---

Manual Reference Pages  - GLUTESSVERTEX (3G)

---

gluTessVertex - specify a vertex on a polygon

CONTENTS

C Specification
Parameters
Description
Example
Notes
See Also

void gluTessVertex( GLUtesselator* tess,

                  GLdouble *location,
                  GLvoid* data )

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).

 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).

A quadrilateral with a triangular hole in it can be described as follows:

.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

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:
.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

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).

 gluTessBeginPolygon(3G),  gluNewTess(3G),  gluTessBeginContour(3G),  gluTessCallback(3G),  gluTessProperty(3G),  gluTessNormal(3G),  gluTessEndPolygon(3G)

Jump to page    or go to Top of page |  Section 3G |  Main Index.