fgluTessVertex(3G)

NAME
     fgluTessVertex - specify a vertex on a polygon


FORTRAN SPECIFICATION
     SUBROUTINE fgluTessVertex( CHARACTER*8 tess,
                                CHARACTER*8 location,
                                CHARACTER*8 data )


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

     location  Specifies the location of the vertex.

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


DESCRIPTION
     fgluTessVertex describes a vertex on a polygon that the user is defining.
     Successive fgluTessVertex calls describe a closed contour.  For example,
     if the user wants to describe a quadrilateral, then fgluTessVertex should
     be called four times.  fgluTessVertex can only be called between
     fgluTessBeginContour and fgluTessEndContour.

     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
     fgluTessCallback 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 will not work.  Because the pointers specified by  location and data
     might not be dereferenced until fgluTessEndPolygon is executed, all the
     vertex coordinates but the very last set could be overwritten before
     tessellation begins.

     Two common symptoms of this problem are a GLU_TESS_NEED_COMBINE_CALLBACK
     error (when a local variable is used for location) and an output polygon
     that consists of a single point (when a local variable is used for data).


SEE ALSO
     fgluTessBeginPolygon, fgluNewTess, fgluTessBeginContour,
     fgluTessCallback, fgluTessProperty, fgluTessNormal, fgluTessEndPolygon