[vtk-developers] significant slow-down (6x) of vtkPiecewiseFunction::GetValue() with new pipeline

[Charl P. Botha]

Dear developers,

I have attached a very interesting example that illustrates a 6x
slow-down with vtkPiecewiseFunction::GetValue() calls.  I *think* that
in this case it's due to certain overheads associated with the new
pipeline implementation (Update() is called in GetValue(), and this
triggers bunches of other logic).  The comment in the attached example
shows my exact performance figures and the VTK checkouts I tried it
with.

This is a significant problem, as for example the VTK RayCasting code
routinely does 65536 lookups more than once (for the opacity and
colour lookups of shorts).  On my machine, a single set of 65536
lookups now takes 2.4 seconds (instead of 0.4 seconds).

I'll file this in the bug tracker as well, but I thought it was
interesting enough to deserve a mention on this list.

Thanks,
Charl

-- 
charl p. botha http://cpbotha.net/ http://visualisation.tudelft.nl/
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