[vtk-developers] Filters and active attributes

[Cory Quammen]

+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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