Why the model is not displayed in the center of screen? - c++

Question

I want to show a point cloud with VTK. I inherit a class named VTKWidget from QVTKOpenGLNativeWidget, its constructor is that：
VTKWidget::VTKWidget(QVTKOpenGLNativeWidget* parent)
:QVTKOpenGLNativeWidget(parent)
{
QSurfaceFormat::setDefaultFormat(QVTKOpenGLNativeWidget::defaultFormat());
_renderWindow = vtkSmartPointer<vtkGenericOpenGLRenderWindow>::New();
_render = vtkSmartPointer<vtkRenderer>::New();
_actor = vtkSmartPointer<vtkActor>::New();
_points = vtkSmartPointer<vtkPoints>::New();
_mapper = vtkSmartPointer<vtkPolyDataMapper>::New();
_polyData = vtkSmartPointer<vtkPolyData>::New();
_verts = vtkSmartPointer<vtkCellArray>::New();
_polyData->SetPoints(_points);
_polyData->SetVerts(_verts);
_mapper->SetInputData(_polyData);
_actor->SetMapper(_mapper);
_actor->GetProperty()->SetColor(1.0, 0.0, 0.0);
_actor->GetProperty()->SetPointSize(2.0f);
_render->AddActor(_actor);
double color[] = {0.5, 0.5, 0.5};
_render->SetBackground(color);
_renderWindow->AddRenderer(_render);
//setRenderWindow(_renderWindow);
}
Points will be modified in the function updateData, the updateData function is that:
void VTKWidget::updateData(const QVector<QVector<QVector3D>>& data)
{
setRenderWindow(_renderWindow);
_points->Reset();
long long w = data.size();
long long h = data[0].size();
_points->SetNumberOfPoints(w * h);
_polyData->Reset();
_verts->Reset();
for (int i = 0; i < data.size(); ++i)
{
for (int j = 0; j < data[0].size(); ++j)
{
vtkIdType pid;
pid = _points->InsertNextPoint(data[i][j].x(), data[i][j].y(), data[i][j].z());
_verts->InsertNextCell(1, &pid);
}
}
_polyData->Modified();
_mapper->Update();
}
The question is that if the code setRenderWindow (_renderWindow); is in the constructor, the point cloud will not show in the center of this widget, but will be if the code is in the function updateData.

Answer 1

If you want to see the whole point cloud at the end of updateData, you should use _renderer->ResetCamera().
(https://vtk.org/doc/nightly/html/classvtkRenderer.html#ae8055043e676defbbacff6f1ea65ad1e)
The fact that the location of setRenderWindow() impact the rendering is a side effect.