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Cracks on NURBS sphere

Hi,

I am currently working on VectorWorks 9.0 and it seems to me that there is a
serious problem of NURBS modeling in Apple's OpenGL library. Basically, we
generate just a single NURBS patch and feed its control points and knots to
GLU NURBS to model just a sphere, but the rendered the NURBS surface has
very obvious cracks on it, and the whole sphere is evenly divided into 8
patches along the crack lines and each patch has different color of shading
on. Why I am blaming on Apple's OpenGL lib? Because the exact same data fed
to OpenGL lib on windows produced very smooth sphere. Obviously, the
tessellated the triangles generated by NURBS modeler got the wrong normals
on Mac.

If Apple wants, I can provide the geometry data and some code fragments. The
code is strictly based on the red book. Or, maybe, can Apple OpenGL people
simply try just modeling a sphere using NURBS in house and see whether you
can get it successfully. I think this is very basic test for the NURBS
modeler in OpenGL lib. If you can not even make a NURBS sphere, how can you
claim you even can do NURBS in OpenGL rendering on Mac?

I try on every version of OpenGL engine, 1.1.2, 1.1.3, 1.1.4, 1.1.5 even
1.2, and on G3, G4, they all have the same problem.

Look forward to hearing some comments. Thanks!

Shirley Carter
Nemetschek North America



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