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1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd"> | |
4 | <refentry id="gluTessProperty"> | |
5 | <refmeta> | |
6 | <refmetainfo> | |
7 | <copyright> | |
8 | <year>1991-2006</year> | |
9 | <holder>Silicon Graphics, Inc.</holder> | |
10 | </copyright> | |
11 | </refmetainfo> | |
12 | <refentrytitle>gluTessProperty</refentrytitle> | |
13 | <manvolnum>3G</manvolnum> | |
14 | </refmeta> | |
15 | <refnamediv> | |
16 | <refname>gluTessProperty</refname> | |
17 | <refpurpose>set a tessellation object property</refpurpose> | |
18 | </refnamediv> | |
19 | <refsynopsisdiv><title>C Specification</title> | |
20 | <funcsynopsis> | |
21 | <funcprototype> | |
22 | <funcdef>void <function>gluTessProperty</function></funcdef> | |
23 | <paramdef>GLUtesselator* <parameter>tess</parameter></paramdef> | |
24 | <paramdef>GLenum <parameter>which</parameter></paramdef> | |
25 | <paramdef>GLdouble <parameter>data</parameter></paramdef> | |
26 | </funcprototype> | |
27 | </funcsynopsis> | |
28 | </refsynopsisdiv> | |
29 | <!-- eqn: ignoring delim $$ --> | |
30 | <refsect1 id="parameters"><title>Parameters</title> | |
31 | <variablelist> | |
32 | <varlistentry> | |
33 | <term><parameter>tess</parameter></term> | |
34 | <listitem> | |
35 | <para> | |
36 | Specifies the tessellation object (created with <citerefentry><refentrytitle>gluNewTess</refentrytitle></citerefentry>). | |
37 | </para> | |
38 | </listitem> | |
39 | </varlistentry> | |
40 | <varlistentry> | |
41 | <term><parameter>which</parameter></term> | |
42 | <listitem> | |
43 | <para> | |
44 | Specifies the property to be set. Valid values are | |
45 | <constant>GLU_TESS_WINDING_RULE</constant>, | |
46 | <constant>GLU_TESS_BOUNDARY_ONLY</constant>, and | |
47 | <constant>GLU_TESS_TOLERANCE</constant>. | |
48 | </para> | |
49 | </listitem> | |
50 | </varlistentry> | |
51 | <varlistentry> | |
52 | <term><parameter>data</parameter></term> | |
53 | <listitem> | |
54 | <para> | |
55 | Specifies the value of the indicated property. | |
56 | </para> | |
57 | </listitem> | |
58 | </varlistentry> | |
59 | </variablelist> | |
60 | </refsect1> | |
61 | <refsect1 id="description"><title>Description</title> | |
62 | <para> | |
63 | <function>gluTessProperty</function> is used to control properties stored in a tessellation object. These | |
64 | properties affect the way that the polygons are interpreted and rendered. | |
65 | The legal values for <parameter>which</parameter> are as follows: | |
66 | </para> | |
67 | <variablelist> | |
68 | <varlistentry> | |
69 | <term><constant>GLU_TESS_WINDING_RULE</constant> </term> | |
70 | <listitem> | |
71 | <para> | |
72 | Determines which parts of the polygon are on the ``interior''. | |
73 | <parameter>data</parameter> may be set to one of <constant>GLU_TESS_WINDING_ODD</constant>, | |
74 | <constant>GLU_TESS_WINDING_NONZERO</constant>, <constant>GLU_TESS_WINDING_POSITIVE</constant>, | |
75 | <constant>GLU_TESS_WINDING_NEGATIVE</constant>, or <constant>GLU_TESS_WINDING_ABS_GEQ_TWO</constant>. | |
76 | </para> | |
77 | <para> | |
78 | To understand how the winding rule works, consider that the input | |
79 | contours partition the plane into regions. The winding rule determines which | |
80 | of these regions are inside the polygon. | |
81 | </para> | |
82 | <para> | |
83 | For a single contour C, the winding number of a point x is simply the signed | |
84 | number of revolutions we make around x as we travel once around C | |
85 | (where CCW is positive). When there are several contours, the individual | |
86 | winding numbers are summed. This procedure associates a signed integer | |
87 | value with each point x in the plane. Note that the winding number is the | |
88 | same for all points in a single region. | |
89 | </para> | |
90 | <para> | |
91 | The winding rule classifies a region as ``inside'' if its winding number | |
92 | belongs to the chosen category (odd, nonzero, positive, negative, or | |
93 | absolute value of at least two). The previous GLU tessellator (prior to | |
94 | GLU 1.2) used the ``odd'' rule. The ``nonzero'' rule is another common way to | |
95 | define the interior. The other three rules are useful for polygon CSG | |
96 | operations. | |
97 | </para> | |
98 | </listitem> | |
99 | </varlistentry> | |
100 | <varlistentry> | |
101 | <term><constant>GLU_TESS_BOUNDARY_ONLY</constant> </term> | |
102 | <listitem> | |
103 | <para> | |
104 | Is a boolean value (``value'' should be set | |
105 | to GL_TRUE or GL_FALSE). When set to GL_TRUE, a set of closed contours | |
106 | separating the polygon interior and exterior are returned instead of a | |
107 | tessellation. Exterior contours are oriented CCW with respect to the | |
108 | normal; interior contours are oriented CW. The <constant>GLU_TESS_BEGIN</constant> | |
109 | and <constant>GLU_TESS_BEGIN_DATA</constant> callbacks use the type GL_LINE_LOOP for | |
110 | each contour. | |
111 | </para> | |
112 | </listitem> | |
113 | </varlistentry> | |
114 | <varlistentry> | |
115 | <term><constant>GLU_TESS_TOLERANCE</constant></term> | |
116 | <listitem> | |
117 | <para> | |
118 | Specifies a tolerance for merging features to reduce the size of the output. | |
119 | For example, two vertices that are very close to each other might be | |
120 | replaced by a single vertex. The tolerance is multiplied by the largest | |
121 | coordinate magnitude of any input vertex; this specifies the maximum | |
122 | distance that any feature can move as the result of a single merge | |
123 | operation. If a single feature takes part in several merge operations, the | |
124 | total distance moved could be larger. | |
125 | </para> | |
126 | <para> | |
127 | Feature merging is completely optional; the tolerance is only a hint. | |
128 | The implementation is free to merge in some cases and not in others, or to | |
129 | never merge features at all. The initial tolerance is 0. | |
130 | </para> | |
131 | <para> | |
132 | The current implementation merges vertices only if they are exactly | |
133 | coincident, regardless of the current tolerance. A vertex is spliced into | |
134 | an edge only if the implementation is unable to distinguish which side of | |
135 | the edge the vertex lies on. Two edges are merged only when both endpoints | |
136 | are identical. | |
137 | </para> | |
138 | </listitem> | |
139 | </varlistentry> | |
140 | </variablelist> | |
141 | </refsect1> | |
142 | <refsect1 id="seealso"><title>See Also</title> | |
143 | <para> | |
144 | <citerefentry><refentrytitle>gluGetTessProperty</refentrytitle></citerefentry>, | |
145 | <citerefentry><refentrytitle>gluNewTess</refentrytitle></citerefentry> | |
146 | </para> | |
147 | </refsect1> | |
148 | <refsect1 id="Copyright"><title>Copyright</title> | |
149 | <para> | |
150 | Copyright <trademark class="copyright"></trademark> 1991-2006 | |
151 | Silicon Graphics, Inc. This document is licensed under the SGI | |
152 | Free Software B License. For details, see | |
153 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. | |
154 | </para> | |
155 | </refsect1> | |
156 | </refentry> |