glBlendEquation(3) glBlendEquation(3)
NAME
glBlendEquation - set the blend equation
C SPECIFICATION
void glBlendEquation( GLenum mode )
PARAMETERS
mode specifies how source and destination colors are combined. It
must be GL_FUNC_ADD, GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT,
GL_MIN, GL_MAX.
DESCRIPTION
The blend equation determines how a new pixel (the ``source'' color) is
combined with a pixel already in the framebuffer (the ``destination''
color).
GL_MIN sets the blend equation so that each component of the result
color is the minimum of the corresponding components of the
source and destination colors.
GL_MAX sets the blend equation so that each component of the result
color is the maximum of the corresponding components of the
source and destination colors.
The remaining blend equations use the source and destination blend fac-
tors specified by glBlendFunc. See glBlendFunc for a description of
the various blend factors.
In the equations that follow, source and destination color components
are referred to as (Rs, Gs, Bs, As ) and (Rd, Gd, Bd, Ad ), respec-
tively. The result color is referred to as (Rr, Gr, Br, Ar ). The
source and destination blend factors are denoted (sR, sG, sB, sA ) and
(dR, dG, dB, dA ), respectively. For these equations all color compo-
nents are understood to have values in the range [0, 1].
GL_FUNC_ADD
sets the blend equation so that the source and destination data
are added. Each component of the source color is multiplied by
the corresponding source factor, then each component of the des-
tination color is multiplied by the corresponding destination
factor. The result is the componentwise sum of the two prod-
ucts, clamped to the range [0, 1].
Rr = min (1, Rs sR + Rd dR )
Gr = min (1, Gs sG + Gd dG )
Br = min (1, Bs sB + Bd dB )
Ar = min (1, As sA + Ad dA )
GL_FUNC_SUBTRACT
Is like GL_FUNC_ADD except the product of the destination factor
and the destination color is componentwise subtracted from the
product of the source factor and the source color. The result
is clamped to the range [0, 1].
Rr = max (0 , Rs sR - Rd dR )
Gr = max (0 , Gs sG - Gd dG )
Br = max (0 , Bs sB - Bd dB )
Ar = max (0 , As sA - Ad dA )
GL_FUNC_REVERSE_SUBTRACT
Is like GL_FUNC_ADD except the product of the source factor and
the source color is componentwise subtracted from the product of
the destination factor and the destination color. The result is
clamped to the range [0, 1].
Rr = max (0 , Rd dR - Rs sR )
Gr = max (0 , Gd dG - Gs sG )
Br = max (0 , Bd dB - Bs sB )
Ar = max (0 , Ad dA - As sA )
The GL_MIN and GL_MAX equations are useful for applications that ana-
lyze
image data (image thresholding against a constant color, for example).
The GL_FUNC_ADD equation is useful for antialiasing and transparency,
among other things.
Initially, the blend equation is set to GL_FUNC_ADD.
NOTES
glBlendEquation is part of the GL_ARB_imaging subset. glBlendEquation
is present only if GL_ARB_imaging is returned when glGetString is
called with GL_EXTENSIONS as its argument.
The GL_MIN, and GL_MAX equations do not use the source or destination
factors, only the source and destination colors.
ERRORS
GL_INVALID_ENUM is generated if mode is not one of GL_FUNC_ADD,
GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT, GL_MAX, or GL_MIN.
GL_INVALID_OPERATION is generated if glBlendEquation is executed
between the execution of glBegin and the corresponding execution of
glEnd.
ASSOCIATED GETS
glGet with an argument of GL_BLEND_EQUATION
SEE ALSO
glGetString(3), glBlendColor(3), glBlendFunc(3)
glBlendEquation(3)
Mac OS X 10.6 - Generated Thu Sep 17 20:20:14 CDT 2009