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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
<!-- Converted by db4-upgrade version 1.1 -->
<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glPolygonOffset">
<info>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
<copyright>
<year>2010-2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>glPolygonOffset</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glPolygonOffset</refname>
<refpurpose>set the scale and units used to calculate depth values</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glPolygonOffset</function></funcdef>
<paramdef>GLfloat <parameter>factor</parameter></paramdef>
<paramdef>GLfloat <parameter>units</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 xml:id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>factor</parameter></term>
<listitem>
<para>
Specifies a scale factor that is used to create a variable
depth offset for each polygon. The initial value is 0.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>units</parameter></term>
<listitem>
<para>
Is multiplied by an implementation-specific value to
create a constant depth offset. The initial value is 0.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description"><title>Description</title>
<para>
When <constant>GL_POLYGON_OFFSET_FILL</constant>, <constant>GL_POLYGON_OFFSET_LINE</constant>, or
<constant>GL_POLYGON_OFFSET_POINT</constant> is enabled, each
fragment's <emphasis>depth</emphasis> value will be offset after it is interpolated
from the <emphasis>depth</emphasis> values of the appropriate vertices.
The value of the offset is
<inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<!-- eqn: factor * DZ + r * units: -->
<mml:mrow>
<mml:mrow>
<mml:mi mathvariant="italic">factor</mml:mi>
<mml:mo>×</mml:mo>
<mml:mi mathvariant="italic">DZ</mml:mi>
</mml:mrow>
<mml:mo>+</mml:mo>
<mml:mrow>
<mml:mi mathvariant="italic">r</mml:mi>
<mml:mo>×</mml:mo>
<mml:mi mathvariant="italic">units</mml:mi>
</mml:mrow>
</mml:mrow>
</mml:math></inlineequation>,
where
<inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<!-- eqn: DZ: -->
<mml:mi mathvariant="italic">DZ</mml:mi>
</mml:math></inlineequation>
is a measurement of the change in depth relative to the screen
area of the polygon, and
<inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">r</mml:mi></mml:math></inlineequation>
is the smallest value that is guaranteed to
produce a resolvable offset for a given implementation.
The offset is added before the depth test is performed and before
the value is written into the depth buffer.
</para>
<para>
<function>glPolygonOffset</function> is useful for rendering hidden-line images, for applying decals
to surfaces, and for rendering solids with highlighted edges.
</para>
</refsect1>
<refsect1 xml:id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument
<constant>GL_POLYGON_OFFSET_FILL</constant>,
<constant>GL_POLYGON_OFFSET_LINE</constant>,
or <constant>GL_POLYGON_OFFSET_POINT</constant>.
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POLYGON_OFFSET_FACTOR</constant> or
<constant>GL_POLYGON_OFFSET_UNITS</constant>.
</para>
</refsect1>
<refsect1 xml:id="versions"><title>Version Support</title>
<informaltable>
<tgroup cols="13" align="left">
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry><function>glPolygonOffset</function></entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='20']/*)"/>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 xml:id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 xml:id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"/> 1991-2006 Silicon Graphics, Inc.
Copyright <trademark class="copyright"/> 2010-2014 Khronos Group.
This document is licensed under the SGI Free Software B License.
For details, see
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</link>.
</para>
</refsect1>
</refentry>
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