Bug on transparency between actor and widgetin VTK9?

Development
10

Took the exact code, but replaced the widget with my own widget (made using the old design, no representation). Here things look correct. I can reproduce the above behavior for the code Laure provided.

#include <vtkActor.h>
#include <vtkImplicitRectangleWidget.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSmartPointer.h>
#include <vtkSphereRepresentation.h>
#include <vtkSphereSource.h>
#include <vtkSphereWidget2.h>

int main(int, char*[])
{
  // Create a sphere/mapper/actor
  auto sphereSource = vtkSmartPointer<vtkSphereSource>::New();
  sphereSource->SetRadius(2.0);
  auto mapper = vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputConnection(sphereSource->GetOutputPort());
  auto actor = vtkSmartPointer<vtkActor>::New();
  actor->SetMapper(mapper);
  actor->GetProperty()->SetColor(1.0, 0.0, 0.0);
  actor->GetProperty()->SetOpacity(0.5);

  // Create a renderer/render window/interactor
  auto renderer = vtkSmartPointer<vtkRenderer>::New();
  renderer->AddActor(actor);
  renderer->SetBackground(0, 0, 0);

  auto renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);
  auto renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);

  vtkNew<vtkImplicitRectangleWidget> widget;
  widget->SetInteractor(renderWindow->GetInteractor());
  widget->GetHandleProperty()->SetOpacity(0.99);

  renderWindow->SetMultiSamples(0);   // Disable multi-sampling (for clarity)
  renderWindow->SetAlphaBitPlanes(1); // Ensure alpha channel if blending is used

  // Start the rendering loop
  renderWindow->Render();
  renderer->ResetCamera();
  renderWindowInteractor->Initialize();
  widget->On();
  renderWindowInteractor->Start();

  return 0;
}

The widget I used can be found here, gist:c949a1841bb003a9368170b05f34e869 ยท GitHub

The shape I use with transparency is a cone. Perhaps, something is implemented wrongly for the translucent pass in the vtkSphereWidget2