[vtkusers] SetInputData and extents

[David Gobbi]

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/
VTK/Tutorials/New_Pipeline

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>
wrote:

> 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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