[vtk-developers] Marking data modified

[Will Schroeder]

FYI- Just to provide more background context: there are several
triangulation classes like vtkDelaunay2D, vtkQuadricDecimation, and
vtkGreedyTerrainDecimation that routinely swap the diagonal of the
quadrilateral consisting of two adjacent triangles (sharing an edge). The
edge swap is done to improve the triangulation quality. As Dave and Berk
indicated, this is considered an atomic operation performed in tight loops
so it is expected that Modified() is called at the end.

Best,
W

On Mon, Aug 15, 2016 at 12:54 PM, David Cole via vtk-developers <
vtk-developers at vtk.org> wrote:

> I don't specifically know the answer to this one, but in general,
> these sorts of things are on purpose for performance in VTK.
>
> If you want to replace 100 (or even more) cells, you'd want
> ReplaceCell NOT to call Modified, and just do it once at the end of
> your bulk replacement. I'd be surprised if somebody chimed in and
> contradicted this... so I would think just fixing the docs is the
> right way to go here.
>
>
> HTH,
> David C.
>
>
> On Mon, Aug 15, 2016 at 11:59 AM, Shawn Waldon <shawn.waldon at kitware.com>
> wrote:
> > Hi all,
> >
> > I have been tracking down a bug in the vtkBoxRepresentation where the
> > selected face never updated.  The issue was that the widget was calling
> > ReplaceCell on the vtkCellArray for the selected face polydata, but never
> > calling Modified() on the cell array (though it did call Modified() on
> the
> > polydata).  With the new OpenGL backend this matters.  The documentation
> for
> > ReplaceCell doesn't say that you have to do this afterward and the
> writer of
> > vtkBoxRepresentation used that documentation.
> >
> > So my question is this: why doesn't ReplaceCell mark the cell array as
> > modified? Is this a bug or on purpose for performance reasons?  I will
> > update the docs or fix ReplaceCell once I know which is wrong.
> >
> > Thank you,
> > Shawn
> >
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-- 
William J. Schroeder, PhD
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