glBlendEquation

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), 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),
       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 destina-
	      tion 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 fac-
	      tor 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)
		     Ar=max(0,AssA−AddA)

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

       The  GL_MIN and GL_MAX equations are useful for applications that ana-
       lyze
       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)