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GLBLENDEQUATION(3G)                                                                      GLBLENDEQUATION(3G)



NAME
       glBlendEquation - set the blend equation


C SPECIFICATION
       void glBlendEquation( GLenum mode )


PARAMETERS
       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.


DESCRIPTION
       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 sets  the blend equation so that each component of the result color is the minimum of the cor-responding corresponding
              responding components of the source and destination colors.

       GL_MAX sets the blend equation so that each component of the result color is the maximum of the  cor-responding corresponding
              responding 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 (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  ),  respec-tively. respectively.
       tively.   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 = 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
              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 = 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
              Is like GL_FUNC_ADD except the product of the source factor and the source color is component-wise componentwise
              wise 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 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.


NOTES
       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.


ERRORS
       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.

ASSOCIATED GETS
       glGet with an argument of GL_BLEND_EQUATION

SEE ALSO
       glGetString(3G), glBlendColor(3G), glBlendFunc(3G)




                                                                                         GLBLENDEQUATION(3G)