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Name
OES_texture_env_crossbar
Name Strings
GL_OES_texture_env_crossbar
Contact
Notice
Copyright (c) 2005-2013 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 ES 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
Version
Last modified date: May 18, 2005
Number
OpenGL ES Extension #21
Dependencies
OpenGL ES 1.1 is required.
This extension is based on the ARB_texture_env_crossbar
extension specification.
Overview
This extension adds the capability to use the texture color from
other texture units as sources to the COMBINE enviornment
function. OpenGL ES 1.1 defined texture combine functions which
could use the color from the current texture unit as a source.
This extension adds the ability to use the color from any texture
unit as a source.
Issues
Please refer to the ARB_texture_env_crossbar extension specification.
New Procedures and Functions
None
New Tokens
Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv,
and TexEnviv when the <pname> parameter value is SOURCE0_RGB,
SOURCE1_RGB, SOURCE2_RGB, SOURCE0_ALPHA,
SOURCE1_ALPHA, or SOURCE2_ALPHA
TEXTURE<n> 0x84C0+<n>
where <n> is in the range 0 to MAX_TEXTURE_UNITS.
Additions to Chapter 2 of the GL Specification (OpenGL Operation)
None
Additions to Chapter 3 of the GL Specification (Rasterization)
The arguments Arg0, Arg1 and Arg2 are determined by the values of
SOURCE<n>_RGB, SOURCE<n>_ALPHA, OPERAND<n>_RGB and
OPERAND<n>_ALPHA. In the following two tables, Ct and At are
the filtered texture RGB and alpha values; Ct<n> and At<n> are the
filtered texture RGB and alpha values from the texture bound to
texture unit <n>; 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 table 3.5 and 3.6 of the OpenGL ES 1.2
specification.
Added to table 3.5 of the OpenGL ES 1.2 specification:
SOURCE<n>_RGB OPERAND<n>_RGB Argument
------------- -------------- --------
TEXTURE<n> SRC_COLOR Ct<n>
ONE_MINUS_SRC_COLOR (1-Ct<n>)
SRC_ALPHA At<n>
ONE_MINUS_SRC_ALPHA (1-At<n>)
Table 3.6: COMBINE_RGB texture functions
Added to table 3.6 of the OpenGL ES 1.2 specification:
SOURCE<n>_ALPHA OPERAND<n>_ALPHA Argument
--------------- ---------------- --------
TEXTURE<n> SRC_ALPHA At<n>
ONE_MINUS_SRC_ALPHA (1-At<n>)
Table 3.6: COMBINE_ALPHA texture functions
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, the texture
function associated with a given texture unit is computed using
the values specified by SOURCE<n>_RGB, SOURCE<n>_ALPHA,
OPERAND<n>_RGB and OPERAND<n>_ALPHA. If TEXTURE<n> is
specified as SOURCE<n>_RGB or SOURCE<n>_ALPHA, 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 blending 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 or COMBINE_ALPHA.
Additions to the GLX Specification
None
GLX Protocol
None
Errors
INVALID_ENUM is generated if <params> value for SOURCE0_RGB,
SOURCE1_RGB, SOURCE2_RGB, SOURCE0_ALPHA,
SOURCE1_ALPHA or SOURCE2_ALPHA is not one of TEXTURE,
CONSTANT, PRIMARY_COLOR, PREVIOUS, or TEXTURE<n>,
where <n> is in the range 0 to MAX_TEXTURE_UNITS.
New State
None