[Paraview] caching output pipelines

[Olesen, Mark]

I'm working on bits of an add-on reader and would like to figure out how
the pipeline caching is supposed to work. Unfortunately I only have
immediate access to a somewhat older "VTK Visualization Toolkit" book
and not the "VTK User's Guide", where the required information might
presumably be found.

I have a time-invariant geometry (organized as a vtkMultiBlockDataSet
with several blocks) and a number of time-steps. To avoid pulling the
geometry data from disk at each time step, the geometry is cached in an
internal (non-vtk) format. I've tried various means of updating field
values only without needing to update the underlying geometry, but have
had thus far no luck.

I was inspired by the Biddiscombe et al. IEEE 2007 publication and
started digging through the VTK/IO directory for suitable examples.
I can't, however, see that any of them have implemented the combination
of an invariant geometry and transient fields.

At the moment I have a RequestInformation() method with
    outInfo->Set
    (
        vtkStreamingDemandDrivenPipeline::TIME_STEPS(),
        timeSteps,
        nTimeSteps
    );

    outInfo->Set
    (
        vtkStreamingDemandDrivenPipeline::TIME_RANGE(),
        timeRange,
        2
    );

and a RequestData() method that responds to

    vtkStreamingDemandDrivenPipeline::UPDATE_TIME_STEPS()


I suspect that UPDATE_TIME_STEPS could be combined with
PREVIOUS_UPDATE_TIME_STEPS to a time change, but at each evaluation of
RequestData(), the output DATA_OBJECT is always reset to having zero
blocks anyhow. Since I haven't fiddled with the ReleaseData settings,
(ie., the output block has "Global Release Data: Off" and "Release Data:
Off") I assume this is a feature.

Are there other Request...() methods that I should be using here?

Is there an example somewhere in the VTK source that approaches what I
am attempting or a pseudo-code snippet somewhere?
What is the canonical method for tackling this problem?
I could save my own private vtkMultiBlockDataSet within the class and
then copy it to the output as required, but I somehow suspect that that
isn't quite how it supposed to be done. It also feels funny (and slow)
updating geometry that hasn't changed at all.

I would be very appreciative of any tips or hints for solving this
problem.

/mark
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