glLogicOp(3G)		       OpenGL Reference			 glLogicOp(3G)

NAME    [Toc]    [Back]

     glLogicOp - specify a logical pixel operation for color index rendering

C SPECIFICATION    [Toc]    [Back]

     void glLogicOp( GLenum opcode )

PARAMETERS    [Toc]    [Back]

     opcode  Specifies a symbolic constant that	selects	a logical operation.
	     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 initial value is GL_COPY.

DESCRIPTION    [Toc]    [Back]

     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 Clanguage
 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.







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glLogicOp(3G)		       OpenGL Reference			 glLogicOp(3G)



NOTES
     Color index logical operations are	always supported. RGBA logical
     operations	are supported only if the GL version is	1.1 or greater.
     (However, if the GL version is 1.0, then in RGBA mode, glLogicOp is used
     to	specify	a blending operation. The specified logicop is used if
     blending is enabled and the blend equation	is set to GL_LOGIC_OP (see
     glBlendEquationExt).)

     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    [Toc]    [Back]

     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    [Toc]    [Back]

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

SEE ALSO    [Toc]    [Back]

     glAlphaFunc, glBlendFunc, glBlendEquationEXT, glDrawBuffer, glEnable,
     glStencilOp


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