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301 lines
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301 lines
17 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="gluNurbsProperty">
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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>gluNurbsProperty</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>gluNurbsProperty</refname>
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<refpurpose>set a NURBS property</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>gluNurbsProperty</function></funcdef>
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<paramdef>GLUnurbs* <parameter>nurb</parameter></paramdef>
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<paramdef>GLenum <parameter>property</parameter></paramdef>
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<paramdef>GLfloat <parameter>value</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>nurb</parameter></term>
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<listitem>
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<para>
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Specifies the NURBS object (created with <citerefentry><refentrytitle>gluNewNurbsRenderer</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>property</parameter></term>
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<listitem>
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<para>
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Specifies the property to be set. Valid values are
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<constant>GLU_SAMPLING_TOLERANCE</constant>,
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<constant>GLU_DISPLAY_MODE</constant>,
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<constant>GLU_CULLING</constant>,
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<constant>GLU_AUTO_LOAD_MATRIX</constant>,
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<constant>GLU_PARAMETRIC_TOLERANCE</constant>,
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<constant>GLU_SAMPLING_METHOD</constant>,
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<constant>GLU_U_STEP</constant>,
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<constant>GLU_V_STEP</constant>, or
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<constant>GLU_NURBS_MODE</constant>.
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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>value</parameter></term>
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<listitem>
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<para>
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Specifies the value of the indicated property.
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It may be a numeric value or one of
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<constant>GLU_OUTLINE_POLYGON</constant>,
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<constant>GLU_FILL</constant>,
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<constant>GLU_OUTLINE_PATCH</constant>,
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<constant>GLU_TRUE</constant>,
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<constant>GLU_FALSE</constant>,
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<constant>GLU_PATH_LENGTH</constant>,
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<constant>GLU_PARAMETRIC_ERROR</constant>,
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<constant>GLU_DOMAIN_DISTANCE</constant>,
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<constant>GLU_NURBS_RENDERER</constant>, or
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<constant>GLU_NURBS_TESSELLATOR</constant>.
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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>gluNurbsProperty</function> is used to control properties stored in a NURBS object. These
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properties affect the way that a NURBS curve is rendered. The accepted
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values for <parameter>property</parameter> are as follows:
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</para>
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<variablelist>
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<varlistentry>
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<term><constant>GLU_NURBS_MODE</constant></term>
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<listitem>
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<para>
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<parameter>value</parameter> should be set to be either <constant>GLU_NURBS_RENDERER</constant> or
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<constant>GLU_NURBS_TESSELLATOR</constant>. When set to <constant>GLU_NURBS_RENDERER</constant>, NURBS objects
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are tessellated into OpenGL primitives and sent to the pipeline for
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rendering. When set to <constant>GLU_NURBS_TESSELLATOR</constant>, NURBS objects are
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tessellated into OpenGL primitives but the vertices, normals, colors, and/or textures are
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retrieved back through a callback interface (see <citerefentry><refentrytitle>gluNurbsCallback</refentrytitle></citerefentry>). This allows the user to cache the
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tessellated results for further processing.
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The initial value is <constant>GLU_NURBS_RENDERER</constant>.
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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><constant>GLU_SAMPLING_METHOD</constant> </term>
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<listitem>
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<para>
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Specifies how a NURBS surface should be
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tessellated.
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<parameter>value</parameter> may be one of <constant>GLU_PATH_LENGTH</constant>,
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<constant>GLU_PARAMETRIC_ERROR</constant>, <constant>GLU_DOMAIN_DISTANCE</constant>,
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<constant>GLU_OBJECT_PATH_LENGTH</constant>, or
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<constant>GLU_OBJECT_PARAMETRIC_ERROR</constant>.
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When set to <constant>GLU_PATH_LENGTH</constant>, the surface is rendered so that
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the maximum length, in
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pixels, of the edges of the tessellation polygons is no greater than
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what is specified by <constant>GLU_SAMPLING_TOLERANCE</constant>.
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</para>
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<para>
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<constant>GLU_PARAMETRIC_ERROR</constant> specifies that the surface is rendered in such a
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way that the value specified by <constant>GLU_PARAMETRIC_TOLERANCE</constant> describes the
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maximum distance, in pixels, between the tessellation polygons and the
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surfaces they approximate.
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</para>
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<para>
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<constant>GLU_DOMAIN_DISTANCE</constant> allows users to specify, in parametric coordinates,
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how many sample points per unit length are taken in <emphasis>u</emphasis>, <emphasis>v</emphasis>
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direction.
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</para>
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<para>
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<constant>GLU_OBJECT_PATH_LENGTH</constant> is similar to <constant>GLU_PATH_LENGTH</constant>
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except that it is view independent; that is, the surface is rendered so that the maximum length, in object space, of edges of the tessellation polygons is no greater than what is specified by <constant>GLU_SAMPLING_TOLERANCE</constant>.
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</para>
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<para>
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<constant>GLU_OBJECT_PARAMETRIC_ERROR</constant> is similar to <constant>GLU_PARAMETRIC_ERROR</constant> except that it is view independent; that is, the surface is rendered in such a way that the value specified by <constant>GLU_PARAMETRIC_TOLERANCE</constant> describes the maximum distance, in object space, between the tessellation polygons and the surfaces they approximate.
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</para>
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<para>
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The initial value of <constant>GLU_SAMPLING_METHOD</constant> is <constant>GLU_PATH_LENGTH</constant>.
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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><constant>GLU_SAMPLING_TOLERANCE</constant></term>
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<listitem>
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<para>
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Specifies the maximum length, in pixels or in object space length unit,
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to use when the sampling method is set to <constant>GLU_PATH_LENGTH</constant> or
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<constant>GLU_OBJECT_PATH_LENGTH</constant>.
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The NURBS code is conservative when rendering a curve
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or surface, so the actual length can be somewhat shorter. The initial
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value is 50.0 pixels.
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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><constant>GLU_PARAMETRIC_TOLERANCE</constant></term>
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<listitem>
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<para>
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Specifies the maximum distance, in pixels or in object space length unit,
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to use when the sampling method is <constant>GLU_PARAMETRIC_ERROR</constant> or
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<constant>GLU_OBJECT_PARAMETRIC_ERROR</constant>.
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The initial value is 0.5.
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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><constant>GLU_U_STEP</constant></term>
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<listitem>
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<para>
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Specifies the number of sample points per unit length taken
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along the <emphasis>u</emphasis> axis in parametric coordinates. It is needed when
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<constant>GLU_SAMPLING_METHOD</constant> is set to <constant>GLU_DOMAIN_DISTANCE</constant>.
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The initial value is 100.
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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><constant>GLU_V_STEP</constant></term>
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<listitem>
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<para>
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Specifies the number of sample points per unit length taken
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along the <emphasis>v</emphasis> axis in parametric coordinate. It is needed when
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<constant>GLU_SAMPLING_METHOD</constant> is set to <constant>GLU_DOMAIN_DISTANCE</constant>. The initial
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value is 100.
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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><constant>GLU_DISPLAY_MODE</constant></term>
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<listitem>
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<para>
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<parameter>value</parameter> can be set to
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<constant>GLU_OUTLINE_POLYGON</constant>, <constant>GLU_FILL</constant>, or
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<constant>GLU_OUTLINE_PATCH</constant>.
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When <constant>GLU_NURBS_MODE</constant> is set to be <constant>GLU_NURBS_RENDERER</constant>,
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<parameter>value</parameter> defines how a NURBS surface should be rendered.
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When <parameter>value</parameter> is set to <constant>GLU_FILL</constant>, the surface is rendered as a
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set of polygons. When <parameter>value</parameter> is set to
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<constant>GLU_OUTLINE_POLYGON</constant>, the NURBS library draws only the outlines
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of the polygons created by tessellation. When <parameter>value</parameter> is set to
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<constant>GLU_OUTLINE_PATCH</constant> just the outlines of patches and trim
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curves defined by the user are drawn.
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</para>
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<para>
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When <constant>GLU_NURBS_MODE</constant> is set to be <constant>GLU_NURBS_TESSELLATOR</constant>,
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<parameter>value</parameter> defines how a NURBS surface should be tessellated.
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When <constant>GLU_DISPLAY_MODE</constant> is set to <constant>GLU_FILL</constant> or
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<constant>GLU_OUTLINE_POLYGON</constant>,
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the NURBS surface is tessellated into OpenGL triangle primitives that can be
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retrieved back through callback functions. If <constant>GLU_DISPLAY_MODE</constant> is set to
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<constant>GLU_OUTLINE_PATCH</constant>, only the outlines of the patches and trim curves are generated as a sequence of line strips that can be retrieved back through callback functions.
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</para>
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<para>
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The initial value is <constant>GLU_FILL</constant>.
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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><constant>GLU_CULLING</constant></term>
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<listitem>
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<para>
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<parameter>value</parameter> is a boolean value that, when set to <constant>GLU_TRUE</constant>, indicates that
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a NURBS curve should be discarded prior to tessellation if its control points
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lie outside the current viewport. The initial value is <constant>GLU_FALSE</constant>.
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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><constant>GLU_AUTO_LOAD_MATRIX</constant></term>
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<listitem>
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<para>
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<parameter>value</parameter> is a boolean value. When set to <constant>GLU_TRUE</constant>, the NURBS code
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downloads the projection matrix, the modelview matrix, and the
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viewport from the GL server to compute sampling and
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culling
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matrices for each NURBS curve that is rendered. Sampling and culling matrices
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are required to determine the tessellation of a NURBS surface into line segments
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or polygons and to cull a NURBS surface if it lies outside the viewport.
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</para>
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<para>
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If this mode is set to <constant>GLU_FALSE</constant>, then the program needs
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to provide a projection matrix, a modelview matrix, and a viewport
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for the NURBS renderer to use to construct sampling and culling matrices.
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This can be done with the <citerefentry><refentrytitle>gluLoadSamplingMatrices</refentrytitle></citerefentry> function.
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This mode is initially set to <constant>GLU_TRUE</constant>.
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Changing it from <constant>GLU_TRUE</constant> to <constant>GLU_FALSE</constant> does not affect
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the sampling and culling matrices until
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<citerefentry><refentrytitle>gluLoadSamplingMatrices</refentrytitle></citerefentry>
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is called.
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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="notes"><title>Notes</title>
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<para>
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If <constant>GLU_AUTO_LOAD_MATRIX</constant> is true, sampling and culling may be
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executed incorrectly if NURBS routines are compiled into a display list.
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</para>
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<para>
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A <parameter>property</parameter> of
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<constant>GLU_PARAMETRIC_TOLERANCE</constant>,
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<constant>GLU_SAMPLING_METHOD</constant>,
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<constant>GLU_U_STEP</constant>, or
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<constant>GLU_V_STEP</constant>,
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or a <parameter>value</parameter> of
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<constant>GLU_PATH_LENGTH</constant>,
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<constant>GLU_PARAMETRIC_ERROR</constant>,
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<constant>GLU_DOMAIN_DISTANCE</constant>
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are only available if the GLU version is 1.1 or greater. They are not
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valid parameters in GLU 1.0.
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</para>
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<para>
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<citerefentry><refentrytitle>gluGetString</refentrytitle></citerefentry> can
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be used to determine the GLU version.
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</para>
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<para>
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<constant>GLU_NURBS_MODE</constant> is only available if the GLU version is 1.3 or
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greater.
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</para>
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<para>
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The <constant>GLU_OBJECT_PATH_LENGTH</constant> and <constant>GLU_OBJECT_PARAMETRIC_ERROR</constant>
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values for the <constant>GLU_SAMPLING_METHOD</constant> property are only available if
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the GLU version is 1.3 or greater.
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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>gluGetNurbsProperty</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>gluGetString</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>gluLoadSamplingMatrices</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>gluNewNurbsRenderer</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>gluNurbsCallback</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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