[vtk-developers] Filters and active attributes

Patrick Bergeron pbergeron at spiria.com
Sun Jul 15 14:56:34 EDT 2018


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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>>> 
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>> 
>> 
>> --
>> Cory Quammen
>> Staff R&D Engineer
>> Kitware, Inc.
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