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NAME
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. This document is licensed under the SGI Free
Software B License. For details, see http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org