[vtkusers] SetInputData and extents

David Gobbi david.gobbi at gmail.com
Mon Jan 16 14:04:35 EST 2017

Hi Kit,

The VTK image pipeline updates occur in three passes (RequestInformation(),
RequestUpdateExtent(), RequestData()), which are discussed in the VTK
Users's Guide and also on the following web page: http://www.vtk.org/Wiki/

A filter should never directly set the WHOLE_EXTENT of its input.  It is
only allowed to set the WHOLE_EXTENT of its output.

With respect to the extent, the three passes of the pipeline work like this:

In RequestInformation(), a filter sets the WHOLE_EXTENT of its output.
This is how a filter tells the pipeline "this is how data I can produce".
A filter can be asked to produce less that this (as described in
RequestUpdateExtent, below).  In most cases, what a filter does in
RequestInformation() is check the WHOLE_EXTENT of its input, and then use
that same WHOLE_EXTENT for its output.

In RequestUpdateExtent(), a filter can request that an produce less than
the WHOLE_EXTENT of that input.  It does this by setting the UPDATE_EXTENT
of the input, while tells the pipeline "I need at least this much data from
this input".  Usually, it will set the UPDATE_EXTENT of the input to the
WHOLE_EXTENT of the input.  If a filter also sets EXACT_EXTENT for the
input, that tells the pipeline "I need exactly this much data from this
input".  If you do not set EXACT_EXTENT, then the pipeline will produce at
least as much data as requested by UPDATE_EXTENT, but possibly more.

Finally, in RequestData() a filter should call GetExtent() on each input
data object to see how data is actually there.

 - David

On Mon, Jan 16, 2017 at 10:17 AM, Kit Chambers <kit.chambers.kc at gmail.com>

> Hi All,
> I did some more digging on the and found a solution that works (at least
> so far). My custom VTK filter class (derived from vtkImageAlgorithm)
> contained a method RequestUpdateExtent, which contained the following code:
>   for (int i=0; i<numInputPorts; i++)
>     {
>     int numInputConnections = this->GetNumberOfInputConnections(i);
>     for (int j=0; j<numInputConnections; j++)
>       {
>       vtkInformation* inputInfo = inputVector[i]->GetInformationObject(j);
>       inputInfo->Set(vtkStreamingDemandDrivenPipeline::EXACT_EXTENT(), 1);
>       }
>     }
> I changed:
>         inputInfo->Set(vtkStreamingDemandDrivenPipeline::EXACT_EXTENT(),
> 1);
> to:
>         inputInfo->Set(vtkStreamingDemandDrivenPipeline::WHOLE_EXTENT(),
> WholeExtent,6);
> where the array WholeExtent is the maximum extent computed over all input
> and output ports.
> This seems to work, but I am not sure why. If anyone could point me in the
> direction of some explanation of the purpose behind extents in the VTK
> pipeline and how they are best used I would be very grateful.
> Thanks
> Kit
> > On 4 Jan 2017, at 12:56, Kit Chambers <kit.chambers.kc at googlemail.com>
> wrote:
> >
> > Hi All,
> >
> > I have a custom datatype (myType) derived from vtkImageData and a custom
> filter derived from vtkImageAlgorithm. The filter takes input on two ports
> which are both myType objects with different sizes.
> >
> > So in principle I should be able to set these inputs using either
> SetInputData() or SetInputConnection() right? However, when I run the
> filter  I get errors like:
> >
> > ERROR: In …. /vtk/Common/ExecutionModel/vtkStreamingDemandDrivenPipeline.cxx,
> line 857
> > vtkStreamingDemandDrivenPipeline (0x7fc6fa444a00): The update extent
> specified in the information for output port 0 on algorithm
> vtkTrivialProducer(0x7fc6fa4444a0) is 0 31 0 0 0 0, which is outside the
> whole extent 0 5 0 0 0 0.
> >
> > ERROR: In …. /vtk/src/vtk/Common/ExecutionModel/vtkTrivialProducer.cxx,
> line 264
> > vtkTrivialProducer (0x7fc6fa4444a0): This data object does not contain
> the requested extent.
> >
> > Any suggestions? Is there something I am missing here?
> >
> > Kit
> >
> >
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