[vtkusers] pieces streaming mechanism

[Frédéric Speisser]

All,

I have a data object stored in pvti format (splitted in several pieces) 
and I would like to be able to stream only pieces involved in rendering. 
This should be possible in vtk, referring documentation.
I use vtkStreamindDemandDrivenPipeline and 
vtkStreamindDemandDrivenPipeline::UPDATE_EXTENT, but despite the fact I 
set bounds defining only a little part of my dataobject in update_extent 
key, the reader(vtkXMLPImageDataReader) always loads all pieces...
I have made plenty of tests but I'm not able to make this mechanism working.

I need some help/hints !

Thank you