[Paraview] Bug for vti in Paraview 4.3

[Gabe Weymouth]

I downloaded the newest stable build of paraview yesterday (upgrading from
4.1) so I could utilize the new features in pvpython (Screenshot, etc).
Unfortunately, I ran into what appears to be a bug in the handling of
clipping/opacity for vti files.

I have a 2D field that ranges from -20 to 110 and I need to isolate the
negative regions and discard the positive regions. I do this by clipping
(type: scalar, value: 0, inside out). In the new version, this clips the
entire field - nothing remains.

An alternative method that smooths out the transition is to map the scalar
from -2 to 2, setting zero opacity at 2. In the new version of paraview,
this blanks out both the positive and negative values, leaving only the
region between -2 to 2. A color map without opacity works as expected, and
the legend shows the correct opacity behaviour.

Playing around with the range of the transfer function, the negative values
begin to blank out when the positive limit is set below 20. This would seem
to indicate a bug in the application of the transfer function to the image
grid surface render.

If I repeat the tests using a vtr file and identical data, both clipping
and opacity work as expected. I see the same results on my mac and linux
workstation.


*Gabriel D Weymouth*
Southampton Marine and Maritime Institute Lecturer
University of Southampton
Boldrewood Campus, Building 176, Room 3029
Southampton, SO16 7QF, UK
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