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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="glLogicOp">
<refentryinfo>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
<copyright>
<year>2010-2013</year>
<holder>Khronos Group</holder>
</copyright>
</refentryinfo>
<refmeta>
<refentrytitle>glLogicOp</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glLogicOp</refname>
<refpurpose>specify a logical pixel operation for rendering</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glLogicOp</function></funcdef>
<paramdef>GLenum <parameter>opcode</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>opcode</parameter></term>
<listitem>
<para>
Specifies a symbolic constant that selects a logical operation.
The following symbols are accepted:
<constant>GL_CLEAR</constant>,
<constant>GL_SET</constant>,
<constant>GL_COPY</constant>,
<constant>GL_COPY_INVERTED</constant>,
<constant>GL_NOOP</constant>,
<constant>GL_INVERT</constant>,
<constant>GL_AND</constant>,
<constant>GL_NAND</constant>,
<constant>GL_OR</constant>,
<constant>GL_NOR</constant>,
<constant>GL_XOR</constant>,
<constant>GL_EQUIV</constant>,
<constant>GL_AND_REVERSE</constant>,
<constant>GL_AND_INVERTED</constant>,
<constant>GL_OR_REVERSE</constant>, and
<constant>GL_OR_INVERTED</constant>. The initial value is <constant>GL_COPY</constant>.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
<function>glLogicOp</function> 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
<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>
using the symbolic constant <constant>GL_COLOR_LOGIC_OP</constant>. The initial value is
disabled.
</para>
<para>
</para>
<informaltable>
<tgroup cols="2">
<colspec align="left" />
<colspec align="center" />
<thead>
<row>
<entry>
<emphasis role="bold"> Opcode </emphasis>
</entry>
<entry>
<emphasis role="bold"> Resulting Operation </emphasis>
</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<constant>GL_CLEAR</constant>
</entry>
<entry>
0
</entry>
</row>
<row>
<entry>
<constant>GL_SET</constant>
</entry>
<entry>
1
</entry>
</row>
<row>
<entry>
<constant>GL_COPY</constant>
</entry>
<entry>
s
</entry>
</row>
<row>
<entry>
<constant>GL_COPY_INVERTED</constant>
</entry>
<entry>
~s
</entry>
</row>
<row>
<entry>
<constant>GL_NOOP</constant>
</entry>
<entry>
d
</entry>
</row>
<row>
<entry>
<constant>GL_INVERT</constant>
</entry>
<entry>
~d
</entry>
</row>
<row>
<entry>
<constant>GL_AND</constant>
</entry>
<entry>
s & d
</entry>
</row>
<row>
<entry>
<constant>GL_NAND</constant>
</entry>
<entry>
~(s & d)
</entry>
</row>
<row>
<entry>
<constant>GL_OR</constant>
</entry>
<entry>
s | d
</entry>
</row>
<row>
<entry>
<constant>GL_NOR</constant>
</entry>
<entry>
~(s | d)
</entry>
</row>
<row>
<entry>
<constant>GL_XOR</constant>
</entry>
<entry>
s ^ d
</entry>
</row>
<row>
<entry>
<constant>GL_EQUIV</constant>
</entry>
<entry>
~(s ^ d)
</entry>
</row>
<row>
<entry>
<constant>GL_AND_REVERSE</constant>
</entry>
<entry>
s & ~d
</entry>
</row>
<row>
<entry>
<constant>GL_AND_INVERTED</constant>
</entry>
<entry>
~s & d
</entry>
</row>
<row>
<entry>
<constant>GL_OR_REVERSE</constant>
</entry>
<entry>
s | ~d
</entry>
</row>
<row>
<entry>
<constant>GL_OR_INVERTED</constant>
</entry>
<entry>
~s | d
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
<parameter>opcode</parameter> is a symbolic constant chosen from the list above.
In the explanation of the logical operations,
<emphasis>s</emphasis> represents the incoming color and
<emphasis>d</emphasis> 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.
</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para>
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 <citerefentry><refentrytitle>glDrawBuffer</refentrytitle></citerefentry>).
</para>
<para>
Logic operations have no effect on floating point draw buffers. However, if
<constant>GL_COLOR_LOGIC_OP</constant> is enabled, blending is still disabled
in this case.
</para>
</refsect1>
<refsect1 id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_ENUM</constant> is generated if <parameter>opcode</parameter> is not an accepted value.
</para>
</refsect1>
<refsect1 id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LOGIC_OP_MODE</constant>.
</para>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_COLOR_LOGIC_OP</constant>.
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDrawBuffer</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 1991-2006 Silicon Graphics, Inc.
Copyright <trademark class="copyright"></trademark> 2010-2013 Khronos Group.
This document is licensed under the SGI Free Software B License.
For details, see
<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
</para>
</refsect1>
</refentry>
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