fgluTessVertex(3G) OpenGL Reference fgluTessVertex(3G)NAME
fgluTessVertex - specify a vertex on a polygon
FORTRAN SPECIFICATION
SUBROUTINE fgluTessVertex( CHARACTER*8 tess,
CHARACTER*8 location,
CHARACTER*8 data )
PARAMETERS
tess Specifies the tessellation object (created with fgluNewTess).
location Specifies the location of the vertex.
data Specifies an opaque pointer passed back to the program with the
vertex callback (as specified by fgluTessCallback).
DESCRIPTION
fgluTessVertex describes a vertex on a polygon that the program defines.
Successive fgluTessVertex calls describe a closed contour. For example,
to describe a quadrilateral fgluTessVertex should be called four times.
fgluTessVertex can only be called between fgluTessBeginContour and
fgluTessEndContour.
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
fgluTessCallback 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);
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fgluTessVertex(3G) OpenGL Reference fgluTessVertex(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 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 fgluTessEndPolygon 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 ALSO
fgluTessBeginPolygon, fgluNewTess, fgluTessBeginContour,
fgluTessCallback, fgluTessProperty, fgluTessNormal, fgluTessEndPolygon
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