glLogicOp — specify a logical pixel operation for 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 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.
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.
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/.