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	``destina-
       tion'' 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 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  ),  respec-
       tively.	 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 ), respectively.  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 componentwise 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  trans-
       parency, 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)