[vtkusers] Filtered polydata

[Nil Goyette]

Hi all,

We decided to port our old vtk application to vtk8 and I have some 
questions concerning the jump to OpenGL2+. We load a streamlines file 
(tck/trk/fib/vtk), which is simply a list of lines in 3D [1], to view it 
with an image, compute some stats on it, etc. This is already working 
well, thanks to the MITK framework.

The problem is that we need to filter the streamlines when the user 
moves a selection box. It needs to be real-time, even with million(s) of 
streamlines. By 'filter', I simply mean that the user won't see all the 
data, but the data still should be in memory. Last time I simply created 
my own mapper, extending vtkPolyDataMapper, looping over a shared QSet 
containing the indices I wanted to draw. It was kind of a hack but it 
was super fast because there was no data duplication, only the qset was 
modified.

vtk changed a lot so I prefer asking before coding anything. Is there a 
standard way to filter a huge polydata in real-time? If not, I started 
studying OpenGL2/vtkOpenGLPolyDataMapper.cxx and I have some questions 
about the best way to draw only the lines I want, probably concerning 
glDrawRangeElements and Primitives.IBO.

Nil Goyette

[1] https://i.imgur.com/krzBvJV.png