GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
CentOS 5.3 |
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glBlendEquation(3gl) |
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glBlendEquation − set the blend equation
void glBlendEquation( GLenum mode )
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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. |
The blend equation determines how a new pixel (the ’’source’’ color) is combined with a pixel already in the framebuffer (the ’’destination’’ color).
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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. | ||
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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 factors 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 $(R sub s, G sub s, B sub s, A
sub s )$ and $(R sub d, G sub d, B sub d, A sub d )$,
respectively. The result color is referred to as $(R sub r,
G sub r, B sub r, A sub r )$. The source and destination
blend factors are denoted $(s sub R, s sub G, s sub B, s sub
A )$ and $(d sub R, d sub G, d sub B, d sub A )$,
respectively. For these equations all color components 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 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].
$Rr ~=~ mark
min (1, ~R sub s~s sub R ~+~ R sub d~d sub R )$
$Gr ~=~ lineup min (1, ~G sub s~s sub G ~+~ G sub d~d sub G
)$
$Br ~=~ lineup min (1, ~B sub s~s sub B ~+~ B sub d~d sub B
)$
$Ar ~=~ lineup min (1, ~A sub s~s sub A ~+~ A sub d~d sub A
)$
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].
$Rr ~=~ mark
max (0 , ~R sub s~s sub R ~-~ R sub d~d sub R )$
$Gr ~=~ lineup max (0 , ~G sub s~s sub G ~-~ G sub d~d sub G
)$
$Br ~=~ lineup max (0 , ~B sub s~s sub B ~-~ B sub d~d sub B
)$
$Ar ~=~ lineup max (0 , ~A sub s~s sub A ~-~ A sub d~d sub A
)$
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].
$Rr ~=~ mark
max (0 , ~R sub d~d sub R ~-~ R sub s~s sub R )$
$Gr ~=~ lineup max (0 , ~G sub d~d sub G ~-~ G sub s~s sub G
)$
$Br ~=~ lineup max (0 , ~B sub d~d sub B ~-~ B sub s~s sub B
)$
$Ar ~=~ lineup max (0 , ~A sub d~d sub A ~-~ A sub s~s sub A
)$
The
GL_MIN and GL_MAX equations are useful for
applications that analyze
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.
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.
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.
glGet with an argument of GL_BLEND_EQUATION
glGetString(3G), glBlendColor(3G), glBlendFunc(3G)
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glBlendEquation(3gl) | |