1991-2006 Silicon Graphics, Inc.
glLogicOp 3G
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 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

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

`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, glBlendFunc, glDrawBuffer, glEnable, glStencilOp

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.