upstream-man-pages/man2/xhtml/gluTessProperty.xml

   1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd">
   2 <!-- saved from url=(0013)about:internet -->
   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>gluTessProperty</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="gluTessProperty"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gluTessProperty — set a tessellation object property</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">gluTessProperty</b>(</code></td><td>GLUtesselator*  </td><td><var class="pdparam">tess</var>, </td></tr><tr><td> </td><td>GLenum  </td><td><var class="pdparam">which</var>, </td></tr><tr><td> </td><td>GLdouble  </td><td><var class="pdparam">data</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>which</code></em></span></dt><dd><p>
   6                     Specifies the property to be set. Valid values are
   7                     <code class="constant">GLU_TESS_WINDING_RULE</code>,
   8                     <code class="constant">GLU_TESS_BOUNDARY_ONLY</code>, and
   9                     <code class="constant">GLU_TESS_TOLERANCE</code>.
  10                 </p></dd><dt><span class="term"><em class="parameter"><code>data</code></em></span></dt><dd><p>
  11                     Specifies the value of the indicated property.
  12                 </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
  13             <code class="function">gluTessProperty</code> is used to control properties stored in a tessellation object. These
  14             properties affect the way that the polygons are interpreted and rendered.
  15             The legal values for <em class="parameter"><code>which</code></em> are as follows:
  16         </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GLU_TESS_WINDING_RULE</code> </span></dt><dd><p>
  17                         Determines which parts of the polygon are on the ``interior''.
  18                         <em class="parameter"><code>data</code></em> may be set to one of <code class="constant">GLU_TESS_WINDING_ODD</code>,
  19                         <code class="constant">GLU_TESS_WINDING_NONZERO</code>, <code class="constant">GLU_TESS_WINDING_POSITIVE</code>,
  20                         <code class="constant">GLU_TESS_WINDING_NEGATIVE</code>, or <code class="constant">GLU_TESS_WINDING_ABS_GEQ_TWO</code>.
  21                     </p><p>
  22                         To understand how the winding rule works, consider that the input
  23                         contours partition the plane into regions. The winding rule determines which
  24                         of these regions are inside the polygon.
  25                     </p><p>
  26                         For a single contour C, the winding number of a point x is simply the signed
  27                         number of revolutions we make around x as we travel once around C
  28                         (where CCW is positive). When there are several contours, the individual
  29                         winding numbers are summed. This procedure associates a signed integer
  30                         value with each point x in the plane. Note that the winding number is the
  31                         same for all points in a single region.
  32                     </p><p>
  33                         The winding rule classifies a region as ``inside'' if its winding number
  34                         belongs to the chosen category (odd, nonzero, positive, negative, or
  35                         absolute value of at least two). The previous GLU tessellator (prior to
  36                         GLU 1.2) used the ``odd'' rule. The ``nonzero'' rule is another common way to
  37                         define the interior. The other three rules are useful for polygon CSG
  38                         operations.
  39                     </p></dd><dt><span class="term"><code class="constant">GLU_TESS_BOUNDARY_ONLY</code> </span></dt><dd><p>
  40                         Is a boolean value (``value'' should be set
  41                         to GL_TRUE or GL_FALSE). When set to GL_TRUE, a set of closed contours
  42                         separating the polygon interior and exterior are returned instead of a
  43                         tessellation. Exterior contours are oriented CCW with respect to the
  44                         normal; interior contours are oriented CW. The <code class="constant">GLU_TESS_BEGIN</code>
  45                         and <code class="constant">GLU_TESS_BEGIN_DATA</code> callbacks use the type GL_LINE_LOOP for
  46                         each contour.
  47                     </p></dd><dt><span class="term"><code class="constant">GLU_TESS_TOLERANCE</code></span></dt><dd><p>
  48                         Specifies a tolerance for merging features to reduce the size of the output.
  49                         For example, two vertices that are very close to each other might be
  50                         replaced by a single vertex. The tolerance is multiplied by the largest
  51                         coordinate magnitude of any input vertex; this specifies the maximum
  52                         distance that any feature can move as the result of a single merge
  53                         operation. If a single feature takes part in several merge operations, the
  54                         total distance moved could be larger.
  55                     </p><p>
  56                         Feature merging is completely optional; the tolerance is only a hint.
  57                         The implementation is free to merge in some cases and not in others, or to
  58                         never merge features at all. The initial tolerance is 0.
  59                     </p><p>
  60                         The current implementation merges vertices only if they are exactly
  61                         coincident, regardless of the current tolerance. A vertex is spliced into
  62                         an edge only if the implementation is unable to distinguish which side of
  63                         the edge the vertex lies on. Two edges are merged only when both endpoints
  64                         are identical.
  65                     </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
  66             <a class="citerefentry" href="gluGetTessProperty.xml"><span class="citerefentry"><span class="refentrytitle">gluGetTessProperty</span></span></a>,
  67             <a class="citerefentry" href="gluNewTess.xml"><span class="citerefentry"><span class="refentrytitle">gluNewTess</span></span></a>
  68         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
  69             Copyright <span class="trademark"></span>© 1991-2006
  70             Silicon Graphics, Inc. This document is licensed under the SGI
  71             Free Software B License. For details, see
  72             <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
  73         </p></div></div></body></html>