NCMesh2D.cpp

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#include <polyfem/mesh/mesh2D/NCMesh2D.hpp>
 
#include <polyfem/utils/Logger.hpp>
 
#include <igl/writeOBJ.h>
 
#include <polyfem/mesh/MeshUtils.hpp>
 
namespace polyfem
{
    namespace mesh
    {
        bool NCMesh2D::is_boundary_element(const int element_global_id) const
        {
            assert(index_prepared);
            for (int le = 0; le < n_face_vertices(element_global_id); le++)
                if (is_boundary_edge(face_edge(element_global_id, le)))
                    return true;
 
            return false;
        }
 
        void NCMesh2D::refine(const int n_refinement, const double t)
        {
            if (n_refinement <= 0)
                return;
            std::vector<bool> refine_mask(elements.size(), false);
            for (int i = 0; i < elements.size(); i++)
                if (elements[i].is_valid())
                    refine_mask[i] = true;
 
            for (int i = 0; i < refine_mask.size(); i++)
                if (refine_mask[i])
                    refine_element(i);
 
            refine(n_refinement - 1, t);
        }
 
        bool NCMesh2D::build_from_matrices(const Eigen::MatrixXd &V, const Eigen::MatrixXi &F)
        {
            GEO::Mesh mesh_;
            mesh_.clear(false, false);
            to_geogram_mesh(V, F, mesh_);
            orient_normals_2d(mesh_);
 
            n_elements = 0;
            elements.clear();
            vertices.clear();
            edges.clear();
            midpointMap.clear();
            edgeMap.clear();
            refineHistory.clear();
            index_prepared = false;
            adj_prepared = false;
 
            vertices.reserve(V.rows());
            for (int i = 0; i < V.rows(); i++)
            {
                vertices.emplace_back(V.row(i));
            }
            for (int i = 0; i < F.rows(); i++)
            {
                add_element(F.row(i), -1);
            }
 
            prepare_mesh();
 
            return true;
        }
 
        void NCMesh2D::attach_higher_order_nodes(const Eigen::MatrixXd &V, const std::vector<std::vector<int>> &nodes)
        {
            for (int f = 0; f < n_faces(); ++f)
                if (nodes[f].size() != 3)
                    throw std::runtime_error("NCMesh doesn't support high order mesh!");
        }
        std::pair<RowVectorNd, int> NCMesh2D::edge_node(const Navigation::Index &index, const int n_new_nodes, const int i) const
        {
            const auto v1 = point(index.vertex);
            const auto v2 = point(switch_vertex(index).vertex);
 
            const double t = i / (n_new_nodes + 1.0);
 
            return std::make_pair((1 - t) * v1 + t * v2, -1);
        }
        std::pair<RowVectorNd, int> NCMesh2D::face_node(const Navigation::Index &index, const int n_new_nodes, const int i, const int j) const
        {
            const auto v1 = point(index.vertex);
            const auto v2 = point(switch_vertex(index).vertex);
            const auto v3 = point(switch_vertex(switch_edge(index)).vertex);
 
            const double b2 = i / (n_new_nodes + 2.0);
            const double b3 = j / (n_new_nodes + 2.0);
            const double b1 = 1 - b3 - b2;
            assert(b3 < 1);
            assert(b3 > 0);
 
            return std::make_pair(b1 * v1 + b2 * v2 + b3 * v3, -1);
        }
 
        int NCMesh2D::find_vertex(Eigen::Vector2i v) const
        {
            std::sort(v.data(), v.data() + v.size());
            auto search = midpointMap.find(v);
            if (search != midpointMap.end())
                return search->second;
            else
                return -1;
        }
 
        int NCMesh2D::get_vertex(Eigen::Vector2i v)
        {
            std::sort(v.data(), v.data() + v.size());
            int id = find_vertex(v);
            if (id < 0)
            {
                Eigen::VectorXd v_mid = (vertices[v[0]].pos + vertices[v[1]].pos) / 2.;
                id = vertices.size();
                vertices.emplace_back(v_mid);
                midpointMap.emplace(v, id);
            }
            return id;
        }
 
        int NCMesh2D::find_edge(Eigen::Vector2i v) const
        {
            std::sort(v.data(), v.data() + v.size());
            auto search = edgeMap.find(v);
            if (search != edgeMap.end())
                return search->second;
            else
                return -1;
        }
 
        int NCMesh2D::get_edge(Eigen::Vector2i v)
        {
            std::sort(v.data(), v.data() + v.size());
            int id = find_edge(v);
            if (id < 0)
            {
                edges.emplace_back(v);
                id = edges.size() - 1;
                edgeMap.emplace(v, id);
            }
            return id;
        }
 
        int NCMesh2D::add_element(Eigen::Vector3i v, int parent)
        {
            const int id = elements.size();
            const int level = (parent < 0) ? 0 : elements[parent].level + 1;
            elements.emplace_back(2, v, level, parent);
 
            if (parent >= 0)
                elements[id].body_id = elements[parent].body_id;
 
            for (int i = 0; i < v.size(); i++)
                vertices[v(i)].n_elem++;
 
            // add edges if not exist
            int edge01 = get_edge(Eigen::Vector2i(v[0], v[1]));
            int edge12 = get_edge(Eigen::Vector2i(v[2], v[1]));
            int edge20 = get_edge(Eigen::Vector2i(v[0], v[2]));
 
            elements[id].edges << edge01, edge12, edge20;
 
            edges[edge01].add_element(id);
            edges[edge12].add_element(id);
            edges[edge20].add_element(id);
 
            n_elements++;
            index_prepared = false;
            adj_prepared = false;
 
            return id;
        }
 
        void NCMesh2D::refine_element(int id_full)
        {
            auto &elem = elements[id_full];
            if (elem.is_not_valid())
                throw std::runtime_error("Cannot refine an invalid element!");
 
            const auto v = elem.vertices;
            elem.is_refined = true;
            n_elements--;
 
            // remove the old element from edge reference
            for (int e = 0; e < 3; e++)
                edges[elem.edges(e)].remove_element(id_full);
 
            for (int i = 0; i < v.size(); i++)
                vertices[v(i)].n_elem--;
 
            if (elem.children(0) >= 0)
            {
                for (int c = 0; c < elem.children.size(); c++)
                {
                    auto &child = elements[elem.children(c)];
                    child.is_ghost = false;
                    n_elements++;
                    for (int le = 0; le < child.edges.size(); le++)
                        edges[child.edges(le)].add_element(child.children(c));
                    for (int i = 0; i < child.vertices.size(); i++)
                        vertices[child.vertices(i)].n_elem++;
                }
            }
            else
            {
                // create mid-points if not exist
                const int v01 = get_vertex(Eigen::Vector2i(v[0], v[1]));
                const int v12 = get_vertex(Eigen::Vector2i(v[2], v[1]));
                const int v20 = get_vertex(Eigen::Vector2i(v[0], v[2]));
 
                // inherite line singularity flag from parent edge
                for (int i = 0; i < v.size(); i++)
                    for (int j = 0; j < i; j++)
                    {
                        int mid_id = find_vertex(v[i], v[j]);
                        int edge_id = find_edge(v[i], v[j]);
                        int edge1 = get_edge(v[i], mid_id);
                        int edge2 = get_edge(v[j], mid_id);
                        edges[edge1].boundary_id = edges[edge_id].boundary_id;
                        edges[edge2].boundary_id = edges[edge_id].boundary_id;
                    }
 
                // create and insert child elements
                elements[id_full].children(0) = elements.size();
                add_element(Eigen::Vector3i(v[0], v01, v20), id_full);
                elements[id_full].children(1) = elements.size();
                add_element(Eigen::Vector3i(v[1], v12, v01), id_full);
                elements[id_full].children(2) = elements.size();
                add_element(Eigen::Vector3i(v[2], v20, v12), id_full);
                elements[id_full].children(3) = elements.size();
                add_element(Eigen::Vector3i(v12, v20, v01), id_full);
            }
 
            refineHistory.push_back(id_full);
 
            index_prepared = false;
            adj_prepared = false;
        }
 
        void NCMesh2D::refine_elements(const std::vector<int> &ids)
        {
            std::vector<int> full_ids(ids.size());
            for (int i = 0; i < ids.size(); i++)
                full_ids[i] = valid_to_all_elem(ids[i]);
 
            for (int i : full_ids)
                refine_element(i);
        }
 
        void NCMesh2D::coarsen_element(int id_full)
        {
            const int parent_id = elements[id_full].parent;
            auto &parent = elements[parent_id];
 
            for (int i = 0; i < parent.children.size(); i++)
                if (elements[parent.children(i)].is_not_valid())
                    throw std::runtime_error("Coarsen operation invalid!");
 
            // remove elements
            for (int i = 0; i < parent.children.size(); i++)
            {
                auto &elem = elements[parent.children(i)];
                elem.is_ghost = true;
                n_elements--;
                for (int le = 0; le < elem.edges.size(); le++)
                    edges[elem.edges(le)].remove_element(parent.children(i));
                for (int v = 0; v < elem.vertices.size(); v++)
                    vertices[elem.vertices(v)].n_elem--;
            }
 
            // add element
            parent.is_refined = false;
            n_elements++;
            for (int le = 0; le < parent.edges.size(); le++)
                edges[parent.edges(le)].add_element(parent_id);
            for (int v = 0; v < parent.vertices.size(); v++)
                vertices[parent.vertices(v)].n_elem++;
 
            refineHistory.push_back(parent_id);
 
            index_prepared = false;
            adj_prepared = false;
        }
 
        int find(const Eigen::VectorXi &vec, int x)
        {
            for (int i = 0; i < vec.size(); i++)
            {
                if (x == vec[i])
                    return i;
            }
            return -1;
        }
 
        void NCMesh2D::build_edge_follower_chain()
        {
            for (auto &edge : edges)
            {
                edge.leader = -1;
                edge.followers.clear();
                edge.weights.setConstant(-1);
            }
 
            Eigen::Vector2i v;
            std::vector<follower_edge> followers;
            for (int e_id = 0; e_id < elements.size(); e_id++)
            {
                const auto &element = elements[e_id];
                if (element.is_not_valid())
                    continue;
                for (int edge_local = 0; edge_local < 3; edge_local++)
                {
                    v << element.vertices[edge_local], element.vertices[(edge_local + 1) % 3]; // order is important here!
                    int edge_global = element.edges[edge_local];
                    assert(edge_global >= 0);
                    traverse_edge(v, 0, 1, 0, followers);
                    for (auto &s : followers)
                    {
                        edges[s.id].leader = edge_global;
                        edges[edge_global].followers.push_back(s.id);
                        edges[s.id].weights << s.p1, s.p2;
                    }
                    followers.clear();
                }
            }
        }
 
        void NCMesh2D::mark_boundary()
        {
            for (auto &edge : edges)
            {
                if (edge.n_elem() == 1)
                    edge.isboundary = true;
                else
                    edge.isboundary = false;
            }
 
            for (auto &edge : edges)
            {
                if (edge.leader >= 0)
                {
                    edge.isboundary = false;
                    edges[edge.leader].isboundary = false;
                }
            }
 
            for (auto &vert : vertices)
                vert.isboundary = false;
 
            for (auto &edge : edges)
            {
                if (edge.isboundary && edge.n_elem())
                {
                    for (int j = 0; j < 2; j++)
                        vertices[edge.vertices(j)].isboundary = true;
                }
            }
        }
 
        double line_weight(Eigen::Matrix<double, 2, 2> &e, Eigen::VectorXd &v)
        {
            assert(v.size() == 2);
            double w1 = (v(0) - e(0, 0)) / (e(1, 0) - e(0, 0));
            double w2 = (v(1) - e(0, 1)) / (e(1, 1) - e(0, 1));
            if (0 <= w1 && w1 <= 1)
                return w1;
            else
                return w2;
        }
 
        void NCMesh2D::build_element_vertex_adjacency()
        {
            for (auto &vert : vertices)
            {
                vert.edge = -1;
                vert.weight = -1;
            }
 
            Eigen::VectorXi vertexEdgeAdjacency;
            vertexEdgeAdjacency.setConstant(vertices.size(), 1, -1);
 
            for (int small_edge = 0; small_edge < edges.size(); small_edge++)
            {
                if (edges[small_edge].n_elem() == 0)
                    continue;
 
                int large_edge = edges[small_edge].leader;
                if (large_edge < 0)
                    continue;
 
                int large_elem = edges[large_edge].get_element();
                for (int j = 0; j < 2; j++)
                {
                    int v_id = edges[small_edge].vertices(j);
                    if (find(elements[large_elem].vertices, v_id) < 0) // or maybe 0 < weights(large_edge, v_id) < 1
                        vertexEdgeAdjacency[v_id] = large_edge;
                }
            }
 
            for (auto &element : elements)
            {
                if (element.is_not_valid())
                    continue;
                for (int v_local = 0; v_local < 3; v_local++)
                {
                    int v_global = element.vertices[v_local];
                    if (vertexEdgeAdjacency[v_global] < 0)
                        continue;
 
                    auto &large_edge = edges[vertexEdgeAdjacency[v_global]];
                    auto &large_element = elements[large_edge.get_element()];
                    vertices[v_global].edge = vertexEdgeAdjacency[v_global];
 
                    int e_local = find(large_element.edges, vertices[v_global].edge);
                    Eigen::Matrix<double, 2, 2> edge;
                    edge.row(0) = vertices[large_element.vertices[e_local]].pos;
                    edge.row(1) = vertices[large_element.vertices[(e_local + 1) % 3]].pos;
                    vertices[v_global].weight = line_weight(edge, vertices[v_global].pos);
                }
            }
        }
 
        double NCMesh2D::element_weight_to_edge_weight(const int l, const Eigen::Vector2d &pos)
        {
            double w = -1;
            switch (l)
            {
            case 0:
                w = pos(0);
                assert(fabs(pos(1)) < 1e-12);
                break;
            case 1:
                w = pos(1);
                assert(fabs(pos(0) + pos(1) - 1) < 1e-12);
                break;
            case 2:
                w = 1 - pos(1);
                assert(fabs(pos(0)) < 1e-12);
                break;
            default:
                assert(false);
            }
            return w;
        }
 
        void NCMesh2D::build_index_mapping()
        {
            all_to_valid_elemMap.assign(elements.size(), -1);
            valid_to_all_elemMap.resize(n_elements);
 
            for (int i = 0, e = 0; i < elements.size(); i++)
            {
                if (elements[i].is_not_valid())
                    continue;
                all_to_valid_elemMap[i] = e;
                valid_to_all_elemMap[e] = i;
                e++;
            }
 
            const int n_verts = n_vertices();
 
            all_to_valid_vertexMap.assign(vertices.size(), -1);
            valid_to_all_vertexMap.resize(n_verts);
 
            for (int i = 0, j = 0; i < vertices.size(); i++)
            {
                if (vertices[i].n_elem == 0)
                    continue;
                all_to_valid_vertexMap[i] = j;
                valid_to_all_vertexMap[j] = i;
                j++;
            }
 
            all_to_valid_edgeMap.assign(edges.size(), -1);
            valid_to_all_edgeMap.resize(n_edges());
 
            for (int i = 0, j = 0; i < edges.size(); i++)
            {
                if (edges[i].n_elem() == 0)
                    continue;
                all_to_valid_edgeMap[i] = j;
                valid_to_all_edgeMap[j] = i;
                j++;
            }
            index_prepared = true;
        }
 
        void NCMesh2D::append(const Mesh &mesh)
        {
            assert(typeid(mesh) == typeid(NCMesh2D));
            Mesh::append(mesh);
 
            const NCMesh2D &mesh2d = dynamic_cast<const NCMesh2D &>(mesh);
 
            const int n_v = n_vertices();
            const int n_f = n_faces();
 
            vertices.reserve(n_v + mesh2d.n_vertices());
            for (int i = 0; i < mesh2d.n_vertices(); i++)
            {
                vertices.emplace_back(mesh2d.vertices[i].pos);
            }
            for (int i = 0; i < mesh2d.n_faces(); i++)
            {
                Eigen::Vector3i face = mesh2d.elements[i].vertices;
                face = face.array() + n_v;
                add_element(face, -1);
            }
 
            prepare_mesh();
        }
 
        std::unique_ptr<Mesh> NCMesh2D::copy() const
        {
            return std::make_unique<NCMesh2D>(*this);
        }
 
        void NCMesh2D::traverse_edge(Eigen::Vector2i v, double p1, double p2, int depth, std::vector<follower_edge> &list) const
        {
            int v_mid = find_vertex(v);
            std::vector<follower_edge> list1, list2;
            if (v_mid >= 0)
            {
                double p_mid = (p1 + p2) / 2;
                traverse_edge(Eigen::Vector2i(v[0], v_mid), p1, p_mid, depth + 1, list1);
                list.insert(
                    list.end(),
                    std::make_move_iterator(list1.begin()),
                    std::make_move_iterator(list1.end()));
                traverse_edge(Eigen::Vector2i(v_mid, v[1]), p_mid, p2, depth + 1, list2);
                list.insert(
                    list.end(),
                    std::make_move_iterator(list2.begin()),
                    std::make_move_iterator(list2.end()));
            }
            if (depth > 0)
            {
                int follower_id = find_edge(v);
                if (follower_id >= 0 && edges[follower_id].n_elem() > 0)
                    list.emplace_back(follower_id, p1, p2);
            }
        }
 
        bool NCMesh2D::load(const std::string &path)
        {
            assert(false);
            return false;
        }
 
        bool NCMesh2D::load(const GEO::Mesh &mesh)
        {
            GEO::Mesh mesh_;
            mesh_.clear(false, false);
            mesh_.copy(mesh);
            orient_normals_2d(mesh_);
 
            Eigen::MatrixXd V(mesh_.vertices.nb(), 2);
            Eigen::MatrixXi F(mesh_.facets.nb(), 3);
 
            for (int v = 0; v < V.rows(); v++)
            {
                const double *ptr = mesh_.vertices.point_ptr(v);
                V.row(v) << ptr[0], ptr[1];
            }
 
            for (int f = 0; f < F.rows(); f++)
                for (int i = 0; i < F.cols(); i++)
                    F(f, i) = mesh_.facets.vertex(f, i);
 
            n_elements = 0;
            vertices.reserve(V.rows());
            for (int i = 0; i < V.rows(); i++)
            {
                vertices.emplace_back(V.row(i));
            }
            for (int i = 0; i < F.rows(); i++)
            {
                add_element(F.row(i), -1);
            }
 
            prepare_mesh();
 
            return true;
        }
 
        void NCMesh2D::bounding_box(RowVectorNd &min, RowVectorNd &max) const
        {
            min = vertices[0].pos;
            max = vertices[0].pos;
 
            for (const auto &v : vertices)
            {
                for (int d = 0; d < 2; d++)
                {
                    if (v.pos[d] > max[d])
                        max[d] = v.pos[d];
                    if (v.pos[d] < min[d])
                        min[d] = v.pos[d];
                }
            }
        }
 
        Navigation::Index NCMesh2D::get_index_from_face(int f, int lv) const
        {
            const auto &elem = elements[valid_to_all_elem(f)];
 
            Navigation::Index idx2;
            idx2.face = f;
            idx2.vertex = all_to_valid_vertex(elem.vertices(lv));
            idx2.edge = all_to_valid_edge(elem.edges(lv));
            idx2.face_corner = -1;
 
            return idx2;
        }
 
        Navigation::Index NCMesh2D::switch_vertex(Navigation::Index idx) const
        {
            const auto &elem = elements[valid_to_all_elem(idx.face)];
            const auto &edge = edges[valid_to_all_edge(idx.edge)];
 
            Navigation::Index idx2;
            idx2.face = idx.face;
            idx2.edge = idx.edge;
 
            int v1 = valid_to_all_vertex(idx.vertex);
            int v2 = -1;
            for (int i = 0; i < edge.vertices.size(); i++)
                if (edge.vertices(i) != v1)
                {
                    v2 = edge.vertices(i);
                    break;
                }
 
            idx2.vertex = all_to_valid_vertex(v2);
            idx2.face_corner = -1;
 
            return idx2;
        }
 
        Navigation::Index NCMesh2D::switch_edge(Navigation::Index idx) const
        {
            const auto &elem = elements[valid_to_all_elem(idx.face)];
 
            Navigation::Index idx2;
            idx2.face = idx.face;
            idx2.vertex = idx.vertex;
            idx2.face_corner = -1;
 
            for (int i = 0; i < elem.edges.size(); i++)
            {
                const auto &edge = edges[elem.edges(i)];
                const int valid_edge_id = all_to_valid_edge(elem.edges(i));
                if (valid_edge_id != idx.edge && find(edge.vertices, idx.vertex) >= 0)
                {
                    idx2.edge = valid_edge_id;
                    break;
                }
            }
 
            return idx2;
        }
 
        Navigation::Index NCMesh2D::switch_face(Navigation::Index idx) const
        {
            Navigation::Index idx2;
            idx2.edge = idx.edge;
            idx2.vertex = idx.vertex;
            idx2.face_corner = -1;
 
            const auto &edge = edges[valid_to_all_edge(idx.edge)];
            if (edge.n_elem() == 2)
                idx2.face = (edge.find_opposite_element(valid_to_all_elem(idx.face)));
            else
                idx2.face = -1;
 
            return idx2;
        }
 
        void NCMesh2D::normalize()
        {
            polyfem::RowVectorNd min, max;
            bounding_box(min, max);
 
            auto extent = max - min;
            double scale = std::max(extent(0), extent(1));
 
            for (auto &v : vertices)
                v.pos = (v.pos - min.transpose()) / scale;
        }
 
        double NCMesh2D::edge_length(const int gid) const
        {
            const int v1 = edge_vertex(gid, 0);
            const int v2 = edge_vertex(gid, 1);
 
            return (point(v1) - point(v2)).norm();
        }
 
        void NCMesh2D::compute_elements_tag()
        {
            elements_tag_.assign(n_faces(), ElementType::SIMPLEX);
        }
        void NCMesh2D::update_elements_tag()
        {
            elements_tag_.assign(n_faces(), ElementType::SIMPLEX);
        }
 
        void NCMesh2D::set_point(const int global_index, const RowVectorNd &p)
        {
            vertices[valid_to_all_vertex(global_index)].pos = p;
        }
 
        RowVectorNd NCMesh2D::edge_barycenter(const int index) const
        {
            const int v1 = edge_vertex(index, 0);
            const int v2 = edge_vertex(index, 1);
 
            return 0.5 * (point(v1) + point(v2));
        }
 
        // void NCMesh2D::triangulate_faces(Eigen::MatrixXi &tris, Eigen::MatrixXd &pts, std::vector<int> &ranges) const
        // {
        //  ranges.clear();
 
        //  std::vector<Eigen::MatrixXi> local_tris(n_faces());
        //  std::vector<Eigen::MatrixXd> local_pts(n_faces());
 
        //  int total_tris = 0;
        //  int total_pts = 0;
 
        //  ranges.push_back(0);
 
        //  for (int f = 0; f < n_faces(); ++f)
        //  {
        //      const int n_vertices = n_face_vertices(f);
 
        //      Eigen::MatrixXd face_pts(n_vertices, 2);
        //      local_tris[f].resize(n_vertices - 2, 3);
 
        //      for (int i = 0; i < n_vertices; ++i)
        //      {
        //          const int vertex = face_vertex(f, i);
        //          auto pt = point(vertex);
        //          face_pts(i, 0) = pt[0];
        //          face_pts(i, 1) = pt[1];
        //      }
 
        //      for (int i = 1; i < n_vertices - 1; ++i)
        //      {
        //          local_tris[f].row(i - 1) << 0, i, i + 1;
        //      }
 
        //      local_pts[f] = face_pts;
 
        //      total_tris += local_tris[f].rows();
        //      total_pts += local_pts[f].rows();
 
        //      ranges.push_back(total_tris);
 
        //      assert(local_pts[f].rows() == face_pts.rows());
        //  }
 
        //  tris.resize(total_tris, 3);
        //  pts.resize(total_pts, 2);
 
        //  int tri_index = 0;
        //  int pts_index = 0;
        //  for (std::size_t i = 0; i < local_tris.size(); ++i)
        //  {
        //      tris.block(tri_index, 0, local_tris[i].rows(), local_tris[i].cols()) = local_tris[i].array() + pts_index;
        //      tri_index += local_tris[i].rows();
 
        //      pts.block(pts_index, 0, local_pts[i].rows(), local_pts[i].cols()) = local_pts[i];
        //      pts_index += local_pts[i].rows();
        //  }
        // }
 
        void NCMesh2D::set_body_ids(const std::vector<int> &body_ids)
        {
            assert(body_ids.size() == n_faces());
            for (int i = 0; i < body_ids.size(); i++)
            {
                elements[valid_to_all_elem(i)].body_id = body_ids[i];
            }
        }
 
        void NCMesh2D::set_boundary_ids(const std::vector<int> &boundary_ids)
        {
            assert(boundary_ids.size() == n_edges());
            for (int i = 0; i < boundary_ids.size(); i++)
            {
                edges[valid_to_all_edge(i)].boundary_id = boundary_ids[i];
            }
        }
 
        void NCMesh2D::compute_body_ids(const std::function<int(const size_t, const std::vector<int> &, const RowVectorNd &)> &marker)
        {
            body_ids_.resize(n_faces());
            std::fill(body_ids_.begin(), body_ids_.end(), -1);
 
            for (int e = 0; e < n_faces(); ++e)
            {
                const auto bary = face_barycenter(e);
                body_ids_[e] = marker(e, element_vertices(e), bary);
                elements[valid_to_all_elem(e)].body_id = body_ids_[e];
            }
        }
 
        void NCMesh2D::compute_boundary_ids(const std::function<int(const size_t, const std::vector<int> &, const RowVectorNd &, bool)> &marker)
        {
            boundary_ids_.resize(n_edges());
 
            for (int e = 0; e < n_edges(); ++e)
            {
                bool is_boundary = is_boundary_edge(e);
                const auto p = edge_barycenter(e);
 
                std::vector<int> vs = {edge_vertex(e, 0), edge_vertex(e, 1)};
                std::sort(vs.begin(), vs.end());
                boundary_ids_[e] = marker(e, vs, p, is_boundary);
                edges[valid_to_all_edge(e)].boundary_id = boundary_ids_[e];
            }
        }
 
    } // namespace mesh
} // namespace polyfem