg2, so all of the 1.2 modes can be expressed? If so, should all
color sources be allowed, to maintain orthogonality?
- RESOLVED: Yes. This seems to be a reasonable area to expand
functionality and remain backwards compatible with the EXT
version of the extension.
5. If the texture environment for a given texture unit does not
reference the texture object that is bound to that texture unit,
does a valid texture object need to be bound that unit?
- RESOLVED: Yes. Each texture unit implicitly references the
texture object that is bound to that unit, regardless of the
texture environment function. This may require that
applications bind a dummy texture to the texture unit.
6. Should we allow the secondary color to take part in texture blending?
- RESOLVED: Not in this extension. Secondary color was defined
as a specular part of the lit color and does not have associated
alpha. In order to do this right, the secondary color extension
needs to be fixed first to allow a full featured color and clearly
state the interaction of how it interacts with the color sum stage.
7. How exactly is this ARB extension different from the EXT version?
- RESOLVED:
1) This extension adds the GL_SUBTRACT_ARB mode
2) OPERAND2_RGB_ARB can use SRC_COLOR, ONE_MINUS_SRC_COLOR,
SRC_ALPHA, and ONE_MINUS_SRC_ALPHA instead of just SRC_ALPHA
(NV_texture_env_combine4 already provides this).
3) OPERAND2_ALPHA_ARB can use SRC_ALPHA and ONE_MINUS_SRC_ALPHA
instead of just SRC_ALPHA (NV_texture_env_combine4 already
provides this).
New Procedures and Functions
None
New Tokens
Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <pname> parameter value is TEXTURE_ENV_MODE
COMBINE_ARB 0x8570
Accepted by the <pname> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <target> parameter value is TEXTURE_ENV
COMBINE_RGB_ARB 0x8571
COMBINE_ALPHA_ARB 0x8572
SOURCE0_RGB_ARB 0x8580
SOURCE1_RGB_ARB 0x8581
SOURCE2_RGB_ARB 0x8582
SOURCE0_ALPHA_ARB 0x8588
SOURCE1_ALPHA_ARB 0x8589
SOURCE2_ALPHA_ARB 0x858A
OPERAND0_RGB_ARB 0x8590
OPERAND1_RGB_ARB 0x8591
OPERAND2_RGB_ARB 0x8592
OPERAND0_ALPHA_ARB 0x8598
OPERAND1_ALPHA_ARB 0x8599
OPERAND2_ALPHA_ARB 0x859A
RGB_SCALE_ARB 0x8573
ALPHA_SCALE
Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <pname> parameter value is COMBINE_RGB_ARB
or COMBINE_ALPHA_ARB
REPLACE
MODULATE
ADD
ADD_SIGNED_ARB 0x8574
INTERPOLATE_ARB 0x8575
SUBTRACT_ARB 0x84E7
Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <pname> parameter value is SOURCE0_RGB_ARB,
SOURCE1_RGB_ARB, SOURCE2_RGB_ARB, SOURCE0_ALPHA_ARB,
SOURCE1_ALPHA_ARB, or SOURCE2_ALPHA_ARB
TEXTURE
CONSTANT_ARB 0x8576
PRIMARY_COLOR_ARB 0x8577
PREVIOUS_ARB 0x8578
Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <pname> parameter value is
OPERAND0_RGB_ARB, OPERAND1_RGB_ARB, or OPERAND2_RGB_ARB
SRC_COLOR
ONE_MINUS_SRC_COLOR
SRC_ALPHA
ONE_MINUS_SRC_ALPHA
Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <pname> parameter value is
OPERAND0_ALPHA_ARB, OPERAND1_ALPHA_ARB, or OPERAND2_ALPHA_ARB
SRC_ALPHA
ONE_MINUS_SRC_ALPHA
Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <pname> parameter value is RGB_SCALE_ARB or
ALPHA_SCALE
1.0
2.0
4.0
Additions to Chapter 2 of the GL Specification (OpenGL Operation)
None
Additions to Chapter 3 of the GL Specification (Rasterization)
Added to subsection 3.8.9, before the paragraph describing the
state requirements:
If the value of TEXTURE_ENV_MODE is COMBINE_ARB, the form of the
texture function depends on the values of COMBINE_RGB_ARB and
COMBINE_ALPHA_ARB, according to table 3.20. The RGB and ALPHA
results of the texture function are then multiplied by the values
of RGB_SCALE_ARB and ALPHA_SCALE, respectively. The results are
clamped to [0,1].
COMBINE_RGB_ARB Texture Function
------------------ ----------------
REPLACE Arg0
MODULATE Arg0 * Arg1
ADD Arg0 + Arg1
ADD_SIGNED_ARB Arg0 + Arg1 - 0.5
INTERPOLATE_ARB Arg0 * (Arg2) + Arg1 * (1-Arg2)
SUBTRACT_ARB Arg0 - Arg1
COMBINE_ALPHA_ARB Texture Function
------------------ ----------------
REPLACE Arg0
MODULATE Arg0 * Arg1
ADD Arg0 + Arg1
ADD_SIGNED_ARB Arg0 + Arg1 - 0.5
INTERPOLATE_ARB Arg0 * (Arg2) + Arg1 * (1-Arg2)
SUBTRACT_ARB Arg0 - Arg1
Table 3.20: COMBINE_ARB texture functions
The arguments Arg0, Arg1 and Arg2 are determined by the values of
SOURCE<n>_RGB_ARB, SOURCE<n>_ALPHA_ARB, OPERAND<n>_RGB_ARB and
OPERAND<n>_ALPHA_ARB. In the following two tables, Ct and At are
the filtered texture RGB and alpha values; Cc and Ac are the
texture environment RGB and alpha values; Cf and Af are the RGB
and alpha of the primary color of the incoming fragment; and Cp
and Ap are the RGB and alpha values resulting from the previous
texture environment. On texture environment 0, Cp and Ap are
identical to Cf and Af, respectively. The relationship is
described in tables 3.21 and 3.22.
SOURCE<n>_RGB_ARB OPERAND<n>_RGB_ARB Argument
----------------- -------------- --------
TEXTURE SRC_COLOR Ct
ONE_MINUS_SRC_COLOR (1-Ct)
SRC_ALPHA At
ONE_MINUS_SRC_ALPHA (1-At)
CONSTANT_ARB SRC_COLOR Cc
ONE_MINUS_SRC_COLOR (1-Cc)
SRC_ALPHA Ac
ONE_MINUS_SRC_ALPHA (1-Ac)
PRIMARY_COLOR_ARB SRC_COLOR Cf
ONE_MINUS_SRC_COLOR (1-Cf)
SRC_ALPHA Af
ONE_MINUS_SRC_ALPHA (1-Af)
PREVIOUS_ARB SRC_COLOR Cp
ONE_MINUS_SRC_COLOR (1-Cp)
SRC_ALPHA Ap
ONE_MINUS_SRC_ALPHA (1-Ap)
Table 3.21: Arguments for COMBINE_RGB_ARB functions
SOURCE<n>_ALPHA_ARB OPERAND<n>_ALPHA_ARB Argument
----------------- -------------- --------
TEXTURE SRC_ALPHA At
ONE_MINUS_SRC_ALPHA (1-At)
CONSTANT_ARB SRC_ALPHA Ac
ONE_MINUS_SRC_ALPHA (1-Ac)
PRIMARY_COLOR_ARB SRC_ALPHA Af
ONE_MINUS_SRC_ALPHA (1-Af)
PREVIOUS_ARB SRC_ALPHA Ap
ONE_MINUS_SRC_ALPHA (1-Ap)
Table 3.22: Arguments for COMBINE_ALPHA_ARB functions
The mapping of texture components to source components is
summarized in Table 3.23. In the following table, At, Lt, It, Rt,
Gt and Bt are the filtered texel values.
Base Internal Format RGB Values Alpha Value
-------------------- ---------- -----------
ALPHA 0, 0, 0 At
LUMINANCE Lt, Lt, Lt 1
LUMINANCE_ALPHA Lt, Lt, Lt At
INTENSITY It, It, It It
RGB Rt, Gt, Bt 1
RGBA Rt, Gt, Bt At
Table 3.23: Correspondence of texture components to source
components for COMBINE_RGB_ARB and COMBINE_ALPHA_ARB arguments
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)
None
Additions to Chapter 6 of the GL Specification (State and State Requests)
None
Additions to Appendix F of the GL Specification (ARB Extensions)
Inserted after the second paragraph of F.2.12:
If the value of TEXTURE_ENV_MODE is COMBINE_ARB, the texture
function associated with a given texture unit is computed using
the values specified by SOURCE<n>_RGB_ARB, SOURCE<n>_ALPHA_ARB,
OPERAND<n>_RGB_ARB and OPERAND<n>_ALPHA_ARB. If TEXTURE<n>_ARB is
specified as SOURCE<n>_RGB_ARB or SOURCE<n>_ALPHA_ARB, the texture
value from texture unit <n> will be used in computing the texture
function for this texture unit.
Inserted after the third paragraph of F.2.12:
If a texture environment for a given texture unit references a
texture unit that is disabled or does not have a valid texture
object bound to it, then it is as if texture is disabled for the
given texture unit. Every texture unit implicitly references the
texture object that is bound to it, regardless of the texture
function specified by COMBINE_RGB_ARB or COMBINE_ALPHA_ARB.
Additions to the GLX Specification
None
GLX Protocol
None
Errors
INVALID_ENUM is generated if <params> value for COMBINE_RGB_ARB or
COMBINE_ALPHA_ARB is not one of REPLACE, MODULATE, ADD,
ADD_SIGNED_ARB, INTERPOLATE_ARB, or SUBTRACT_ARB
INVALID_ENUM is generated if <params> value for SOURCE0_RGB_ARB,
SOURCE1_RGB_ARB, SOURCE2_RGB_ARB, SOURCE0_ALPHA_ARB,
SOURCE1_ALPHA_ARB or SOURCE2_ALPHA_ARB is not one of TEXTURE,
CONSTANT_ARB, PRIMARY_COLOR_ARB, or PREVIOUS_ARB.
INVALID_ENUM is generated if <params> value for OPERAND0_RGB_ARB,
OPERAND1_RGB_ARB, or OPERAND2_RGB_ARB is not one of SRC_COLOR,
ONE_MINUS_SRC_COLOR, SRC_ALPHA or ONE_MINUS_SRC_ALPHA.
INVALID_ENUM is generated if <params> value for OPERAND0_ALPHA_ARB,
OPERAND1_ALPHA_ARB, or OPERAND2_ALPHA_ARB is not one of SRC_ALPHA
or ONE_MINUS_SRC_ALPHA.
INVALID_VALUE is generated if <params> value for RGB_SCALE_ARB or
ALPHA_SCALE is not one of 1.0, 2.0, or 4.0.
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
COMBINE_RGB_ARB GetTexEnviv n x Z4 MODULATE texture
COMBINE_ALPHA_ARB GetTexEnviv n x Z4 MODULATE texture
SOURCE0_RGB_ARB GetTexEnviv n x Z3 TEXTURE texture
SOURCE1_RGB_ARB GetTexEnviv n x Z3 PREVIOUS_ARB texture
SOURCE2_RGB_ARB GetTexEnviv n x Z3 CONSTANT_ARB texture
SOURCE0_ALPHA_ARB GetTexEnviv n x Z3 TEXTURE texture
SOURCE1_ALPHA_ARB GetTexEnviv n x Z3 PREVIOUS_ARB texture
SOURCE2_ALPHA_ARB GetTexEnviv n x Z3 CONSTANT_ARB texture
OPERAND0_RGB_ARB GetTexEnviv n x Z6 SRC_COLOR texture
OPERAND1_RGB_ARB GetTexEnviv n x Z6 SRC_COLOR texture
OPERAND2_RGB_ARB GetTexEnviv n x Z1 SRC_ALPHA texture
OPERAND0_ALPHA_ARB GetTexEnviv n x Z4 SRC_ALPHA texture
OPERAND1_ALPHA_ARB GetTexEnviv n x Z4 SRC_ALPHA texture
OPERAND2_ALPHA_ARB GetTexEnviv n x Z1 SRC_ALPHA texture
RGB_SCALE_ARB GetTexEnvfv n x R3 1.0 texture
ALPHA_SCALE GetTexEnvfv n x R3 1.0 texture
New Implementation Dependent State
None
Revision History
06/11/04 benj Updated contact info after ATI/AMD merger.
01/05/21 mjk Added ARB versus EXT differences issue
01/02/02 bpoddar Added original EXT/ARB contributors to the contact
list
00/12/13 bpoddar Added enum value for SUBTRACT_ARB
00/12/06 bpoddar Moved references to Ct<n> and At<n> to
ARB_texture_env_crossbar spec.
00/12/01 bpoddar Removed TEXTURE<n>_ARB since several companies
had problems with this addition in the base spec.
00/11/13 bpoddar Recreated 6/20 spec with language for dealing
with inconsistent textures moved to appendix F.
00/06/20 rhammers Changed behavior when dealing with references
do disabled and inconsistent textures.
00/05/23 rhammers Cleaned up for first draft of ARB version.
Added issue -- TEXTURE with TEXTURE<n>_ARB
Added issue .. "upstream" textures
Listed get functions with description of
enumerants.
Added 1.1 and multitexture to dependencies
00/05/18 rhammers First rev of ARB version of the spec. Based on
EXT_texture_env_combine.
Relaxed restriction on Arg2.
Added support for TEXTURE<n>_ARB.
Added SUBTRACT_ARB combiner function.
do disabled and inconsistent textures.
