[vtk-developers] Filters and active attributes

[Utkarsh Ayachit]

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.