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GLLOGICOP(3G)                                                                                  GLLOGICOP(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: 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  opera-tions, operations,
       tions,  s  represents the incoming color index and d represents the index in the frame buffer.  Stan-dard Standard
       dard 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
       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  per-formed performed
       formed  separately  for  each  enabled  buffer,  using for the destination value the contents of that
       buffer (see glDrawBuffer).

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

SEE ALSO
       glAlphaFunc(3G), glBlendFunc(3G), glDrawBuffer(3G), glEnable(3G), glStencilOp(3G)




                                                                                               GLLOGICOP(3G)

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