glLogicOp

GLLOGICOP(3G)							GLLOGICOP(3G)



NAME
       glLogicOp  - specify a logical pixel operation for color index render-
       ing


C SPECIFICATION
       void glLogicOp( GLenum opcode )


PARAMETERS
       opcode  Specifies a symbolic constant that selects  a  logical  opera-
	       tion.   The  following symbols are accepted: GL_CLEAR, GL_SET,
	       GL_COPY,	  GL_COPY_INVERTED,   GL_NOOP,	 GL_INVERT,   GL_AND,
	       GL_NAND,	 GL_OR,	 GL_NOR,  GL_XOR,  GL_EQUIV,  GL_AND_REVERSE,
	       GL_AND_INVERTED, GL_OR_REVERSE, and GL_OR_INVERTED.  The	 ini-
	       tial value is GL_COPY.

DESCRIPTION
       glLogicOp specifies a logical operation that, when enabled, is applied
       between the incoming color index or RGBA color and the color index  or
       RGBA  color  at	the  corresponding  location in the frame buffer.  To
       enable or disable the logical operation, call glEnable  and  glDisable
       using  the  symbolic  constant  GL_COLOR_LOGIC_OP  for  RGBA  mode  or
       GL_INDEX_LOGIC_OP for color index mode. The initial value is  disabled
       for both operations.


		       ---------------------------------------
		       Opcode		  Resulting Operation
		       ---------------------------------------
		       GL_CLEAR			   0
		       GL_SET			   1
		       GL_COPY			   s
		       GL_COPY_INVERTED		  ~s
		       GL_NOOP			   d
		       GL_INVERT		  ~d
		       GL_AND			 s & d
		       GL_NAND		       ~(s & d)
		       GL_OR			 s | d
		       GL_NOR		       ~(s | d)
		       GL_XOR			 s ^ d
		       GL_EQUIV		       ~(s ^ d)
		       GL_AND_REVERSE		s & ~d
		       GL_AND_INVERTED		~s & d
		       GL_OR_REVERSE		s | ~d
		       GL_OR_INVERTED		~s | d
		       ---------------------------------------

       opcode  is  a  symbolic	constant  chosen from the list above.  In the
       explanation of the logical operations, s represents the incoming color
       index and d represents the index in the frame buffer.  Standard C-lan-
       guage operators are used.  As these  bitwise  operators	suggest,  the
       logical	operation  is  applied	independently to each bit pair of the
       source and destination indices or colors.

NOTES
       Color index logical operations  are  always  supported.	RGBA  logical
       operations are supported only if the GL version is 1.1 or greater.

       When  more than one RGBA color or index buffer is enabled for drawing,
       logical operations are performed separately for each  enabled  buffer,
       using  for  the	destination  value  the	 contents of that buffer (see
       glDrawBuffer).

ERRORS
       GL_INVALID_ENUM is generated if opcode is not an accepted value.

       GL_INVALID_OPERATION is generated if glLogicOp is executed between the
       execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS
       glGet with argument GL_LOGIC_OP_MODE.
       glIsEnabled with argument GL_COLOR_LOGIC_OP or GL_INDEX_LOGIC_OP.

SEE ALSO
       glAlphaFunc(3G),	  glBlendFunc(3G),   glDrawBuffer(3G),	glEnable(3G),
       glStencilOp(3G)



								GLLOGICOP(3G)