code: public LineElement generateInnerElement(IBond bond, IRing ring, RendererModel model) {
          Point2d center = GeometryUtil.get2DCenter(ring);
          Point2d a = bond.getBegin().getPoint2d();
          Point2d b = bond.getEnd().getPoint2d();
  
          // the proportion to move in towards the ring center
          double distanceFactor = model.getParameter(TowardsRingCenterProportion.class).getValue();
          double ringDistance = distanceFactor * IDEAL_RINGSIZE / ring.getAtomCount();
          if (ringDistance < distanceFactor / MIN_RINGSIZE_FACTOR) ringDistance = distanceFactor / MIN_RINGSIZE_FACTOR;
  
          Point2d w = new Point2d();
          w.interpolate(a, center, ringDistance);
          Point2d u = new Point2d();
          u.interpolate(b, center, ringDistance);
  
          double alpha = 0.2;
          Point2d ww = new Point2d();
          ww.interpolate(w, u, alpha);
          Point2d uu = new Point2d();
          uu.interpolate(u, w, alpha);
  
          double width = getWidthForBond(bond, model);
          Color color = getColorForBond(bond, model);
  
          return new LineElement(u.x, u.y, w.x, w.y, width, color);
      }
docs: Make the inner ring bond, which is slightly shorter than the outer bond.
  
  @param bond the ring bond
  @param ring the ring that the bond is in
  @param model the renderer model
  @return the line element