[vtkusers] how to handle an empty pipeline?

Wed Oct 18 11:58:00 EDT 2017

When the input is modified I call Update() on the filter and check the output to see if the result is empty.

Andras

-----Original Message-----
From: Langer, Stephen A. (Fed) [mailto:stephen.langer at nist.gov] 
Sent: Wednesday, October 18, 2017 11:47 AM
To: Andras Lasso <lasso at queensu.ca>; Bill Lorensen <bill.lorensen at gmail.com>
Cc: vtkusers at vtk.org
Subject: Re: [vtkusers] how to handle an empty pipeline?

What do you do if you don't know that the pipeline will be empty?  There might be a filter that doesn't pass any of the data, but the data source and the controlling code can't know that until the pipeline executes.

 -- Steve

On 10/18/17, 11:26 AM, "Andras Lasso" <lasso at queensu.ca> wrote:

    I don't know if it's good practice, but when there is no input data I usually do either of the followings:
    - hide the actor so that no pipeline updates are requested by the renderer
    - detach the data processing pipeline from the visualization pipeline (SetInputData(NULL))
    - add a dummy data set (such as polydata with a single point) as input

    I would be interested if there is a particular method recommended by VTK core developers.

    Andras

    -----Original Message-----
    From: vtkusers [mailto:vtkusers-bounces at vtk.org] On Behalf Of Langer, Stephen A. (Fed)
    Sent: Wednesday, October 18, 2017 11:04 AM
    To: Bill Lorensen <bill.lorensen at gmail.com>
    Cc: vtkusers at vtk.org
    Subject: Re: [vtkusers] how to handle an empty pipeline?

    Thanks for the suggestion, but it won't work in this case.  The warning messages come from a vtkDataSetSurfaceFilter that's created as a protected member of the vtkDataSetMapper class, so I can't call vtkDataSetSurfaceFilter::AddObserver.   Subclassing vtkDatatSetMapper and overriding Render to get access to the filter would work, but feels wrong…

    Is this a bug?  A warning is raised when the input to the vtkDataSetMapper is empty, except when the input type is VTK_POLY_DATA.

     -- Steve

    On 10/17/17, 6:36 PM, "Bill Lorensen" <bill.lorensen at gmail.com> wrote:

        You can catch the warnings/errors like this:
        https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Florensen.github.io%2FVTKExamples%2Fsite%2FCxx%2FUtilities%2FObserveError%2F&data=02%7C01%7Cstephen.langer%40nist.gov%7C42ff580323ed40df553608d515af87f8%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C636438765996499743&sdata=Jse9qOUuZCUa9o7yU3%2FLH2HH5I0%2FlkyeL2DtyHoPjCU%3D&reserved=0

        On Tue, Oct 17, 2017 at 2:34 PM, Langer, Stephen A. (Fed)
        <stephen.langer at nist.gov> wrote:
        > Hi --
        >
        > What's the right way to handle a pipeline that might at times have no data in it?   I'm connecting to a vtkDataSetMapper,  and if the input stream is empty vtk prints a warning "vtkDataSetSurfaceFilter: Number of cells is zero, no data to process".    I don't create the vtkDataSetSurfaceFilter myself -- it's been inserted into the pipeline by the mapper.  It doesn't do that if the input data is poly data, and if I change the input to poly data, the mapper seems quite happy with the empty pipeline, so it's odd that it complains in one case but not the other.
        >
        > Is there something that I should do at the pipeline source to tell the pipeline not to run?  Is there a way to suppress just this one warning message?
        >
        > I'm using vtk 7.1.1 in C++.
        >
        > Thanks.
        >  -- Steve
        >
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