[vtkusers] Please help me use vtkLinearExtrusionFilter
cmbruns at stanford.edu
Thu Jun 29 15:54:10 EDT 2006
Thank you so much Obada, for your thorough and diligent discovery of the
underlying cause of the crashes that I experienced.
I applied your patch, and now it works beautifully.
Rebuilding my vtk libraries including your change to vtkRibbonFilter.cxx
is probably the approach that I will take. I tried inserting a
vtkCleanPolyData filter to correct the data corruption, but that filter
crashed as well. I wish I could discover a way to work around the
problem for existing vtk builds, without writing/reading to/from the
My own feeble attempts to diagnose the problem included using
vtkPolyDataWriter to view the object contents. It's ironic that your
suggested workaround involved using vtkPolyDataWriter as a filter to
clean up the data.
May I ask what was your technique for tracking down this problem?
Thanks again for your kind and generous solution.
Obada Mahdi wrote:
> Hi Christopher,
> I have made an attempt to track down the problem and might have found at
> least the reason.
> Christopher Bruns wrote:
>> I get a "Access violation reading location 0x00000000" when
>> attempting to use vtkLinearExtrusionFilter with certain input
>> pipelines, while I can get it to work with others.
>> Presumably I am neglecting to populate part of the input data
>> pipeline correctly. Can someone please suggest how I might fix my
>> error here? Is there some other filter I need to add?
>> In my debugger the crash appears to occur at line 214 of
>> vtklinearextrusionfilter.cxx in the method RequestData, which contains
>> the statement "outputPD->CopyData(pd,ptId,ptId);" The variable pd
>> contains input vtkPointData. Deeper in the stack,
>> pd->Data->GetVoidPointer(0) returns 0x0000000 instead of returning
>> a valid pointer, because pd->Data->Array is zero as well.
> The problem seems to be caused by a small typo in vtkRibbonFilter.cxx
> that leads to some bogus data array entries in the PointData struct,
> messing up the extrusion filter later: There is a line
> | outPD->CopyAllocate(pd,numNewCells);
> which should read
> | outCD->CopyAllocate(cd,numNewCells);
> (see attached diff).
> I was able to perfectly reproduce all the results (and crashes) you
> mentioned with a recent CVS version of VTK, and your test program
> appears to work fine with the above line corrected.
> If rebuilding VTK is not an option for you, and you do not need CellData
> to be filtered through, there might be other ways to work around that
> problem and get colored thick ribbons :-) After all, no point data
> information is destroyed, and you only need to get rid of any bogus
> (empty) data field introduced by vtkRibbonFilter. For example, writing
> the the output of vtkRibbonFilter to a file (using vtkPolyDataWriter)
> and feeding that same file to vtkExtrusionFilter using a
> vtkPolyDataReader did also work for me.
> Good luck :-)
> diff -u -r1.80 vtkRibbonFilter.cxx
> --- Graphics/vtkRibbonFilter.cxx 21 Apr 2005 13:42:16 -0000 1.80
> +++ Graphics/vtkRibbonFilter.cxx 24 Jun 2006 04:21:38 -0000
> @@ -176,7 +176,7 @@
> numNewCells = inLines->GetNumberOfCells();
> - outPD->CopyAllocate(pd,numNewCells);
> + outCD->CopyAllocate(cd,numNewCells);
> // Create points along each polyline that are connected into NumberOfSides
> // triangle strips. Texture coordinates are optionally generated.
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