glLogicOp - specify a	logical	pixel operation	for color
index	rendering

glLogicOp
	glLogicOp(opcode) -> None

void glLogicOp( GLenum opcode	)

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.

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 value |
            |_________________|_________________|
            |    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-language 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.

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).

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.

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

glAlphaFunc, glBlendFunc, glDrawBuffer, glEnable,
glStencilOp