code: private double getWidthForMappingLine(RendererModel model) {
          double scale = model.getParameter(Scale.class).getValue();
          return mappingLineWidth.getValue() / scale;
      }
docs: Determine the width of an atom atom mapping, returning the width defined
  in the model. Note that this will be scaled
  to the space of the model.
  
  @param model the renderer model
  @return a double in chem-model space