NAME    [Toc]    [Back]

       glLogicOp  -  specify  a logical pixel operation for color
       index rendering

SYNOPSIS    [Toc]    [Back]

       void glLogicOp(
               GLenum opcode );

PARAMETERS    [Toc]    [Back]

       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 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.

NOTES    [Toc]    [Back]

       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()).

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(3),  glBlendFunc(3),  glDrawBuffer(3),   glEnable(3), glStencilOp(3)



                                                    glLogicOp(3G)