[vtk-developers] Filters and active attributes

[Utkarsh Ayachit]

Patrick,

Consider this, even now, if you have a long chain of filters and the
first source added M arrays, all M, except may be an active attribute
or two, will get propagated through to the output.
On Sun, Jul 15, 2018 at 2:56 PM Patrick Bergeron <pbergeron at spiria.com> wrote:
>
> Please forgive my newbiness, but what happens when you have a long chain of filters?
>
> Will the output have 25 Unused arrays?
>
> Sent from my iPhone
>
> > On Jul 15, 2018, at 09:57, Utkarsh Ayachit <utkarsh.ayachit at kitware.com> wrote:
> >
> > Thanks folks! Since there seem to be no objections to the proposal
> > (b), I'll create an MR in the near future and see if that exposes any
> > legitimate reasons for the original implementation (a).
> >
> > Utkarsh
> >
> >> On Wed, Jul 11, 2018 at 3:16 PM Cory Quammen <cory.quammen at kitware.com> wrote:
> >>
> >> +1 for (b) as well. There is no reason an array should disappear simply because it was marked as active in the input. I remember being stunned when first encountering this behavior and have had to work around it. I don't foresee any backwards compatibility issues with changing the behavior since arrays will be added to the output and will likely be ignored.
> >>
> >> Cory
> >>
> >>> On Tue, Jul 10, 2018 at 9:58 PM Mathieu Westphal <mathieu.westphal at kitware.com> wrote:
> >>>
> >>> My vote is definitelly (b), but I may be influenced by the fact I'm working on VTK mostly trough ParaView where this kind of behavior is most of the time not expected.
> >>>
> >>> Mathieu Westphal
> >>>
> >>>> On Tue, Jul 10, 2018 at 4:08 PM, Utkarsh Ayachit <utkarsh.ayachit at kitware.com> wrote:
> >>>>
> >>>> Folks,
> >>>>
> >>>> I have a philosophical question. Suppose I am writing a filter that
> >>>> takes in an input dataset and generates a new vector field for the
> >>>> input. Such a filter will do something like the following in its
> >>>> RequestData:
> >>>>
> >>>> output->ShallowCopy(input);
> >>>> output->GetPointData()->SetVectors(newVectors);
> >>>>
> >>>> Now the question is this: if the input had an active vectors array
> >>>> set, what should the output look like? Should it (a) drop the input
> >>>> vectors array entirely or should it (b) pass the input vectors array,
> >>>> just not flag it as active vectors and instead mark my "newVectors" as
> >>>> the active vectors.
> >>>>
> >>>> My vote is (b), currently most filters do (a). The curious side effect
> >>>> of A is that if I apply a filter like vtkGlyph3D to a dataset, the
> >>>> output will have arrays passed on from the input based on whether or
> >>>> not they were marked as active attributes on the input!
> >>>>
> >>>> The change to fix this is quite non-intrusive. We simply change the
> >>>> behavior of SetAttribute/SetVector etc. in vtkDataSetAttributes.
> >>>>
> >>>> Thanks in advance
> >>>>
> >>>> Utkarsh
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> >>
> >>
> >> --
> >> Cory Quammen
> >> Staff R&D Engineer
> >> Kitware, Inc.
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