[vtkusers] segfault on cell picking, and solution

[Robert Dean]

Hello,

I was building the polydata from scratch, so no filters were involved.
 Main reason for posting this was that I could not find a solution online,
and thought it might be useful. Does the documentation about how to build
filters include directions on how to use DeleteCells/BuildCells?

-Bob


On Fri, Mar 1, 2013 at 2:12 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi Robert,
>
> I'd like to get a feel for whether or not this might be is a bug.
>
> Were you building the polydata yourself (i.e. from scratch)
> or was it produced by a filter?  And if the latter, what filter
> was producing it?
>
> Going a bit further, was the polydata that you were picking
> also being used as an input to a filter, i.e. were you picking
> a polydata that was somewhere in the middle of a pipeline?
> And if so, what filter?
>
> It seems to me that your application shouldn't have to call
> DeleteCells() unless your application is also building the
> polydata from scratch.  If your application is using VTK
> sources, readers, or filters to produce the polydata then
> really VTK should be calling DeleteCells()/BuildCells()
> automatically, and if VTK isn't doing this, then there must
> be a bug somewhere e.g. in one of the filters you are using.
>
>  - David
>
>
> On Fri, Mar 1, 2013 at 10:35 AM, Robert Dean <bob.dean at gmail.com> wrote:
> > Hello,
> >
> > For a long time I had an issue where my application would randomly crash
> > while picking cells. Each time the stack dump was in the depths of  the
> vtk
> > code.  What I tracked it down to was that when an actor is first clicked,
> > vtk allocates an internal cell array to assist in mapping the click to
> cell
> > index.  This array is not automatically resized on future clicks.
> >
> > Therefore when the actor is first clicked an array of N is allocated. If
> the
> > array is then updated to contain N*2 cells, clicking cells N through 2N-1
> > will access outside the cell index array, resulting in the segfault.
> >
> > As cell picking is a rare event in the application timing, the solution
> was
> > to call polydata->DeleteCells() method on each update.
> >
> > Posting in case someone else runs into the same problem.   I am currently
> > using vtk 5.10, so I do not know if a newer version addresses this issue.
> >
> > -Bob
>
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