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glLogicOp — specify a logical pixel operation for color index rendering
void glLogicOp(GLenum opcode);
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.
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.
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).
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.
glGet with argument GL_LOGIC_OP_MODE.
glIsEnabled with argument GL_COLOR_LOGIC_OP or GL_INDEX_LOGIC_OP.
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/.