gluTessVertex(3G)	       OpenGL Reference		     gluTessVertex(3G)

NAME    [Toc]    [Back]

     gluTessVertex - specify a vertex on a polygon

C SPECIFICATION    [Toc]    [Back]

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

PARAMETERS    [Toc]    [Back]

     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    [Toc]    [Back]

     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 gluTessCallback
     reference page).

EXAMPLE    [Toc]    [Back]

     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);







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gluTessVertex(3G)	       OpenGL Reference		     gluTessVertex(3G)

NOTES    [Toc]    [Back]

     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    [Toc]    [Back]

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


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