GLLOGICOP() MachTen Programmer’s Manual GLLOGICOP()

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 logi-
cal 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 corre-
sponding location in the frame buffer. To enable or dis-
able 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 ini-
tial value is disabled for both operations.

center box ; ci | ci c | c . opcode resulting value =
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, glSten-
cilOp

MachTen 2