linkResultDirectedEdges method

void linkResultDirectedEdges()

Traverse the star of DirectedEdges, linking the included edges together. To link two dirEdges, the next pointer for an incoming dirEdge is set to the next outgoing edge.

DirEdges are only linked if:

• they belong to an area (i.e. they have sides)
• they are marked as being in the result

Edges are linked in CCW order (the order they are stored). This means that rings have their face on the Right (in other words, the topological location of the face is given by the RHS label of the DirectedEdge)

PRECONDITION: No pair of dirEdges are both marked as being in the result

Implementation

void linkResultDirectedEdges() {
  // make sure edges are copied to resultAreaEdges list
  getResultAreaEdges();
  // find first area edge (if any) to start linking at
  DirectedEdge? firstOut = null;
  DirectedEdge? incoming = null;
  int state = SCANNING_FOR_INCOMING;
  // link edges in CCW order
  for (int i = 0; i < resultAreaEdgeList!.length; i++) {
    DirectedEdge nextOut = resultAreaEdgeList![i] as DirectedEdge;
    DirectedEdge nextIn = nextOut.getSym();

    // skip de's that we're not interested in
    if (!nextOut.getLabel()!.isArea()) continue;

    // record first outgoing edge, in order to link the last incoming edge
    if (firstOut == null && nextOut.isInResult()) firstOut = nextOut;
    // assert: sym.isInResult() == false, since pairs of dirEdges should have been removed already

    switch (state) {
      case SCANNING_FOR_INCOMING:
        if (!nextIn.isInResult()) continue;
        incoming = nextIn;
        state = LINKING_TO_OUTGOING;
        break;
      case LINKING_TO_OUTGOING:
        if (!nextOut.isInResult()) continue;
        incoming!.setNext(nextOut);
        state = SCANNING_FOR_INCOMING;
        break;
    }
  }
//Debug.print(this);
  if (state == LINKING_TO_OUTGOING) {
//Debug.print(firstOut == null, this);
    if (firstOut == null)
      throw new TopologyException(
          "no outgoing dirEdge found ${getCoordinate()}");
    //Assert.isTrue(firstOut != null, "no outgoing dirEdge found (at " + getCoordinate() );
    assert(firstOut.isInResult(), "unable to link last incoming dirEdge");
    incoming!.setNext(firstOut);
  }
}