1991-2006
Silicon Graphics, Inc.
2010-2013
Khronos Group
glLogicOp
3G

# glLogicOp

specify a logical pixel operation for 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 RGBA color and the 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`. The initial value is disabled.

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 and d represents the color 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 colors.

## Notes

When more than one RGBA color 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).

Logic operations have no effect on floating point draw buffers. However, if `GL_COLOR_LOGIC_OP` is enabled, blending is still disabled in this case.

## Errors

`GL_INVALID_ENUM` is generated if `opcode` is not an accepted value.

## Associated Gets

glGet with argument `GL_LOGIC_OP_MODE`.

glIsEnabled with argument `GL_COLOR_LOGIC_OP`.

## See Also

glBlendFunc, glDrawBuffer, glEnable, glStencilOp

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. Copyright 2010-2013 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.