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EXT_blend_minmax.txt
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Name
EXT_blend_minmax
Name Strings
GL_EXT_blend_minmax
Version
Last Modified Date: September 17, 2009
Version: 1.5
Number
OpenGL Extension #37
OpenGL ES Extension #65
Dependencies
There is an interaction with OpenGL ES.
Overview
Blending capability is extended by respecifying the entire blend
equation. While this document defines only two new equations, the
BlendEquationEXT procedure that it defines will be used by subsequent
extensions to define additional blending equations.
The two new equations defined by this extension produce the minimum
(or maximum) color components of the source and destination colors.
Taking the maximum is useful for applications such as maximum projection
in medical imaging.
Issues
* I've prefixed the ADD token with FUNC, to indicate that the blend
equation includes the parameters specified by BlendFunc. (The min
and max equations don't.) Is this necessary? Is it too ugly?
Is there a better way to accomplish the same thing?
New Procedures and Functions
void BlendEquationEXT(enum mode);
New Tokens
Accepted by the <mode> parameter of BlendEquationEXT:
FUNC_ADD_EXT 0x8006
MIN_EXT 0x8007
MAX_EXT 0x8008
Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev:
BLEND_EQUATION_EXT 0x8009
Additions to Chapter 2 of the GL Specification (OpenGL Operation)
None
Additions to Chapter 3 of the GL Specification (Rasterization)
None
Additions to Chapter 4 of the GL Specification (Per-Fragment Operations
and the Framebuffer)
The GL Specification defines a single blending equation. This
extension introduces a blend equation mode that is specified by calling
BlendEquationEXT with one of three enumerated values. The default
value FUNC_ADD_EXT specifies that the blending equation defined in
the GL Specification be used. This equation is
C' = (Cs * S) + (Cd * D)
/ 1.0 C' > 1.0
C = (
\ C' C' <= 1.0
where Cs and Cd are the source and destination colors, and S and D are
as specified by BlendFunc.
If BlendEquationEXT is called with <mode> set to MIN_EXT, the
blending equation becomes
C = min (Cs, Cd)
Finally, if BlendEquationEXT is called with <mode> set to MAX_EXT, the
blending equation becomes
C = max (Cs, Cd)
In all cases the blending equation is evaluated separately for each
color component.
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 the GLX Specification
None
GLX Protocol
A new GL rendering command is added. The following command is sent to the
server as part of a glXRender request:
BlendEquationEXT
2 8 rendering command length
2 4097 rendering command opcode
4 ENUM mode
Dependencies on OpenGL ES
If the GL is OpenGL ES, only the new MIN_EXT and MAX_EXT blend equations
are introduced by this extension. BlendEquationOES, FUNC_ADD_OES, and
BLEND_EQUATION_OES are introduced by the OES_blend_subtract extension,
which is required for this extension to operate. Alternatively,
OpenGL ES 2.0 is required, which introduces BlendEquation, FUNC_ADD, and
BLEND_EQUATION without the suffixes.
MIN_EXT and MAX_EXT should be added to Table 4.blendeq described in the
OES_blend_subtract extension specification, and Table 4.1 of the OpenGL
ES 2.0 specification.
Mentions of GetDoublev, Begin/End, and GLX in this extension specification
can be ignored for OpenGL ES. Also, BlendEquationEXT and FUNC_ADD_EXT
instead have the OES suffix courtesy of OES_blend_subtract, or no suffix
courtesy of core OpenGL ES 2.0.
Errors
INVALID_ENUM is generated by BlendEquationEXT if its single parameter
is not FUNC_ADD_EXT, MIN_EXT, or MAX_EXT.
INVALID_OPERATION is generated if BlendEquationEXT is executed between
the execution of Begin and the corresponding execution to End.
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
BLEND_EQUATION_EXT GetIntegerv Z3 FUNC_ADD_EXT color-buffer
New Implementation Dependent State
None
Revision History
Version 1.5, September 17, 2009 (Jon Leech) -
Merge into OpenGL Registry version of the extension and assign
OpenGL ES extension number.
Version 1.4, May 19, 2009 (Benj Lipchak) -
Adapted for OpenGL ES.
Version 1.3, May 31, 1995 -
Last SGI revision.