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<STRONG>NAME</STRONG>
<STRONG>gluTessVertex</STRONG> - specify a vertex on a polygon
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>gluTessVertex</STRONG>( GLUtesselator* <EM>tess</EM>,
GLdouble *<EM>location</EM>,
GLvoid* <EM>data</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>tess</EM> Specifies the tessellation object (created with
<STRONG>gluNewTess</STRONG>).
<EM>location</EM> Specifies the location of the vertex.
<EM>data</EM> Specifies an opaque pointer passed back to the
program with the vertex callback (as specified by
<STRONG>gluTessCallback</STRONG>).
<STRONG>DESCRIPTION</STRONG>
<STRONG>gluTessVertex</STRONG> describes a vertex on a polygon that the
program defines. Successive <STRONG>gluTessVertex</STRONG> calls describe a
closed contour. For example, to describe a quadrilateral
<STRONG>gluTessVertex</STRONG> should be called four times. <STRONG>gluTessVertex</STRONG>
can only be called between <STRONG>gluTessBeginContour</STRONG> and
<STRONG>gluTessEndContour</STRONG>.
<EM>data</EM> 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 <STRONG>GLU_TESS_VERTEX</STRONG> or <STRONG>GLU_TESS_VERTEX_DATA</STRONG> callback
after tessellation (see the <STRONG>gluTessCallback</STRONG> reference page).
<STRONG>EXAMPLE</STRONG>
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);
<STRONG>NOTES</STRONG>
It is a common error to use a local variable for <EM>location</EM> or
<EM>data</EM> 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
<EM>location</EM> and <EM>data</EM> might not be dereferenced until
<STRONG>gluTessEndPolygon</STRONG> 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 <EM>data</EM>) and a
<STRONG>GLU_TESS_NEED_COMBINE_CALLBACK</STRONG> error (when a local variable
is used for <EM>location</EM>).
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>gluTessBeginPolygon</STRONG>, <STRONG>gluNewTess</STRONG>, <STRONG>gluTessBeginContour</STRONG>,
<STRONG>gluTessCallback</STRONG>, <STRONG>gluTessProperty</STRONG>, <STRONG>gluTessNormal</STRONG>,
<STRONG>gluTessEndPolygon</STRONG>
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