gluTessVertex()gluTessVertex()NAMEgluTessVertex - specify a vertex on a polygon
SYNOPSIS
void gluTessVertex(
GLUtesselator* tess,
GLdouble *location,
GLvoid* data );
PARAMETERS
Specifies the tessellation object (created with gluNewTess()). Speci‐
fies the location of the vertex. Specifies an opaque pointer passed
back to the program with the vertex callback (as specified by gluTess‐
Callback()).
DESCRIPTIONgluTessVertex() 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 gluTess‐
BeginContour() 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 gluTessCall‐
back() 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_COM‐
BINE_CALLBACK error (when a local variable is used for location).
EXAMPLE
A quadrilateral with a triangular hole in it can be described as fol‐
lows: 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 ALSOgluNewTess(3), gluTessBeginPolygon(3), gluTessBeginContour(3), gluTess‐
Callback(3), gluTessProperty(3), gluTessNormal(3), gluTessEndPolygon(3)gluTessVertex()
