GLUTESSVERTEX(3G) UNIX Programmer's Manual GLUTESSVERTEX(3G)
NAME
gluTessVertex - specify a vertex on a polygon
C SPECIFICATION
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 pro-
gram 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).
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);
MirBSD #10-current Printed 2021-12-07 1
GLUTESSVERTEX(3G) UNIX Programmer's Manual GLUTESSVERTEX(3G)
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 exam-
ple: 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 loca-
tion and data might not be dereferenced until
gluTessEndPolygon is executed, all the vertex coordinates
but the very last set could be overwritten before tessella-
tion 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).
SEE ALSO
gluTessBeginPolygon(3G), gluNewTess(3G),
gluTessBeginContour(3G), gluTessCallback(3G),
gluTessProperty(3G), gluTessNormal(3G),
gluTessEndPolygon(3G)
MirBSD #10-current Printed 2021-12-07 2