GLUTESVERTEX(3G)                                            GLUTESVERTEX(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  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 GLUTESVERTEX or
       GLUTESVERTEXDATA   callback    after    tessellation    (see    the
       gluTessCallback reference page).

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

       gluTessBeginPolygon(tobj, NUL);
        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
       GLUTESNEDCOMBINECALBACK error (when a local variable is used for
       location).

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





                                                             GLUTESVERTEX(3G)