'\"! eqn | mmdoc
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 6 March 1997
.ds Re Release 1.2.0
.ds Dp Mar 17 18:20
.ds Dm  Mar  6 19:5
.ds Xs 30328 6 tessvertex.gl
.TH GLUTESSVERTEX
.SH NAME
.B "gluTessVertex
\- specify a vertex on a polygon

.SH C SPECIFICATION
void \f3gluTessVertex\fP(
GLUtesselator* \fItess\fP,
.nf
.ta \w'\f3void \fPgluTessVertex( 'u
	GLdouble \fI*location\fP,
	GLvoid* \fIdata\fP )
.fi

.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\fIlocation\fP\ \ 'u 
\f2tess\fP
Specifies the tessellation object (created with \f3gluNewTess\fP).
.TP
\f2location\fP
Specifies the location of the vertex.
.TP
\f2data\fP
Specifies an opaque pointer passed back to the program with the vertex callback
(as specified by \f3gluTessCallback\fP).
.SH DESCRIPTION
\f3gluTessVertex\fP describes a vertex on a polygon that the program defines. Successive
\f3gluTessVertex\fP calls describe a closed contour. For example, 
to describe a quadrilateral \f3gluTessVertex\fP should be called four times.
\f3gluTessVertex\fP can only be called between \f3gluTessBeginContour\fP and 
\f3gluTessEndContour\fP.
.P
\f2data\fP 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 \f3GLU_TESS_VERTEX\fP
or \f3GLU_TESS_VERTEX_DATA\fP callback after tessellation 
(see the \f3gluTessCallback\fP reference page).
.SH EXAMPLE
A quadrilateral with a triangular hole in it can be described as follows:
.sp
.Ex
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);
.Ee
.sp
.SH NOTES
It is a common error to use a local variable for \f2location\fP or \f2data\fP and store
values into it as part of a loop.
For example:
.Ex
for (i = 0; i < NVERTICES; ++i) {
  GLdouble data[3];
  data[0] = vertex[i][0];
  data[1] = vertex[i][1];
  data[2] = vertex[i][2];
  gluTessVertex(tobj, data, data);
  }
.Ee
.P
This doesn't work.
Because the pointers specified by \f2location\fP and \f2data\fP might not be 
dereferenced until \f3gluTessEndPolygon\fP is executed,
all the vertex coordinates but the very last set could be overwritten
before tessellation begins.
.P
Two common symptoms of this problem are consists of a single point
(when a local variable is used for \f2data\fP) and a
\f3GLU_TESS_NEED_COMBINE_CALLBACK\fP error (when a local variable is
used for \f2location\fP).
.SH SEE ALSO
\f3gluTessBeginPolygon\fP, \f3gluNewTess\fP, \f3gluTessBeginContour\fP, 
\f3gluTessCallback\fP, 
\f3gluTessProperty\fP, \f3gluTessNormal\fP,
\f3gluTessEndPolygon\fP