osx man page for glutessvertex

GLUTESSVERTEX(3G)														 GLUTESSVERTEX(3G)

NAME
       gluTessVertex - specify a vertex on a polygon

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

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 exam-
       ple, 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 gluTessCallback
       reference page).

EXAMPLE
       A quadrilateral with a triangular hole in it can be described as follows:

       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_COMBINE_CALLBACK error (when a local variable is used for location).

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

																 GLUTESSVERTEX(3G)