glBlendEquationEXT(3G) OpenGL Reference glBlendEquationEXT(3G)
glBlendEquationEXT - set the blend equation
void glBlendEquationEXT( GLenum mode )
mode specifies how source and destination colors are combined. It must
be GL_FUNC_ADD_EXT, GL_FUNC_SUBTRACT_EXT,
GL_FUNC_REVERSE_SUBTRACT_EXT, GL_MIN_EXT, GL_MAX_EXT,
GL_ALPHA_MIN_SGIX, GL_ALPHA_MAX_SGIX, or GL_LOGIC_OP.
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_EXT [Toc] [Back]
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_EXT [Toc] [Back]
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.
GL_ALPHA_MIN_SGIX [Toc] [Back]
sets the blend equation so that the result color is either the
source or destination color, according to whether the alpha
component of the source color is less than, or greater than or equal
to, the alpha component of the destination color, respectively.
GL_ALPHA_MAX_SGIX [Toc] [Back]
sets the blend equation so that the result color is either the
source or destination color, according to whether the alpha
component of the source color is greater than, or less than or equal
to, the alpha component of the destination color, respectively.
GL_LOGIC_OP [Toc] [Back]
sets the blend equation so that each component of the result color
is a bitwise logical combination of the corresponding components of
the source and destination colors. Use the glLogicOp command to
specify the logical operator.
The remaining blend equations use the source and destination blend
factors specified by glBlendFunc. See glBlendFunc for a description of
the various blend factors.
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glBlendEquationEXT(3G) OpenGL Reference glBlendEquationEXT(3G)
In the equations that follow, source and destination color components are
referred to as (Rs,Gs,Bs,As) and (Rd,Gd,Bd,Ad), respectively. 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 components are understood to have values
between 0.0 and 1.0, inclusive.
GL_FUNC_ADD_EXT [Toc] [Back]
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 destination
color is multiplied by the corresponding destination factor. The
result is the componentwise sum of the two products, 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_EXT [Toc] [Back]
Is like GL_FUNC_ADD_EXT 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_EXT [Toc] [Back]
Is like GL_FUNC_ADD_EXT 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_EXT and GL_MAX_EXT equations are useful for applications that
analyze image data (image thresholding against a constant color, for
example). The GL_LOGIC_OP equation is most commonly used with GL_XOR for
reversible drawing. The GL_FUNC_ADD_EXT equation is useful for antialiasing
and transparency, among other things.
Initially the blend equation is set to GL_FUNC_ADD_EXT.
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glBlendEquationEXT(3G) OpenGL Reference glBlendEquationEXT(3G)
NOTES
The GL_MIN_EXT, GL_MAX_EXT, GL_ALPHA_MIN_SGIX, GL_ALPHA_MAX_SGIX and
GL_LOGIC_OP equations do not use the source or destination factors, only
the source and destination colors.
GL_INVALID_ENUM is generated if mode is not one of GL_FUNC_ADD_EXT,
GL_FUNC_SUBTRACT_EXT, GL_FUNC_REVERSE_SUBTRACT_EXT, GL_MAX_EXT,
GL_MIN_EXT, or GL_LOGIC_OP.
GL_INVALID_OPERATION is generated if glBlendEquationEXT is executed
between the execution of glBegin and the corresponding execution of
glEnd.
glGet with an argument of GL_BLEND_EQUATION_EXT.
glGetString with an argument of GL_EXTENSIONS.
This feature is not part of standard GL. The extensions string of
glGetString will contain the name blend_minmax if GL_MIN_EXT and
GL_MAX_EXT are supported. It will contain the name blend_logic_op
if GL_LOGIC_OP is supported in RGB mode. It will contain the name
blend_subtract if GL_FUNC_SUBTRACT_EXT and
GL_FUNC_REVERSE_SUBTRACT_EXT are supported.
MACHINE DEPENDENCIES
RealityEngine, RealityEngine2, and VTX systems do not support the use of
blend factor GL_SRC_ALPHA_SATURATE with blend equation
GL_FUNC_REVERSE_SUBTRACT_EXT; this combination produces incorrect
results.
The SGIX_blend_alpha_minmax extension is supported only on Octane2 VPro
systems.
glGetString, glBlendColorEXT, glBlendFunc.
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