diff --git a/src/libslic3r/Fill/Fill.cpp b/src/libslic3r/Fill/Fill.cpp
index a3e4aee31..e6b820188 100644
--- a/src/libslic3r/Fill/Fill.cpp
+++ b/src/libslic3r/Fill/Fill.cpp
@@ -11,6 +11,7 @@
 
 #include "FillBase.hpp"
 #include "FillRectilinear.hpp"
+#include "FillLightning.hpp"
 
 namespace Slic3r {
 
@@ -318,7 +319,7 @@ void export_group_fills_to_svg(const char *path, const std::vector<SurfaceFill>
 #endif
 
 // friend to Layer
-void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive::Octree* support_fill_octree)
+void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive::Octree* support_fill_octree, FillLightning::Generator* lightning_generator)
 {
 	for (LayerRegion *layerm : m_regions)
 		layerm->fills.clear();
@@ -348,6 +349,9 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
         f->angle 	= surface_fill.params.angle;
         f->adapt_fill_octree = (surface_fill.params.pattern == ipSupportCubic) ? support_fill_octree : adaptive_fill_octree;
 
+        if (surface_fill.params.pattern == ipLightning)
+            dynamic_cast<FillLightning::Filler*>(f.get())->generator = lightning_generator;
+
         // calculate flow spacing for infill pattern generation
         bool using_internal_flow = ! surface_fill.surface.is_solid() && ! surface_fill.params.bridge;
         double link_max_length = 0.;
diff --git a/src/libslic3r/Fill/FillBase.cpp b/src/libslic3r/Fill/FillBase.cpp
index 7ca0699c0..c4f8d6f08 100644
--- a/src/libslic3r/Fill/FillBase.cpp
+++ b/src/libslic3r/Fill/FillBase.cpp
@@ -46,9 +46,7 @@ Fill* Fill::new_from_type(const InfillPattern type)
     case ipAdaptiveCubic:       return new FillAdaptive::Filler();
     case ipSupportCubic:        return new FillAdaptive::Filler();
     case ipSupportBase:         return new FillSupportBase();
-#if HAS_LIGHTNING_INFILL
     case ipLightning:           return new FillLightning::Filler();
-#endif // HAS_LIGHTNING_INFILL
     default: throw Slic3r::InvalidArgument("unknown type");
     }
 }
diff --git a/src/libslic3r/Fill/FillLightning.cpp b/src/libslic3r/Fill/FillLightning.cpp
index 447fd8057..dd2189e6b 100644
--- a/src/libslic3r/Fill/FillLightning.cpp
+++ b/src/libslic3r/Fill/FillLightning.cpp
@@ -1,29 +1,34 @@
 #include "../Print.hpp"
+#include "../ShortestPath.hpp"
 
 #include "FillLightning.hpp"
 #include "Lightning/Generator.hpp"
-#include "../Surface.hpp"
-
-#include <cstdlib>
-#include <cmath>
-#include <algorithm>
-#include <numeric>
 
 namespace Slic3r::FillLightning {
 
-Polylines Filler::fill_surface(const Surface *surface, const FillParams &params)
+void Filler::_fill_surface_single(
+    const FillParams              &params,
+    unsigned int                   thickness_layers,
+    const std::pair<float, Point> &direction,
+    ExPolygon                      expolygon,
+    Polylines                     &polylines_out)
 {
-    const Layer &layer = generator->getTreesForLayer(this->layer_id);
-    return layer.convertToLines(to_polygons(surface->expolygon), generator->infilll_extrusion_width());
+    const Layer &layer      = generator->getTreesForLayer(this->layer_id);
+    Polylines    fill_lines = layer.convertToLines(to_polygons(expolygon), scaled<coord_t>(0.5 * this->spacing - this->overlap));
+
+    if (params.dont_connect() || fill_lines.size() <= 1) {
+        append(polylines_out, chain_polylines(std::move(fill_lines)));
+    } else
+        connect_infill(std::move(fill_lines), expolygon, polylines_out, this->spacing, params);
 }
 
 void GeneratorDeleter::operator()(Generator *p) {
     delete p;
 }
 
-GeneratorPtr build_generator(const PrintObject &print_object)
+GeneratorPtr build_generator(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback)
 {
-    return GeneratorPtr(new Generator(print_object));
+    return GeneratorPtr(new Generator(print_object, throw_on_cancel_callback));
 }
 
 } // namespace Slic3r::FillAdaptive
diff --git a/src/libslic3r/Fill/FillLightning.hpp b/src/libslic3r/Fill/FillLightning.hpp
index b4e7e35f1..6e672783a 100644
--- a/src/libslic3r/Fill/FillLightning.hpp
+++ b/src/libslic3r/Fill/FillLightning.hpp
@@ -14,7 +14,7 @@ class Generator;
 struct GeneratorDeleter { void operator()(Generator *p); };
 using  GeneratorPtr = std::unique_ptr<Generator, GeneratorDeleter>;
 
-GeneratorPtr build_generator(const PrintObject &print_object);
+GeneratorPtr build_generator(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback);
 
 class Filler : public Slic3r::Fill
 {
@@ -24,8 +24,13 @@ public:
     Generator   *generator { nullptr };
 protected:
     Fill* clone() const override { return new Filler(*this); }
-    // Perform the fill.
-    Polylines fill_surface(const Surface *surface, const FillParams &params) override;
+
+    void _fill_surface_single(const FillParams              &params,
+                              unsigned int                   thickness_layers,
+                              const std::pair<float, Point> &direction,
+                              ExPolygon                      expolygon,
+                              Polylines &polylines_out) override;
+
     // Let the G-code export reoder the infill lines.
 	bool no_sort() const override { return false; }
 };
diff --git a/src/libslic3r/Fill/FillRectilinear.cpp b/src/libslic3r/Fill/FillRectilinear.cpp
index 69476175e..bcff05197 100644
--- a/src/libslic3r/Fill/FillRectilinear.cpp
+++ b/src/libslic3r/Fill/FillRectilinear.cpp
@@ -406,13 +406,15 @@ public:
         // for the infill pattern, don't cut the corners.
         // default miterLimt = 3
         //double miterLimit = 10.;
-        assert(aoffset1 < 0);
+        // FIXME: Resolve properly the cases when it is constructed with aoffset1 = 0 and aoffset2 = 0,
+        //        that is used in sample_grid_pattern() for Lightning infill.
+        // assert(aoffset1 < 0);
         assert(aoffset2 <= 0);
-        assert(aoffset2 == 0 || aoffset2 < aoffset1);
+        // assert(aoffset2 == 0 || aoffset2 < aoffset1);
 //        bool sticks_removed = 
         remove_sticks(polygons_src);
 //        if (sticks_removed) BOOST_LOG_TRIVIAL(error) << "Sticks removed!";
-        polygons_outer = offset(polygons_src, float(aoffset1), ClipperLib::jtMiter, miterLimit);
+        polygons_outer = aoffset1 == 0 ? polygons_src : offset(polygons_src, float(aoffset1), ClipperLib::jtMiter, miterLimit);
         if (aoffset2 < 0)
             polygons_inner = shrink(polygons_outer, float(aoffset1 - aoffset2), ClipperLib::jtMiter, miterLimit);
 		// Filter out contours with zero area or small area, contours with 2 points only.
diff --git a/src/libslic3r/Fill/Lightning/DistanceField.cpp b/src/libslic3r/Fill/Lightning/DistanceField.cpp
index 6df1d043c..ef407664c 100644
--- a/src/libslic3r/Fill/Lightning/DistanceField.cpp
+++ b/src/libslic3r/Fill/Lightning/DistanceField.cpp
@@ -5,44 +5,60 @@
 #include "../FillRectilinear.hpp"
 #include "../../ClipperUtils.hpp"
 
+#include <tbb/parallel_for.h>
+
 namespace Slic3r::FillLightning
 {
 
 constexpr coord_t radius_per_cell_size = 6;  // The cell-size should be small compared to the radius, but not so small as to be inefficient.
 
-DistanceField::DistanceField(const coord_t& radius, const Polygons& current_outline, const Polygons& current_overhang) : 
-    m_cell_size(radius / radius_per_cell_size), 
-    m_supporting_radius(radius)
+DistanceField::DistanceField(const coord_t& radius, const Polygons& current_outline, const BoundingBox& current_outlines_bbox, const Polygons& current_overhang) :
+    m_cell_size(radius / radius_per_cell_size),
+    m_supporting_radius(radius),
+    m_unsupported_points_bbox(current_outlines_bbox)
 {
-    m_supporting_radius2 = double(radius) * double(radius);
+    m_supporting_radius2 = Slic3r::sqr(int64_t(radius));
     // Sample source polygons with a regular grid sampling pattern.
-    for (const ExPolygon &expoly : union_ex(current_outline)) {
-        for (const Point &p : sample_grid_pattern(expoly, m_cell_size)) {
-            // Find a squared distance to the source expolygon boundary.
-            double d2 = std::numeric_limits<double>::max();
-            for (size_t icontour = 0; icontour <= expoly.holes.size(); ++ icontour) {
-                const Polygon &contour = icontour == 0 ? expoly.contour : expoly.holes[icontour - 1];
-                if (contour.size() > 2) {
-                    Point prev = contour.points.back();
-                    for (const Point &p2 : contour.points) {
-                        d2 = std::min(d2, Line::distance_to_squared(p, prev, p2));
-                        prev = p2;
+    for (const ExPolygon &expoly : union_ex(current_overhang)) {
+        const Points sampled_points               = sample_grid_pattern(expoly, m_cell_size);
+        const size_t unsupported_points_prev_size = m_unsupported_points.size();
+        m_unsupported_points.resize(unsupported_points_prev_size + sampled_points.size());
+
+        tbb::parallel_for(tbb::blocked_range<size_t>(0, sampled_points.size()), [&self = *this, &expoly = std::as_const(expoly), &sampled_points = std::as_const(sampled_points), &unsupported_points_prev_size = std::as_const(unsupported_points_prev_size)](const tbb::blocked_range<size_t> &range) -> void {
+            for (size_t sp_idx = range.begin(); sp_idx < range.end(); ++sp_idx) {
+                const Point &sp = sampled_points[sp_idx];
+                // Find a squared distance to the source expolygon boundary.
+                double d2 = std::numeric_limits<double>::max();
+                for (size_t icontour = 0; icontour <= expoly.holes.size(); ++icontour) {
+                    const Polygon &contour = icontour == 0 ? expoly.contour : expoly.holes[icontour - 1];
+                    if (contour.size() > 2) {
+                        Point prev = contour.points.back();
+                        for (const Point &p2 : contour.points) {
+                            d2   = std::min(d2, Line::distance_to_squared(sp, prev, p2));
+                            prev = p2;
+                        }
                     }
                 }
+                self.m_unsupported_points[unsupported_points_prev_size + sp_idx] = {sp, coord_t(std::sqrt(d2))};
+                assert(self.m_unsupported_points_bbox.contains(sp));
             }
-            m_unsupported_points.emplace_back(p, sqrt(d2));
-        }
+        }); // end of parallel_for
     }
-    m_unsupported_points.sort([&radius](const UnsupportedCell &a, const UnsupportedCell &b) {
+    std::stable_sort(m_unsupported_points.begin(), m_unsupported_points.end(), [&radius](const UnsupportedCell &a, const UnsupportedCell &b) {
         constexpr coord_t prime_for_hash = 191;
         return std::abs(b.dist_to_boundary - a.dist_to_boundary) > radius ?
                a.dist_to_boundary < b.dist_to_boundary :
                (PointHash{}(a.loc) % prime_for_hash) < (PointHash{}(b.loc) % prime_for_hash);
         });
-    for (auto it = m_unsupported_points.begin(); it != m_unsupported_points.end(); ++it) {
-        UnsupportedCell& cell = *it;
-        m_unsupported_points_grid.emplace(Point{ cell.loc.x() / m_cell_size, cell.loc.y() / m_cell_size }, it);
-    }
+
+    m_unsupported_points_erased.resize(m_unsupported_points.size());
+    std::fill(m_unsupported_points_erased.begin(), m_unsupported_points_erased.end(), false);
+
+    m_unsupported_points_grid.initialize(m_unsupported_points, [&self = std::as_const(*this)](const Point &p) -> Point { return self.to_grid_point(p); });
+
+    // Because the distance between two points is at least one axis equal to m_cell_size, every cell
+    // in m_unsupported_points_grid contains exactly one point.
+    assert(m_unsupported_points.size() == m_unsupported_points_grid.size());
 }
 
 void DistanceField::update(const Point& to_node, const Point& added_leaf)
@@ -60,17 +76,24 @@ void DistanceField::update(const Point& to_node, const Point& added_leaf)
         grid.merge(to_node + iextent);
         grid.merge(added_leaf - iextent);
         grid.merge(added_leaf + iextent);
-        grid.min /= m_cell_size;
-        grid.max /= m_cell_size;
+
+        // Clip grid by m_unsupported_points_bbox. Mainly to ensure that grid.min is a non-negative value.
+        grid.min.x() = std::max(grid.min.x(), m_unsupported_points_bbox.min.x());
+        grid.min.y() = std::max(grid.min.y(), m_unsupported_points_bbox.min.y());
+        grid.max.x() = std::min(grid.max.x(), m_unsupported_points_bbox.max.x());
+        grid.max.y() = std::min(grid.max.y(), m_unsupported_points_bbox.max.y());
+
+        grid.min = this->to_grid_point(grid.min);
+        grid.max = this->to_grid_point(grid.max);
     }
 
+    Point grid_addr;
     Point grid_loc;
-    for (coord_t row = grid.min.y(); row <= grid.max.y(); ++ row) {
-        grid_loc.y() = row * m_cell_size;
-        for (coord_t col = grid.min.x(); col <= grid.max.y(); ++ col) {
-            grid_loc.x() = col * m_cell_size;
+    for (grid_addr.y() = grid.min.y(); grid_addr.y() <= grid.max.y(); ++grid_addr.y()) {
+        for (grid_addr.x() = grid.min.x(); grid_addr.x() <= grid.max.x(); ++grid_addr.x()) {
+            grid_loc = this->from_grid_point(grid_addr);
             // Test inside a circle at the new leaf.
-            if ((grid_loc - added_leaf).cast<double>().squaredNorm() > m_supporting_radius2) {
+            if ((grid_loc - added_leaf).cast<int64_t>().squaredNorm() > m_supporting_radius2) {
                 // Not inside a circle at the end of the new leaf.
                 // Test inside a rotated rectangle.
                 Vec2d  vx = (grid_loc - to_node).cast<double>();
@@ -84,10 +107,29 @@ void DistanceField::update(const Point& to_node, const Point& added_leaf)
             }
             // Inside a circle at the end of the new leaf, or inside a rotated rectangle.
             // Remove unsupported leafs at this grid location.
-            if (auto it = m_unsupported_points_grid.find(grid_loc); it != m_unsupported_points_grid.end()) {
-                std::list<UnsupportedCell>::iterator& list_it = it->second;
-                UnsupportedCell& cell = *list_it;
-                if ((cell.loc - added_leaf).cast<double>().squaredNorm() <= m_supporting_radius2) {
+            if (const size_t cell_idx = m_unsupported_points_grid.find_cell_idx(grid_addr); cell_idx != std::numeric_limits<size_t>::max()) {
+                const UnsupportedCell &cell = m_unsupported_points[cell_idx];
+                if ((cell.loc - added_leaf).cast<int64_t>().squaredNorm() <= m_supporting_radius2) {
+                    m_unsupported_points_erased[cell_idx] = true;
+                    m_unsupported_points_grid.mark_erased(grid_addr);
+                }
+            }
+        }
+    }
+}
+
+#if 0
+void DistanceField::update(const Point &to_node, const Point &added_leaf)
+{
+    const Point supporting_radius_point(m_supporting_radius, m_supporting_radius);
+    const BoundingBox grid(this->to_grid_point(added_leaf - supporting_radius_point), this->to_grid_point(added_leaf + supporting_radius_point));
+
+    for (coord_t grid_y = grid.min.y(); grid_y <= grid.max.y(); ++grid_y) {
+        for (coord_t grid_x = grid.min.x(); grid_x <= grid.max.x(); ++grid_x) {
+            if (auto it = m_unsupported_points_grid.find({grid_x, grid_y}); it != m_unsupported_points_grid.end()) {
+                std::list<UnsupportedCell>::iterator &list_it = it->second;
+                UnsupportedCell                      &cell    = *list_it;
+                if ((cell.loc - added_leaf).cast<int64_t>().squaredNorm() <= m_supporting_radius2) {
                     m_unsupported_points.erase(list_it);
                     m_unsupported_points_grid.erase(it);
                 }
@@ -95,5 +137,6 @@ void DistanceField::update(const Point& to_node, const Point& added_leaf)
         }
     }
 }
+#endif
 
 } // namespace Slic3r::FillLightning
diff --git a/src/libslic3r/Fill/Lightning/DistanceField.hpp b/src/libslic3r/Fill/Lightning/DistanceField.hpp
index 7fdce434c..1a47ee6ca 100644
--- a/src/libslic3r/Fill/Lightning/DistanceField.hpp
+++ b/src/libslic3r/Fill/Lightning/DistanceField.hpp
@@ -4,6 +4,7 @@
 #ifndef LIGHTNING_DISTANCE_FIELD_H
 #define LIGHTNING_DISTANCE_FIELD_H
 
+#include "../../BoundingBox.hpp"
 #include "../../Point.hpp"
 #include "../../Polygon.hpp"
 
@@ -29,7 +30,7 @@ public:
      * \param current_overhang The overhang that needs to be supported on this
      * layer.
      */
-    DistanceField(const coord_t& radius, const Polygons& current_outline, const Polygons& current_overhang);
+    DistanceField(const coord_t& radius, const Polygons& current_outline, const BoundingBox& current_outlines_bbox, const Polygons& current_overhang);
     
     /*!
      * Gets the next unsupported location to be supported by a new branch.
@@ -37,11 +38,17 @@ public:
      * \return ``true`` if successful, or ``false`` if there are no more points
      * to consider.
      */
-    bool tryGetNextPoint(Point* p) const {
-        if (m_unsupported_points.empty())
-            return false;
-        *p = m_unsupported_points.front().loc;
-        return true;
+    bool tryGetNextPoint(Point *out_unsupported_location, size_t *out_unsupported_cell_idx, const size_t start_idx = 0) const
+    {
+        for (size_t point_idx = start_idx; point_idx < m_unsupported_points.size(); ++point_idx) {
+            if (!m_unsupported_points_erased[point_idx]) {
+                *out_unsupported_cell_idx = point_idx;
+                *out_unsupported_location = m_unsupported_points[point_idx].loc;
+                return true;
+            }
+        }
+
+        return false;
     }
 
     /*!
@@ -69,14 +76,13 @@ protected:
      * branch of a tree.
      */
     coord_t m_supporting_radius;
-    double  m_supporting_radius2;
+    int64_t m_supporting_radius2;
 
     /*!
      * Represents a small discrete area of infill that needs to be supported.
      */
     struct UnsupportedCell
     {
-        UnsupportedCell(Point loc, coord_t dist_to_boundary) : loc(loc), dist_to_boundary(dist_to_boundary) {}
         // The position of the center of this cell.
         Point loc;
         // How far this cell is removed from the ``current_outline`` polygon, the edge of the infill area.
@@ -86,13 +92,110 @@ protected:
     /*!
      * Cells which still need to be supported at some point.
      */
-    std::list<UnsupportedCell> m_unsupported_points;
+    std::vector<UnsupportedCell> m_unsupported_points;
+    std::vector<bool>            m_unsupported_points_erased;
+
+    /*!
+     * BoundingBox of all points in m_unsupported_points. Used for mapping of sign integer numbers to positive integer numbers.
+     */
+    const BoundingBox          m_unsupported_points_bbox;
 
     /*!
      * Links the unsupported points to a grid point, so that we can quickly look
      * up the cell belonging to a certain position in the grid.
      */
-    std::unordered_map<Point, std::list<UnsupportedCell>::iterator, PointHash> m_unsupported_points_grid;
+
+    class UnsupportedPointsGrid
+    {
+    public:
+        UnsupportedPointsGrid() = default;
+        void initialize(const std::vector<UnsupportedCell> &unsupported_points, const std::function<Point(const Point &)> &map_cell_to_grid)
+        {
+            if (unsupported_points.empty())
+                return;
+
+            BoundingBox unsupported_points_bbox;
+            for (const UnsupportedCell &cell : unsupported_points)
+                unsupported_points_bbox.merge(cell.loc);
+
+            m_size        = unsupported_points.size();
+            m_grid_range  = BoundingBox(map_cell_to_grid(unsupported_points_bbox.min), map_cell_to_grid(unsupported_points_bbox.max));
+            m_grid_size   = m_grid_range.size() + Point::Ones();
+
+            m_data.assign(m_grid_size.y() * m_grid_size.x(), std::numeric_limits<size_t>::max());
+            m_data_erased.assign(m_grid_size.y() * m_grid_size.x(), true);
+
+            for (size_t cell_idx = 0; cell_idx < unsupported_points.size(); ++cell_idx) {
+                const size_t flat_idx   = map_to_flat_array(map_cell_to_grid(unsupported_points[cell_idx].loc));
+                assert(m_data[flat_idx] == std::numeric_limits<size_t>::max());
+                m_data[flat_idx]        = cell_idx;
+                m_data_erased[flat_idx] = false;
+            }
+        }
+
+        size_t size() const { return m_size; }
+
+        size_t find_cell_idx(const Point &grid_addr)
+        {
+            if (!m_grid_range.contains(grid_addr))
+                return std::numeric_limits<size_t>::max();
+
+            if (const size_t flat_idx = map_to_flat_array(grid_addr); !m_data_erased[flat_idx]) {
+                assert(m_data[flat_idx] != std::numeric_limits<size_t>::max());
+                return m_data[flat_idx];
+            }
+
+            return std::numeric_limits<size_t>::max();
+        }
+
+        void mark_erased(const Point &grid_addr)
+        {
+            assert(m_grid_range.contains(grid_addr));
+            if (!m_grid_range.contains(grid_addr))
+                return;
+
+            const size_t flat_idx = map_to_flat_array(grid_addr);
+            assert(!m_data_erased[flat_idx] && m_data[flat_idx] != std::numeric_limits<size_t>::max());
+            assert(m_size != 0);
+
+            m_data_erased[flat_idx] = true;
+            --m_size;
+        }
+
+    private:
+        size_t m_size = 0;
+
+        BoundingBox m_grid_range;
+        Point       m_grid_size;
+
+        std::vector<size_t> m_data;
+        std::vector<bool>   m_data_erased;
+
+        inline size_t map_to_flat_array(const Point &loc) const
+        {
+            const Point  offset_loc = loc - m_grid_range.min;
+            const size_t flat_idx   = m_grid_size.x() * offset_loc.y() + offset_loc.x();
+            assert(offset_loc.x() >= 0 && offset_loc.y() >= 0);
+            assert(flat_idx < size_t(m_grid_size.y() * m_grid_size.x()));
+            return flat_idx;
+        }
+    };
+
+    UnsupportedPointsGrid m_unsupported_points_grid;
+
+    /*!
+     * Maps the point to the grid coordinates.
+     */
+    Point to_grid_point(const Point &point) const {
+        return (point - m_unsupported_points_bbox.min) / m_cell_size;
+    }
+
+    /*!
+     * Maps the point to the grid coordinates.
+     */
+    Point from_grid_point(const Point &point) const {
+        return point * m_cell_size + m_unsupported_points_bbox.min;
+    }
 };
 
 } // namespace Slic3r::FillLightning
diff --git a/src/libslic3r/Fill/Lightning/Generator.cpp b/src/libslic3r/Fill/Lightning/Generator.cpp
index 87b593f89..4aba7202d 100644
--- a/src/libslic3r/Fill/Lightning/Generator.cpp
+++ b/src/libslic3r/Fill/Lightning/Generator.cpp
@@ -7,7 +7,6 @@
 #include "../../ClipperUtils.hpp"
 #include "../../Layer.hpp"
 #include "../../Print.hpp"
-#include "../../Surface.hpp"
 
 /* Possible future tasks/optimizations,etc.:
  * - Improve connecting heuristic to favor connecting to shorter trees
@@ -25,7 +24,7 @@
 
 namespace Slic3r::FillLightning {
 
-Generator::Generator(const PrintObject &print_object)
+Generator::Generator(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback)
 {
     const PrintConfig         &print_config         = print_object.print()->config();
     const PrintObjectConfig   &object_config        = print_object.config();
@@ -35,38 +34,38 @@ Generator::Generator(const PrintObject &print_object)
 //    const int                  infill_extruder      = region_config.infill_extruder.value;
     const double               default_infill_extrusion_width = Flow::auto_extrusion_width(FlowRole::frInfill, float(max_nozzle_diameter));
     // Note: There's not going to be a layer below the first one, so the 'initial layer height' doesn't have to be taken into account.
-    const double               layer_thickness      = object_config.layer_height;
+    const double               layer_thickness      = scaled<double>(object_config.layer_height.value);
 
     m_infill_extrusion_width = scaled<float>(region_config.infill_extrusion_width.percent ? default_infill_extrusion_width * 0.01 * region_config.infill_extrusion_width : region_config.infill_extrusion_width);
-    m_supporting_radius = scaled<coord_t>(m_infill_extrusion_width * 0.001 / region_config.fill_density);
+    m_supporting_radius      = coord_t(m_infill_extrusion_width) * 100 / coord_t(region_config.fill_density.value);
 
-    const double lightning_infill_overhang_angle = M_PI / 4; // 45 degrees
-    const double lightning_infill_prune_angle = M_PI / 4; // 45 degrees
+    const double lightning_infill_overhang_angle      = M_PI / 4; // 45 degrees
+    const double lightning_infill_prune_angle         = M_PI / 4; // 45 degrees
     const double lightning_infill_straightening_angle = M_PI / 4; // 45 degrees
-    m_wall_supporting_radius = layer_thickness * std::tan(lightning_infill_overhang_angle);
-    m_prune_length = layer_thickness * std::tan(lightning_infill_prune_angle);
-    m_straightening_max_distance = layer_thickness * std::tan(lightning_infill_straightening_angle);
+    m_wall_supporting_radius                          = coord_t(layer_thickness * std::tan(lightning_infill_overhang_angle));
+    m_prune_length                                    = coord_t(layer_thickness * std::tan(lightning_infill_prune_angle));
+    m_straightening_max_distance                      = coord_t(layer_thickness * std::tan(lightning_infill_straightening_angle));
 
-    generateInitialInternalOverhangs(print_object);
-    generateTrees(print_object);
+    generateInitialInternalOverhangs(print_object, throw_on_cancel_callback);
+    generateTrees(print_object, throw_on_cancel_callback);
 }
 
-void Generator::generateInitialInternalOverhangs(const PrintObject &print_object)
+void Generator::generateInitialInternalOverhangs(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback)
 {
     m_overhang_per_layer.resize(print_object.layers().size());
-    const float infill_wall_offset = - m_infill_extrusion_width;
 
     Polygons infill_area_above;
     //Iterate from top to bottom, to subtract the overhang areas above from the overhang areas on the layer below, to get only overhang in the top layer where it is overhanging.
-    for (int layer_nr = print_object.layers().size() - 1; layer_nr >= 0; layer_nr--) {
+    for (int layer_nr = int(print_object.layers().size()) - 1; layer_nr >= 0; --layer_nr) {
+        throw_on_cancel_callback();
         Polygons infill_area_here;
         for (const LayerRegion* layerm : print_object.get_layer(layer_nr)->regions())
             for (const Surface& surface : layerm->fill_surfaces.surfaces)
-                if (surface.surface_type == stInternal)
-                    append(infill_area_here, offset(surface.expolygon, infill_wall_offset));
+                if (surface.surface_type == stInternal || surface.surface_type == stInternalVoid)
+                    infill_area_here.emplace_back(surface.expolygon);
 
         //Remove the part of the infill area that is already supported by the walls.
-        Polygons overhang = diff(offset(infill_area_here, -m_wall_supporting_radius), infill_area_above);
+        Polygons overhang = diff(offset(infill_area_here, -float(m_wall_supporting_radius)), infill_area_above);
 
         m_overhang_per_layer[layer_nr] = overhang;
         infill_area_above = std::move(infill_area_here);
@@ -79,19 +78,20 @@ const Layer& Generator::getTreesForLayer(const size_t& layer_id) const
     return m_lightning_layers[layer_id];
 }
 
-void Generator::generateTrees(const PrintObject &print_object)
+void Generator::generateTrees(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback)
 {
     m_lightning_layers.resize(print_object.layers().size());
-    const coord_t infill_wall_offset = - m_infill_extrusion_width;
 
     std::vector<Polygons> infill_outlines(print_object.layers().size(), Polygons());
 
     // For-each layer from top to bottom:
-    for (int layer_id = print_object.layers().size() - 1; layer_id >= 0; layer_id--)
+    for (int layer_id = int(print_object.layers().size()) - 1; layer_id >= 0; layer_id--) {
+        throw_on_cancel_callback();
         for (const LayerRegion *layerm : print_object.get_layer(layer_id)->regions())
             for (const Surface &surface : layerm->fill_surfaces.surfaces)
-                if (surface.surface_type == stInternal)
-                    append(infill_outlines[layer_id], offset(surface.expolygon, infill_wall_offset));
+                if (surface.surface_type == stInternal || surface.surface_type == stInternalVoid)
+                    infill_outlines[layer_id].emplace_back(surface.expolygon);
+    }
 
     // For various operations its beneficial to quickly locate nearby features on the polygon:
     const size_t top_layer_id = print_object.layers().size() - 1;
@@ -99,23 +99,31 @@ void Generator::generateTrees(const PrintObject &print_object)
     outlines_locator.create(infill_outlines[top_layer_id], locator_cell_size);
 
     // For-each layer from top to bottom:
-    for (int layer_id = top_layer_id; layer_id >= 0; layer_id--)
-    {
-        Layer& current_lightning_layer = m_lightning_layers[layer_id];
-        Polygons& current_outlines = infill_outlines[layer_id];
+    for (int layer_id = int(top_layer_id); layer_id >= 0; layer_id--) {
+        throw_on_cancel_callback();
+        Layer             &current_lightning_layer = m_lightning_layers[layer_id];
+        const Polygons    &current_outlines        = infill_outlines[layer_id];
+        const BoundingBox &current_outlines_bbox   = get_extents(current_outlines);
 
         // register all trees propagated from the previous layer as to-be-reconnected
         std::vector<NodeSPtr> to_be_reconnected_tree_roots = current_lightning_layer.tree_roots;
 
-        current_lightning_layer.generateNewTrees(m_overhang_per_layer[layer_id], current_outlines, outlines_locator, m_supporting_radius, m_wall_supporting_radius);
-        current_lightning_layer.reconnectRoots(to_be_reconnected_tree_roots, current_outlines, outlines_locator, m_supporting_radius, m_wall_supporting_radius);
+        current_lightning_layer.generateNewTrees(m_overhang_per_layer[layer_id], current_outlines, current_outlines_bbox, outlines_locator, m_supporting_radius, m_wall_supporting_radius, throw_on_cancel_callback);
+        current_lightning_layer.reconnectRoots(to_be_reconnected_tree_roots, current_outlines, current_outlines_bbox, outlines_locator, m_supporting_radius, m_wall_supporting_radius);
 
         // Initialize trees for next lower layer from the current one.
         if (layer_id == 0)
             return;
 
-        const Polygons& below_outlines = infill_outlines[layer_id - 1];
-        outlines_locator.set_bbox(get_extents(below_outlines).inflated(SCALED_EPSILON));
+        const Polygons &below_outlines      = infill_outlines[layer_id - 1];
+        BoundingBox     below_outlines_bbox = get_extents(below_outlines).inflated(SCALED_EPSILON);
+        if (const BoundingBox &outlines_locator_bbox = outlines_locator.bbox(); outlines_locator_bbox.defined)
+            below_outlines_bbox.merge(outlines_locator_bbox);
+
+        if (!current_lightning_layer.tree_roots.empty())
+            below_outlines_bbox.merge(get_extents(current_lightning_layer.tree_roots).inflated(SCALED_EPSILON));
+
+        outlines_locator.set_bbox(below_outlines_bbox);
         outlines_locator.create(below_outlines, locator_cell_size);
 
         std::vector<NodeSPtr>& lower_trees = m_lightning_layers[layer_id - 1].tree_roots;
diff --git a/src/libslic3r/Fill/Lightning/Generator.hpp b/src/libslic3r/Fill/Lightning/Generator.hpp
index c44ecfe7a..d7e5f63f9 100644
--- a/src/libslic3r/Fill/Lightning/Generator.hpp
+++ b/src/libslic3r/Fill/Lightning/Generator.hpp
@@ -43,9 +43,8 @@ public:
      * This generator will pre-compute things in preparation of generating
      * Lightning Infill for the infill areas in that mesh. The infill areas must
      * already be calculated at this point.
-     * \param mesh The mesh to generate infill for.
      */
-    Generator(const PrintObject &print_object);
+    explicit Generator(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback);
 
     /*!
      * Get a tree of paths generated for a certain layer of the mesh.
@@ -69,12 +68,12 @@ protected:
      * only when support is generated. For this pattern, we also need to
      * generate overhang areas for the inside of the model.
      */
-    void generateInitialInternalOverhangs(const PrintObject &print_object);
+    void generateInitialInternalOverhangs(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback);
 
     /*!
      * Calculate the tree structure of all layers.
      */
-    void generateTrees(const PrintObject &print_object);
+    void generateTrees(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback);
 
     float m_infill_extrusion_width;
 
diff --git a/src/libslic3r/Fill/Lightning/Layer.cpp b/src/libslic3r/Fill/Lightning/Layer.cpp
index 1b3936e34..354623e51 100644
--- a/src/libslic3r/Fill/Lightning/Layer.cpp
+++ b/src/libslic3r/Fill/Lightning/Layer.cpp
@@ -3,12 +3,16 @@
 
 #include "Layer.hpp" //The class we're implementing.
 
-#include <iterator> // advance
-
 #include "DistanceField.hpp"
 #include "TreeNode.hpp"
 
+#include "../../ClipperUtils.hpp"
 #include "../../Geometry.hpp"
+#include "Utils.hpp"
+
+#include <tbb/parallel_for.h>
+#include <tbb/blocked_range2d.h>
+#include <mutex>
 
 namespace Slic3r::FillLightning {
 
@@ -23,10 +27,15 @@ Point GroundingLocation::p() const
     return tree_node ? tree_node->getLocation() : *boundary_location;
 }
 
-void Layer::fillLocator(SparseNodeGrid &tree_node_locator)
+inline static Point to_grid_point(const Point &point, const BoundingBox &bbox)
 {
-    std::function<void(NodeSPtr)> add_node_to_locator_func = [&tree_node_locator](NodeSPtr node) {
-        tree_node_locator.insert(std::make_pair(Point(node->getLocation().x() / locator_cell_size, node->getLocation().y() / locator_cell_size), node)); 
+    return (point - bbox.min) / locator_cell_size;
+}
+
+void Layer::fillLocator(SparseNodeGrid &tree_node_locator, const BoundingBox& current_outlines_bbox)
+{
+    std::function<void(NodeSPtr)> add_node_to_locator_func = [&tree_node_locator, &current_outlines_bbox](const NodeSPtr &node) {
+        tree_node_locator.insert(std::make_pair(to_grid_point(node->getLocation(), current_outlines_bbox), node));
     };
     for (auto& tree : tree_roots)
         tree->visitNodes(add_node_to_locator_func);
@@ -36,38 +45,50 @@ void Layer::generateNewTrees
 (
     const Polygons& current_overhang,
     const Polygons& current_outlines,
+    const BoundingBox& current_outlines_bbox,
     const EdgeGrid::Grid& outlines_locator,
     const coord_t supporting_radius,
-    const coord_t wall_supporting_radius
+    const coord_t wall_supporting_radius,
+    const std::function<void()> &throw_on_cancel_callback
 )
 {
-    DistanceField distance_field(supporting_radius, current_outlines, current_overhang);
+    DistanceField distance_field(supporting_radius, current_outlines, current_outlines_bbox, current_overhang);
+    throw_on_cancel_callback();
 
     SparseNodeGrid tree_node_locator;
-    fillLocator(tree_node_locator);
+    fillLocator(tree_node_locator, current_outlines_bbox);
 
     // Until no more points need to be added to support all:
     // Determine next point from tree/outline areas via distance-field
-    Point unsupported_location;
-    while (distance_field.tryGetNextPoint(&unsupported_location)) {
+    size_t unsupported_cell_idx = 0;
+    Point  unsupported_location;
+    while (distance_field.tryGetNextPoint(&unsupported_location, &unsupported_cell_idx, unsupported_cell_idx)) {
+        throw_on_cancel_callback();
         GroundingLocation grounding_loc = getBestGroundingLocation(
-            unsupported_location, current_outlines, outlines_locator, supporting_radius, wall_supporting_radius, tree_node_locator);
+            unsupported_location, current_outlines, current_outlines_bbox, outlines_locator, supporting_radius, wall_supporting_radius, tree_node_locator);
 
         NodeSPtr new_parent;
         NodeSPtr new_child;
         this->attach(unsupported_location, grounding_loc, new_child, new_parent);
-        tree_node_locator.insert(std::make_pair(Point(new_child->getLocation().x() / locator_cell_size, new_child->getLocation().y() / locator_cell_size), new_child));
+        tree_node_locator.insert(std::make_pair(to_grid_point(new_child->getLocation(), current_outlines_bbox), new_child));
         if (new_parent)
-            tree_node_locator.insert(std::make_pair(Point(new_parent->getLocation().x() / locator_cell_size, new_parent->getLocation().y() / locator_cell_size), new_parent));
+            tree_node_locator.insert(std::make_pair(to_grid_point(new_parent->getLocation(), current_outlines_bbox), new_parent));
         // update distance field
         distance_field.update(grounding_loc.p(), unsupported_location);
     }
+
+#ifdef LIGHTNING_TREE_NODE_DEBUG_OUTPUT
+    {
+        static int iRun = 0;
+        export_to_svg(debug_out_path("FillLightning-TreeNodes-%d.svg", iRun++), current_outlines, this->tree_roots);
+    }
+#endif /* LIGHTNING_TREE_NODE_DEBUG_OUTPUT */
 }
 
-static bool polygonCollidesWithLineSegment(const Point from, const Point to, const EdgeGrid::Grid &loc_to_line)
+static bool polygonCollidesWithLineSegment(const Point &from, const Point &to, const EdgeGrid::Grid &loc_to_line)
 {
     struct Visitor {
-        explicit Visitor(const EdgeGrid::Grid &grid) : grid(grid) {}
+        explicit Visitor(const EdgeGrid::Grid &grid, const Line &line) : grid(grid), line(line) {}
 
         bool operator()(coord_t iy, coord_t ix) {
             // Called with a row and colum of the grid cell, which is intersected by a line.
@@ -87,7 +108,7 @@ static bool polygonCollidesWithLineSegment(const Point from, const Point to, con
         const EdgeGrid::Grid& grid;
         Line                  line;
         bool                  intersect = false;
-    } visitor(loc_to_line);
+    } visitor(loc_to_line, {from, to});
 
     loc_to_line.visit_cells_intersecting_line(from, to, visitor);
     return visitor.intersect;
@@ -97,6 +118,7 @@ GroundingLocation Layer::getBestGroundingLocation
 (
     const Point& unsupported_location,
     const Polygons& current_outlines,
+    const BoundingBox& current_outlines_bbox,
     const EdgeGrid::Grid& outline_locator,
     const coord_t supporting_radius,
     const coord_t wall_supporting_radius,
@@ -112,9 +134,10 @@ GroundingLocation Layer::getBestGroundingLocation
             if (contour.size() > 2) {
                 Point prev = contour.points.back();
                 for (const Point &p2 : contour.points) {
-                    if (double d = Line::distance_to_squared(unsupported_location, prev, p2); d < d2) {
+                    Point closest_point;
+                    if (double d = line_alg::distance_to_squared(Line{prev, p2}, unsupported_location, &closest_point); d < d2) {
                         d2 = d;
-                        node_location = Geometry::foot_pt({ prev, p2 }, unsupported_location).cast<coord_t>();
+                        node_location = closest_point;
                     }
                     prev = p2;
                 }
@@ -123,30 +146,52 @@ GroundingLocation Layer::getBestGroundingLocation
 
     const auto within_dist = coord_t((node_location - unsupported_location).cast<double>().norm());
 
-    NodeSPtr sub_tree{ nullptr };
-    coord_t current_dist = getWeightedDistance(node_location, unsupported_location);
+    NodeSPtr sub_tree{nullptr};
+    coord_t  current_dist = getWeightedDistance(node_location, unsupported_location);
     if (current_dist >= wall_supporting_radius) { // Only reconnect tree roots to other trees if they are not already close to the outlines.
         const coord_t search_radius = std::min(current_dist, within_dist);
         BoundingBox region(unsupported_location - Point(search_radius, search_radius), unsupported_location + Point(search_radius + locator_cell_size, search_radius + locator_cell_size));
-        region.min /= locator_cell_size;
-        region.max /= locator_cell_size;
-        Point grid_addr;
-        for (grid_addr.y() = region.min.y(); grid_addr.y() < region.max.y(); ++ grid_addr.y())
-            for (grid_addr.x() = region.min.x(); grid_addr.x() < region.max.x(); ++ grid_addr.x()) {
-                auto it_range = tree_node_locator.equal_range(grid_addr);
-                for (auto it = it_range.first; it != it_range.second; ++ it) {
-                    auto candidate_sub_tree = it->second.lock();
-                    if ((candidate_sub_tree && candidate_sub_tree != exclude_tree) &&
-                        !(exclude_tree && exclude_tree->hasOffspring(candidate_sub_tree)) &&
-                        !polygonCollidesWithLineSegment(unsupported_location, candidate_sub_tree->getLocation(), outline_locator)) {
-                        const coord_t candidate_dist = candidate_sub_tree->getWeightedDistance(unsupported_location, supporting_radius);
-                        if (candidate_dist < current_dist) {
-                            current_dist = candidate_dist;
-                            sub_tree = candidate_sub_tree;
+        region.min = to_grid_point(region.min, current_outlines_bbox);
+        region.max = to_grid_point(region.max, current_outlines_bbox);
+
+        Point      current_dist_grid_addr{std::numeric_limits<coord_t>::lowest(), std::numeric_limits<coord_t>::lowest()};
+        std::mutex current_dist_mutex;
+        tbb::parallel_for(tbb::blocked_range2d<coord_t>(region.min.y(), region.max.y(), region.min.x(), region.max.x()), [&current_dist, current_dist_copy = current_dist, &current_dist_mutex, &sub_tree, &current_dist_grid_addr, &exclude_tree = std::as_const(exclude_tree), &outline_locator = std::as_const(outline_locator), &supporting_radius = std::as_const(supporting_radius), &tree_node_locator = std::as_const(tree_node_locator), &unsupported_location = std::as_const(unsupported_location)](const tbb::blocked_range2d<coord_t> &range) -> void {
+            for (coord_t grid_addr_y = range.rows().begin(); grid_addr_y < range.rows().end(); ++grid_addr_y)
+                for (coord_t grid_addr_x = range.cols().begin(); grid_addr_x < range.cols().end(); ++grid_addr_x) {
+                    const Point local_grid_addr{grid_addr_x, grid_addr_y};
+                    NodeSPtr    local_sub_tree{nullptr};
+                    coord_t     local_current_dist = current_dist_copy;
+                    const auto  it_range           = tree_node_locator.equal_range(local_grid_addr);
+                    for (auto it = it_range.first; it != it_range.second; ++it) {
+                        const NodeSPtr candidate_sub_tree = it->second.lock();
+                        if ((candidate_sub_tree && candidate_sub_tree != exclude_tree) &&
+                            !(exclude_tree && exclude_tree->hasOffspring(candidate_sub_tree)) &&
+                            !polygonCollidesWithLineSegment(unsupported_location, candidate_sub_tree->getLocation(), outline_locator)) {
+                            if (const coord_t candidate_dist = candidate_sub_tree->getWeightedDistance(unsupported_location, supporting_radius); candidate_dist < local_current_dist) {
+                                local_current_dist = candidate_dist;
+                                local_sub_tree     = candidate_sub_tree;
+                            }
+                        }
+                    }
+                    // To always get the same result in a parallel version as in a non-parallel version,
+                    // we need to preserve that for the same current_dist, we select the same sub_tree
+                    // as in the non-parallel version. For this purpose, inside the variable
+                    // current_dist_grid_addr is stored from with 2D grid position assigned sub_tree comes.
+                    // And when there are two sub_tree with the same current_dist, one which will be found
+                    // the first in the non-parallel version is selected.
+                    {
+                        std::lock_guard<std::mutex> lock(current_dist_mutex);
+                        if (local_current_dist < current_dist ||
+                            (local_current_dist == current_dist && (grid_addr_y < current_dist_grid_addr.y() ||
+                              (grid_addr_y == current_dist_grid_addr.y() && grid_addr_x < current_dist_grid_addr.x())))) {
+                            current_dist           = local_current_dist;
+                            sub_tree               = local_sub_tree;
+                            current_dist_grid_addr = local_grid_addr;
                         }
                     }
                 }
-        }
+        }); // end of parallel_for
     }
 
     return ! sub_tree ?
@@ -176,6 +221,7 @@ void Layer::reconnectRoots
 (
     std::vector<NodeSPtr>& to_be_reconnected_tree_roots,
     const Polygons& current_outlines,
+    const BoundingBox& current_outlines_bbox,
     const EdgeGrid::Grid& outline_locator,
     const coord_t supporting_radius,
     const coord_t wall_supporting_radius
@@ -184,10 +230,10 @@ void Layer::reconnectRoots
     constexpr coord_t tree_connecting_ignore_offset = 100;
 
     SparseNodeGrid tree_node_locator;
-    fillLocator(tree_node_locator);
+    fillLocator(tree_node_locator, current_outlines_bbox);
 
     const coord_t within_max_dist = outline_locator.resolution() * 2;
-    for (auto root_ptr : to_be_reconnected_tree_roots)
+    for (const auto &root_ptr : to_be_reconnected_tree_roots)
     {
         auto old_root_it = std::find(tree_roots.begin(), tree_roots.end(), root_ptr);
 
@@ -203,7 +249,7 @@ void Layer::reconnectRoots
                     root_ptr->addChild(new_root);
                     new_root->reroot();
 
-                    tree_node_locator.insert(std::make_pair(Point(new_root->getLocation().x() / locator_cell_size, new_root->getLocation().y() / locator_cell_size), new_root));
+                    tree_node_locator.insert(std::make_pair(to_grid_point(new_root->getLocation(), current_outlines_bbox), new_root));
 
                     *old_root_it = std::move(new_root); // replace old root with new root
                     continue;
@@ -217,6 +263,7 @@ void Layer::reconnectRoots
             (
                 root_ptr->getLocation(),
                 current_outlines,
+                current_outlines_bbox,
                 outline_locator,
                 supporting_radius,
                 tree_connecting_ignore_width,
@@ -233,7 +280,7 @@ void Layer::reconnectRoots
             attach_ptr->reroot();
 
             new_root->addChild(attach_ptr);
-            tree_node_locator.insert(std::make_pair(new_root->getLocation(), new_root));
+            tree_node_locator.insert(std::make_pair(to_grid_point(new_root->getLocation(), current_outlines_bbox), new_root));
 
             *old_root_it = std::move(new_root); // replace old root with new root
         }
@@ -256,15 +303,26 @@ void Layer::reconnectRoots
     }
 }
 
-/*
- * Implementation assumes moving inside, but moving outside should just as well be possible.
+#if 0
+/*!
+    * Moves the point \p from onto the nearest polygon or leaves the point as-is, when the comb boundary is not within the root of \p max_dist2 distance.
+    * Given a \p distance more than zero, the point will end up inside, and conversely outside.
+    * When the point is already in/outside by more than \p distance, \p from is unaltered, but the polygon is returned.
+    * When the point is in/outside by less than \p distance, \p from is moved to the correct place.
+    * Implementation assumes moving inside, but moving outside should just as well be possible.
+    *
+    * \param polygons The polygons onto which to move the point
+    * \param from[in,out] The point to move.
+    * \param distance The distance by which to move the point.
+    * \param max_dist2 The squared maximal allowed distance from the point to the nearest polygon.
+    * \return The index to the polygon onto which we have moved the point.
  */
 static unsigned int moveInside(const Polygons& polygons, Point& from, int distance, int64_t maxDist2)
 {
-    Point ret = from;
-    int64_t bestDist2 = std::numeric_limits<int64_t>::max();
-    unsigned int bestPoly = static_cast<unsigned int>(-1);
-    bool is_already_on_correct_side_of_boundary = false; // whether [from] is already on the right side of the boundary
+    Point   ret                                    = from;
+    int64_t bestDist2                              = std::numeric_limits<int64_t>::max();
+    auto    bestPoly                               = static_cast<unsigned int>(-1);
+    bool    is_already_on_correct_side_of_boundary = false; // whether [from] is already on the right side of the boundary
     for (unsigned int poly_idx = 0; poly_idx < polygons.size(); poly_idx++)
     {
         const Polygon &poly = polygons[poly_idx];
@@ -333,7 +391,7 @@ static unsigned int moveInside(const Polygons& polygons, Point& from, int distan
             else
             { // x is projected to a point properly on the line segment (not onto a vertex). The case which looks like | .
                 projected_p_beyond_prev_segment = false;
-                Point x = a + ab * dot_prod / ab_length2;
+                Point x = (a.cast<int64_t>() + ab.cast<int64_t>() * dot_prod / ab_length2).cast<coord_t>();
 
                 int64_t dist2 = (p - x).cast<int64_t>().squaredNorm();
                 if (dist2 < bestDist2)
@@ -373,38 +431,18 @@ static unsigned int moveInside(const Polygons& polygons, Point& from, int distan
     }
     return static_cast<unsigned int>(-1);
 }
+#endif
 
-// Returns 'added someting'.
-Polylines Layer::convertToLines(const Polygons& limit_to_outline, const coord_t line_width) const
+Polylines Layer::convertToLines(const Polygons& limit_to_outline, const coord_t line_overlap) const
 {
     if (tree_roots.empty())
         return {};
 
-    Polygons result_lines;
-    for (const auto& tree : tree_roots) {
-        // If even the furthest location in the tree is inside the polygon, the entire tree must be inside of the polygon.
-        // (Don't take the root as that may be on the edge and cause rounding errors to register as 'outside'.)
-        constexpr coord_t epsilon = 5;
-        Point should_be_inside = tree->getLocation();
-        moveInside(limit_to_outline, should_be_inside, epsilon, epsilon * epsilon);
-        if (inside(limit_to_outline, should_be_inside))
-            tree->convertToPolylines(result_lines, line_width);
-    }
+    Polylines result_lines;
+    for (const auto &tree : tree_roots)
+        tree->convertToPolylines(result_lines, line_overlap);
 
-    // TODO: allow for polylines!
-    Polylines split_lines;
-    for (Polygon &line : result_lines) {
-        if (line.size() <= 1)
-            continue;
-        Point last = line[0];
-        for (size_t point_idx = 1; point_idx < line.size(); point_idx++) {
-            Point here = line[point_idx];
-            split_lines.push_back({ last, here });
-            last = here;
-        }
-    }
-
-    return split_lines;
+    return intersection_pl(result_lines, limit_to_outline);
 }
 
 } // namespace Slic3r::Lightning
diff --git a/src/libslic3r/Fill/Lightning/Layer.hpp b/src/libslic3r/Fill/Lightning/Layer.hpp
index 853c634f2..e8c0a38b4 100644
--- a/src/libslic3r/Fill/Lightning/Layer.hpp
+++ b/src/libslic3r/Fill/Lightning/Layer.hpp
@@ -41,9 +41,11 @@ public:
     (
         const Polygons& current_overhang,
         const Polygons& current_outlines,
+        const BoundingBox& current_outlines_bbox,
         const EdgeGrid::Grid& outline_locator,
-        const coord_t supporting_radius,
-        const coord_t wall_supporting_radius
+        coord_t supporting_radius,
+        coord_t wall_supporting_radius,
+        const std::function<void()> &throw_on_cancel_callback
     );
 
     /*! Determine & connect to connection point in tree/outline.
@@ -53,9 +55,10 @@ public:
     (
         const Point& unsupported_location,
         const Polygons& current_outlines,
+        const BoundingBox& current_outlines_bbox,
         const EdgeGrid::Grid& outline_locator,
-        const coord_t supporting_radius,
-        const coord_t wall_supporting_radius,
+        coord_t supporting_radius,
+        coord_t wall_supporting_radius,
         const SparseNodeGrid& tree_node_locator,
         const NodeSPtr& exclude_tree = nullptr
     );
@@ -71,16 +74,17 @@ public:
     (
         std::vector<NodeSPtr>& to_be_reconnected_tree_roots,
         const Polygons& current_outlines,
+        const BoundingBox& current_outlines_bbox,
         const EdgeGrid::Grid& outline_locator,
-        const coord_t supporting_radius,
-        const coord_t wall_supporting_radius
+        coord_t supporting_radius,
+        coord_t wall_supporting_radius
     );
 
-    Polylines convertToLines(const Polygons& limit_to_outline, const coord_t line_width) const;
+    Polylines convertToLines(const Polygons& limit_to_outline, coord_t line_overlap) const;
 
     coord_t getWeightedDistance(const Point& boundary_loc, const Point& unsupported_location);
 
-    void fillLocator(SparseNodeGrid& tree_node_locator);
+    void fillLocator(SparseNodeGrid& tree_node_locator, const BoundingBox& current_outlines_bbox);
 };
 
 } // namespace Slic3r::FillLightning
diff --git a/src/libslic3r/Fill/Lightning/TreeNode.cpp b/src/libslic3r/Fill/Lightning/TreeNode.cpp
index 8ab11bd6d..982d47b10 100644
--- a/src/libslic3r/Fill/Lightning/TreeNode.cpp
+++ b/src/libslic3r/Fill/Lightning/TreeNode.cpp
@@ -4,7 +4,6 @@
 #include "TreeNode.hpp"
 
 #include "../../Geometry.hpp"
-#include "../../ClipperUtils.hpp"
 
 namespace Slic3r::FillLightning {
 
@@ -107,7 +106,7 @@ NodeSPtr Node::deepCopy() const
     return local_root;
 }
 
-void Node::reroot(NodeSPtr new_parent /*= nullptr*/)
+void Node::reroot(const NodeSPtr &new_parent)
 {
     if (! m_is_root) {
         auto old_parent = m_parent.lock();
@@ -142,7 +141,7 @@ NodeSPtr Node::closestNode(const Point& loc)
     return result;
 }
 
-bool inside(const Polygons &polygons, const Point p)
+bool inside(const Polygons &polygons, const Point &p)
 {
     int poly_count_inside = 0;
     for (const Polygon &poly : polygons) {
@@ -181,7 +180,11 @@ bool lineSegmentPolygonsIntersection(const Point& a, const Point& b, const EdgeG
     } visitor { outline_locator, a.cast<double>(), b.cast<double>() };
 
     outline_locator.visit_cells_intersecting_line(a, b, visitor);
-    return visitor.d2min < within_max_dist * within_max_dist;
+    if (visitor.d2min < double(within_max_dist) * double(within_max_dist)) {
+        result = Point(visitor.intersection_pt);
+        return true;
+    }
+    return false;
 }
 
 bool Node::realign(const Polygons& outlines, const EdgeGrid::Grid& outline_locator, std::vector<NodeSPtr>& rerooted_parts)
@@ -226,14 +229,14 @@ bool Node::realign(const Polygons& outlines, const EdgeGrid::Grid& outline_locat
 
 void Node::straighten(const coord_t magnitude, const coord_t max_remove_colinear_dist)
 {
-    straighten(magnitude, m_p, 0, max_remove_colinear_dist * max_remove_colinear_dist);
+    straighten(magnitude, m_p, 0, int64_t(max_remove_colinear_dist) * int64_t(max_remove_colinear_dist));
 }
 
 Node::RectilinearJunction Node::straighten(
     const coord_t magnitude,
     const Point& junction_above,
     const coord_t accumulated_dist,
-    const coord_t max_remove_colinear_dist2)
+    const int64_t max_remove_colinear_dist2)
 {
     constexpr coord_t junction_magnitude_factor_numerator = 3;
     constexpr coord_t junction_magnitude_factor_denominator = 4;
@@ -245,13 +248,13 @@ Node::RectilinearJunction Node::straighten(
         auto child_dist = coord_t((m_p - child_p->m_p).cast<double>().norm());
         RectilinearJunction junction_below = child_p->straighten(magnitude, junction_above, accumulated_dist + child_dist, max_remove_colinear_dist2);
         coord_t total_dist_to_junction_below = junction_below.total_recti_dist;
-        Point a = junction_above;
-        Point b = junction_below.junction_loc;
+        const Point& a = junction_above;
+        Point        b = junction_below.junction_loc;
         if (a != b) // should always be true!
         {
             Point ab = b - a;
-            Point destination = a + ab * accumulated_dist / std::max(coord_t(1), total_dist_to_junction_below);
-            if ((destination - m_p).cast<double>().squaredNorm() <= magnitude * magnitude)
+            Point destination = (a.cast<int64_t>() + ab.cast<int64_t>() * int64_t(accumulated_dist) / std::max(int64_t(1), int64_t(total_dist_to_junction_below))).cast<coord_t>();
+            if ((destination - m_p).cast<int64_t>().squaredNorm() <= int64_t(magnitude) * int64_t(magnitude))
                 m_p = destination;
             else
                 m_p += ((destination - m_p).cast<double>().normalized() * magnitude).cast<coord_t>();
@@ -262,7 +265,7 @@ Node::RectilinearJunction Node::straighten(
             child_p = m_children.front(); //recursive call to straighten might have removed the child
             const NodeSPtr& parent_node = m_parent.lock();
             if (parent_node &&
-                (child_p->m_p - parent_node->m_p).cast<double>().squaredNorm() < max_remove_colinear_dist2 &&
+                (child_p->m_p - parent_node->m_p).cast<int64_t>().squaredNorm() < max_remove_colinear_dist2 &&
                 Line::distance_to_squared(m_p, parent_node->m_p, child_p->m_p) < close_enough * close_enough) {
                 child_p->m_parent = m_parent;
                 for (auto& sibling : parent_node->m_children)
@@ -344,16 +347,16 @@ coord_t Node::prune(const coord_t& pruning_distance)
     return max_distance_pruned;
 }
 
-void Node::convertToPolylines(Polygons& output, const coord_t line_width) const
+void Node::convertToPolylines(Polylines &output, const coord_t line_overlap) const
 {
-    Polygons result;
-    output.emplace_back();
+    Polylines result;
+    result.emplace_back();
     convertToPolylines(0, result);
-    removeJunctionOverlap(result, line_width);
+    removeJunctionOverlap(result, line_overlap);
     append(output, std::move(result));
 }
 
-void Node::convertToPolylines(size_t long_line_idx, Polygons& output) const
+void Node::convertToPolylines(size_t long_line_idx, Polylines &output) const
 {
     if (m_children.empty()) {
         output[long_line_idx].points.push_back(m_p);
@@ -373,11 +376,12 @@ void Node::convertToPolylines(size_t long_line_idx, Polygons& output) const
     }
 }
 
-void Node::removeJunctionOverlap(Polygons& result_lines, const coord_t line_width) const
+void Node::removeJunctionOverlap(Polylines &result_lines, const coord_t line_overlap) const
 {
-    const coord_t reduction = line_width / 2; // TODO make configurable?
-    for (auto poly_it = result_lines.begin(); poly_it != result_lines.end(); ) {
-        Polygon &polyline = *poly_it;
+    const coord_t reduction    = line_overlap;
+    size_t        res_line_idx = 0;
+    while (res_line_idx < result_lines.size()) {
+        Polyline &polyline = result_lines[res_line_idx];
         if (polyline.size() <= 1) {
             polyline = std::move(result_lines.back());
             result_lines.pop_back();
@@ -386,8 +390,8 @@ void Node::removeJunctionOverlap(Polygons& result_lines, const coord_t line_widt
 
         coord_t to_be_reduced = reduction;
         Point a = polyline.back();
-        for (int point_idx = polyline.size() - 2; point_idx >= 0; point_idx--) {
-            const Point b = polyline[point_idx];
+        for (int point_idx = int(polyline.size()) - 2; point_idx >= 0; point_idx--) {
+            const Point b = polyline.points[point_idx];
             const Point ab = b - a;
             const auto ab_len = coord_t(ab.cast<double>().norm());
             if (ab_len >= to_be_reduced) {
@@ -404,8 +408,33 @@ void Node::removeJunctionOverlap(Polygons& result_lines, const coord_t line_widt
             polyline = std::move(result_lines.back());
             result_lines.pop_back();
         } else
-            ++ poly_it;
+            ++ res_line_idx;
     }
 }
 
+#ifdef LIGHTNING_TREE_NODE_DEBUG_OUTPUT
+void export_to_svg(const NodeSPtr &root_node, SVG &svg)
+{
+    for (const NodeSPtr &children : root_node->m_children) {
+        svg.draw(Line(root_node->getLocation(), children->getLocation()), "red");
+        export_to_svg(children, svg);
+    }
+}
+
+void export_to_svg(const std::string &path, const Polygons &contour, const std::vector<NodeSPtr> &root_nodes) {
+    BoundingBox bbox = get_extents(contour);
+
+    bbox.offset(SCALED_EPSILON);
+    SVG svg(path, bbox);
+    svg.draw_outline(contour, "blue");
+
+    for (const NodeSPtr &root_node: root_nodes) {
+        for (const NodeSPtr &children: root_node->m_children) {
+            svg.draw(Line(root_node->getLocation(), children->getLocation()), "red");
+            export_to_svg(children, svg);
+        }
+    }
+}
+#endif /* LIGHTNING_TREE_NODE_DEBUG_OUTPUT */
+
 } // namespace Slic3r::FillLightning
diff --git a/src/libslic3r/Fill/Lightning/TreeNode.hpp b/src/libslic3r/Fill/Lightning/TreeNode.hpp
index bc2e76dc2..8791b4331 100644
--- a/src/libslic3r/Fill/Lightning/TreeNode.hpp
+++ b/src/libslic3r/Fill/Lightning/TreeNode.hpp
@@ -11,6 +11,9 @@
 
 #include "../../EdgeGrid.hpp"
 #include "../../Polygon.hpp"
+#include "SVG.hpp"
+
+//#define LIGHTNING_TREE_NODE_DEBUG_OUTPUT
 
 namespace Slic3r::FillLightning
 {
@@ -43,7 +46,7 @@ public:
     {
         struct EnableMakeShared : public Node
         {
-            EnableMakeShared(Arg&&...arg) : Node(std::forward<Arg>(arg)...) {}
+            explicit EnableMakeShared(Arg&&...arg) : Node(std::forward<Arg>(arg)...) {}
         };
         return std::make_shared<EnableMakeShared>(std::forward<Arg>(arg)...);
     }
@@ -99,9 +102,9 @@ public:
         std::vector<NodeSPtr>& next_trees,
         const Polygons& next_outlines,
         const EdgeGrid::Grid& outline_locator,
-        const coord_t prune_distance,
-        const coord_t smooth_magnitude,
-        const coord_t max_remove_colinear_dist
+        coord_t prune_distance,
+        coord_t smooth_magnitude,
+        coord_t max_remove_colinear_dist
     ) const;
 
     /*!
@@ -156,7 +159,7 @@ public:
      * This is then recursively bubbled up until it reaches the (former) root, which then will become a leaf.
      * \param new_parent The (new) parent-node of the root, useful for recursing or immediately attaching the node to another tree.
      */
-    void reroot(NodeSPtr new_parent = nullptr);
+    void reroot(const NodeSPtr &new_parent = nullptr);
 
     /*!
      * Retrieves the closest node to the specified location.
@@ -176,16 +179,16 @@ public:
      */
     bool hasOffspring(const NodeSPtr& to_be_checked) const;
 
-protected:
     Node() = delete; // Don't allow empty contruction
 
+protected:
     /*!
      * Construct a new node, either for insertion in a tree or as root.
      * \param p The physical location in the 2D layer that this node represents.
      * Connecting other nodes to this node indicates that a line segment should
      * be drawn between those two physical positions.
      */
-    Node(const Point& p, const std::optional<Point>& last_grounding_location = std::nullopt);
+    explicit Node(const Point& p, const std::optional<Point>& last_grounding_location = std::nullopt);
 
     /*!
      * Copy this node and its entire sub-tree.
@@ -211,7 +214,7 @@ protected:
      * \param magnitude The maximum allowed distance to move the node.
      * \param max_remove_colinear_dist Maximum distance of the (compound) line-segment from which a co-linear point may be removed.
      */
-    void straighten(const coord_t magnitude, const coord_t max_remove_colinear_dist);
+    void straighten(coord_t magnitude, coord_t max_remove_colinear_dist);
 
     /*! Recursive part of \ref straighten(.)
      * \param junction_above The last seen junction with multiple children above
@@ -219,7 +222,7 @@ protected:
      * \param max_remove_colinear_dist2 Maximum distance _squared_ of the (compound) line-segment from which a co-linear point may be removed.
      * \return the total distance along the tree from the last junction above to the first next junction below and the location of the next junction below
      */
-    RectilinearJunction straighten(const coord_t magnitude, const Point& junction_above, const coord_t accumulated_dist, const coord_t max_remove_colinear_dist2);
+    RectilinearJunction straighten(coord_t magnitude, const Point& junction_above, coord_t accumulated_dist, int64_t max_remove_colinear_dist2);
 
     /*! Prune the tree from the extremeties (leaf-nodes) until the pruning distance is reached.
      * \return The distance that has been pruned. If less than \p distance, then the whole tree was puned away.
@@ -236,7 +239,7 @@ public:
      * 
      * \param output all branches in this tree connected into polylines
      */
-    void convertToPolylines(Polygons& output, const coord_t line_width) const;
+    void convertToPolylines(Polylines &output, coord_t line_overlap) const;
 
     /*! If this was ever a direct child of the root, it'll have a previous grounding location.
      *
@@ -255,9 +258,9 @@ protected:
      * \param long_line a reference to a polyline in \p output which to continue building on in the recursion
      * \param output all branches in this tree connected into polylines
      */
-    void convertToPolylines(size_t long_line_idx, Polygons& output) const;
+    void convertToPolylines(size_t long_line_idx, Polylines &output) const;
 
-    void removeJunctionOverlap(Polygons& polylines, const coord_t line_width) const;
+    void removeJunctionOverlap(Polylines &polylines, coord_t line_overlap) const;
 
     bool m_is_root;
     Point m_p;
@@ -265,10 +268,40 @@ protected:
     std::vector<NodeSPtr> m_children;
 
     std::optional<Point> m_last_grounding_location;  //<! The last known grounding location, see 'getLastGroundingLocation()'.
+
+    friend BoundingBox get_extents(const NodeSPtr &root_node);
+    friend BoundingBox get_extents(const std::vector<NodeSPtr> &tree_roots);
+
+#ifdef LIGHTNING_TREE_NODE_DEBUG_OUTPUT
+    friend void export_to_svg(const NodeSPtr &root_node, Slic3r::SVG &svg);
+    friend void export_to_svg(const std::string &path, const Polygons &contour, const std::vector<NodeSPtr> &root_nodes);
+#endif /* LIGHTNING_TREE_NODE_DEBUG_OUTPUT */
 };
 
-bool inside(const Polygons &polygons, const Point p);
-bool lineSegmentPolygonsIntersection(const Point& a, const Point& b, const EdgeGrid::Grid& outline_locator, Point& result, const coord_t within_max_dist);
+bool inside(const Polygons &polygons, const Point &p);
+bool lineSegmentPolygonsIntersection(const Point& a, const Point& b, const EdgeGrid::Grid& outline_locator, Point& result, coord_t within_max_dist);
+
+inline BoundingBox get_extents(const NodeSPtr &root_node)
+{
+    BoundingBox bbox;
+    for (const NodeSPtr &children : root_node->m_children)
+        bbox.merge(get_extents(children));
+    bbox.merge(root_node->getLocation());
+    return bbox;
+}
+
+inline BoundingBox get_extents(const std::vector<NodeSPtr> &tree_roots)
+{
+    BoundingBox bbox;
+    for (const NodeSPtr &root_node : tree_roots)
+        bbox.merge(get_extents(root_node));
+    return bbox;
+}
+
+#ifdef LIGHTNING_TREE_NODE_DEBUG_OUTPUT
+void export_to_svg(const NodeSPtr &root_node, SVG &svg);
+void export_to_svg(const std::string &path, const Polygons &contour, const std::vector<NodeSPtr> &root_nodes);
+#endif /* LIGHTNING_TREE_NODE_DEBUG_OUTPUT */
 
 } // namespace Slic3r::FillLightning
 
diff --git a/src/libslic3r/Layer.hpp b/src/libslic3r/Layer.hpp
index 0071c7f6e..a308ac0b6 100644
--- a/src/libslic3r/Layer.hpp
+++ b/src/libslic3r/Layer.hpp
@@ -20,6 +20,10 @@ namespace FillAdaptive {
     struct Octree;
 };
 
+namespace FillLightning {
+    class Generator;
+};
+
 class LayerRegion
 {
 public:
@@ -151,8 +155,8 @@ public:
     }
     void                    make_perimeters();
     // Phony version of make_fills() without parameters for Perl integration only.
-    void                    make_fills() { this->make_fills(nullptr, nullptr); }
-    void                    make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive::Octree* support_fill_octree);
+    void                    make_fills() { this->make_fills(nullptr, nullptr, nullptr); }
+    void                    make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive::Octree* support_fill_octree, FillLightning::Generator* lightning_generator);
     void 					make_ironing();
 
     void                    export_region_slices_to_svg(const char *path) const;
diff --git a/src/libslic3r/Point.hpp b/src/libslic3r/Point.hpp
index e5dc334f5..6b430c2fe 100644
--- a/src/libslic3r/Point.hpp
+++ b/src/libslic3r/Point.hpp
@@ -177,6 +177,11 @@ inline bool operator<(const Point &l, const Point &r)
     return l.x() < r.x() || (l.x() == r.x() && l.y() < r.y());
 }
 
+inline Point operator* (const Point& l, const double &r)
+{
+    return {coord_t(l.x() * r), coord_t(l.y() * r)};
+}
+
 inline bool is_approx(const Point &p1, const Point &p2, coord_t epsilon = coord_t(SCALED_EPSILON))
 {
 	Point d = (p2 - p1).cwiseAbs();
diff --git a/src/libslic3r/Print.hpp b/src/libslic3r/Print.hpp
index c2babd53c..61151babd 100644
--- a/src/libslic3r/Print.hpp
+++ b/src/libslic3r/Print.hpp
@@ -35,7 +35,13 @@ namespace FillAdaptive {
     struct Octree;
     struct OctreeDeleter;
     using OctreePtr = std::unique_ptr<Octree, OctreeDeleter>;
-};
+}; // namespace FillAdaptive
+
+namespace FillLightning {
+    class Generator;
+    struct GeneratorDeleter;
+    using GeneratorPtr = std::unique_ptr<Generator, GeneratorDeleter>;
+}; // namespace FillLightning
 
 // Print step IDs for keeping track of the print state.
 // The Print steps are applied in this order.
@@ -382,6 +388,7 @@ private:
     void combine_infill();
     void _generate_support_material();
     std::pair<FillAdaptive::OctreePtr, FillAdaptive::OctreePtr> prepare_adaptive_infill_data();
+    FillLightning::GeneratorPtr prepare_lightning_infill_data();
 
     // XYZ in scaled coordinates
     Vec3crd									m_size;
diff --git a/src/libslic3r/PrintConfig.cpp b/src/libslic3r/PrintConfig.cpp
index b1a25829b..4afc22667 100644
--- a/src/libslic3r/PrintConfig.cpp
+++ b/src/libslic3r/PrintConfig.cpp
@@ -108,9 +108,7 @@ static t_config_enum_values s_keys_map_InfillPattern {
     { "octagramspiral",     ipOctagramSpiral },
     { "adaptivecubic",      ipAdaptiveCubic },
     { "supportcubic",       ipSupportCubic },
-#if HAS_LIGHTNING_INFILL
     { "lightning",          ipLightning }
-#endif // HAS_LIGHTNING_INFILL
 };
 CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(InfillPattern)
 
@@ -1138,9 +1136,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_values.push_back("octagramspiral");
     def->enum_values.push_back("adaptivecubic");
     def->enum_values.push_back("supportcubic");
-#if HAS_LIGHTNING_INFILL
     def->enum_values.push_back("lightning");
-#endif // HAS_LIGHTNING_INFILL
     def->enum_labels.push_back(L("Rectilinear"));
     def->enum_labels.push_back(L("Aligned Rectilinear"));
     def->enum_labels.push_back(L("Grid"));
@@ -1157,9 +1153,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_labels.push_back(L("Octagram Spiral"));
     def->enum_labels.push_back(L("Adaptive Cubic"));
     def->enum_labels.push_back(L("Support Cubic"));
-#if HAS_LIGHTNING_INFILL
     def->enum_labels.push_back(L("Lightning"));
-#endif // HAS_LIGHTNING_INFILL
     def->set_default_value(new ConfigOptionEnum<InfillPattern>(ipStars));
 
     def = this->add("first_layer_acceleration", coFloat);
diff --git a/src/libslic3r/PrintConfig.hpp b/src/libslic3r/PrintConfig.hpp
index 2cc758e7b..c473cde4c 100644
--- a/src/libslic3r/PrintConfig.hpp
+++ b/src/libslic3r/PrintConfig.hpp
@@ -57,14 +57,10 @@ enum class FuzzySkinType {
     All,
 };
 
-#define HAS_LIGHTNING_INFILL 0
-
 enum InfillPattern : int {
     ipRectilinear, ipMonotonic, ipAlignedRectilinear, ipGrid, ipTriangles, ipStars, ipCubic, ipLine, ipConcentric, ipHoneycomb, ip3DHoneycomb,
-    ipGyroid, ipHilbertCurve, ipArchimedeanChords, ipOctagramSpiral, ipAdaptiveCubic, ipSupportCubic, ipSupportBase, 
-#if HAS_LIGHTNING_INFILL
-    ipLightning, 
-#endif // HAS_LIGHTNING_INFILL
+    ipGyroid, ipHilbertCurve, ipArchimedeanChords, ipOctagramSpiral, ipAdaptiveCubic, ipSupportCubic, ipSupportBase,
+    ipLightning,
 ipCount,
 };
 
diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index 31d948db9..eeaf1b13c 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -14,6 +14,7 @@
 #include "TriangleMeshSlicer.hpp"
 #include "Utils.hpp"
 #include "Fill/FillAdaptive.hpp"
+#include "Fill/FillLightning.hpp"
 #include "Format/STL.hpp"
 
 #include <float.h>
@@ -353,14 +354,15 @@ void PrintObject::infill()
 
     if (this->set_started(posInfill)) {
         auto [adaptive_fill_octree, support_fill_octree] = this->prepare_adaptive_infill_data();
+        auto lightning_generator                         = this->prepare_lightning_infill_data();
 
         BOOST_LOG_TRIVIAL(debug) << "Filling layers in parallel - start";
         tbb::parallel_for(
             tbb::blocked_range<size_t>(0, m_layers.size()),
-            [this, &adaptive_fill_octree = adaptive_fill_octree, &support_fill_octree = support_fill_octree](const tbb::blocked_range<size_t>& range) {
+            [this, &adaptive_fill_octree = adaptive_fill_octree, &support_fill_octree = support_fill_octree, &lightning_generator](const tbb::blocked_range<size_t>& range) {
                 for (size_t layer_idx = range.begin(); layer_idx < range.end(); ++ layer_idx) {
                     m_print->throw_if_canceled();
-                    m_layers[layer_idx]->make_fills(adaptive_fill_octree.get(), support_fill_octree.get());
+                    m_layers[layer_idx]->make_fills(adaptive_fill_octree.get(), support_fill_octree.get(), lightning_generator.get());
                 }
             }
         );
@@ -453,6 +455,18 @@ std::pair<FillAdaptive::OctreePtr, FillAdaptive::OctreePtr> PrintObject::prepare
         support_line_spacing  ? build_octree(mesh, overhangs.front(), support_line_spacing, true) : OctreePtr());
 }
 
+FillLightning::GeneratorPtr PrintObject::prepare_lightning_infill_data()
+{
+    bool has_lightning_infill = false;
+    for (size_t region_id = 0; region_id < this->num_printing_regions(); ++region_id)
+        if (const PrintRegionConfig &config = this->printing_region(region_id).config(); config.fill_density > 0 && config.fill_pattern == ipLightning) {
+            has_lightning_infill = true;
+            break;
+        }
+
+    return has_lightning_infill ? FillLightning::build_generator(std::as_const(*this), [this]() -> void { this->throw_if_canceled(); }) : FillLightning::GeneratorPtr();
+}
+
 void PrintObject::clear_layers()
 {
     for (Layer *l : m_layers)