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+<?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="gluTessCallback">
+ <refmeta>
+ <refmetainfo>
+ <copyright>
+ <year>1991-2006</year>
+ <holder>Silicon Graphics, Inc.</holder>
+ </copyright>
+ </refmetainfo>
+ <refentrytitle>gluTessCallback</refentrytitle>
+ <manvolnum>3G</manvolnum>
+ </refmeta>
+ <refnamediv>
+ <refname>gluTessCallback</refname>
+ <refpurpose>define a callback for a tessellation object</refpurpose>
+ </refnamediv>
+ <refsynopsisdiv><title>C Specification</title>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>void <function>gluTessCallback</function></funcdef>
+ <paramdef>GLUtesselator* <parameter>tess</parameter></paramdef>
+ <paramdef>GLenum <parameter>which</parameter></paramdef>
+ <paramdef>_GLUfuncptr <parameter>CallBackFunc</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>which</parameter></term>
+ <listitem>
+ <para>
+ Specifies the callback being defined. The following values are valid:
+ <constant>GLU_TESS_BEGIN</constant>,
+ <constant>GLU_TESS_BEGIN_DATA</constant>,
+ <constant>GLU_TESS_EDGE_FLAG</constant>,
+ <constant>GLU_TESS_EDGE_FLAG_DATA</constant>,
+ <constant>GLU_TESS_VERTEX</constant>,
+ <constant>GLU_TESS_VERTEX_DATA</constant>,
+ <constant>GLU_TESS_END</constant>,
+ <constant>GLU_TESS_END_DATA</constant>,
+ <constant>GLU_TESS_COMBINE</constant>,
+ <constant>GLU_TESS_COMBINE_DATA</constant>,
+ <constant>GLU_TESS_ERROR</constant>, and
+ <constant>GLU_TESS_ERROR_DATA</constant>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>CallBackFunc</parameter></term>
+ <listitem>
+ <para>
+ Specifies the function to be called.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+ <refsect1 id="description"><title>Description</title>
+ <para>
+ <function>gluTessCallback</function> is used to indicate a callback to be used by a tessellation object.
+ If the specified callback is already defined, then it is replaced. If
+ <parameter>CallBackFunc</parameter> is NULL, then the existing callback becomes undefined.
+ </para>
+ <para>
+ These callbacks are used by the tessellation object to describe how a
+ polygon specified by the user is broken into triangles. Note that there
+ are two versions of each callback: one with user-specified polygon data
+ and one without. If both versions of a particular callback are specified,
+ then the callback with user-specified polygon data will be used. Note
+ that the <emphasis>polygon_data</emphasis> parameter used by some of the functions is
+ a copy of the pointer that was specified when
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry> was called. The legal callbacks are as follows:
+ </para>
+ <variablelist>
+ <varlistentry>
+ <term><constant>GLU_TESS_BEGIN</constant></term>
+ <listitem>
+ <para>
+ The begin callback is invoked like <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> to indicate the start of
+ a (triangle) primitive. The function takes a single argument of type
+ GLenum. If the <constant>GLU_TESS_BOUNDARY_ONLY</constant> property is set to
+ <constant>GLU_FALSE</constant>, then the argument is set to either
+ <constant>GLU_TRIANGLE_FAN</constant>, <constant>GLU_TRIANGLE_STRIP</constant>, or <constant>GLU_TRIANGLES</constant>.
+ If the <constant>GLU_TESS_BOUNDARY_ONLY</constant> property is set to <constant>GLU_TRUE</constant>,
+ then the argument will be set to <constant>GLU_LINE_LOOP</constant>. The function
+ prototype for this callback is:
+ <programlisting>
+void begin( GLenum type );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_BEGIN_DATA</constant></term>
+ <listitem>
+ <para>
+ The same as the <constant>GLU_TESS_BEGIN</constant> callback except that it
+ takes an additional pointer argument. This pointer is identical to the
+ opaque pointer provided when
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry> was called. The function prototype for this callback
+ is:
+ <programlisting>
+void beginData( GLenum type, void *polygon_data );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_EDGE_FLAG</constant></term>
+ <listitem>
+ <para>
+ The edge flag callback is similar to <citerefentry><refentrytitle>glEdgeFlag</refentrytitle></citerefentry>. The function
+ takes a single boolean flag that indicates which edges lie on the
+ polygon boundary. If the flag is <constant>GLU_TRUE</constant>, then each vertex
+ that follows begins an edge that lies on the polygon boundary, that is,
+ an edge that separates an interior region from an exterior one.
+ If the flag is <constant>GLU_FALSE</constant>, then each vertex that follows begins an edge
+ that lies in the polygon interior. The edge flag callback (if defined) is
+ invoked before the first vertex callback.
+ </para>
+ <para>
+ Since triangle fans and triangle strips do not support edge flags, the begin
+ callback is not called with <constant>GLU_TRIANGLE_FAN</constant> or <constant>GLU_TRIANGLE_STRIP</constant>
+ if a non-NULL edge flag callback is provided. (If the callback is
+ initialized to NULL, there is no impact on performance). Instead, the fans and
+ strips are converted to independent triangles. The function prototype
+ for this callback is:
+ <programlisting>
+void edgeFlag( GLboolean flag );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_EDGE_FLAG_DATA</constant></term>
+ <listitem>
+ <para>
+ The same as the <constant>GLU_TESS_EDGE_FLAG</constant> callback except that it takes an additional pointer
+ argument. This pointer is identical to the opaque pointer provided when
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry> was called. The function prototype for this callback
+ is:
+ <programlisting>
+void edgeFlagData( GLboolean flag, void *polygon_data );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_VERTEX</constant></term>
+ <listitem>
+ <para>
+ The vertex callback is invoked between the begin and end callbacks.
+ It is similar to <citerefentry><refentrytitle>glVertex</refentrytitle></citerefentry>, and it defines the vertices of the triangles
+ created by the tessellation process. The function
+ takes a pointer as its only argument. This pointer is identical to
+ the opaque pointer provided by the user when the vertex was described
+ (see <citerefentry><refentrytitle>gluTessVertex</refentrytitle></citerefentry>). The function prototype for this callback is:
+ <programlisting>
+void vertex( void *vertex_data );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_VERTEX_DATA</constant></term>
+ <listitem>
+ <para>
+ The same as the <constant>GLU_TESS_VERTEX</constant> callback except that it takes an additional pointer
+ argument. This pointer is identical to the opaque pointer provided when
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry> was called. The function prototype for this callback
+ is:
+ <programlisting>
+void vertexData( void *vertex_data, void *polygon_data );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_END</constant></term>
+ <listitem>
+ <para>
+ The end callback serves the same purpose as <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. It indicates the
+ end of a primitive and it takes no arguments. The function prototype for this
+ callback is:
+ <programlisting>
+void end( void );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_END_DATA</constant></term>
+ <listitem>
+ <para>
+ The same as the <constant>GLU_TESS_END</constant> callback except that it takes an additional pointer
+ argument. This pointer is identical to the opaque pointer provided when
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry> was called. The function prototype for this callback
+ is:
+ <programlisting>
+void endData( void *polygon_data );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_COMBINE</constant></term>
+ <listitem>
+ <para>
+ The combine callback is called to create a new vertex when the tessellation
+ detects an intersection or wishes to merge features. The function takes
+ four arguments: an array of three elements each of type GLdouble, an array
+ of four pointers, an array of four elements each of type GLfloat, and a
+ pointer to a pointer. The prototype is:
+ <programlisting>
+void combine( GLdouble coords[3], void *vertex_data[4],
+ GLfloat weight[4], void **outData );
+ </programlisting>
+ </para>
+ <para>
+ The vertex is defined as a linear combination of up to four existing vertices,
+ stored in <emphasis>vertex_data</emphasis>. The coefficients of the linear
+ combination are given by <emphasis>weight</emphasis>; these weights always add up to 1.
+ All vertex pointers are valid even when some of the weights are 0.
+ <emphasis>coords</emphasis> gives the location of the new vertex.
+ </para>
+ <para>
+ The user must allocate another vertex, interpolate parameters using
+ <emphasis>vertex_data</emphasis> and <emphasis>weight</emphasis>, and return the new vertex pointer in
+ <emphasis>outData</emphasis>. This handle is supplied during rendering callbacks.
+ The user is responsible for freeing the memory some time after
+ <citerefentry><refentrytitle>gluTessEndPolygon</refentrytitle></citerefentry> is called.
+ </para>
+ <para>
+ For example, if the polygon lies in an arbitrary plane in 3-space,
+ and a color is associated with each vertex, the
+ <constant>GLU_TESS_COMBINE</constant> callback might look like this:
+ <programlisting>
+void myCombine( GLdouble coords[3], VERTEX *d[4],
+ GLfloat w[4], VERTEX **dataOut )
+{
+ VERTEX *new = new_vertex();
+
+ new->x = coords[0];
+ new->y = coords[1];
+ new->z = coords[2];
+ new->r = w[0]*d[0]->r + w[1]*d[1]->r + w[2]*d[2]->r + w[3]*d[3]->r;
+ new->g = w[0]*d[0]->g + w[1]*d[1]->g + w[2]*d[2]->g + w[3]*d[3]->g;
+ new->b = w[0]*d[0]->b + w[1]*d[1]->b + w[2]*d[2]->b + w[3]*d[3]->b;
+ new->a = w[0]*d[0]->a + w[1]*d[1]->a + w[2]*d[2]->a + w[3]*d[3]->a;
+ *dataOut = new;
+}
+ </programlisting>
+ </para>
+ <para>
+ If the tessellation detects an intersection, then the <constant>GLU_TESS_COMBINE</constant> or
+ <constant>GLU_TESS_COMBINE_DATA</constant> callback (see below) must be defined, and it must
+ write a non-NULL pointer into <emphasis>dataOut</emphasis>. Otherwise the
+ <constant>GLU_TESS_NEED_COMBINE_CALLBACK</constant> error occurs, and no
+ output is generated.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_COMBINE_DATA</constant></term>
+ <listitem>
+ <para>
+ The same as the <constant>GLU_TESS_COMBINE</constant> callback except that it takes an additional pointer
+ argument. This pointer is identical to the opaque pointer provided when
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry> was called. The function prototype for this callback
+ is:
+ <programlisting>
+void combineData( GLdouble coords[3], void *vertex_data[4],
+ GLfloat weight[4], void **outData,
+ void *polygon_data );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_ERROR</constant></term>
+ <listitem>
+ <para>
+ The error callback is called when an error is encountered. The one argument
+ is of type GLenum; it indicates the specific error that occurred and will be
+ set to one of <constant>GLU_TESS_MISSING_BEGIN_POLYGON</constant>, <constant>GLU_TESS_MISSING_END_POLYGON</constant>,
+ <constant>GLU_TESS_MISSING_BEGIN_CONTOUR</constant>, <constant>GLU_TESS_MISSING_END_CONTOUR</constant>,
+ <constant>GLU_TESS_COORD_TOO_LARGE</constant>, <constant>GLU_TESS_NEED_COMBINE_CALLBACK</constant>, or
+ <constant>GLU_OUT_OF_MEMORY</constant>. Character
+ strings describing these errors can be retrieved with the
+ <citerefentry><refentrytitle>gluErrorString</refentrytitle></citerefentry> call. The function prototype for this callback is:
+ <programlisting>
+void error( GLenum errno );
+ </programlisting>
+ </para>
+ <para>
+ The GLU library will recover from the first four
+ errors by inserting the missing call(s).
+ <constant>GLU_TESS_COORD_TOO_LARGE</constant> indicates that some vertex coordinate exceeded
+ the predefined constant <constant>GLU_TESS_MAX_COORD</constant> in absolute value, and
+ that the value has been clamped. (Coordinate values must be small
+ enough so that two can be multiplied together without overflow.)
+ <constant>GLU_TESS_NEED_COMBINE_CALLBACK</constant> indicates that the tessellation
+ detected an intersection between two edges in the input data, and the
+ <constant>GLU_TESS_COMBINE</constant> or <constant>GLU_TESS_COMBINE_DATA</constant> callback was
+ not provided. No output is generated. <constant>GLU_OUT_OF_MEMORY</constant> indicates
+ that there is not enough memory so no output is generated.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><constant>GLU_TESS_ERROR_DATA</constant></term>
+ <listitem>
+ <para>
+ The same as the <constant>GLU_TESS_ERROR</constant> callback except that it takes an additional pointer
+ argument. This pointer is identical to the opaque pointer provided when
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry> was called. The function prototype for this callback
+ is:
+ <programlisting>
+void errorData( GLenum errno, void *polygon_data );
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+ <refsect1 id="example"><title>Example</title>
+ <para>
+ Polygons tessellated can be rendered directly like this:
+ <programlisting>
+gluTessCallback(tobj, GLU_TESS_BEGIN, glBegin);
+gluTessCallback(tobj, GLU_TESS_VERTEX, glVertex3dv);
+gluTessCallback(tobj, GLU_TESS_END, glEnd);
+gluTessCallback(tobj, GLU_TESS_COMBINE, myCombine);
+gluTessBeginPolygon(tobj, NULL);
+ gluTessBeginContour(tobj);
+ gluTessVertex(tobj, v, v);
+ ...
+ gluTessEndContour(tobj);
+gluTessEndPolygon(tobj);
+ </programlisting>
+ Typically, the tessellated polygon should be stored in a display list so that
+ it does not need to be retessellated every time it is rendered.
+ </para>
+ </refsect1>
+ <refsect1 id="seealso"><title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>gluErrorString</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>gluNewTess</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>gluTessBeginContour</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>gluTessBeginPolygon</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>gluTessNormal</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>gluTessProperty</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>gluTessVertex</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glEdgeFlag</refentrytitle></citerefentry>,
+ <citerefentry><refentrytitle>glVertex</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>
HCoop / clinton / guile-figl.git / blobdiff