SelectVisiblePoints misbehaving after UserMatrix set

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1

Hi,
I’m trying to use vtkSelectVisiblePoints on a vtkActor that has been moved through setUserMatrix, but I cannot manage to make it work as intended.
With the code below, I press the “space” key to obtain the number of visible points in the render.
When I move the camera with the mouse to make the actor partially or completely out of the field of view, the number of visible points is correct.
When I use the Left/Right keys to move the actor by changing its UserMatrix, the number of visible points do not change.
I feel like this is related to the zbuffer not being updated, despite the Render() call after changing the UserMatrix.
Thank you for your help,
S.

#include <vtkPolyData.h>
#include <vtkPointSource.h>
#include <vtkSphereSource.h>
#include <vtkSmartPointer.h>
#include <vtkSelectVisiblePoints.h>
#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkCamera.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkObjectFactory.h>
#include <vtkMatrix4x4.h>

class MyInteractorStyle : public vtkInteractorStyleTrackballCamera
{
public:
  static MyInteractorStyle* New();
  vtkTypeMacro(MyInteractorStyle, vtkInteractorStyleTrackballCamera);

  virtual void OnKeyPress() override
  {
    std::string key = this->Interactor->GetKeySym();
    if (key == "space")
    {
      this->filter->Update();
      std::cout << this->filter->GetOutput()->GetNumberOfPoints() << " visible points." << std::endl;
    }
    if (key == "Left")
    {
      vtkMatrix4x4*  mat = this->actor->GetUserMatrix();
      mat->SetElement(0, 3, mat->GetElement(0, 3) - 0.1);
      this->Interactor->GetRenderWindow()->Render();
    }
    if (key == "Right")
    {
      vtkMatrix4x4* mat = this->actor->GetUserMatrix();
      mat->SetElement(0, 3, mat->GetElement(0, 3) + 0.1);
      this->Interactor->GetRenderWindow()->Render();
    }
    vtkInteractorStyleTrackballCamera::OnKeyPress();
  }

  void SetFilter(vtkSmartPointer<vtkSelectVisiblePoints> vis) { this->filter = vis; }
  void SetActor(vtkSmartPointer<vtkActor> act) { this->actor = act; }
private:
  vtkSmartPointer<vtkSelectVisiblePoints> filter;
  vtkSmartPointer<vtkActor> actor;
};

vtkStandardNewMacro(MyInteractorStyle);

int main(int, char* [])
{
  vtkNew<vtkSphereSource> sphereSource;
  sphereSource->SetCenter(0, 0, 0);
  vtkNew<vtkPolyDataMapper> mapper;
  mapper->SetInputConnection(sphereSource->GetOutputPort());
  vtkNew<vtkActor> actor;
  actor->SetMapper(mapper);
  vtkNew<vtkMatrix4x4> mat;
  actor->SetUserMatrix(mat);

  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->SetSize(800, 800);

  vtkNew<vtkRenderer> renderer;
  renderWindow->AddRenderer(renderer);
  renderer->AddActor(actor);

  vtkNew<vtkSelectVisiblePoints> selectVisiblePoints;
  selectVisiblePoints->SetInputConnection(sphereSource->GetOutputPort());
  selectVisiblePoints->SetRenderer(renderer);

  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  renderWindowInteractor->SetRenderWindow(renderWindow);
  vtkNew<MyInteractorStyle> style;
  style->SetFilter(selectVisiblePoints);
  style->SetActor(actor);
  renderWindowInteractor->SetInteractorStyle(style);

  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}