[cctbxbb] Fast way to enable/disable individual scatterers in structure factor calculation

Hi, I'm looking for a simple and fast way to set individual scatterers to be either included or excluded from structure factor calculation. As I see from the source (structure_factors_direct.h) the selection toggle does not seem to be evaluated for this. Of course an additional check for the selection flag would harm performance in most standard cases, so I'd rather like to have a separate c++ function for this, which could be swapped in for the normal f_calc calculation by a boolean toggle in the python part of f_calc. As I'm not that much into the c++ part of cctbx, I'd really appreciate if somebody more knowledgeable could monkey patch this. Cheers, Jan