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  corresponding  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  corresponding  components  of  the
              source and destination colors.

       The  remaining blend equations use the source and destination blend fac‐
       tors 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 destina‐
       tion blend factors are denoted (sR,sG,sB,sA) and (dR,dG,dB,dA),  respec‐
       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  des‐
              tination  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,RssR+RddR)
                     Gr=min(1,GssG+GddG)
                     Br=min(1,BssB+BddB)
                     Ar=min(1,AssA+AddA)

       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,RssR−RddR)
                     Gr=max(0,GssG−GddG)
                     Br=max(0,BssB−BddB)

       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, glBlendColor, glBlendFunc

                                                            GLBLENDEQUATION(3G)