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))