Value probe returns unexpected results

[kahrpatrick]

Setting: Two groups with one or multiple nodes of type DiscreteScalarImage3D
Observation: Value probe (CTRL + mouse pointer) does not return the values of the currently visible image but of the one that was first 'made visible' in the scene, even if hidden by another image (from the same or a different group node).
Expected behaviour: Always return results for the currently visible image.
Problems: How to deal with overlay of images with opacity other than 0 or 100% ? Should the probe be deactivated in that case?

[clangguth]

Correct me if I'm wrong, but I'm afraid that this is a fundamental issue which stems from VTK itself, so it will be very difficult to work around.

The only code which determines the object to inspect (and thus can trigger this behavior) is here:

scalismo-ui/src/main/scala/scalismo/ui/rendering/internal/RendererStateImplementation.scala

Line 95 in bec9586

val prop = cellPicker.GetProp3D()

... and there, we rely on the VTK cell picker to return the "correct" object.

[kahrpatrick]

Thanks for pointing to the relevant code. I have looked a bit more into it. The only solution I see so far would be to make use of the vtkPickingManager (https://blog.kitware.com/vtk-6-new-feature-picking-manager/) to pick the object that is closest to the camera. When making objects 'invisible' in the UI, the corresponding picker could be removed from the PickingManager such that it is not considered.