📄 tessvertex.html

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<HTML><BODY><PRE>     <STRONG>NAME</STRONG>	  <STRONG>gluTessVertex</STRONG>	- specify a vertex on a	polygon     <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>	  void <STRONG>gluTessVertex</STRONG>( GLUtesselator* <EM>tess</EM>,			      GLdouble *<EM>location</EM>,			      GLvoid* <EM>data</EM> )     <STRONG>PARAMETERS</STRONG>	  <EM>tess</EM>	    Specifies the tessellation object (created with		    <STRONG>gluNewTess</STRONG>).	  <EM>location</EM>  Specifies the location of the vertex.	  <EM>data</EM>	    Specifies an opaque	pointer	passed back to the		    program with the vertex callback (as specified by		    <STRONG>gluTessCallback</STRONG>).     <STRONG>DESCRIPTION</STRONG>	  <STRONG>gluTessVertex</STRONG>	describes a vertex on a	polygon	that the	  program defines. Successive <STRONG>gluTessVertex</STRONG> calls describe a	  closed contour. For example, to describe a quadrilateral	  <STRONG>gluTessVertex</STRONG>	should be called four times.  <STRONG>gluTessVertex</STRONG>	  can only be called between <STRONG>gluTessBeginContour</STRONG> and	  <STRONG>gluTessEndContour</STRONG>.	  <EM>data</EM> 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 <STRONG>GLU_TESS_VERTEX</STRONG> or <STRONG>GLU_TESS_VERTEX_DATA</STRONG> callback	  after	tessellation (see the <STRONG>gluTessCallback</STRONG> reference	page).     <STRONG>EXAMPLE</STRONG>	  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);     <STRONG>NOTES</STRONG>	  It is	a common error to use a	local variable for <EM>location</EM> or	  <EM>data</EM> and store values	into it	as part	of a loop.  For	  example:  for	(i = 0;	i &lt; 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	  <EM>location</EM> and <EM>data</EM> might not be dereferenced until	  <STRONG>gluTessEndPolygon</STRONG> 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 <EM>data</EM>) and a	  <STRONG>GLU_TESS_NEED_COMBINE_CALLBACK</STRONG> error (when a local variable	  is used for <EM>location</EM>).     <STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>	  <STRONG>gluTessBeginPolygon</STRONG>, <STRONG>gluNewTess</STRONG>, <STRONG>gluTessBeginContour</STRONG>,	  <STRONG>gluTessCallback</STRONG>, <STRONG>gluTessProperty</STRONG>, <STRONG>gluTessNormal</STRONG>,	  <STRONG>gluTessEndPolygon</STRONG></PRE></BODY></HTML>
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