Unexpected behavior of cv::viz::WCloudCollection::finalize()

[pauljurczak]

I get the same results with opencv 4.5.1-dev on Ubuntu 18.04 built with VTK 6.3 and opencv 4.5.2-dev on Ubuntu 20.04 built with VTK 9.0.1 using gcc-9.3 and gcc-10.1. This code snippet:

  constexpr int n = 2;

  Viz3d window{"Cloud"};
  WCloudCollection cloud;

  for (int i = 0; i < n; i++) {
    Mat_<Vec3f> pc(100, 100);

    randu(pc, Scalar{0, 0, 0}, Scalar{1, 1, 1});
    cloud.addCloud(pc, Color::yellow());
    cloud.finalize(); 
  }

  window.setFullScreen();
  window.setBackgroundColor(Color::gray());
  window.showWidget("cloud", cloud);
  window.spin();

crashes with Segmentation fault when n > 1. It runs fine for any n when cloud.finalize(); is commented out.

I'm guessing that intended use is:

  constexpr int n = 2;

  Viz3d window{"Cloud"};
  WCloudCollection cloud;

  for (int i = 0; i < n; i++) {
    Mat_<Vec3f> pc(100, 100);

    randu(pc, Scalar{0, 0, 0}, Scalar{1, 1, 1});
    cloud.addCloud(pc, Color::yellow());
  }

  cloud.finalize(); 
  window.setFullScreen();
  window.setBackgroundColor(Color::gray());
  window.showWidget("cloud", cloud);
  window.spin();

but this is not described in documentation. Additionally, rendering is quickly getting slow when WCloudCollection grows.

[pauljurczak]

Related note: version built with VTK 9.0.1 produces this deprecation warning:

2021-04-28 14:39:47.361 (   0.115s) [        8201E740]vtkOpenGLPolyDataMapper:270   WARN| vtkOpenGLPolyDataMapper::GetVertexShaderCode was deprecated for VTK 9.0 and will be removed in a future version.  Use vtkOpenGLShaderProperty::GetVertexShaderCode instead.

[LaurentBerger]

@alalek a bug in doc?

There is a sample here