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108 lines
4.7 KiB
XML
108 lines
4.7 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="gluTessNormal">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>gluTessNormal</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>gluTessNormal</refname>
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<refpurpose>specify a normal for a polygon</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>gluTessNormal</function></funcdef>
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<paramdef>GLUtesselator* <parameter>tess</parameter></paramdef>
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<paramdef>GLdouble <parameter>valueX</parameter></paramdef>
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<paramdef>GLdouble <parameter>valueY</parameter></paramdef>
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<paramdef>GLdouble <parameter>valueZ</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>tess</parameter></term>
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<listitem>
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<para>
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Specifies the tessellation object (created with <citerefentry><refentrytitle>gluNewTess</refentrytitle></citerefentry>).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>valueX</parameter></term>
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<listitem>
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<para>
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Specifies the first component of the normal.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>valueY</parameter></term>
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<listitem>
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<para>
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Specifies the second component of the normal.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>valueZ</parameter></term>
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<listitem>
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<para>
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Specifies the third component of the normal.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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<function>gluTessNormal</function> describes a normal for a polygon that the program is defining.
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All input data will be projected onto a plane perpendicular to one of
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the three coordinate axes before tessellation and all output triangles
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will be oriented CCW with
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respect to the normal (CW orientation can be obtained by reversing the
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sign of the supplied normal). For example, if you know that all polygons
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lie in the x-y plane, call <function>gluTessNormal</function>(tess, 0.0, 0.0, 1.0)
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before rendering any polygons.
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</para>
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<para>
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If the supplied normal is (0.0, 0.0, 0.0) (the initial value), the normal is
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determined as follows. The direction of the normal, up to its sign, is
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found by fitting a plane to the vertices, without regard to how the
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vertices are connected. It is expected that the input data lies approximately
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in the plane; otherwise, projection perpendicular to one of the three
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coordinate axes may substantially change the geometry. The sign of the
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normal is chosen so that the sum of the signed areas of all input
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contours is nonnegative (where a CCW contour has positive area).
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</para>
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<para>
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The supplied normal persists until it is changed by another call to
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<function>gluTessNormal</function>.
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>gluTessEndPolygon</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 1991-2006
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Silicon Graphics, Inc. This document is licensed under the SGI
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Free Software B License. For details, see
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<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
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</para>
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</refsect1>
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</refentry>
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