[vtk-developers] Usage of filters inside filters

David E DeMarle dave.demarle at kitware.com
Tue Feb 28 09:49:31 EST 2012

Internal variable (aka member). There is probably some technical
distinction I've forgotten and may be getting wrong.

In any case, in pseudocode:
class myivarstype;
class vtksomething : public vtksomethingsparent
vtkSet/Get/ObjectMacro(myivarsname, myivarstype;
myivarstype *myivarsname;

And you can use vtk's smart pointers for ivars.

David E DeMarle
Kitware, Inc.
R&D Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4909

On Tue, Feb 28, 2012 at 9:33 AM, Francisco Caraballo
<francisco.caraballo at gmail.com> wrote:
> Thanks a lot for your answer David.
> I have one doubt about it though, what are ivars?
> Generally when I instantiate filters I assign them to vtkSmartPointers.
> Are ivars something different?
> Greetings.
> Francisco Caraballo
> On Tue, Feb 28, 2012 at 2:31 PM, David E DeMarle
> <dave.demarle at kitware.com> wrote:
>> It is fine to do so.
>> In the outer filter, create the internal filters as ivars. You can
>> New() into those pointers in your constructor and Delete() them in
>> your destructor to keep it simple.
>> In your RequestData method, set up the internal connections of the
>> internal pipeline with SetInputConnection(GetOutputPort) like you
>> would anywhere else. The only real trick is that you have have to
>> ShallowCopy the outer filter's input into the first filter in the
>> internal pipeline and ShallowCopy the last filter's output into the
>> outer filter's output. Otherwise the Executives get confused about
>> what is connected to what and how to schedule updates.
>> If the internal filters are visible and controlled outside of the
>> outer filter, you probably want to override the outer filter's
>> ModififiedTime to take into account the MTimes of the internal ones
>> too.
>> David E DeMarle
>> Kitware, Inc.
>> R&D Engineer
>> 21 Corporate Drive
>> Clifton Park, NY 12065-8662
>> Phone: 518-881-4909
>> On Tue, Feb 28, 2012 at 8:10 AM, Francisco Caraballo
>> <francisco.caraballo at gmail.com> wrote:
>>> Hello everyone.
>>> I'm developing a filter for image segmentation and i'm rather new to
>>> the VTK workflow and would like to ask you guys for some help.
>>> It would help me a lot if I could call several other filters from
>>> within my own filter (i.e Image Mathematics, Gaussian, Gradient). I
>>> have searched in the mailing list archives and found some old messages
>>> where some people was against doing it and other people was for it.
>>> What is the current position of the community on this subject,
>>> considering I'm using VTK 5.8? Is it an accepted practice? If
>>> positive, could you give me some advice as to how to do it? I'm
>>> particularly confused about the pipeline calls and how to go around
>>> calling the filters outside of the "main" pipeline.
>>> Thanks a lot in advance.
>>> Francisco Caraballo
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