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• Author : matthieu
  Date : 2006-11-29 17:01:51
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  Message : GLU manual pages from monolithic tree

• doc/gl-docs/GLU/tessvertex.3gl

• '\" e
  '\"! eqn | mmdoc
  '\"macro stdmacro
  .ds Vn Version 1.2
  .ds Dt 6 March 1997
  .ds Re Release 1.2.0
  .ds Dp May 02 11:53
  .ds Dm 37 tessverte
  .ds Xs 55990 5 tessvertex.gl
  .TH GLUTESSVERTEX 3G
  .SH NAME
  .B "gluTessVertex
  \- specify a vertex on a polygon
  
  .SH C SPECIFICATION
  void \f3gluTessVertex\fP(
  GLUtesselator* \fItess\fP,
  .nf
  .ta \w'\f3void \fPgluTessVertex( 'u
  	GLdouble \fI*location\fP,
  	GLvoid* \fIdata\fP )
  .fi
  
  .EQ
  delim $$
  .EN
  .SH PARAMETERS
  .TP \w'\fIlocation\fP\ \ 'u 
  \f2tess\fP
  Specifies the tessellation object (created with \%\f3gluNewTess\fP).
  .TP
  \f2location\fP
  Specifies the location of the vertex.
  .TP
  \f2data\fP
  Specifies an opaque pointer passed back to the program with the vertex callback
  (as specified by \%\f3gluTessCallback\fP).
  .SH DESCRIPTION
  \%\f3gluTessVertex\fP describes a vertex on a polygon that the program defines. Successive
  \%\f3gluTessVertex\fP calls describe a closed contour. For example, 
  to describe a quadrilateral \%\f3gluTessVertex\fP should be called four times.
  \%\f3gluTessVertex\fP can only be called between \%\f3gluTessBeginContour\fP and 
  \%\f3gluTessEndContour\fP.
  .P
  \f2data\fP 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 \%\f3GLU_TESS_VERTEX\fP
  or \%\f3GLU_TESS_VERTEX_DATA\fP callback after tessellation 
  (see the \%\f3gluTessCallback\fP reference page).
  .SH EXAMPLE
  A quadrilateral with a triangular hole in it can be described as follows:
  .sp
  .Ex
  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);
  .Ee
  .sp
  .SH NOTES
  It is a common error to use a local variable for \f2location\fP or \f2data\fP and store
  values into it as part of a loop.
  For example:
  .Ex
  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);
    }
  .Ee
  .P
  This doesn't work.
  Because the pointers specified by \f2location\fP and \f2data\fP might not be 
  dereferenced until \%\f3gluTessEndPolygon\fP is executed,
  all the vertex coordinates but the very last set could be overwritten
  before tessellation begins.
  .P
  Two common symptoms of this problem are consists of a single point
  (when a local variable is used for \f2data\fP) and a
  \%\f3GLU_TESS_NEED_COMBINE_CALLBACK\fP error (when a local variable is
  used for \f2location\fP).
  .SH SEE ALSO
  \%\f3gluTessBeginPolygon(3G)\fP, \%\f3gluNewTess(3G)\fP, \%\f3gluTessBeginContour(3G)\fP, 
  \%\f3gluTessCallback(3G)\fP, 
  \%\f3gluTessProperty(3G)\fP, \%\f3gluTessNormal(3G)\fP,
  \%\f3gluTessEndPolygon(3G)\fP