PARAMETERS
       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
       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 expla‐
       nation  of the logical operations, s represents the incoming color index
       and d represents the index in the frame buffer.  Standard C-language op‐
       erators are used.  As these bitwise operators suggest, the logical oper‐
       ation is applied independently to each bit pair of the source and desti‐
       nation indices or colors.

NOTES
       Color index logical operations are always supported. RGBA logical opera‐
       tions 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, us‐
       ing  for  the  destination  value  the  contents  of  that  buffer  (see
       glDrawBuffer).
                                                                  GLLOGICOP(3G)