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

[Jan Marten Simons]

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