Hover Points/Cells Implementation

We are writing a VTK based application and would like to implement a points/cells hover capability that gives information about what is hovered. We tried a few different approaches using both vtkHardwarePicker and vtkCellPicker/vtkPointPicker. For the hardware picker unstructured grids work just fine but when hovering over a vtkImagData the Cell Ids that the picker selects is just plain wrong. We tried the vtkCellPicker which gives the correct answer but takes about 10 seconds to get that answer ( in release mode on a fairly recent machine). When we tried out ParaView’s hover cells feature it is very quick to highlight the cell and give a correct answer under all the various types of geometries that we throw at it.

Could any of the ParaView developers give some thoughts on ParaView’s implementation? I tried working through the ParaView code but got as far as the SMProxyRender class then got lost in that implememtation.

Thank you.