NAME
glBlendEquation
- set the blend equation
C SPECIFICATION
void ggllBBlleennddEEqquuaattiioonn(
GLenum _m_o_d_e )
delim $$
PARAMETERS
-
_m_o_d_e
-
specifies how source and destination colors are combined.
It must be GGLL__FFUUNNCC__AADDDD, GGLL__FFUUNNCC__SSUUBBTTRRAACCTT,
GGLL__FFUUNNCC__RREEVVEERRSSEE__SSUUBBTTRRAACCTT, GGLL__MMIINN, GGLL__MMAAXX.
DESCRIPTION
The blend equation determines how a new pixel (the ``source'' color)
is combined with a pixel already in the framebuffer (the ``destination''
color).
-
GGLL__MMIINN
-
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.
-
GGLL__MMAAXX
-
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 ggllBBlleennddFFuunncc.
See ggllBBlleennddFFuunncc 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].
-
GGLL__FFUUNNCC__AADDDD
-
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].
-
$Rr ~=~ mark min (1, ~R sub s~s sub R ~+~ R sub d~d sub R )$
-
$Gr ~=~ lineup min (1, ~G sub s~s sub G ~+~ G sub d~d sub G )$
$Br ~=~ lineup min (1, ~B sub s~s sub B ~+~ B sub d~d sub B )$
$Ar ~=~ lineup min (1, ~A sub s~s sub A ~+~ A sub d~d sub A )$
-
GGLL__FFUUNNCC__SSUUBBTTRRAACCTT
-
Is like GGLL__FFUUNNCC__AADDDD 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].
-
$Rr ~=~ mark max (0 , ~R sub s~s sub R ~-~ R sub d~d sub R )$
-
$Gr ~=~ lineup max (0 , ~G sub s~s sub G ~-~ G sub d~d sub G )$
$Br ~=~ lineup max (0 , ~B sub s~s sub B ~-~ B sub d~d sub B )$
$Ar ~=~ lineup max (0 , ~A sub s~s sub A ~-~ A sub d~d sub A )$
-
GGLL__FFUUNNCC__RREEVVEERRSSEE__SSUUBBTTRRAACCTT
-
Is like GGLL__FFUUNNCC__AADDDD 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 GGLL__MMIINN and GGLL__MMAAXX equations are useful for applications
that analyze
image data (image thresholding against a constant color,
for example).
The GGLL__FFUUNNCC__AADDDD equation is useful
for antialiasing and transparency, among other things.
Initially, the blend equation is set to GGLL__FFUUNNCC__AADDDD.
NOTES
ggllBBlleennddEEqquuaattiioonn is part of the GGLL__AARRBB__iimmaaggiinngg subset. ggllBBlleennddEEqquuaattiioonn is present only
if GGLL__AARRBB__iimmaaggiinngg is returned when ggllGGeettSSttrriinngg is called with
GGLL__EEXXTTEENNSSIIOONNSS as its argument.
The GGLL__MMIINN, and GGLL__MMAAXX equations do not use
the source or destination factors, only the source and destination colors.
ERRORS
GGLL__IINNVVAALLIIDD__EENNUUMM is generated if _m_o_d_e is not one of
GGLL__FFUUNNCC__AADDDD, GGLL__FFUUNNCC__SSUUBBTTRRAACCTT, GGLL__FFUUNNCC__RREEVVEERRSSEE__SSUUBBTTRRAACCTT,
GGLL__MMAAXX, or GGLL__MMIINN.
GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if ggllBBlleennddEEqquuaattiioonn is executed
between the execution of ggllBBeeggiinn and the corresponding
execution of ggllEEnndd.
ASSOCIATED GETS
-
ggllGGeett with an argument of GGLL__BBLLEENNDD__EEQQUUAATTIIOONN
-
SEE ALSO
ggllGGeettSSttrriinngg((33GG)),
ggllBBlleennddCCoolloorr((33GG)),
ggllBBlleennddFFuunncc((33GG))