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GLUTESSVERTEX()						       GLUTESSVERTEX()

NAME
       gluTessVertex - specify a vertex	on a polygon

C SPECIFICATION
       void gluTessVertex( GLUtesselator* tess,
			   GLdouble *location,
			   GLvoid* data	)

       delim $$

PARAMETERS
       tess	 Specifies the tessellation object (created with gluNewTess).

       location	 Specifies the location	of the vertex.

       data	 Specifies  an	opaque pointer passed back to the program with
		 the vertex callback (as specified by gluTessCallback).

DESCRIPTION
       gluTessVertex describes a vertex	on a polygon that the program defines.
       Successive gluTessVertex	calls describe a closed	contour. For  example,
       to  describe a quadrilateral gluTessVertex should be called four	times.
       gluTessVertex  can  only	 be  called  between  gluTessBeginContour  and
       gluTessEndContour.

       data  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 GLU_TESS_VERTEX or
       GLU_TESS_VERTEX_DATA callback after tessellation	(see the  gluTessCall-
       back reference page).

EXAMPLE
       A  quadrilateral	 with a	triangular hole	in it can be described as fol-
       lows:

       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);

NOTES
       It is a common error to use a local variable for	location or  data  and
       store  values  into it as part of a loop.  For example: 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);
	 }

       This doesn't work.  Because the pointers	specified by location and data
       might not be dereferenced until gluTessEndPolygon is executed, all  the
       vertex  coordinates  but	 the very last set could be overwritten	before
       tessellation begins.

       Two common symptoms of this problem are	consists  of  a	 single	 point
       (when  a	 local	variable  is  used  for	data) and a GLU_TESS_NEED_COM-
       BINE_CALLBACK error (when a local variable is used for location).

SEE ALSO
       gluTessBeginPolygon, gluNewTess,	gluTessBeginContour,  gluTessCallback,
       gluTessProperty,	gluTessNormal, gluTessEndPolygon

							       GLUTESSVERTEX()

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