[vtkusers] Persistent data across time step changes in programmable filter

[Sean Ziegeler]

I came up with a rather simple solution.  If I'm trying to cache some 
numpy array x (or really any variable x) for the next time step's 
execution in the Programmable Filter, I just make x a member of the 
object.  For example:

if 'x' in dir(self):
     x = self.x
else:
     x = make_my_x()
     self.x = x
do_whatever_with_x(x)

I realize this also reuses self.x for other pipeline updates, including 
changes applied to the Programmable Filter code or changes to the 
upstream pipeline data.  I'm sure I could check for upstream grid 
modifications (if anyone has suggestions, I'd appreciate them).  For now 
though, I just add an extra boolean flag to override the caching manually.

However, are there any pitfalls in using this approach?

Thanks,
Sean

On 11/15/12 16:50, Sean Ziegeler wrote:
> I previously sent this to the ParaView list and got no answer, but I
> realize now that it's really more of a VTK pipeline question anyway.
>
> I'm writing a programmable filter that makes changes to a vector field
> based on grid point properties (it's a polar orthographic transform
> using a highly accurate Earth shape model).
>
> This works well.  However, when one changes the timestep, it recomputes
> those grid point properties to apply to the next timestep's vector
> field.  This is a very expensive operation, and is quite unnecessary
> since the grid doesn't change over time.  I'd like to somehow cache the
> grid point property array so that I could simply reuse it for future
> timesteps if it's already been computed.
>
> I thought about storing it as a Field Data array.  However, with some
> experimentation, I find that Field Data arrays are cleared from the
> filter output when the pipeline re-executes for a new timestep.  Is
> there a way to keep a Field Data array around for subsequent time steps?
>   If not, is there some other mechanism for a programmable filter to
> retain data that won't change after the first timestep?
>
> Thanks!
> Sean
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