[vtkusers] remove vtkImageBlend item

[David Gobbi]

Hi Mauro,

I don't think that converting the image to a vtkImageStencilData is the
correct approach.

When you call blend->AddInputConnection(0, color->GetOutputPort())
the first argument should always be 0.  All of the image inputs for
vtkImageBlend go into port zero.  It is what VTK calls a "multiple
input port," meaning that it is a port that can take multiple input
connections.

If you call blend->AddInputConnection(1, ...) then you are adding
a connection to the second port, which is not an image port (as
you have seen, it is a vtkImageStencilData port).  This is not what
you want to do.

Take a look at the documentation for vtkAlgorithm for more info on
how ports/connections work.  The main idea is that VTK inputs are
identified by two numbers: (port number, connection number), i.e.
there is really a 2D array of inputs.

 - David


On Thu, Feb 3, 2011 at 6:46 AM, Mauro Maiorca <mauromaiorca at gmail.com>wrote:

> Hi David,
>
> thank you very much for your quick reply.
> The function RemoveInputConnection was what I was actually looking
> for, and works fine with the canvas objects.
> I'll also take into account your clever suggestion to don't mess up
> with the indexes!!
> The "only" problem left is with AddInputConnection and the grayscale
> 2D image (to which I have to attach/detach the canvas objects).
> Before your input, I was using "blend->SetInput(color->GetOutput());"
> where color is an instance of vtkImageMapToColors, that gets as input
> a casted image (vtkImageCast) and a lookup table (vtkLookupTable).
> Unfortunately, AddInputConnection wants vtkImageStencilData (while
> SetInput is happy with vtkImageData), so I had to convert vtkImageData
> into vtkImageStencilData. You actually helped a lot on that (you
> replied few years ago to a similar help request), recommending the
> good old Rube Goldberg machine and few handy tricks! However I'm still
> far from the solution, what I've got till now (and still not quite
> there) is:
>
> //convert poly to image data
> vtkSmartPointer<vtkPolyDataToImageStencil> dataToStencil =
> vtkSmartPointer<vtkPolyDataToImageStencil>::New();
> dataToStencil->SetInputConnection (color->GetOutputPort());
> dataToStencil -> Update();
>
> // Create an empty image
> vtkSmartPointer<vtkImageGridSource> source =
> vtkSmartPointer<vtkImageGridSource>::New();
> source->SetFillValue(0);
> source->SetLineValue (0);
> source -> SetDataExtent ((imageCast->GetOutput())->GetExtent());
> source->Update();
>
> //apply the stencil to the image
> vtkSmartPointer<vtkImageStencil> stencil =
> vtkSmartPointer<vtkImageStencil>::New();
> stencil->SetInputConnection (source->GetOutputPort());
> stencil -> SetStencil (dataToStencil->GetOutput() );
> stencil -> ReverseStencilOn();
> stencil -> Update();
>
> //blend
> blend->AddInputConnection(0, stencil->GetOutputPort());
>
>
> but nothing, it compiles but I get segmentation fault in runtime. The
> segmentation fault goes away if I comment out the line:
> blend->AddInputConnection(0, stencil->GetOutputPort());
> I'm definitely forgetting something, but not sure what exactly! Any
> suggestion would be appreciated!!!
>
> thanks a lot for your help!
>
> cheers,
> Mauro
>
>
>
> On Mon, Jan 31, 2011 at 4:12 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
> > Hi Mauro,
> >
> > The inputs can be added/removed with these vtkAlgorithm methods:
> >   blend->AddInputConnection(0, canvas->GetOutputPort());
> >   blend->RemoveInputConnection(0, canvas->GetOutputPort());
> >
> > In all honesty, though, I find it easiest to call this:
> >   blend->RemoveAllInputs();
> > Then I can start over again by adding all the inputs. Otherwise,
> > it can be difficult to keep the inputs in the correct order.
> >
> >  - David
> >
> > On Sun, Jan 30, 2011 at 9:11 PM, Mauro Maiorca <mauromaiorca at gmail.com>
> wrote:
> >>
> >> Hello vtk users,
> >>
> >> I'm struggling to understand how to remove an item from a vtkImageBlend
> object.
> >>
> >> To be more specific, I have a (grayscale) 2D image and few
> >> vtkImageCanvasSource2D objects to interactively attach/detach to the
> >> greyscale image.
> >> In order to attach the objects to the grayscale image I'm using
> >> vtkImageBlend, and it's working fine.
> >> The problem is to detach the vtkImageCanvasSource2D objects from
> >> vtkImageBlend: I don't see any "remove" function in vtkImageBlend.
> >> Do you know whether it is possible? If vtkImageBlend is not the best
> >> approach to solve my problem, do you know a better (VTK) approach to
> >> it?
> >> As a quick and dirty solution, I create a new vtkImageBlend and I
> >> attach to it the grayscale image plus all the
> >> vtkImageCanvasSource2Dobjects except the one I want to "remove", it's
> >> working but it's (obviously) slow with a big image and a big number of
> >> objects.
> >>
> >> cheers,
> >> Mauro
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