[Paraview] Magic Crop Filter

[Christian Werner]

Hi!

Today, I made a very interesting experience. I wanted to have the 
vtkImageClip functionality available in Paraview and performed the same 
steps as always to get a Paraview-Plugin out of a VTK Filter. I compiled 
the plugin, called it ImageClip and copied it over to my Paraview Plugin 
directory. Then I started Paraview. When browsing through my custom 
"Extensions" Filters-entry, I found that there is no ImageClip but a 
Crop! And this crop provided me with a nice GUI, letting me change the 
output size with spinbuttons and already providing the maximum x/y/z 
extents! Wow! It was like if Paraview said "Ah, I know that vtk Filter 
and I happen to know which parameters it likes and how to preset its 
values. You surely won't mind if I ignore your ServerManager xml and do 
all by myself, do you?"

How comes? And the most interesting part is: how can I make the 
ServerManager xml define default values that are actually variables 
(such as the image extents)? And why does Paraview handle vtkImageClip 
differently?

Best regards,
Christian