code: protected boolean showCarbon(IAtom carbonAtom, IAtomContainer container, RendererModel model) {
  
          if ((Boolean) model.get(KekuleStructure.class)) return true;
  
          if (carbonAtom.getFormalCharge() != 0) return true;
  
          int connectedBondCount = container.getConnectedBondsList(carbonAtom).size();
  
          if (connectedBondCount < 1) return true;
  
          if ((Boolean) model.get(ShowEndCarbons.class) && connectedBondCount == 1) return true;
  
          if (carbonAtom.getProperty(ProblemMarker.ERROR_MARKER) != null) return true;
  
          if (container.getConnectedSingleElectronsCount(carbonAtom) > 0) return true;
  
          return false;
      }
docs: Checks a carbon atom to see if it should be shown.
  
  @param carbonAtom the carbon atom to check
  @param container the atom container
  @param model the renderer model
  @return true if the carbon should be shown