glLogicOp(3G) OpenGL Reference glLogicOp(3G)NAMEglLogicOp - 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.
DESCRIPTIONglLogicOp 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.
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Opcode Resulting Operation
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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.
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glLogicOp(3G) OpenGL Reference glLogicOp(3G)NOTES
Color index logical operations are always supported. RGBA logical
operations are supported only if the GL version is 1.1 or greater.
(However, if the GL version is 1.0, then in RGBA mode, glLogicOp is used
to specify a blending operation. The specified logicop is used if
blending is enabled and the blend equation is set to GL_LOGIC_OP (see
glBlendEquationExt).)
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, glBlendEquationEXT, glDrawBuffer, glEnable,
glStencilOp
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