[Paraview] Caching within a class, avoiding vtkGeometryFilter

[Olesen, Mark]

I've now had a bit of time to picking up on my old problem:
[http://www.paraview.org/pipermail/paraview/2008-May/007917.html]

Even after I have some caching within the reader (thus sparing most
I/O), I see that a large amount of time is actually being spent in
vtkGeometryFilter.

If we assume, for simplicity, that the geometry represented by the
reader is invariant over time but the field values can change, how can
this be coded to have the pipeline not update the geometry, but just
update the field values?  Since the geometry doesn't change, the speed
of examining such transient data should only be marginally slower than
changing between various fields at a single time step.

To make it a bit easier, I'm ignoring the field values and within the
RequestData() method I have something like this:


vtkMultiBlockDataSet* output = vtkMultiBlockDataSet::SafeDownCast
(
    outputVector
        ->GetInformationObject(0)
        ->Get(vtkMultiBlockDataSet::DATA_OBJECT())
);

... do something with UPDATE_TIME_STEPS() and set 
    bool needsUpdate = true/false;


// first time
if (!output0_)
{
    output0_ = vtkMultiBlockDataSet::New();
    needsUpdate = true;
}

if (needsUpdate)
{
    UpdateReaderGeometry(output);
    output0_->ShallowCopy(output);
    cout<< "full UPDATE ---------\n";
}
else
{
    output->ShallowCopy(output0_);
    cout<< "cached UPDATE ---------\n";
}

I actually don't know if this is a reasonable approach, but it doesn't
segfault and paraview still displays the geometry at each time step.
Nonetheless, the modification time of 'output' still causes the
GeometryFilter to execute and the field values are not yet copied.

Rebuilding the field values from scratch is fast enough that I may not
need to cache them, but how can I get the output not to re-trigger the
GeometryFilter?

Thanks,

/mark
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