GLOGICOP(3G)                                                    GLOGICOP(3G)



NAME
       glLogicOp - specify a logical pixel operation for color index rendering


C SPECIFICATION
       void glLogicOp( GLenum opcode )


PARAMETERS
       opcode  Specifies a symbolic constant that selects a logical operation.
               The  following symbols are accepted: GLCLEAR, GLSET, GLCOPY,
               GLCOPYINVERTED, GLNOP, GLINVERT, GLAND,  GLNAND,  GLOR,
               GLNOR,   GLXOR,  GLEQUIV,  GLANDREVERSE,  GLANDINVERTED,
               GLOREVERSE,  and  GLORINVERTED.  The  initial   value   is
               GLCOPY.

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  GLCOLORLOGICOP  for  RGBA  mode  or
       GLINDEXLOGICOP for color index mode. The initial value  is  disabled
       for both operations.


        Opcode             Resulting Operation
        GLCLEAR           0
        GLSET             1
        GLCOPY            s
        GLCOPYINVERTED   ~s
        GLNOP            d
        GLINVERT          ~d
        GLAND             s & d
        GLNAND            ~(s & d)
        GLOR              s  d
        GLNOR             ~(s  d)
        GLXOR             s ^ d
        GLEQUIV           ~(s ^ d)
        GLANDREVERSE     s & ~d
        GLANDINVERTED    ~s & d
        GLOREVERSE      s  ~d
        GLORINVERTED     ~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.

       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).

ERORS
       GLINVALIDENUM is generated if opcode is not an accepted value.

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

ASOCIATED GETS
       glGet with argument GLOGICOPMODE.
       glIsEnabled with argument GLCOLORLOGICOP or GLINDEXLOGICOP.

SEE ALSO
       glAlphaFunc, glBlendFunc, glDrawBuffer, glEnable, glStencilOp



                                                                 GLOGICOP(3G)