upstream-doc/man2/xhtml/gluTessNormal.xml

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   3 <?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>gluTessNormal</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="gluTessNormal"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gluTessNormal — specify a normal for a polygon</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">gluTessNormal</b>(</code></td><td>GLUtesselator*  </td><td><var class="pdparam">tess</var>, </td></tr><tr><td> </td><td>GLdouble  </td><td><var class="pdparam">valueX</var>, </td></tr><tr><td> </td><td>GLdouble  </td><td><var class="pdparam">valueY</var>, </td></tr><tr><td> </td><td>GLdouble  </td><td><var class="pdparam">valueZ</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>tess</code></em></span></dt><dd><p>
   4                     Specifies the tessellation object (created with <a class="citerefentry" href="gluNewTess.xml"><span class="citerefentry"><span class="refentrytitle">gluNewTess</span></span></a>).
   5                 </p></dd><dt><span class="term"><em class="parameter"><code>valueX</code></em></span></dt><dd><p>
   6                     Specifies the first component of the normal.
   7                 </p></dd><dt><span class="term"><em class="parameter"><code>valueY</code></em></span></dt><dd><p>
   8                     Specifies the second component of the normal.
   9                 </p></dd><dt><span class="term"><em class="parameter"><code>valueZ</code></em></span></dt><dd><p>
  10                     Specifies the third component of the normal.
  11                 </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
  12             <code class="function">gluTessNormal</code> describes a normal for a polygon that the program is defining.
  13             All input data will be projected onto a plane perpendicular to one of
  14             the three coordinate axes before tessellation and all output triangles
  15             will be oriented CCW with
  16             respect to the normal (CW orientation can be obtained by reversing the
  17             sign of the supplied normal). For example, if you know that all polygons
  18             lie in the x-y plane, call <code class="function">gluTessNormal</code>(tess, 0.0, 0.0, 1.0)
  19             before rendering any polygons.
  20         </p><p>
  21             If the supplied normal is (0.0, 0.0, 0.0) (the initial value), the normal is
  22             determined as follows. The direction of the normal, up to its sign, is
  23             found by fitting a plane to the vertices, without regard to how the
  24             vertices are connected. It is expected that the input data lies approximately
  25             in the plane; otherwise, projection perpendicular to one of the three
  26             coordinate axes may substantially change the geometry. The sign of the
  27             normal is chosen so that the sum of the signed areas of all input
  28             contours is nonnegative (where a CCW contour has positive area).
  29         </p><p>
  30             The supplied normal persists until it is changed by another call to
  31             <code class="function">gluTessNormal</code>.
  32         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
  33             <a class="citerefentry" href="gluTessBeginPolygon.xml"><span class="citerefentry"><span class="refentrytitle">gluTessBeginPolygon</span></span></a>,
  34             <a class="citerefentry" href="gluTessEndPolygon.xml"><span class="citerefentry"><span class="refentrytitle">gluTessEndPolygon</span></span></a>
  35         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
  36             Copyright <span class="trademark"></span>© 1991-2006
  37             Silicon Graphics, Inc. This document is licensed under the SGI
  38             Free Software B License. For details, see
  39             <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
  40         </p></div></div></body></html>