'\" te '\"macro stdmacro .ds Vn Version 1.2 .ds Dt 24 September 1999 .ds Re Release 1.2.1 .ds Dp May 22 14:44 .ds Dm 1 May 22 14: .ds Xs 36751 7 .TH GLBLENDEQUATION 3G .SH NAME .B "glBlendEquation \- set the blend equation .SH C SPECIFICATION void \f3glBlendEquation\fP( GLenum \fImode\fP ) .nf .fi .EQ delim $$ .EN .SH PARAMETERS .TP \w'\f2mode\fP\ \ 'u \f2mode\fP specifies how source and destination colors are combined. It must be \%\f3GL_FUNC_ADD\fP, \%\f3GL_FUNC_SUBTRACT\fP, \%\f3GL_FUNC_REVERSE_SUBTRACT\fP, \%\f3GL_MIN\fP, \%\f3GL_MAX\fP. .SH DESCRIPTION The blend equation determines how a new pixel (the ``source'' color) is combined with a pixel already in the framebuffer (the ``destination'' color). .TP \%\f3GL_MIN\fP 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. .TP \%\f3GL_MAX\fP 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. .P The remaining blend equations use the source and destination blend factors specified by \%\f3glBlendFunc\fP. See \%\f3glBlendFunc\fP for a description of the various blend factors. .P 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]. .TP \%\f3GL_FUNC_ADD\fP 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]. .P .RS .nf .IP $Rr ~=~ mark min (1, ~R sub s~s sub R ~+~ R sub d~d sub R )$ $Gr ~=~ lineup min (1, ~G sub s~s sub G ~+~ G sub d~d sub G )$ $Br ~=~ lineup min (1, ~B sub s~s sub B ~+~ B sub d~d sub B )$ $Ar ~=~ lineup min (1, ~A sub s~s sub A ~+~ A sub d~d sub A )$ .fi .RE .TP \%\f3GL_FUNC_SUBTRACT\fP Is like \%\f3GL_FUNC_ADD\fP 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]. .RS .nf .IP $Rr ~=~ mark max (0 , ~R sub s~s sub R ~-~ R sub d~d sub R )$ $Gr ~=~ lineup max (0 , ~G sub s~s sub G ~-~ G sub d~d sub G )$ $Br ~=~ lineup max (0 , ~B sub s~s sub B ~-~ B sub d~d sub B )$ $Ar ~=~ lineup max (0 , ~A sub s~s sub A ~-~ A sub d~d sub A )$ .fi .RE .TP \%\f3GL_FUNC_REVERSE_SUBTRACT\fP Is like \%\f3GL_FUNC_ADD\fP 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]. .RS .nf .IP $Rr ~=~ mark max (0 , ~R sub d~d sub R ~-~ R sub s~s sub R )$ $Gr ~=~ lineup max (0 , ~G sub d~d sub G ~-~ G sub s~s sub G )$ $Br ~=~ lineup max (0 , ~B sub d~d sub B ~-~ B sub s~s sub B )$ $Ar ~=~ lineup max (0 , ~A sub d~d sub A ~-~ A sub s~s sub A )$ .fi .RE .P The \%\f3GL_MIN\fP and \%\f3GL_MAX\fP equations are useful for applications that analyze .br image data (image thresholding against a constant color, for example). The \%\f3GL_FUNC_ADD\fP equation is useful for antialiasing and transparency, among other things. .P Initially, the blend equation is set to \%\f3GL_FUNC_ADD\fP. .P .SH NOTES \%\f3glBlendEquation\fP is part of the \%\f3GL_ARB_imaging\fP subset. \%\f3glBlendEquation\fP is present only if \%\f3GL_ARB_imaging\fP is returned when \%\f3glGetString\fP is called with \%\f3GL_EXTENSIONS\fP as its argument. .P The \%\f3GL_MIN\fP, and \%\f3GL_MAX\fP equations do not use the source or destination factors, only the source and destination colors. .P .SH ERRORS \%\f3GL_INVALID_ENUM\fP is generated if \f2mode\fP is not one of \%\f3GL_FUNC_ADD\fP, \%\f3GL_FUNC_SUBTRACT\fP, \%\f3GL_FUNC_REVERSE_SUBTRACT\fP, \%\f3GL_MAX\fP, or \%\f3GL_MIN\fP. .P \%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glBlendEquation\fP is executed between the execution of \%\f3glBegin\fP and the corresponding execution of \%\f3glEnd\fP. .SH ASSOCIATED GETS .TP \%\f3glGet\fP with an argument of \%\f3GL_BLEND_EQUATION\fP .SH SEE ALSO \%\f3glGetString\fP, \%\f3glBlendColor\fP, \%\f3glBlendFunc\fP