GLUTESSVERTEX(3G)GLUTESSVERTEX(3G)NAMEgluTessVertex - 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).
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 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);
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_COMBINE_CALLBACK error (when a local variable is used for
location).
SEE ALSOgluTessBeginPolygon(3G), gluNewTess(3G), gluTessBeginContour(3G),
gluTessCallback(3G), gluTessProperty(3G), gluTessNormal(3G),
gluTessEndPolygon(3G)
March 1, 2011
