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Alphabetical listing for G

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gluTessVertex()
NAME
  gluTessVertex - specify a vertex on a polygon

SYNOPSIS
  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 GLU_TESS_VERTEX or GLU_TESS_VERTEX_DATA
  callback after tessellation (see the gluTessCallback() reference page).

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 GLU_TESS_NEED_COMBINE_CALLBACK error
  (when a local variable is used for location).

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);

SEE ALSO
  gluNewTess(3), gluTessBeginPolygon(3), gluTessBeginContour(3),
  gluTessCallback(3), gluTessProperty(3), gluTessNormal(3),
  gluTessEndPolygon(3)

Index for Section 3

Alphabetical listing for G

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