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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>glPolygonOffset - OpenGL 4 Reference Pages</title>
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<header/>
<div class="refentry" id="glPolygonOffset">
<div class="titlepage"/>
<div class="refnamediv">
<h2>Name</h2>
<p>glPolygonOffset — set the scale and units used to calculate depth values</p>
</div>
<div class="refsynopsisdiv">
<h2>C Specification</h2>
<div class="funcsynopsis">
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">void <strong class="fsfunc">glPolygonOffset</strong>(</code>
</td>
<td>GLfloat <var class="pdparam">factor</var>, </td>
</tr>
<tr>
<td> </td>
<td>GLfloat <var class="pdparam">units</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
</div>
</div>
<div class="refsect1" id="parameters">
<h2>Parameters</h2>
<div class="variablelist">
<dl class="variablelist">
<dt>
<span class="term">
<em class="parameter">
<code>factor</code>
</em>
</span>
</dt>
<dd>
<p>
Specifies a scale factor that is used to create a variable
depth offset for each polygon. The initial value is 0.
</p>
</dd>
<dt>
<span class="term">
<em class="parameter">
<code>units</code>
</em>
</span>
</dt>
<dd>
<p>
Is multiplied by an implementation-specific value to
create a constant depth offset. The initial value is 0.
</p>
</dd>
</dl>
</div>
</div>
<div class="refsect1" id="description">
<h2>Description</h2>
<p>
When <code class="constant">GL_POLYGON_OFFSET_FILL</code>, <code class="constant">GL_POLYGON_OFFSET_LINE</code>, or
<code class="constant">GL_POLYGON_OFFSET_POINT</code> is enabled, each
fragment's <span class="emphasis"><em>depth</em></span> value will be offset after it is interpolated
from the <span class="emphasis"><em>depth</em></span> values of the appropriate vertices.
The value of the offset is
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<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>,
where
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mi mathvariant="italic">DZ</mml:mi>
</mml:math>
is a measurement of the change in depth relative to the screen
area of the polygon, and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">r</mml:mi></mml:math>
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.
</p>
<p>
<code class="function">glPolygonOffset</code> is useful for rendering hidden-line images, for applying decals
to surfaces, and for rendering solids with highlighted edges.
</p>
</div>
<div class="refsect1" id="associatedgets">
<h2>Associated Gets</h2>
<p>
<a class="citerefentry" href="glIsEnabled.xhtml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument
<code class="constant">GL_POLYGON_OFFSET_FILL</code>,
<code class="constant">GL_POLYGON_OFFSET_LINE</code>,
or <code class="constant">GL_POLYGON_OFFSET_POINT</code>.
</p>
<p>
<a class="citerefentry" href="glGet.xhtml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_POLYGON_OFFSET_FACTOR</code> or
<code class="constant">GL_POLYGON_OFFSET_UNITS</code>.
</p>
</div>
<div class="refsect1" id="versions">
<h2>Version Support</h2>
<div class="informaltable">
<table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">
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<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; " class="lastvers"/>
</colgroup>
<thead>
<tr>
<th style="text-align: left; border-right: 2px solid ; ">
</th>
<th style="text-align: center; border-bottom: 2px solid ; " colspan="12">
<span class="bold"><strong>OpenGL Version</strong></span>
</th>
</tr>
<tr>
<th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>Function / Feature Name</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>2.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>2.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.2</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.3</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.2</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.3</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.4</strong></span>
</th>
<th style="text-align: center; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.5</strong></span>
</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: left; border-right: 2px solid ; ">
<code class="function">glPolygonOffset</code>
</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; ">✔</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="refsect1" id="seealso">
<h2>See Also</h2>
<p>
<a class="citerefentry" href="glDepthFunc.xhtml"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>,
<a class="citerefentry" href="glEnable.xhtml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
<a class="citerefentry" href="glGet.xhtml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>,
<a class="citerefentry" href="glIsEnabled.xhtml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a>
</p>
</div>
<div class="refsect1" id="Copyright">
<h2>Copyright</h2>
<p>
Copyright <span class="trademark"/>© 1991-2006 Silicon Graphics, Inc.
Copyright <span class="trademark"/>© 2010-2014 Khronos Group.
This document is licensed under the SGI Free Software B License.
For details, see
<a class="link" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
</p>
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