Is it possible to pick transparent actors?
For vtkPicker it is documented that it only works on nontransparent objects.
vtkPropPicker used vtkWorldPointPicker which uses renderer.GetZ. This returns 1.0 (on my machine) for actors with opacity < 1.0.
I understand that picking using a Z-buffer based method in combination with transparency is asking for trouble. But maybe there is a way around it? (disable transparency, render, pick, enable transparency,…?)