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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="glSampleCoverage">
<refmeta>
<refmetainfo>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
</refmetainfo>
<refentrytitle>glSampleCoverage</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glSampleCoverage</refname>
<refpurpose>specify multisample coverage parameters</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glSampleCoverage</function></funcdef>
<paramdef>GLclampf <parameter>value</parameter></paramdef>
<paramdef>GLboolean <parameter>invert</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<!-- eqn: ignoring delim $$ -->
<refsect1 id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>value</parameter></term>
<listitem>
<para>
Specify a single floating-point sample coverage value. The value is
clamped to the range
<inlineequation><mml:math>
<!-- eqn: [0 ,1]:-->
<mml:mfenced open="[" close="]">
<mml:mn>0</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
</mml:math></inlineequation>.
The initial value is 1.0.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>invert</parameter></term>
<listitem>
<para>
Specify a single boolean value representing if the coverage masks should be
inverted. <constant>GL_TRUE</constant> and <constant>GL_FALSE</constant> are accepted. The initial value
is <constant>GL_FALSE</constant>.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
Multisampling samples a pixel multiple times at various
implementation-dependent subpixel locations to generate antialiasing
effects. Multisampling transparently antialiases points, lines, polygons,
bitmaps, and images if it is enabled.
</para>
<para>
<parameter>value</parameter> is used in constructing a temporary mask used in determining which
samples will be used in resolving the final fragment color. This mask is
bitwise-anded with the coverage mask generated from the multisampling
computation. If the <parameter>invert</parameter> flag is set, the temporary mask is inverted
(all bits flipped) and then the bitwise-and is computed.
</para>
<para>
If an implementation does not have any multisample buffers available, or
multisampling is disabled, rasterization occurs with only a single sample
computing a pixel's final RGB color.
</para>
<para>
Provided an implementation supports multisample buffers, and multisampling
is enabled, then a pixel's final color is generated by combining several
samples per pixel. Each sample contains color, depth, and stencil
information, allowing those operations to be performed on each sample.
</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para>
<function>glSampleCoverage</function> is available only if the GL version is 1.3 or greater.
</para>
</refsect1>
<refsect1 id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated if <function>glSampleCoverage</function> is executed between the
execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
</para>
</refsect1>
<refsect1 id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SAMPLE_COVERAGE_VALUE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SAMPLE_COVERAGE_INVERT</constant>
</para>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MULTISAMPLE</constant>
</para>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_SAMPLE_ALPHA_TO_COVERAGE</constant>
</para>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_SAMPLE_ALPHA_TO_ONE</constant>
</para>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_SAMPLE_COVERAGE</constant>
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glPushAttrib</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 1991-2006
Silicon Graphics, Inc. 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>