[vtkusers] tensor glyph, inward pointing surface normals

[burlen]

Hi all,

I recently started to experiment with vtkTensorGlyph and found that some 
of the glyphs apear as "black bodies"(see attached images). This happens 
because their surface normals point inward. I noticed that if the 
transform applied to the glyph has a negative determinant the glyph 
surface and its surface normals get turned inside out, and that I could 
"fix" these flipped surface normals by applying a scale of -1,-1,-1 to 
the transform.

I'm not sure if these inward pointing surface normals are really a bug. 
It sure looked like one at first, but the fact that the glyph surface is 
turned inside out is, maybe, useful information about the tensor field. 
Although, If one is using a black background the these glyphs disappear, 
which is not useful, and without shading they can be tricky to "see" the 
shape at different angles.

Is this a bug or a feature? Is the inversion of the glyph surface useful 
information?

I filed a bug report about this, with a more images, patch with the 
flipped normals "fix" and two other fixes (one for parallel use, and 
another for naming output arrays), and a small test script that 
demonstrates the behavior. http://public.kitware.com/Bug/view.php?id=12179

Thanks
Burlen

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