[clinton/guile-figl.git] / upstream-doc / man2 / gluTessVertex.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
              "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="gluTessVertex">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>gluTessVertex</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>gluTessVertex</refname>
        <refpurpose>specify a vertex on a polygon</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>gluTessVertex</function></funcdef>
                <paramdef>GLUtesselator* <parameter>tess</parameter></paramdef>
                <paramdef>GLdouble * <parameter>location</parameter></paramdef>
                <paramdef>GLvoid* <parameter>data</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <!-- eqn: ignoring delim $$ -->
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>tess</parameter></term>
            <listitem>
                <para>
                    Specifies the tessellation object (created with <citerefentry><refentrytitle>gluNewTess</refentrytitle></citerefentry>).
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>location</parameter></term>
            <listitem>
                <para>
                    Specifies the location of the vertex.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>data</parameter></term>
            <listitem>
                <para>
                    Specifies an opaque pointer passed back to the program with the vertex callback
                    (as specified by <citerefentry><refentrytitle>gluTessCallback</refentrytitle></citerefentry>).
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>gluTessVertex</function> describes a vertex on a polygon that the program defines. Successive
            <function>gluTessVertex</function> calls describe a closed contour. For example, 
            to describe a quadrilateral, <function>gluTessVertex</function> should be called four times.
            <function>gluTessVertex</function> can only be called between <citerefentry><refentrytitle>gluTessBeginContour</refentrytitle></citerefentry> and 
            <citerefentry><refentrytitle>gluTessEndContour</refentrytitle></citerefentry>.
        </para>
        <para>
            <parameter>data</parameter> normally points to a structure containing the vertex
            location, as well as other per-vertex attributes such as color and normal.
            This pointer is passed back to the user through the <constant>GLU_TESS_VERTEX</constant>
            or <constant>GLU_TESS_VERTEX_DATA</constant> callback after tessellation 
            (see the <citerefentry><refentrytitle>gluTessCallback</refentrytitle></citerefentry> reference page).
        </para>
    </refsect1>
    <refsect1 id="example"><title>Example</title>
        <para>
            A quadrilateral with a triangular hole in it can be described as follows:
            <programlisting>
gluTessBeginPolygon(tobj, NULL);
   gluTessBeginContour(tobj);
      gluTessVertex(tobj, v1, v1);
      gluTessVertex(tobj, v2, v2);
      gluTessVertex(tobj, v3, v3);
      gluTessVertex(tobj, v4, v4);
   gluTessEndContour(tobj);
   gluTessBeginContour(tobj);
      gluTessVertex(tobj, v5, v5);
      gluTessVertex(tobj, v6, v6);
      gluTessVertex(tobj, v7, v7);
   gluTessEndContour(tobj);
gluTessEndPolygon(tobj);
            </programlisting>
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            It is a common error to use a local variable for <parameter>location</parameter> or <parameter>data</parameter> and store
            values into it as part of a loop.
            For example:
            <programlisting>
for (i = 0; i &lt; NVERTICES; ++i) {
   GLdouble data[3];
   data[0] = vertex[i][0];
   data[1] = vertex[i][1];
   data[2] = vertex[i][2];
   gluTessVertex(tobj, data, data);
}
            </programlisting>
        </para>
        <para>
            This doesn't work.
            Because the pointers specified by <parameter>location</parameter> and <parameter>data</parameter> might not be 
            dereferenced until <citerefentry><refentrytitle>gluTessEndPolygon</refentrytitle></citerefentry> is executed,
            all the vertex coordinates but the very last set could be overwritten
            before tessellation begins.
        </para>
        <para>
            Two common symptoms of this problem are when the data consists of a single
            point (when a local variable is used for <parameter>data</parameter>) and a
            <constant>GLU_TESS_NEED_COMBINE_CALLBACK</constant> error (when a local variable is
            used for <parameter>location</parameter>).
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>gluNewTess</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluTessBeginContour</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluTessCallback</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluTessEndPolygon</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluTessNormal</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluTessProperty</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
        </para>
    </refsect1>
</refentry>
Commit	Line	Data
7faf1d71 AW	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="gluTessVertex">
	5	<refmeta>
	6	<refmetainfo>
	7	<copyright>
	8	<year>1991-2006</year>
	9	<holder>Silicon Graphics, Inc.</holder>
	10	</copyright>
	11	</refmetainfo>
	12	<refentrytitle>gluTessVertex</refentrytitle>
	13	<manvolnum>3G</manvolnum>
	14	</refmeta>
	15	<refnamediv>
	16	<refname>gluTessVertex</refname>
	17	<refpurpose>specify a vertex on a polygon</refpurpose>
	18	</refnamediv>
	19	<refsynopsisdiv><title>C Specification</title>
	20	<funcsynopsis>
	21	<funcprototype>
	22	<funcdef>void <function>gluTessVertex</function></funcdef>
	23	<paramdef>GLUtesselator* <parameter>tess</parameter></paramdef>
	24	<paramdef>GLdouble * <parameter>location</parameter></paramdef>
	25	<paramdef>GLvoid* <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>location</parameter></term>
	42	<listitem>
	43	<para>
	44	Specifies the location of the vertex.
	45	</para>
	46	</listitem>
	47	</varlistentry>
	48	<varlistentry>
	49	<term><parameter>data</parameter></term>
	50	<listitem>
	51	<para>
	52	Specifies an opaque pointer passed back to the program with the vertex callback
	53	(as specified by <citerefentry><refentrytitle>gluTessCallback</refentrytitle></citerefentry>).
	54	</para>
	55	</listitem>
	56	</varlistentry>
	57	</variablelist>
	58	</refsect1>
	59	<refsect1 id="description"><title>Description</title>
	60	<para>
	61	<function>gluTessVertex</function> describes a vertex on a polygon that the program defines. Successive
	62	<function>gluTessVertex</function> calls describe a closed contour. For example,
	63	to describe a quadrilateral, <function>gluTessVertex</function> should be called four times.
	64	<function>gluTessVertex</function> can only be called between <citerefentry><refentrytitle>gluTessBeginContour</refentrytitle></citerefentry> and
65	<citerefentry><refentrytitle>gluTessEndContour</refentrytitle></citerefentry>.
66	</para>
67	<para>
68	<parameter>data</parameter> normally points to a structure containing the vertex
69	location, as well as other per-vertex attributes such as color and normal.
70	This pointer is passed back to the user through the <constant>GLU_TESS_VERTEX</constant>
71	or <constant>GLU_TESS_VERTEX_DATA</constant> callback after tessellation
72	(see the <citerefentry><refentrytitle>gluTessCallback</refentrytitle></citerefentry> reference page).
73	</para>
74	</refsect1>
75	<refsect1 id="example"><title>Example</title>
76	<para>
77	A quadrilateral with a triangular hole in it can be described as follows:
78	<programlisting>
79	gluTessBeginPolygon(tobj, NULL);
80	gluTessBeginContour(tobj);
81	gluTessVertex(tobj, v1, v1);
82	gluTessVertex(tobj, v2, v2);
83	gluTessVertex(tobj, v3, v3);
84	gluTessVertex(tobj, v4, v4);
85	gluTessEndContour(tobj);
86	gluTessBeginContour(tobj);
87	gluTessVertex(tobj, v5, v5);
88	gluTessVertex(tobj, v6, v6);
89	gluTessVertex(tobj, v7, v7);
90	gluTessEndContour(tobj);
91	gluTessEndPolygon(tobj);
92	</programlisting>
93	</para>
94	</refsect1>
95	<refsect1 id="notes"><title>Notes</title>
96	<para>
97	It is a common error to use a local variable for <parameter>location</parameter> or <parameter>data</parameter> and store
98	values into it as part of a loop.
99	For example:
100	<programlisting>
101	for (i = 0; i < NVERTICES; ++i) {
102	GLdouble data[3];
103	data[0] = vertex[i][0];
104	data[1] = vertex[i][1];
105	data[2] = vertex[i][2];
106	gluTessVertex(tobj, data, data);
107	}
108	</programlisting>
109	</para>
110	<para>
111	This doesn't work.
112	Because the pointers specified by <parameter>location</parameter> and <parameter>data</parameter> might not be
113	dereferenced until <citerefentry><refentrytitle>gluTessEndPolygon</refentrytitle></citerefentry> is executed,
114	all the vertex coordinates but the very last set could be overwritten
115	before tessellation begins.
116	</para>
117	<para>
118	Two common symptoms of this problem are when the data consists of a single
119	point (when a local variable is used for <parameter>data</parameter>) and a
120	<constant>GLU_TESS_NEED_COMBINE_CALLBACK</constant> error (when a local variable is
121	used for <parameter>location</parameter>).
122	</para>
123	</refsect1>
124	<refsect1 id="seealso"><title>See Also</title>
125	<para>
126	<citerefentry><refentrytitle>gluNewTess</refentrytitle></citerefentry>,
127	<citerefentry><refentrytitle>gluTessBeginContour</refentrytitle></citerefentry>,
128	<citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry>,
129	<citerefentry><refentrytitle>gluTessCallback</refentrytitle></citerefentry>,
130	<citerefentry><refentrytitle>gluTessEndPolygon</refentrytitle></citerefentry>,
131	<citerefentry><refentrytitle>gluTessNormal</refentrytitle></citerefentry>,
132	<citerefentry><refentrytitle>gluTessProperty</refentrytitle></citerefentry>
133	</para>
134	</refsect1>
135	<refsect1 id="Copyright"><title>Copyright</title>
136	<para>
137	Copyright <trademark class="copyright"></trademark> 1991-2006
138	Silicon Graphics, Inc. This document is licensed under the SGI
139	Free Software B License. For details, see
140	<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
141	</para>
142	</refsect1>
143	</refentry>