<div class="refentry" title="glPolygonOffset"><a id="glPolygonOffset"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glPolygonOffset — set the scale and units used to calculate depth

values</p></div><div class="refsynopsisdiv" title="C Specification"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glPolygonOffset</b>(</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><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glPolygonOffsetx</b>(</code></td><td>GLfixed <var class="pdparam">factor</var>, </td></tr><tr><td> </td><td>GLfixed <var class="pdparam">units</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Parameters"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><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" title="Description"><a id="description"></a><h2>Description</h2><p>When <code class="constant">GL_POLYGON_OFFSET_FILL</code>

is enabled, each fragment's <em class="parameter"><code>depth</code></em>

value will be offset after it is interpolated from the

<em class="parameter"><code>depth</code></em>

values of the appropriate vertices. The value of the offset is

<math overflow="scroll">

<mi>m</mi>

<mo>*</mo>

<mi>factor</mi>

<mo>+</mo>

<mi>r</mi>

<mo>*</mo>

<mi>units</mi>

</math>,

where <em class="replaceable"><code>m</code></em>

is a measurement of the change in depth relative to the screen

area of the polygon, and <em class="replaceable"><code>r</code></em>

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 for applying decals to surfaces.</p></div><div class="refsect1" title="See Also"><a id="seealso"></a><h2>See Also</h2><p>

<a class="citerefentry" href="glDepthFunc"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>,

<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>

</p></div><div class="refsect1" title="Copyright"><a id="copyright"></a><h2>Copyright</h2><p>

Copyright © 2003-2004

Silicon Graphics, Inc. This document is licensed under the SGI

Free Software B License. For details, see

<a class="ulink" href="https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/" target="_top">https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/</a>.

</p></div></div>