[vtkusers] pipeline update

[David E DeMarle]

The request will propagate up the pipeline but the first filter will
not re-execute. When the request gets to that filter it sees that the
filter has produced an output more recently than any of its settings
(or settings on the upstream filters) have changed, and then passes
the old output down to the downstream filter instead of re-executing.

cheers,
Dave DeMarle


On Tue, Apr 22, 2008 at 1:32 PM, Adrian Albert
<a.albert at jacobs-university.de> wrote:
>
> Dear All,
>
>
> I have a question about the pipeline update mechanism in VTK: If I call
> Update () on an algorithm that has as input the output of another algorithm,
> does the Update command propagate down the pipeline and causes a
> recomputation for all algorithms involved?
>  For example, this code should calculate the gradient of the gradient
> magnitude (a measure of a second order derivative):
>
>   // Gradient magnitude
>   vtkImageGradientMagnitude* grad = vtkImageGradientMagnitude::New();
>    grad->SetDimensionality( 3 );
>   grad->SetInput (this->GetMultivariateField (whichField));
>   grad->Update ();
>
>   // Gradient of gradient magnitude
>   vtkImageGradient* gradGrad = vtkImageGradient::New();
>    gradGrad->SetDimensionality( 3 );
>   gradGrad->SetInput (grad->GetOutput ());
>   gradGrad->Update ();
>
> Specifically, would I cause two computations of the gradient magnitude
> (first 4 lines of code) by calling Update twice?
>
> Thanks!
> Adrian
>
> --
> ---------------------------------------------------
> Adrian Albert
> School of Engineering and Science
> Jacobs University Bremen
> Germany
> Tel.: 00494212003258
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