libigl_Martin/include/igl/cgal/order_facets_around_edge.cpp

#include "order_facets_around_edge.h"

namespace igl {
    namespace cgal {
        namespace order_facets_around_edges_helper {
            template<typename T>
            std::vector<size_t> index_sort(const std::vector<T>& data) {
                const size_t len = data.size();
                std::vector<size_t> order(len);
                for (size_t i=0; i<len; i++) order[i] = i;

                auto comp = [&](size_t i, size_t j) {
                    return data[i] < data[j];
                };
                std::sort(order.begin(), order.end(), comp);
                return order;
            }
        }
    }
}

// adj_faces contains signed index starting from +- 1.
template<
    typename DerivedV,
    typename DerivedF,
    typename DerivedI >
void igl::cgal::order_facets_around_edge(
    const Eigen::PlainObjectBase<DerivedV>& V,
    const Eigen::PlainObjectBase<DerivedF>& F,
    size_t s, size_t d, 
    const std::vector<int>& adj_faces,
    Eigen::PlainObjectBase<DerivedI>& order) {

    using namespace igl::cgal::order_facets_around_edges_helper;

    // Although we only need exact predicates in the algorithm,
    // exact constructions are needed to avoid degeneracies due to
    // casting to double.
    typedef CGAL::Exact_predicates_exact_constructions_kernel K;
    typedef K::Point_3 Point_3;
    typedef K::Plane_3 Plane_3;

    auto get_face_index = [&](int adj_f)->size_t{
        return abs(adj_f) - 1;
    };

    auto get_opposite_vertex = [&](size_t fid)->size_t {
        if (F(fid, 0) != s && F(fid, 0) != d) return F(fid, 0);
        if (F(fid, 1) != s && F(fid, 1) != d) return F(fid, 1);
        if (F(fid, 2) != s && F(fid, 2) != d) return F(fid, 2);
        assert(false);
        return -1;
    };

    // Handle base cases
    if (adj_faces.size() == 0) {
        order.resize(0);
        return;
    } else if (adj_faces.size() == 1) {
        order.resize(1);
        order[0] = 0;
        return;
    } else if (adj_faces.size() == 2) {
        const size_t o1 =
            get_opposite_vertex(get_face_index(adj_faces[0]));
        const size_t o2 =
            get_opposite_vertex(get_face_index(adj_faces[1]));
        const Point_3 ps(V(s, 0), V(s, 1), V(s, 2));
        const Point_3 pd(V(d, 0), V(d, 1), V(d, 2));
        const Point_3 p1(V(o1, 0), V(o1, 1), V(o1, 2));
        const Point_3 p2(V(o2, 0), V(o2, 1), V(o2, 2));
        order.resize(2);
        switch (CGAL::orientation(ps, pd, p1, p2)) {
            case CGAL::POSITIVE:
                order[0] = 1;
                order[1] = 0;
                break;
            case CGAL::NEGATIVE:
                order[0] = 0;
                order[1] = 1;
                break;
            case CGAL::COPLANAR:
                order[0] = adj_faces[0] < adj_faces[1] ? 0:1;
                order[1] = adj_faces[0] < adj_faces[1] ? 1:0;
                break;
            default:
                assert(false);
        }
        return;
    }

    const size_t num_adj_faces = adj_faces.size();
    const size_t o = get_opposite_vertex(
            get_face_index(adj_faces[0]));
    const Point_3 p_s(V(s, 0), V(s, 1), V(s, 2));
    const Point_3 p_d(V(d, 0), V(d, 1), V(d, 2));
    const Point_3 p_o(V(o, 0), V(o, 1), V(o, 2));
    const Plane_3 separator(p_s, p_d, p_o);
    assert(!separator.is_degenerate());

    std::vector<Point_3> opposite_vertices;
    for (size_t i=0; i<num_adj_faces; i++) {
        const size_t o = get_opposite_vertex(
                get_face_index(adj_faces[i]));
        opposite_vertices.emplace_back(
                V(o, 0), V(o, 1), V(o, 2));
    }

    std::vector<int> positive_side;
    std::vector<int> negative_side;
    std::vector<int> tie_positive_oriented;
    std::vector<int> tie_negative_oriented;

    std::vector<size_t> positive_side_index;
    std::vector<size_t> negative_side_index;
    std::vector<size_t> tie_positive_oriented_index;
    std::vector<size_t> tie_negative_oriented_index;

    for (size_t i=0; i<num_adj_faces; i++) {
        const int f = adj_faces[i];
        const Point_3& p_a = opposite_vertices[i];
        auto orientation = separator.oriented_side(p_a);
        switch (orientation) {
            case CGAL::ON_POSITIVE_SIDE:
                positive_side.push_back(f);
                positive_side_index.push_back(i);
                break;
            case CGAL::ON_NEGATIVE_SIDE:
                negative_side.push_back(f);
                negative_side_index.push_back(i);
                break;
            case CGAL::ON_ORIENTED_BOUNDARY:
                {
                    const Plane_3 other(p_s, p_d, p_a);
                    const auto target_dir = separator.orthogonal_direction();
                    const auto query_dir = other.orthogonal_direction();
                    if (target_dir == query_dir) {
                        tie_positive_oriented.push_back(f);
                        tie_positive_oriented_index.push_back(i);
                    } else if (target_dir == -query_dir) {
                        tie_negative_oriented.push_back(f);
                        tie_negative_oriented_index.push_back(i);
                    } else {
                        assert(false);
                    }
                }
                break;
            default:
                // Should not be here.
                assert(false);
        }
    }

    Eigen::PlainObjectBase<DerivedI> positive_order, negative_order;
    order_facets_around_edge(V, F, s, d, positive_side, positive_order);
    order_facets_around_edge(V, F, s, d, negative_side, negative_order);
    std::vector<size_t> tie_positive_order =
        index_sort(tie_positive_oriented);
    std::vector<size_t> tie_negative_order =
        index_sort(tie_negative_oriented);

    // Copy results into order vector.
    const size_t tie_positive_size = tie_positive_oriented.size();
    const size_t tie_negative_size = tie_negative_oriented.size();
    const size_t positive_size = positive_order.size();
    const size_t negative_size = negative_order.size();

    order.resize(tie_positive_size + positive_size +
            tie_negative_size + negative_size);

    size_t count=0;
    for (size_t i=0; i<tie_positive_size; i++) {
        order[count+i] =
            tie_positive_oriented_index[tie_positive_order[i]];
    }
    count += tie_positive_size;

    for (size_t i=0; i<negative_size; i++) {
        order[count+i] = negative_side_index[negative_order[i]];
    }
    count += negative_size;

    for (size_t i=0; i<tie_negative_size; i++) {
        order[count+i] =
            tie_negative_oriented_index[tie_negative_order[i]];
    }
    count += tie_negative_size;

    for (size_t i=0; i<positive_size; i++) {
        order[count+i] = positive_side_index[positive_order[i]];
    }
    count += positive_size;
    assert(count == num_adj_faces);

    // Find the correct start point.
    size_t start_idx = 0;
    for (size_t i=0; i<num_adj_faces; i++) {
        const Point_3& p_a = opposite_vertices[order[i]];
        const Point_3& p_b =
            opposite_vertices[order[(i+1)%num_adj_faces]];
        if (CGAL::orientation(p_s, p_d, p_a, p_b) == CGAL::POSITIVE) {
            start_idx = (i+1)%num_adj_faces;
            break;
        }
    }
    DerivedI circular_order = order;
    for (size_t i=0; i<num_adj_faces; i++) {
        order[i] = circular_order[(start_idx + i)%num_adj_faces];
    }
}