public Vector calculate(Vector left,
    Vector right) 
{
       
        Vector edges = new Vector();
        addEdges(edges, left, AreaOp.CTAG_LEFT);
        addEdges(edges, right, AreaOp.CTAG_RIGHT);
        edges = pruneEdges(edges);
        if (false) {
            System.out.println("result: ");
            int numcurves = edges.size();
            Curve[] curvelist = (Curve[]) edges.toArray(new Curve[numcurves]);
            for (int i = 0; i <  numcurves; i++) {
                System.out.println("curvelist["+i+"] = "+curvelist[i]);
            }
        }
        return edges;
}

 abstract public int classify(Edge e)

 public static  void finalizeSubCurves(Vector subcurves,
    Vector chains) 
{
        int numchains = chains.size();
        if (numchains == 0) {
            return;
        }
        if ((numchains & 1) != 0) {
            throw new InternalError("Odd number of chains!");
        }
        ChainEnd[] endlist = new ChainEnd[numchains];
        chains.toArray(endlist);
        for (int i = 1; i <  numchains; i += 2) {
            ChainEnd open = endlist[i - 1];
            ChainEnd close = endlist[i];
            CurveLink subcurve = open.linkTo(close);
            if (subcurve != null) {
                subcurves.add(subcurve);
            }
        }
        chains.clear();
}

 abstract public int getState()

 abstract public  void newRow()

 public static boolean obstructs(double v1,
    double v2,
    int phase) 
{
        return (((phase & 1) == 0) ? (v1 < = v2) : (v1 <  v2));
}

 public static  void resolveLinks(Vector subcurves,
    Vector chains,
    Vector links) 
{
        
        int numlinks = links.size();
        CurveLink[] linklist;
        if (numlinks == 0) {
            linklist = EmptyLinkList;
        } else {
            if ((numlinks & 1) != 0) {
                throw new InternalError("Odd number of new curves!");
            }
            linklist = new CurveLink[numlinks+2];
            links.toArray(linklist);
        }
        int numchains = chains.size();
        ChainEnd[] endlist;
        if (numchains == 0) {
            endlist = EmptyChainList;
        } else {
            if ((numchains & 1) != 0) {
                throw new InternalError("Odd number of chains!");
            }
            endlist = new ChainEnd[numchains+2];
            chains.toArray(endlist);
        }
        int curchain = 0;
        int curlink = 0;
        chains.clear();
        ChainEnd chain = endlist[0];
        ChainEnd nextchain = endlist[1];
        CurveLink link = linklist[0];
        CurveLink nextlink = linklist[1];
        while (chain != null || link != null) {
            /*
             * Strategy 1:
             * Connect chains or links if they are the only things left...
             */
            boolean connectchains = (link == null);
            boolean connectlinks = (chain == null);
            if (!connectchains && !connectlinks) {
                // assert(link != null && chain != null);
                /*
                 * Strategy 2:
                 * Connect chains or links if they close off an open area...
                 */
                connectchains = ((curchain & 1) == 0 &&
                                 chain.getX() == nextchain.getX());
                connectlinks = ((curlink & 1) == 0 &&
                                link.getX() == nextlink.getX());
                if (!connectchains && !connectlinks) {
                    /*
                     * Strategy 3:
                     * Connect chains or links if their successor is
                     * between them and their potential connectee...
                     */
                    double cx = chain.getX();
                    double lx = link.getX();
                    connectchains =
                        (nextchain != null && cx <  lx &&
                         obstructs(nextchain.getX(), lx, curchain));
                    connectlinks =
                        (nextlink != null && lx <  cx &&
                         obstructs(nextlink.getX(), cx, curlink));
                }
            }
            if (connectchains) {
                CurveLink subcurve = chain.linkTo(nextchain);
                if (subcurve != null) {
                    subcurves.add(subcurve);
                }
                curchain += 2;
                chain = endlist[curchain];
                nextchain = endlist[curchain+1];
            }
            if (connectlinks) {
                ChainEnd openend = new ChainEnd(link, null);
                ChainEnd closeend = new ChainEnd(nextlink, openend);
                openend.setOtherEnd(closeend);
                chains.add(openend);
                chains.add(closeend);
                curlink += 2;
                link = linklist[curlink];
                nextlink = linklist[curlink+1];
            }
            if (!connectchains && !connectlinks) {
                // assert(link != null);
                // assert(chain != null);
                // assert(chain.getEtag() == link.getEtag());
                chain.addLink(link);
                chains.add(chain);
                curchain++;
                chain = nextchain;
                nextchain = endlist[curchain+1];
                curlink++;
                link = nextlink;
                nextlink = linklist[curlink+1];
            }
        }
        if ((chains.size() & 1) != 0) {
            System.out.println("Odd number of chains!");
        }
}