[vtkusers] Understanding vtkSmartPointers

[Mathieu Westphal]

Dear Francois,

The simplest way to go here would be to use only vtkNew and to not use
applyFilters but put the applyFilters code in your main.

Best regards,

Mathieu Westphal

On Mon, May 28, 2018 at 1:43 PM, Fcs <ftpronk at engits.com> wrote:

> Using VTK for one of our projects, we are encountering some memory leaks
> which, in time, cripple our system.  So I'm trying to have a better
> understanding of the  VTK pointers
> <https://blog.kitware.com/a-tour-of-vtk-pointer-classes/>  .
>
> It was my (erroneous..?) belief that the *vtkSmartPointer*s would destroy
> the object they were holding when getting out of scope.  Carefully reading
> the kitware blog post linked hereinabove, and playing around with a test
> code (code sample below), I now understand that it is objects held by
> *vtkNew* that will be destroyed when out-of-scope, and that
> *vtkSmartPointer*s, on the contrary, will keep them alive as long as the
> reference count is non-zero.  Is this correct?
>
> Now, from a practical point of view:  does this mean that I can, in a
> class,
> create an entire VTK pipeline with *vtkSmartPointer*s, and only store the
> latest object in a member variable to keep every object alive (So, in my
> code below, only bookkeep the object returned by applyFilters())?  And that
> when I'm finished, I can call ->Delete() on that object to clean-up the
> entire pipeline?  Is this a good practice?  Until now, I was painstakingly
> storing every object created for the lifetime of a pipeline, and I would
> like to know if I can simplify my code..
>
> Thank you!
>
> Francois.
>
>
>
> Toy code:
> (returns vtkDebugLeaks has found no leaks)
>
>
> #include <vtkPolyData.h>
> #include <vtkSmartPointer.h>
> #include <vtkPolyDataMapper.h>
> #include <vtkActor.h>
> #include <vtkRenderWindow.h>
> #include <vtkRenderer.h>
> #include <vtkRenderWindowInteractor.h>
> #include <vtkStructuredGrid.h>
> #include <vtkPoints.h>
> #include <vtkCellCenters.h>
> #include <vtkDoubleArray.h>
> #include <vtkCellDataToPointData.h>
> #include <vtkCellData.h>
> #include <vtkClipDataSet.h>
> #include <vtkPlane.h>
> #include <vtkCutter.h>
> #include <vtkPolyDataAlgorithm.h>
>
>
> vtkSmartPointer<vtkPolyDataAlgorithm>
> applyFilters(vtkSmartPointer<vtkStructuredGrid> grid)
> {
>   // Convert cell data to point data
>   vtkSmartPointer<vtkCellDataToPointData> c2p =
>       vtkSmartPointer<vtkCellDataToPointData>::New();
>   c2p->PassCellDataOn();
>   c2p->SetInputData(grid);
>
>   // Clip at value r = 4.5
>   vtkSmartPointer<vtkClipDataSet> clip =
>       vtkSmartPointer<vtkClipDataSet>::New();
>   clip->SetInputConnection(c2p->GetOutputPort());
>   clip->SetInputArrayToProcess(0, 0, 0, 0, "R");
>   clip->SetValue(4.5);
>   clip->InsideOutOn();
>
>   // Make plane
>   vtkSmartPointer<vtkPlane> plane =
>       vtkSmartPointer<vtkPlane>::New();
>   plane->SetOrigin(0.,0.,0.);
>   plane->SetNormal(0, 0, 1);
>
>   // Cut
>   vtkSmartPointer<vtkCutter> cutter =
>       vtkSmartPointer<vtkCutter>::New();
>   cutter->SetCutFunction(plane);
>   cutter->SetInputConnection(clip->GetOutputPort());
>
>   return cutter;
> }
>
>
> int main()
> {
>   // Create structured grid
>   int nx = 101, ny = 101, nz = 101;
>   double dx, dy, dz;
>   dx = dy = dz = 10./(nx-1);
>   vtkSmartPointer<vtkStructuredGrid> grid =
>       vtkSmartPointer<vtkStructuredGrid>::New();
>   grid->SetDimensions(nx, ny, nz);
>   vtkSmartPointer<vtkPoints> pts = vtkSmartPointer<vtkPoints>::New();
>   for (int i = 0; i < nx; ++i) {
>     for (int j = 0; j < ny; ++j) {
>       for (int k = 0; k < nz; ++k) {
>         pts->InsertNextPoint(-5+dx*i, -5+dy*j, -5+dz*k);
>       }
>     }
>   }
>   grid->SetPoints(pts);
>
>   // Create cell scalar field
>   vtkSmartPointer<vtkDoubleArray> arr =
>       vtkSmartPointer<vtkDoubleArray>::New();
>   arr->SetNumberOfComponents(1);
>   arr->SetName("R");
>   vtkSmartPointer<vtkCellCenters> cell_centres =
>       vtkSmartPointer<vtkCellCenters>::New();
>   cell_centres->SetInputData(grid);
>   cell_centres->Update();
>   for (int i = 0; i < grid->GetNumberOfCells(); ++i) {
>     double pt[3];
>     cell_centres->GetOutput()->GetPoint(i, pt);
>     double r = pt[0]*pt[0] + pt[1]*pt[1] + pt[2]*pt[2];
>     arr->InsertNextValue(r);
>   }
>   grid->GetCellData()->AddArray(arr);
>
>   // Call clipping functions
>   vtkSmartPointer<vtkPolyDataAlgorithm> poly_algo = applyFilters(grid);
>
>   // Create a mapper and actor
>   vtkSmartPointer<vtkPolyDataMapper> mapper =
>       vtkSmartPointer<vtkPolyDataMapper>::New();
>   mapper->SetInputConnection(poly_algo->GetOutputPort());
>   vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
>   actor->SetMapper(mapper);
>
>   // Create a renderer, render window and interactor
>   vtkSmartPointer<vtkRenderer> renderer =
>       vtkSmartPointer<vtkRenderer>::New();
>   vtkSmartPointer<vtkRenderWindow> render_window =
>       vtkSmartPointer<vtkRenderWindow>::New();
>   render_window->SetWindowName("Plane");
>   render_window->AddRenderer(renderer);
>   vtkSmartPointer<vtkRenderWindowInteractor> window_interactor =
>       vtkSmartPointer<vtkRenderWindowInteractor>::New();
>   window_interactor->SetRenderWindow(render_window);
>
>   // Add the actors to the scene
>   renderer->AddActor(actor);
>
>   // Render and interact
>   render_window->Render();
>   window_interactor->Start();
>
>   return EXIT_SUCCESS;
> }
>
>
>
>
> --
> Sent from: http://vtk.1045678.n5.nabble.com/VTK-Users-f1224199.html
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at http://www.kitware.com/
> opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at:
> http://www.vtk.org/Wiki/VTK_FAQ
>
> Search the list archives at: http://markmail.org/search/?q=vtkusers
>
> Follow this link to subscribe/unsubscribe:
> https://vtk.org/mailman/listinfo/vtkusers
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://vtk.org/pipermail/vtkusers/attachments/20180528/94f47bd8/attachment.html>