156 lines
8 KiB
XML
156 lines
8 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="gluTessProperty">
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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>gluTessProperty</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>gluTessProperty</refname>
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<refpurpose>set a tessellation object 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>gluTessProperty</function></funcdef>
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<paramdef>GLUtesselator* <parameter>tess</parameter></paramdef>
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<paramdef>GLenum <parameter>which</parameter></paramdef>
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<paramdef>GLdouble <parameter>data</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>which</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_TESS_WINDING_RULE</constant>,
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<constant>GLU_TESS_BOUNDARY_ONLY</constant>, and
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<constant>GLU_TESS_TOLERANCE</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>data</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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</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>gluTessProperty</function> is used to control properties stored in a tessellation object. These
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properties affect the way that the polygons are interpreted and rendered.
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The legal values for <parameter>which</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_TESS_WINDING_RULE</constant> </term>
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<listitem>
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<para>
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Determines which parts of the polygon are on the ``interior''.
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<parameter>data</parameter> may be set to one of <constant>GLU_TESS_WINDING_ODD</constant>,
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<constant>GLU_TESS_WINDING_NONZERO</constant>, <constant>GLU_TESS_WINDING_POSITIVE</constant>,
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<constant>GLU_TESS_WINDING_NEGATIVE</constant>, or <constant>GLU_TESS_WINDING_ABS_GEQ_TWO</constant>.
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</para>
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<para>
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To understand how the winding rule works, consider that the input
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contours partition the plane into regions. The winding rule determines which
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of these regions are inside the polygon.
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</para>
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<para>
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For a single contour C, the winding number of a point x is simply the signed
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number of revolutions we make around x as we travel once around C
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(where CCW is positive). When there are several contours, the individual
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winding numbers are summed. This procedure associates a signed integer
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value with each point x in the plane. Note that the winding number is the
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same for all points in a single region.
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</para>
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<para>
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The winding rule classifies a region as ``inside'' if its winding number
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belongs to the chosen category (odd, nonzero, positive, negative, or
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absolute value of at least two). The previous GLU tessellator (prior to
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GLU 1.2) used the ``odd'' rule. The ``nonzero'' rule is another common way to
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define the interior. The other three rules are useful for polygon CSG
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operations.
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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_TESS_BOUNDARY_ONLY</constant> </term>
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<listitem>
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<para>
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Is a boolean value (``value'' should be set
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to GL_TRUE or GL_FALSE). When set to GL_TRUE, a set of closed contours
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separating the polygon interior and exterior are returned instead of a
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tessellation. Exterior contours are oriented CCW with respect to the
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normal; interior contours are oriented CW. The <constant>GLU_TESS_BEGIN</constant>
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and <constant>GLU_TESS_BEGIN_DATA</constant> callbacks use the type GL_LINE_LOOP for
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each contour.
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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_TESS_TOLERANCE</constant></term>
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<listitem>
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<para>
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Specifies a tolerance for merging features to reduce the size of the output.
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For example, two vertices that are very close to each other might be
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replaced by a single vertex. The tolerance is multiplied by the largest
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coordinate magnitude of any input vertex; this specifies the maximum
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distance that any feature can move as the result of a single merge
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operation. If a single feature takes part in several merge operations, the
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total distance moved could be larger.
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</para>
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<para>
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Feature merging is completely optional; the tolerance is only a hint.
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The implementation is free to merge in some cases and not in others, or to
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never merge features at all. The initial tolerance is 0.
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</para>
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<para>
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The current implementation merges vertices only if they are exactly
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coincident, regardless of the current tolerance. A vertex is spliced into
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an edge only if the implementation is unable to distinguish which side of
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the edge the vertex lies on. Two edges are merged only when both endpoints
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are identical.
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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="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>gluGetTessProperty</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>gluNewTess</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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