GLUTESSVERTEX() MachTen Programmer’s Manual GLUTESSVERTEX()

NAME
gluTessVertex - specify a vertex on a polygon

C SPECIFICATION
void gluTessVertex( GLUtesselator* tess,
GLdouble *location,
GLvoid* data )

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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 call-
back after tessellation (see the gluTessCallback reference
page).

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);

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 tessel-
lation begins.

Two common symptoms of this problem are consists of a sin-
gle point (when a local variable is used for data) and a
GLU_TESS_NEED_COMBINE_CALLBACK error (when a local vari-
able is used for location).

SEE ALSO
gluTessBeginPolygon, gluNewTess, gluTessBeginContour,
gluTessCallback, gluTessProperty, gluTessNormal,
gluTessEndPolygon

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