C SPECIFICATION

       void glLogicOp( GLenum opcode )

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
       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 log-
       ical  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 oper-
       ations are supported only if the GL version is 1.1 or greater.

SEE ALSO

       glAlphaFunc, glBlendFunc, glDrawBuffer, glEnable, glStencilOp



                                                                 GLLOGICOP(3G)