code: protected boolean invisibleHydrogen(IAtom atom, RendererModel model) {
          return isHydrogen(atom) && !(Boolean) model.get(ShowExplicitHydrogens.class);
      }
docs: Checks an atom to see if it is an 'invisible hydrogen' - that is, it
  is a) an (explicit) hydrogen, and b) explicit hydrogens are set to off.
  
  @param atom the atom to check
  @param model the renderer model
  @return true if this atom should not be shown