#include "MeshUtils.hpp"

#include "libslic3r/Tesselate.hpp"
#include "libslic3r/TriangleMesh.hpp"
#include "libslic3r/TriangleMeshSlicer.hpp"
#include "libslic3r/ClipperUtils.hpp"
#include "libslic3r/Model.hpp"

#include "slic3r/GUI/GUI_App.hpp"
#include "slic3r/GUI/Plater.hpp"
#include "slic3r/GUI/Camera.hpp"
#include "slic3r/GUI/CameraUtils.hpp"

#include <GL/glew.h>

#include <igl/unproject.h>
#include "CameraUtils.hpp"


namespace Slic3r { namespace GUI {
MeshClipper::~MeshClipper() {
    reset();
}

void MeshClipper::set_behaviour(bool fill_cut, double contour_width)
{
    if (fill_cut != m_fill_cut || !is_approx(contour_width, m_contour_width))
        reset();
    m_fill_cut      = fill_cut;
    m_contour_width = contour_width;
}

void MeshClipper::set_plane(const ClippingPlane &plane)
{
    if (m_plane != plane) {
        m_plane = plane;
        reset();
    }
}

void MeshClipper::set_limiting_plane(const ClippingPlane& plane)
{
    if (m_limiting_plane != plane) {
        m_limiting_plane = plane;
        reset();
    }
}

void MeshClipper::set_mesh(const TriangleMesh& mesh)
{
    if (m_mesh != &mesh) {
        m_mesh = &mesh;
        reset();
    }
}

void MeshClipper::set_negative_mesh(const TriangleMesh& mesh)
{
    if (m_negative_mesh != &mesh) {
        m_negative_mesh = &mesh;
        reset();
    }
}



void MeshClipper::set_transformation(const Geometry::Transformation& trafo)
{
    if (! m_trafo.get_matrix().isApprox(trafo.get_matrix())) {
        m_trafo = trafo;
        reset();
    }
}

void MeshClipper::render_cut(const ColorRGBA &color, const std::vector<size_t> *ignore_idxs)
{
    if (!m_result) recalculate_triangles();
    GLShaderProgram *curr_shader = wxGetApp().get_current_shader();
    if (curr_shader != nullptr) curr_shader->stop_using();

    GLShaderProgram *shader = wxGetApp().get_shader("flat");
    if (shader != nullptr) {
        shader->start_using();
        const Camera &camera = wxGetApp().plater()->get_camera();
        shader->set_uniform("view_model_matrix", camera.get_view_matrix());
        shader->set_uniform("projection_matrix", camera.get_projection_matrix());
        for (size_t i = 0; i < m_result->cut_islands.size(); ++i) {
            if (ignore_idxs && std::binary_search(ignore_idxs->begin(), ignore_idxs->end(), i)) continue;
            auto isl = m_result->cut_islands[i];
            ColorRGBA  gray{0.5f, 0.5f, 0.5f, 1.f};
            isl->model.set_color(-1, isl->disabled ? gray.get_data() : color.get_data());
            isl->model.render();
        }
        shader->stop_using();
    }

    if (curr_shader != nullptr) curr_shader->start_using();
}

void MeshClipper::render_contour(const ColorRGBA &color, const std::vector<size_t> *ignore_idxs)
{
    if (!m_result) recalculate_triangles();

    GLShaderProgram *curr_shader = wxGetApp().get_current_shader();
    if (curr_shader != nullptr) curr_shader->stop_using();

    GLShaderProgram *shader = wxGetApp().get_shader("flat");
    if (shader != nullptr) {
        shader->start_using();
        const Camera &camera = wxGetApp().plater()->get_camera();
        shader->set_uniform("view_model_matrix", camera.get_view_matrix());
        shader->set_uniform("projection_matrix", camera.get_projection_matrix());
        for (size_t i = 0; i < m_result->cut_islands.size(); ++i) {
            if (ignore_idxs && std::binary_search(ignore_idxs->begin(), ignore_idxs->end(), i)) continue;
            auto isl = m_result->cut_islands[i];
            ColorRGBA  red{1.0f, 0.f, 0.f, 1.f};
            isl->model_expanded.set_color(-1, isl->disabled ? red.get_data() : color.get_data());
            isl->model_expanded.render();
        }
        shader->stop_using();
    }

    if (curr_shader != nullptr)
        curr_shader->start_using();
}

int MeshClipper::is_projection_inside_cut(const Vec3d &point_in) const
{
    if (!m_result || m_result->cut_islands.empty())
        return -1;
    Vec3d point = m_result->trafo.inverse() * point_in;
    Point pt_2d = Point::new_scale(Vec2d(point.x(), point.y()));

    for (int i = 0; i < int(m_result->cut_islands.size()); ++i) {
        auto isl = m_result->cut_islands[i];
        if (isl->expoly_bb.contains(pt_2d) && isl->expoly.contains(pt_2d))
            return i; // TODO: handle intersecting contours
    }
    return -1;
}

bool MeshClipper::has_valid_contour() const
{
    return m_result && std::any_of(m_result->cut_islands.begin(), m_result->cut_islands.end(), [](CutIsland *isl) { return isl &&!isl->expoly.empty(); });
}

std::vector<Vec3d> MeshClipper::point_per_contour() const {
    std::vector<Vec3d> out;
    if (m_result == std::nullopt) {
        return out;
    }
    assert(m_result);
    for (auto isl : m_result->cut_islands) {
        assert(isl->expoly.contour.size() > 2);
        // Now return a point lying inside the contour but not in a hole.
        // We do this by taking a point lying close to the edge, repeating
        // this several times for different edges and distances from them.
        // (We prefer point not extremely close to the border.
        bool   done = false;
        Vec2d  p;
        size_t i = 1;
        while (i < isl->expoly.contour.size()) {
            const Vec2d &a = unscale(isl->expoly.contour.points[i - 1]);
            const Vec2d &b = unscale(isl->expoly.contour.points[i]);
            Vec2d        n = (b - a).normalized();
            std::swap(n.x(), n.y());
            n.x()    = -1 * n.x();
            double f = 10.;
            while (f > 0.05) {
                p = (0.5 * (b + a)) + f * n;
                if (isl->expoly.contains(Point::new_scale(p))) {
                    done = true;
                    break;
                }
                f = f / 10.;
            }
            if (done) break;
            i += std::max(size_t(2), isl->expoly.contour.size() / 5);
        }
        // If the above failed, just return the centroid, regardless of whether
        // it is inside the contour or in a hole (we must return something).
        Vec2d c = done ? p : unscale(isl->expoly.contour.centroid());
        out.emplace_back(m_result->trafo * Vec3d(c.x(), c.y(), 0.));
    }
    return out;
}

void MeshClipper::recalculate_triangles()
{
    m_result = ClipResult();

    auto        plane_mesh  = Eigen::Hyperplane<double, 3>(m_plane.get_normal(), -m_plane.distance(Vec3d::Zero())).transform(m_trafo.get_matrix().inverse());
    const Vec3d up          = plane_mesh.normal();
    const float height_mesh = -plane_mesh.offset();

    // Now do the cutting
    MeshSlicingParams slicing_params;
    slicing_params.trafo.rotate(Eigen::Quaternion<double, Eigen::DontAlign>::FromTwoVectors(up, Vec3d::UnitZ()));

    ExPolygons expolys;

    // if (m_csgmesh.empty()) {
    if (m_mesh) {
        expolys = union_ex(slice_mesh(m_mesh->its, height_mesh, slicing_params));
    }
    if (m_negative_mesh && !m_negative_mesh->empty()) {
        const ExPolygons neg_expolys = union_ex(slice_mesh(m_negative_mesh->its, height_mesh, slicing_params));
        expolys                      = diff_ex(expolys, neg_expolys);
    }

    // Triangulate and rotate the cut into world coords:
    Eigen::Quaterniond q;
    q.setFromTwoVectors(Vec3d::UnitZ(), up);
    Transform3d tr = Transform3d::Identity();
    tr.rotate(q);
    tr = m_trafo.get_matrix() * tr;

    m_result->trafo = tr;

    if (m_limiting_plane != ClippingPlane::ClipsNothing()) {
        // Now remove whatever ended up below the limiting plane (e.g. sinking objects).
        // First transform the limiting plane from world to mesh coords.
        // Note that inverse of tr transforms the plane from world to horizontal.
        const Vec3d normal_old = m_limiting_plane.get_normal().normalized();
        const Vec3d normal_new = (tr.matrix().block<3, 3>(0, 0).transpose() * normal_old).normalized();

        // normal_new should now be the plane normal in mesh coords. To find the offset,
        // transform a point and set offset so it belongs to the transformed plane.
        Vec3d        pt           = Vec3d::Zero();
        const double plane_offset = m_limiting_plane.get_data()[3];
        if (std::abs(normal_old.z()) > 0.5) // normal is normalized, at least one of the coords if larger than sqrt(3)/3 = 0.57
            pt.z() = -plane_offset / normal_old.z();
        else if (std::abs(normal_old.y()) > 0.5)
            pt.y() = -plane_offset / normal_old.y();
        else
            pt.x() = -plane_offset / normal_old.x();
        pt                  = tr.inverse() * pt;
        const double offset = -(normal_new.dot(pt));

        if (std::abs(normal_old.dot(m_plane.get_normal().normalized())) > 0.99) {
            // The cuts are parallel, show all or nothing.
            if (normal_old.dot(m_plane.get_normal().normalized()) < 0.0 && offset < height_mesh) expolys.clear();
        } else {
            // The cut is a horizontal plane defined by z=height_mesh.
            // ax+by+e=0 is the line of intersection with the limiting plane.
            // Normalized so a^2 + b^2 = 1.
            const double len = std::hypot(normal_new.x(), normal_new.y());
            if (len == 0.) return;
            const double a = normal_new.x() / len;
            const double b = normal_new.y() / len;
            const double e = (normal_new.z() * height_mesh + offset) / len;

            // We need a half-plane to limit the cut. Get angle of the intersecting line.
            double angle = (b != 0.0) ? std::atan(-a / b) : ((a < 0.0) ? -0.5 * M_PI : 0.5 * M_PI);
            if (b > 0) // select correct half-plane
                angle += M_PI;

            // We'll take a big rectangle above x-axis and rotate and translate
            // it so it lies on our line. This will be the figure to subtract
            // from the cut. The coordinates must not overflow after the transform,
            // make the rectangle a bit smaller.
            const coord_t size = (std::numeric_limits<coord_t>::max() / 2 - scale_(std::max(std::abs(e * a), std::abs(e * b)))) / 4;
            Polygons      ep{Polygon({Point(-size, 0), Point(size, 0), Point(size, 2 * size), Point(-size, 2 * size)})};
            ep.front().rotate(angle);
            ep.front().translate(scale_(-e * a), scale_(-e * b));
            expolys = diff_ex(expolys, ep);
        }
    }

    tr.pretranslate(0.001 * m_plane.get_normal().normalized()); // to avoid z-fighting
    Transform3d tr2 = tr;
    tr2.pretranslate(0.002 * m_plane.get_normal().normalized());

    std::vector<Vec2f> triangles2d;

    m_result->cut_islands.resize(expolys.size());
    int isl_index = 0;
    for (const ExPolygon &exp : expolys) {
        triangles2d.clear();
        if (!m_result->cut_islands[isl_index]) {
            m_result->cut_islands[isl_index] = new CutIsland();
        }
        CutIsland* isl = m_result->cut_islands[isl_index];
        isl_index++;
        if (m_fill_cut) {
            triangles2d = triangulate_expolygon_2f(exp, m_trafo.get_matrix().matrix().determinant() < 0.);
            GLModel::InitializationData init_data; // GLModel::Geometry init_data;
            init_data.entities.push_back(GLModel::InitializationData::Entity());
            init_data.entities.back().type = GLModel::PrimitiveType::Triangles;
            init_data.entities.back().positions.reserve(triangles2d.size() * (init_data.entities.back().type == GLModel::PrimitiveType::Triangles ? 3 : 2));
            init_data.entities.back().normals.reserve(triangles2d.size() * (init_data.entities.back().type == GLModel::PrimitiveType::Triangles ? 3 : 2));
            init_data.entities.back().indices.reserve(triangles2d.size());
            /*init_data.format = {GLModel::Geometry::EPrimitiveType::Triangles, GLModel::Geometry::EVertexLayout::P3N3};
            init_data.reserve_vertices(triangles2d.size());
            init_data.reserve_indices(triangles2d.size());*/

            // vertices + indices
            for (auto it = triangles2d.cbegin(); it != triangles2d.cend(); it = it + 3) {
                /*init_data.add_vertex((Vec3f) (tr * Vec3d((*(it + 0)).x(), (*(it + 0)).y(), height_mesh)).cast<float>(), (Vec3f) up.cast<float>());
                init_data.add_vertex((Vec3f) (tr * Vec3d((*(it + 1)).x(), (*(it + 1)).y(), height_mesh)).cast<float>(), (Vec3f) up.cast<float>());
                init_data.add_vertex((Vec3f) (tr * Vec3d((*(it + 2)).x(), (*(it + 2)).y(), height_mesh)).cast<float>(), (Vec3f) up.cast<float>());
                const size_t idx = it - triangles2d.cbegin();
                init_data.add_triangle((unsigned int) idx, (unsigned int) idx + 1, (unsigned int) idx + 2);*/

                init_data.entities.back().positions.push_back((Vec3f) (tr * Vec3d((*(it + 0)).x(), (*(it + 0)).y(), height_mesh)).cast<float>());
                init_data.entities.back().normals.push_back((Vec3f) up.cast<float>());

                init_data.entities.back().positions.push_back((Vec3f) (tr * Vec3d((*(it + 1)).x(), (*(it + 1)).y(), height_mesh)).cast<float>());
                init_data.entities.back().normals.push_back((Vec3f) up.cast<float>());

                init_data.entities.back().positions.push_back((Vec3f) (tr * Vec3d((*(it + 2)).x(), (*(it + 2)).y(), height_mesh)).cast<float>());
                init_data.entities.back().normals.push_back((Vec3f) up.cast<float>());

                const size_t idx = it - triangles2d.cbegin();
                init_data.entities.back().indices.push_back((unsigned int) idx);
                init_data.entities.back().indices.push_back((unsigned int) idx + 1);
                init_data.entities.back().indices.push_back((unsigned int) idx + 2);
            }

            if (init_data.entities.back().indices.size() != 0) {
                isl->model.reset();
                isl->model.init_from(std::move(init_data));
            }
        }

        if (m_contour_width != 0. && !exp.contour.empty()) {
            triangles2d.clear();

            // The contours must not scale with the object. Check the scale factor
            // in the respective directions, create a scaled copy of the ExPolygon
            // offset it and then unscale the result again.

            Transform3d t   = tr;
            t.translation() = Vec3d::Zero();
            double scale_x  = (t * Vec3d::UnitX()).norm();
            double scale_y  = (t * Vec3d::UnitY()).norm();

            // To prevent overflow after scaling, downscale the input if needed:
            double  extra_scale = 1.;
            int32_t limit       = int32_t(
                std::min(std::numeric_limits<coord_t>::max() / (2. * std::max(1., scale_x)), std::numeric_limits<coord_t>::max() / (2. * std::max(1., scale_y))));
            int32_t max_coord = 0;
            for (const Point &pt : exp.contour) max_coord = std::max(max_coord, std::max(std::abs(pt.x()), std::abs(pt.y())));
            if (max_coord + m_contour_width >= limit) extra_scale = 0.9 * double(limit) / max_coord;

            ExPolygon exp_copy = exp;
            if (extra_scale != 1.) exp_copy.scale(extra_scale);
            exp_copy.scale(scale_x, scale_y);

            ExPolygons expolys_exp = offset_ex(exp_copy, scale_(m_contour_width));
            expolys_exp            = diff_ex(expolys_exp, ExPolygons({exp_copy}));

            for (ExPolygon &e : expolys_exp) {
                e.scale(1. / scale_x, 1. / scale_y);
                if (extra_scale != 1.) e.scale(1. / extra_scale);
            }

            triangles2d = triangulate_expolygons_2f(expolys_exp, m_trafo.get_matrix().matrix().determinant() < 0.);
            GLModel::InitializationData init_data; // GLModel::Geometry init_data;
            init_data.entities.push_back(GLModel::InitializationData::Entity());
            init_data.entities.back().type = GLModel::PrimitiveType::Triangles;
            init_data.entities.back().positions.reserve(triangles2d.size() * (init_data.entities.back().type == GLModel::PrimitiveType::Triangles ? 3 : 2));
            init_data.entities.back().normals.reserve(triangles2d.size() * (init_data.entities.back().type == GLModel::PrimitiveType::Triangles ? 3 : 2));
            init_data.entities.back().indices.reserve(triangles2d.size());
            /*GLModel::Geometry init_data = GLModel::Geometry();
            init_data.format            = {GLModel::Geometry::EPrimitiveType::Triangles, GLModel::Geometry::EVertexLayout::P3N3};
            init_data.reserve_vertices(triangles2d.size());
            init_data.reserve_indices(triangles2d.size());*/

            // vertices + indices
            for (auto it = triangles2d.cbegin(); it != triangles2d.cend(); it = it + 3) {
                init_data.entities.back().positions.push_back((Vec3f) (tr * Vec3d((*(it + 0)).x(), (*(it + 0)).y(), height_mesh)).cast<float>());
                init_data.entities.back().normals.push_back((Vec3f) up.cast<float>());

                init_data.entities.back().positions.push_back((Vec3f) (tr * Vec3d((*(it + 1)).x(), (*(it + 1)).y(), height_mesh)).cast<float>());
                init_data.entities.back().normals.push_back((Vec3f) up.cast<float>());

                init_data.entities.back().positions.push_back((Vec3f) (tr * Vec3d((*(it + 2)).x(), (*(it + 2)).y(), height_mesh)).cast<float>());
                init_data.entities.back().normals.push_back((Vec3f) up.cast<float>());

                const size_t idx = it - triangles2d.cbegin();
                init_data.entities.back().indices.push_back((unsigned int) idx);
                init_data.entities.back().indices.push_back((unsigned int) idx + 1);
                init_data.entities.back().indices.push_back((unsigned int) idx + 2);
            }

            if (init_data.entities.back().indices.size() != 0) { 
                isl->model_expanded.reset();
                isl->model_expanded.init_from(std::move(init_data));
            }
        }

        isl->expoly   = std::move(exp);
        isl->expoly_bb = get_extents(isl->expoly);

        Point centroid_scaled = isl->expoly.contour.centroid();
        Vec3d centroid_world  = m_result->trafo * Vec3d(unscale(centroid_scaled).x(), unscale(centroid_scaled).y(), 0.);
        isl->hash             = isl->expoly.contour.size() + size_t(std::abs(100. * centroid_world.x())) + size_t(std::abs(100. * centroid_world.y())) +
                   size_t(std::abs(100. * centroid_world.z()));
    }

    // Now sort the islands so they are in defined order. This is a hack needed by cut gizmo, which sometimes
    // flips the normal of the cut, in which case the contours stay the same but their order may change.
    std::sort(m_result->cut_islands.begin(), m_result->cut_islands.end(), [](CutIsland *a, CutIsland *b) { return a && b && a->hash < b->hash; });
}

void MeshClipper::reset()
{
    if (m_result) {
        for (auto it = m_result->cut_islands.begin(); it != m_result->cut_islands.end(); ++it) { 
            delete *it;
        }
        std::vector<CutIsland *>().swap(m_result->cut_islands);
    }
    m_result.reset();
}

Vec3f MeshRaycaster::get_triangle_normal(size_t facet_idx) const
{
    return m_normals[facet_idx];
}

MeshRaycaster::MeshRaycaster(const TriangleMesh &mesh)
    : m_emesh(mesh, true) // calculate epsilon for triangle-ray intersection from an average edge length
    , m_normals(its_face_normals(mesh.its))
{
    ;
}

void MeshRaycaster::line_from_mouse_pos_static(const Vec2d &mouse_pos, const Transform3d &trafo, const Camera &camera, Vec3d &point, Vec3d &direction)
{
    CameraUtils::ray_from_screen_pos(camera, mouse_pos, point, direction);
    Transform3d inv = trafo.inverse();
    point           = inv * point;
    direction       = inv.linear() * direction;
}

void MeshRaycaster::line_from_mouse_pos(const Vec2d& mouse_pos, const Transform3d& trafo, const Camera& camera,
                                        Vec3d& point, Vec3d& direction) const
{
    Matrix4d modelview = camera.get_view_matrix().matrix();
    Matrix4d projection= camera.get_projection_matrix().matrix();
    Vec4i viewport(camera.get_viewport().data());

    Vec3d pt1;
    Vec3d pt2;
    igl::unproject(Vec3d(mouse_pos(0), viewport[3] - mouse_pos(1), 0.),
                   modelview, projection, viewport, pt1);
    igl::unproject(Vec3d(mouse_pos(0), viewport[3] - mouse_pos(1), 1.),
                   modelview, projection, viewport, pt2);

    Transform3d inv = trafo.inverse();
    pt1 = inv * pt1;
    pt2 = inv * pt2;

    point = pt1;
    direction = (pt2-pt1).normalized();
}


bool MeshRaycaster::unproject_on_mesh(const Vec2d& mouse_pos, const Transform3d& trafo, const Camera& camera,
                                      Vec3f& position, Vec3f& normal, const ClippingPlane* clipping_plane,
                                      size_t* facet_idx, bool sinking_limit) const
{
    Vec3d point;
    Vec3d direction;
    line_from_mouse_pos(mouse_pos, trafo, camera, point, direction);

    std::vector<sla::IndexedMesh::hit_result> hits = m_emesh.query_ray_hits(point, direction);

    if (hits.empty())
        return false; // no intersection found

    unsigned i = 0;

    // Remove points that are obscured or cut by the clipping plane.
    // Also, remove anything below the bed (sinking objects).
    for (i=0; i<hits.size(); ++i) {
        Vec3d transformed_hit = trafo * hits[i].position();
        if (transformed_hit.z() >= (sinking_limit ? SINKING_Z_THRESHOLD : -std::numeric_limits<double>::max()) &&
            (!clipping_plane || !clipping_plane->is_point_clipped(transformed_hit)))
            break;
    }

    if (i==hits.size() || (hits.size()-i) % 2 != 0) {
        // All hits are either clipped, or there is an odd number of unclipped
        // hits - meaning the nearest must be from inside the mesh.
        return false;
    }

    // Now stuff the points in the provided vector and calculate normals if asked about them:
    position = hits[i].position().cast<float>();
    normal = hits[i].normal().cast<float>();

    if (facet_idx)
        *facet_idx = hits[i].face();

    return true;
}


bool MeshRaycaster::intersects_line(Vec3d point, Vec3d direction, const Transform3d &trafo) const
{
    Transform3d trafo_inv = trafo.inverse();
    Vec3d       to        = trafo_inv * (point + direction);
    point                 = trafo_inv * point;
    direction             = (to - point).normalized();

    std::vector<sla::IndexedMesh::hit_result> hits     = m_emesh.query_ray_hits(point, direction);
    std::vector<sla::IndexedMesh::hit_result> neg_hits = m_emesh.query_ray_hits(point, -direction);

    return !hits.empty() || !neg_hits.empty();
}

std::vector<unsigned> MeshRaycaster::get_unobscured_idxs(const Geometry::Transformation &trafo,
                                                         const Camera &                  camera,
                                                         const std::vector<Vec3f> &      points,
                                                       const ClippingPlane* clipping_plane) const
{
    std::vector<unsigned> out;

    const Transform3d& instance_matrix_no_translation_no_scaling = trafo.get_matrix(true,false,true);
    Vec3d direction_to_camera = -camera.get_dir_forward();
    Vec3d direction_to_camera_mesh = (instance_matrix_no_translation_no_scaling.inverse() * direction_to_camera).normalized().eval();
    direction_to_camera_mesh = direction_to_camera_mesh.cwiseProduct(trafo.get_scaling_factor());
    const Transform3d inverse_trafo = trafo.get_matrix().inverse();

    for (size_t i=0; i<points.size(); ++i) {
        const Vec3f& pt = points[i];
        if (clipping_plane && clipping_plane->is_point_clipped(pt.cast<double>()))
            continue;

        bool is_obscured = false;
        // Cast a ray in the direction of the camera and look for intersection with the mesh:
        std::vector<sla::IndexedMesh::hit_result> hits;
        // Offset the start of the ray by EPSILON to account for numerical inaccuracies.
        hits = m_emesh.query_ray_hits((inverse_trafo * pt.cast<double>() + direction_to_camera_mesh * EPSILON),
                                      direction_to_camera_mesh);

        if (! hits.empty()) {
            // If the closest hit facet normal points in the same direction as the ray,
            // we are looking through the mesh and should therefore discard the point:
            if (hits.front().normal().dot(direction_to_camera_mesh.cast<double>()) > 0)
                is_obscured = true;

            // Eradicate all hits that the caller wants to ignore
            for (unsigned j=0; j<hits.size(); ++j) {
                if (clipping_plane && clipping_plane->is_point_clipped(trafo.get_matrix() * hits[j].position())) {
                    hits.erase(hits.begin()+j);
                    --j;
                }
            }

            // FIXME: the intersection could in theory be behind the camera, but as of now we only have camera direction.
            // Also, the threshold is in mesh coordinates, not in actual dimensions.
            if (! hits.empty())
                is_obscured = true;
        }
        if (! is_obscured)
            out.push_back(i);
    }
    return out;
}

bool MeshRaycaster::closest_hit(
    const Vec2d &mouse_pos, const Transform3d &trafo, const Camera &camera, Vec3f &position, Vec3f &normal, const ClippingPlane *clipping_plane, size_t *facet_idx) const
{
    Vec3d point;
    Vec3d direction;
    line_from_mouse_pos(mouse_pos, trafo, camera, point, direction);

    auto hits = m_emesh.query_ray_hits(point, direction.normalized());

    if (hits.empty()) return false; // no intersection found

    size_t hit_id = 0;
    if (clipping_plane != nullptr) {
        while (hit_id < hits.size() && clipping_plane->is_point_clipped(trafo * hits[hit_id].position())) { 
            ++hit_id;
        }
    }

    if (hit_id == hits.size())
        return false; // all points are obscured or cut by the clipping plane.

    auto &hit = hits[hit_id];

    position = hit.position().cast<float>();
    normal   = hit.normal().cast<float>();

    if (facet_idx != nullptr)
        *facet_idx = hit.face();

    return true;
}

Vec3f MeshRaycaster::get_closest_point(const Vec3f& point, Vec3f* normal) const
{
    int idx = 0;
    Vec3d closest_point;
    m_emesh.squared_distance(point.cast<double>(), idx, closest_point);
    if (normal)
        *normal = m_normals[idx];

    return closest_point.cast<float>();
}

int MeshRaycaster::get_closest_facet(const Vec3f &point) const
{
    int   facet_idx = 0;
    Vec3d closest_point;
    m_emesh.squared_distance(point.cast<double>(), facet_idx, closest_point);
    return facet_idx;
}

} // namespace GUI
} // namespace Slic3r