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Name
EXT_blend_color
Name Strings
GL_EXT_blend_color
Version
$Date: 1995/03/31 04:40:19 $ $Revision: 1.7 $
Number
2
Dependencies
None
Overview
Blending capability is extended by defining a constant color that can
be included in blending equations. A typical usage is blending two
RGB images. Without the constant blend factor, one image must have
an alpha channel with each pixel set to the desired blend factor.
New Procedures and Functions
void BlendColorEXT(clampf red,
clampf green,
clampf blue,
clampf alpha);
New Tokens
Accepted by the <sfactor> and <dfactor> parameters of BlendFunc:
CONSTANT_COLOR_EXT 0x8001
ONE_MINUS_CONSTANT_COLOR_EXT 0x8002
CONSTANT_ALPHA_EXT 0x8003
ONE_MINUS_CONSTANT_ALPHA_EXT 0x8004
Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev:
BLEND_COLOR_EXT 0x8005
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 commands that control blending are now BlendFunc and BlendColorEXT.
A constant color to be used in the blending equation is specified by
BlendColorEXT. The four parameters are clamped to the range [0,1]
before being stored. The default value for the constant blending color
is (0,0,0,0).
The constant color can be used in both the source and destination
blending factors. Four lines are added to table 4.1 and table 4.2:
Value Blend Factors
----- -------------
ZERO (0, 0, 0, 0)
ONE (1, 1, 1, 1)
DST_COLOR (Rd/Kr, Gd/Kg, Bd/Kb, Ad/Ka)
ONE_MINUS_DST_COLOR (1, 1, 1, 1) - (Rd/Kr,Gd/Kg,Bd/Kb,Ad/Ka)
SRC_ALPHA (As, As, As, As) / Ka
ONE_MINUS_SRC_ALPHA (1, 1, 1, 1) - (As, As, As, As) / Ka
DST_ALPHA (Ad, Ad, Ad, Ad) / Ka
ONE_MINUS_DST_ALPHA (1, 1, 1, 1) - (Ad, Ad, Ad, Ad) / Ka
CONSTANT_COLOR_EXT (Rc, Gc, Bc, Ac) NEW
ONE_MINUS_CONSTANT_COLOR_EXT (1, 1, 1, 1) - (Rc, Gc, Bc, Ac) NEW
CONSTANT_ALPHA_EXT (Ac, Ac, Ac, Ac) NEW
ONE_MINUS_CONSTANT_ALPHA_EXT (1, 1, 1, 1) - (Ac, Ac, Ac, Ac) NEW
SRC_ALPHA_SATURATE (f, f, f, 1)
Table 4.1: Values controlling the source blending function and the
source blending values they compute. Ka = 2**m - 1, where m is the
number of bits in the A color component. Kr, Kg, and Kb are similarly
determined by the number of bits in the R, G, and B color components.
f = min(As, 1-Ad) / Ka.
Value Blend Factors
----- -------------
ZERO (0, 0, 0, 0)
ONE (1, 1, 1, 1)
SRC_COLOR (Rs/Kr, Gs/Kg, Bs/Kb, As/Ka)
ONE_MINUS_SRC_COLOR (1, 1, 1, 1) - (Rs/Kr,Gs/Kg,Bs/Kb,As/Ka)
SRC_ALPHA (As, As, As, As) / Ka
ONE_MINUS_SRC_ALPHA (1, 1, 1, 1) - (As, As, As, As) / Ka
DST_ALPHA (Ad, Ad, Ad, Ad) / Ka
ONE_MINUS_DST_ALPHA (1, 1, 1, 1) - (Ad, Ad, Ad, Ad) / Ka
CONSTANT_COLOR_EXT (Rc, Gc, Bc, Ac) NEW
ONE_MINUS_CONSTANT_COLOR_EXT (1, 1, 1, 1) - (Rc, Gc, Bc, Ac) NEW
CONSTANT_ALPHA_EXT (Ac, Ac, Ac, Ac) NEW
ONE_MINUS_CONSTANT_ALPHA_EXT (1, 1, 1, 1) - (Ac, Ac, Ac, Ac) NEW
Table 4.2: Values controlling the destination blending function and
the destination blending values they compute. Ka = 2**m - 1, where
m is the number of bits in the A color component. Kr, Kg, and Kb
are similarly determined by the number of bits in the R, G, and B
color components.
Rc, Gc, Bc, and Ac are the four components of the constant blending
color. These blend factors are not scaled by Kr, Kg, Kb, and Ka,
because they are already in the range [0,1].
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:
BlendColorEXT
2 20 rendering command length
2 4096 rendering command opcode
4 FLOAT32 red
4 FLOAT32 green
4 FLOAT32 blue
4 FLOAT32 alpha
Errors
INVALID_OPERATION is generated if BlendColorEXT is called between
execution of Begin and the corresponding call to End.
New State
Initial
Get Value Get Command Type Value Attrib
--------- ----------- ---- ------- ------
BLEND_COLOR_EXT GetFloatv C (0,0,0,0) color-buffer
New Implementation Dependent State
None