Function extract_loops

tools/Boolean/Clipper/ClipperEngine.cpp:27–65

* Extract boundary loops from an array of boudnary segments. * Assuming boundary segments are orientated consistently. */

     * Assuming boundary segments are orientated consistently.
     */
    Loops extract_loops(const MatrixIr& boundaries) {
        assert(boundaries.cols() == 2);
        const size_t num_boundaries = boundaries.rows();
        std::unordered_map<size_t, std::list<MatrixIr::Scalar> > adjacencies;

        for (size_t i=0; i<num_boundaries; i++) {
            const VectorI& edge = boundaries.row(i);
            auto itr = adjacencies.find(edge[0]);
            if (itr != adjacencies.end()) {
                itr->second.push_back(edge[1]);
            } else {
                adjacencies.insert({edge[0], {edge[1]}});
            }
        }

        Loops loops;
        std::unordered_set<size_t> visited;
        for (const auto& itr : adjacencies) {
            auto i = itr.first;
            if (itr.second.empty()) continue; // Vertex not part of loop.

            Loop loop;
            loop.push_back(i);
            visited.insert(i);
            do {
                auto& neighbors = adjacencies[loop.back()];
                if (neighbors.empty()) {
                    throw RuntimeError("Open loop detected.");
                }
                int next = neighbors.front();
                neighbors.pop_front();
                loop.push_back(next);
                visited.insert(next);
            } while (loop.back() != loop.front());
            loop.pop_back();
            if (loop.size() > 0) loops.push_back(loop);
        }
        return loops;
    }

    class PointConvert {
        public: