Merge branch 'master_slic3rPE_PR'1.41.0-3

17 files changed, 697 insertions, 26 deletions

diff --git a/xs/src/libslic3r/ExtrusionEntity.hpp b/xs/src/libslic3r/ExtrusionEntity.hpp
index 15363e8ed..d338771f4 100644
--- a/xs/src/libslic3r/ExtrusionEntity.hpp
+++ b/xs/src/libslic3r/ExtrusionEntity.hpp
@@ -196,9 +196,10 @@ public:
     // Minimum volumetric velocity of this extrusion entity. Used by the constant nozzle pressure algorithm.
     double min_mm3_per_mm() const;
     Polyline as_polyline() const;
-    virtual double total_volume() const { double volume =0.; for (const auto& path : paths) volume += path.total_volume(); return volume; }
+    virtual double total_volume() const { double volume = 0.; for (const auto& path : paths) volume += path.total_volume(); return volume; }
 };
 
+
 // Single continuous extrusion loop, possibly with varying extrusion thickness, extrusion height or bridging / non bridging.
 class ExtrusionLoop : public ExtrusionEntity
 {
@@ -244,7 +245,7 @@ public:
     // Minimum volumetric velocity of this extrusion entity. Used by the constant nozzle pressure algorithm.
     double min_mm3_per_mm() const;
     Polyline as_polyline() const { return this->polygon().split_at_first_point(); }
-    virtual double total_volume() const { double volume =0.; for (const auto& path : paths) volume += path.total_volume(); return volume; }
+    virtual double total_volume() const { double volume = 0.; for (const auto& path : paths) volume += path.total_volume(); return volume; }
 
 private:
     ExtrusionLoopRole m_loop_role;
diff --git a/xs/src/libslic3r/GCode.cpp b/xs/src/libslic3r/GCode.cpp
index 27c838037..708fe500c 100644
--- a/xs/src/libslic3r/GCode.cpp
+++ b/xs/src/libslic3r/GCode.cpp
@@ -2367,6 +2367,8 @@ std::string GCode::_extrude(const ExtrusionPath &path, std::string description,
             speed = m_config.get_abs_value("top_solid_infill_speed");
         } else if (path.role() == erGapFill) {
             speed = m_config.get_abs_value("gap_fill_speed");
+        } else if (path.role() == erNone) {
+            speed = m_config.get_abs_value("travel_speed");
         } else {
             CONFESS("Invalid speed");
         }
diff --git a/xs/src/libslic3r/Layer.cpp b/xs/src/libslic3r/Layer.cpp
index 652bcdaa0..4b3ecb3f2 100644
--- a/xs/src/libslic3r/Layer.cpp
+++ b/xs/src/libslic3r/Layer.cpp
@@ -101,8 +101,9 @@ void Layer::make_perimeters()
                 && config.gap_fill_speed    == other_config.gap_fill_speed
                 && config.overhangs         == other_config.overhangs
                 && config.serialize("perimeter_extrusion_width").compare(other_config.serialize("perimeter_extrusion_width")) == 0
-                && config.thin_walls        == other_config.thin_walls
-                && config.external_perimeters_first == other_config.external_perimeters_first) {
+                && config.thin_walls == other_config.thin_walls
+                && config.external_perimeters_first == other_config.external_perimeters_first
+                && config.perimeter_loop == other_config.perimeter_loop) {
                 layerms.push_back(other_layerm);
                 done.insert(it - this->regions.begin());
             }
diff --git a/xs/src/libslic3r/Line.cpp b/xs/src/libslic3r/Line.cpp
index e9d5d7742..691d55b80 100644
--- a/xs/src/libslic3r/Line.cpp
+++ b/xs/src/libslic3r/Line.cpp
@@ -218,6 +218,14 @@ Line::ccw(const Point& point) const
     return point.ccw(*this);
 }
 
+coord_t
+Line::dot(Line &l2) const
+{
+    Vector v_1 = vector();
+    Vector v_2 = l2.vector();
+    return v_1.x*v_2.x + v_1.y*v_2.y;
+}
+
 double Line3::length() const
 {
     return a.distance_to(b);
diff --git a/xs/src/libslic3r/Line.hpp b/xs/src/libslic3r/Line.hpp
index 4826017ab..81e86aab0 100644
--- a/xs/src/libslic3r/Line.hpp
+++ b/xs/src/libslic3r/Line.hpp
@@ -47,6 +47,7 @@ public:
     void extend_start(double distance);
     bool intersection(const Line& line, Point* intersection) const;
     double ccw(const Point& point) const;
+    coord_t dot(Line &l2) const;
 };
 
 class ThickLine : public Line
diff --git a/xs/src/libslic3r/MedialAxis.cpp b/xs/src/libslic3r/MedialAxis.cpp
index 27b77e197..4fbbf5344 100644
--- a/xs/src/libslic3r/MedialAxis.cpp
+++ b/xs/src/libslic3r/MedialAxis.cpp
@@ -624,11 +624,15 @@ MedialAxis::extends_line(ThickPolyline& polyline, const ExPolygons& anchors, con
             new_back = polyline.points.back();
         } else {
             (void)this->expolygon.contour.first_intersection(line, &new_back);
+            // safety check if no intersection
+            if (new_back.x == 0 && new_back.y == 0) return;
             polyline.points.push_back(new_back);
             polyline.width.push_back(polyline.width.back());
         }
         Point new_bound;
         (void)bounds.contour.first_intersection(line, &new_bound);
+        // safety check if no intersection
+        if (new_bound.x == 0 && new_bound.y == 0) return;
        /* if (new_bound.coincides_with_epsilon(new_back)) {
             return;
         }*/
diff --git a/xs/src/libslic3r/MultiPoint.cpp b/xs/src/libslic3r/MultiPoint.cpp
index 2e65492cd..bfa0779ef 100644
--- a/xs/src/libslic3r/MultiPoint.cpp
+++ b/xs/src/libslic3r/MultiPoint.cpp
@@ -173,6 +173,43 @@ MultiPoint::dump_perl() const
     return ret.str();
 }
 
+// Projection of a point onto the polygon.
+Point MultiPoint::point_projection(const Point &point) const {
+    Point proj = point;
+    double dmin = std::numeric_limits<double>::max();
+    if (!this->points.empty()) {
+        for (size_t i = 0; i < this->points.size()-1; ++i) {
+            const Point &pt0 = this->points[i];
+            const Point &pt1 = this->points[i + 1];
+            double d = pt0.distance_to(point);
+            if (d < dmin) {
+                dmin = d;
+                proj = pt0;
+            }
+            d = pt1.distance_to(point);
+            if (d < dmin) {
+                dmin = d;
+                proj = pt1;
+            }
+            Pointf v1(coordf_t(pt1.x - pt0.x), coordf_t(pt1.y - pt0.y));
+            coordf_t div = dot(v1);
+            if (div > 0.) {
+                Pointf v2(coordf_t(point.x - pt0.x), coordf_t(point.y - pt0.y));
+                coordf_t t = dot(v1, v2) / div;
+                if (t > 0. && t < 1.) {
+                    Point foot(coord_t(floor(coordf_t(pt0.x) + t * v1.x + 0.5)), coord_t(floor(coordf_t(pt0.y) + t * v1.y + 0.5)));
+                    d = foot.distance_to(point);
+                    if (d < dmin) {
+                        dmin = d;
+                        proj = foot;
+                    }
+                }
+            }
+        }
+    }
+    return proj;
+}
+
 //FIXME This is very inefficient in term of memory use.
 // The recursive algorithm shall run in place, not allocating temporary data in each recursion.
 Points
diff --git a/xs/src/libslic3r/MultiPoint.hpp b/xs/src/libslic3r/MultiPoint.hpp
index 0970e9a67..d97b6b1aa 100644
--- a/xs/src/libslic3r/MultiPoint.hpp
+++ b/xs/src/libslic3r/MultiPoint.hpp
@@ -76,6 +76,8 @@ public:
     bool intersection(const Line& line, Point* intersection) const;
     bool first_intersection(const Line& line, Point* intersection) const;
     std::string dump_perl() const;
+    // Projection of a point onto the lines defined by the points.
+    virtual Point point_projection(const Point &point) const;
     
     static Points _douglas_peucker(const Points &points, const double tolerance);
 };
diff --git a/xs/src/libslic3r/PerimeterGenerator.cpp b/xs/src/libslic3r/PerimeterGenerator.cpp
index 7218e028f..11e9fd12a 100644
--- a/xs/src/libslic3r/PerimeterGenerator.cpp
+++ b/xs/src/libslic3r/PerimeterGenerator.cpp
@@ -5,9 +5,33 @@
 #include "Geometry.hpp"
 #include <cmath>
 #include <cassert>
+#include <vector>
+
+#include "BoundingBox.hpp"
+#include "ExPolygon.hpp"
+#include "Geometry.hpp"
+#include "Polygon.hpp"
+#include "Line.hpp"
+#include "ClipperUtils.hpp"
+#include "SVG.hpp"
+#include "polypartition.h"
+#include "poly2tri/poly2tri.h"
+#include <algorithm>
+#include <cassert>
+#include <list>
 
 namespace Slic3r {
 
+    PerimeterGeneratorLoops get_all_Childs(PerimeterGeneratorLoop loop) {
+        PerimeterGeneratorLoops ret;
+        for (PerimeterGeneratorLoop &child : loop.children) {
+            ret.push_back(child);
+            PerimeterGeneratorLoops vals = get_all_Childs(child);
+            ret.insert(ret.end(), vals.begin(), vals.end());
+        }
+        return ret;
+    }
+
 void PerimeterGenerator::process()
 {
     // other perimeters
@@ -401,8 +425,30 @@ void PerimeterGenerator::process()
                     NEXT_CONTOUR: ;
                 }
             }
-            // at this point, all loops should be in contours[0]
-            ExtrusionEntityCollection entities = this->_traverse_loops(contours.front(), thin_walls);
+            // at this point, all loops should be in contours[0] (= contours.front() )
+            ExtrusionEntityCollection entities;
+            if (config->perimeter_loop.value) {
+                //onlyone_perimter = >fusion all perimeterLoops
+                for (PerimeterGeneratorLoop &loop : contours.front()) {
+                    ExtrusionLoop extr_loop = this->_traverse_and_join_loops(loop, get_all_Childs(loop), loop.polygon.points.front());
+                    //ExtrusionLoop extr_loop = this->_traverse_and_join_loops_old(loop, loop.polygon.points.front(), true);
+                    extr_loop.paths.back().polyline.points.push_back(extr_loop.paths.front().polyline.points.front());
+                    entities.append(extr_loop);
+                }
+
+                // append thin walls
+                if (!thin_walls.empty()) {
+                    ExtrusionEntityCollection tw = this->_variable_width
+                        (thin_walls, erExternalPerimeter, this->ext_perimeter_flow);
+
+                    entities.append(tw.entities);
+                    thin_walls.clear();
+                }
+            } else {
+                entities = this->_traverse_loops(contours.front(), thin_walls);
+            }
+
+
             // if brim will be printed, reverse the order of perimeters so that
             // we continue inwards after having finished the brim
             // TODO: add test for perimeter order
@@ -487,6 +533,7 @@ void PerimeterGenerator::process()
     } // for each island
 }
 
+
 ExtrusionEntityCollection PerimeterGenerator::_traverse_loops(
     const PerimeterGeneratorLoops &loops, ThickPolylines &thin_walls) const
 {
@@ -596,6 +643,547 @@ ExtrusionEntityCollection PerimeterGenerator::_traverse_loops(
     return entities;
 }
 
+PerimeterIntersectionPoint
+get_nearest_point(const PerimeterGeneratorLoops &children, ExtrusionLoop &myPolylines, const coord_t dist_cut, const coord_t max_dist) {
+    //find best points of intersections
+    PerimeterIntersectionPoint intersect;
+    intersect.distance = 0x7FFFFFFF;
+    intersect.idx_polyline_outter = -1;
+    intersect.idx_children = -1;
+    for (size_t idx_child = 0; idx_child < children.size(); idx_child++) {
+        const PerimeterGeneratorLoop &child = children[idx_child];
+        for (size_t idx_poly = 0; idx_poly < myPolylines.paths.size(); idx_poly++) {
+            if (myPolylines.paths[idx_poly].extruder_id == (unsigned int)-1) continue;
+            if (myPolylines.paths[idx_poly].length() < dist_cut + SCALED_RESOLUTION) continue;
+
+            //first, try to find 2 point near enough
+            for (size_t idx_point = 0; idx_point < myPolylines.paths[idx_poly].polyline.points.size(); idx_point++) {
+                const Point &p = myPolylines.paths[idx_poly].polyline.points[idx_point];
+                const Point &nearest_p = *child.polygon.closest_point(p);
+                const coord_t dist = (coord_t)nearest_p.distance_to(p);
+                if (dist + SCALED_EPSILON / 2 < intersect.distance) {
+                    //ok, copy the idx
+                    intersect.distance = dist;
+                    intersect.idx_children = idx_child;
+                    intersect.idx_polyline_outter = idx_poly;
+                    intersect.outter_best = p;
+                    intersect.child_best = nearest_p;
+                }
+            }
+            if (intersect.distance <= max_dist) {
+                return intersect;
+            }
+
+            //second, try to check from one of my points
+            //don't check the last point, as it's used to go outter, can't use it to go inner.
+            for (size_t idx_point = 1; idx_point < myPolylines.paths[idx_poly].polyline.points.size()-1; idx_point++) {
+                const Point &p = myPolylines.paths[idx_poly].polyline.points[idx_point];
+                Point nearest_p = child.polygon.point_projection(p);
+                coord_t dist = (coord_t)nearest_p.distance_to(p);
+                //if no projection, go to next
+                if (dist == 0) continue;
+                //std::cout << " child point " << idx_point << "/" << (myPolylines[idx_poly].me.polyline.points.size() - 1 )<< " dist = " << unscale(dist) << " < ? " << unscale(intersect.distance)<<" \n";
+                if (dist + SCALED_EPSILON / 2 < intersect.distance) {
+                    //ok, copy the idx
+                    intersect.distance = dist;
+                    intersect.idx_children = idx_child;
+                    intersect.idx_polyline_outter = idx_poly;
+                    intersect.outter_best = p;
+                    intersect.child_best = nearest_p;
+                }
+            }
+            if (intersect.distance <= max_dist) {
+                return intersect;
+            }
+            //lastly, try to check from one of his points
+            for (size_t idx_point = 0; idx_point < child.polygon.points.size(); idx_point++) {
+                const Point &p = child.polygon.points[idx_point];
+                Point nearest_p = myPolylines.paths[idx_poly].polyline.point_projection(p);
+                coord_t dist = (coord_t)nearest_p.distance_to(p);
+                //if no projection, go to next
+                if (dist == 0) continue;
+                //if (nearest_p.coincides_with_epsilon(myPolylines.paths[idx_poly].polyline.points.back())) {
+                //    Line segment(*(myPolylines.paths[idx_poly].polyline.points.end() - 2), myPolylines.paths[idx_poly].polyline.points.back());
+                //    dist = (coord_t)segment.point_at(segment.length() - dist_cut).distance_to(p);
+                //}
+                //std::cout << " my point " << idx_point << " dist=" << unscale(dist) << " <? " << unscale(intersect.distance) << " \n";
+                if (dist + SCALED_EPSILON / 2 < intersect.distance) {
+                    //ok, copy the idx
+                    intersect.distance = dist;
+                    intersect.idx_children = idx_child;
+                    intersect.idx_polyline_outter = idx_poly;
+                    intersect.outter_best = nearest_p;
+                    intersect.child_best = p;
+                }
+            }
+        }
+    }
+    return intersect;
+}
+
+
+int id = 0;
+ExtrusionLoop
+PerimeterGenerator::_extrude_and_cut_loop(const PerimeterGeneratorLoop &loop, const Point entry_point, const Line &direction) const
+{
+
+    const int my_id = ++id;
+    bool need_to_reverse = false;
+    Polyline initial_polyline;
+    const coord_t dist_cut = (coord_t)scale_(this->print_config->nozzle_diameter.get_at(this->config->perimeter_extruder - 1));
+
+
+    if (loop.polygon.points.size() < 3) return ExtrusionLoop(elrDefault);
+    if (loop.polygon.length() < dist_cut * 2) {
+        ExtrusionLoop single_point(elrDefault);
+        Polyline poly_point;
+        poly_point.append(loop.polygon.centroid());
+        single_point.paths.emplace_back(
+            loop.is_external() ? erExternalPerimeter : erPerimeter,
+            (double)(loop.is_external() ? this->_ext_mm3_per_mm : this->_mm3_per_mm),
+            (float)(loop.is_external() ? this->ext_perimeter_flow.width : this->perimeter_flow.width),
+            (float)(this->layer_height));
+        single_point.paths.back().polyline = poly_point;
+        return single_point;
+    }
+    //std::cout << "idx_closest_from_entry_point : " << loop.polygon.closest_point_index(entry_point) << "/" << loop.polygon.points.size()<<"\n";
+    const size_t idx_closest_from_entry_point = loop.polygon.closest_point_index(entry_point);
+    //std::cout << "loop.polygon.points[idx_closest_from_entry_point].distance_to(entry_point) : " << unscale(loop.polygon.points[idx_closest_from_entry_point].distance_to(entry_point)) << "\n";
+    if (loop.polygon.points[idx_closest_from_entry_point].distance_to(entry_point) > SCALED_EPSILON) {
+        //create new Point
+        //get first point
+        size_t idx_before = -1;
+        for (size_t idx_p_a = 0; idx_p_a < loop.polygon.points.size(); ++idx_p_a) {
+            Line l(loop.polygon.points[idx_p_a], loop.polygon.points[(idx_p_a + 1 == loop.polygon.points.size()) ? 0 : (idx_p_a + 1)]);
+            if (entry_point.distance_to(l) < SCALED_EPSILON) {
+                idx_before = idx_p_a;
+                break;
+            }
+        }
+        if (idx_before == (size_t)-1) std::cout << "ERROR: _traverse_and_join_loops : idx_before can't be finded to create new point\n";
+        initial_polyline = loop.polygon.split_at_index(idx_before);
+        initial_polyline.points.push_back(entry_point);
+        initial_polyline.points[0] = entry_point;
+    } else {
+        initial_polyline = loop.polygon.split_at_index(idx_closest_from_entry_point);
+    }
+   
+
+    //std::vector<PerimeterPolylineNode> myPolylines;
+    ExtrusionLoop my_loop;
+
+    ExtrusionLoop svg_out(elrDefault);
+    //overhang / notoverhang
+    {
+        bool is_external = loop.is_external();
+
+        ExtrusionRole role;
+        ExtrusionLoopRole loop_role;
+        role = is_external ? erExternalPerimeter : erPerimeter;
+        if (loop.is_internal_contour()) {
+            // Note that we set loop role to ContourInternalPerimeter
+            // also when loop is both internal and external (i.e.
+            // there's only one contour loop).
+            loop_role = elrContourInternalPerimeter;
+        } else {
+            loop_role = elrDefault;
+        }
+
+        // detect overhanging/bridging perimeters
+        if (this->config->overhangs && this->layer_id > 0
+            && !(this->object_config->support_material && this->object_config->support_material_contact_distance.value == 0)) {
+            ExtrusionPaths paths;
+            // get non-overhang paths by intersecting this loop with the grown lower slices
+            extrusion_paths_append(
+                paths,
+                intersection_pl(initial_polyline, this->_lower_slices_p),
+                role,
+                is_external ? this->_ext_mm3_per_mm : this->_mm3_per_mm,
+                is_external ? this->ext_perimeter_flow.width : this->perimeter_flow.width,
+                this->layer_height);
+
+            // get overhang paths by checking what parts of this loop fall 
+            // outside the grown lower slices (thus where the distance between
+            // the loop centerline and original lower slices is >= half nozzle diameter
+            extrusion_paths_append(
+                paths,
+                diff_pl(initial_polyline, this->_lower_slices_p),
+                erOverhangPerimeter,
+                this->_mm3_per_mm_overhang,
+                this->overhang_flow.width,
+                this->overhang_flow.height);
+
+            // reapply the nearest point search for starting point
+            // We allow polyline reversal because Clipper may have randomly
+            // reversed polylines during clipping.
+            paths = (ExtrusionPaths)ExtrusionEntityCollection(paths).chained_path();
+             
+            
+            if (direction.length() > 0) {
+                Polyline direction_polyline;
+                for (ExtrusionPath &path : paths) {
+                    direction_polyline.points.insert(direction_polyline.points.end(), path.polyline.points.begin(), path.polyline.points.end());
+                }
+                direction_polyline.clip_start(SCALED_RESOLUTION);
+                direction_polyline.clip_end(SCALED_RESOLUTION);
+                coord_t dot = direction.dot(Line(direction_polyline.points.back(), direction_polyline.points.front()));
+                need_to_reverse = dot>0;
+            }
+            if (need_to_reverse) {
+                std::reverse(paths.begin(), paths.end());
+            }
+            //search for the first path
+            size_t good_idx = 0; 
+            for (size_t idx_path = 0; idx_path < paths.size(); idx_path++) {
+                const ExtrusionPath &path = paths[idx_path];
+                if (need_to_reverse) {
+                    if (path.polyline.points.back().coincides_with_epsilon(initial_polyline.points.front())) {
+                        good_idx = idx_path;
+                        break;
+                    }
+                } else {
+                    if (path.polyline.points.front().coincides_with_epsilon(initial_polyline.points.front())) {
+                        good_idx = idx_path;
+                        break;
+                    }
+                }
+            }
+            for (size_t idx_path = good_idx; idx_path < paths.size(); idx_path++) {
+                ExtrusionPath &path = paths[idx_path];
+                if (need_to_reverse) path.reverse();
+                my_loop.paths.emplace_back(path);
+            }
+            for (size_t idx_path = 0; idx_path < good_idx; idx_path++) {
+                ExtrusionPath &path = paths[idx_path];
+                if (need_to_reverse) path.reverse();
+                my_loop.paths.emplace_back(path);
+            }
+        } else {
+
+            if (direction.length() > 0) {
+                Polyline direction_polyline = initial_polyline;
+                direction_polyline.clip_start(SCALED_RESOLUTION);
+                direction_polyline.clip_end(SCALED_RESOLUTION);
+                coord_t dot = direction.dot(Line(direction_polyline.points.back(), direction_polyline.points.front()));
+                need_to_reverse = dot>0;
+            }
+
+            ExtrusionPath path(role);
+            path.polyline = initial_polyline;
+            if (need_to_reverse) path.polyline.reverse();
+            path.mm3_per_mm = is_external ? this->_ext_mm3_per_mm : this->_mm3_per_mm;
+            path.width = is_external ? this->ext_perimeter_flow.width : this->perimeter_flow.width;
+            path.height = (float)(this->layer_height);
+            my_loop.paths.emplace_back(path);
+        }
+
+    }
+    
+    return my_loop;
+}
+
+ExtrusionLoop
+PerimeterGenerator::_traverse_and_join_loops(const PerimeterGeneratorLoop &loop, const PerimeterGeneratorLoops &children, const Point entry_point) const
+{
+    //std::cout << " === ==== _traverse_and_join_loops ==== ===\n";
+
+    const coord_t dist_cut = (coord_t)scale_(this->print_config->nozzle_diameter.get_at(this->config->perimeter_extruder - 1));
+    //TODO change this->external_perimeter_flow.scaled_width() if it's the first one!
+    const coord_t max_width_extrusion = this->perimeter_flow.scaled_width();
+    ExtrusionLoop my_loop = _extrude_and_cut_loop(loop, entry_point);
+    vector<bool> path_is_ccw;
+
+    for (size_t idx_poly = 0; idx_poly < my_loop.paths.size(); idx_poly++) {
+        path_is_ccw.push_back(true);
+    }
+
+    //Polylines myPolylines = { myPolyline };
+    //iterate on each point ot find the best place to go into the child
+    vector<PerimeterGeneratorLoop> childs = children;
+    int child_idx = 0;
+    while (!childs.empty()) {
+        child_idx++;
+        PerimeterIntersectionPoint nearest = get_nearest_point(childs, my_loop, this->perimeter_flow.scaled_width(), this->perimeter_flow.scaled_width()* 0.8);
+        if (nearest.idx_children == (size_t)-1) {
+            //return ExtrusionEntityCollection();
+            break;
+        } else {
+            stringstream log_bef;
+            const PerimeterGeneratorLoop &child = childs[nearest.idx_children];
+            log_bef << "dist travel @search swap is : " << unscale(nearest.outter_best.distance_to(nearest.child_best))
+                << " from " << unscale(nearest.outter_best.x) << ":" << unscale(nearest.outter_best.y)
+                << " to " << unscale(nearest.child_best.x) << ":" << unscale(nearest.child_best.y)
+                << "\n";
+            //std::cout << "c." << child_idx << " === i have " << my_loop.paths.size() << " paths" << " == cut_path_is_ccw size " << path_is_ccw.size() << "\n";
+            //std::cout << "change to child " << nearest.idx_children << " @ " << unscale(nearest.outter_best.x) << ":" << unscale(nearest.outter_best.y)
+            //    << ", idxpolyline = " << nearest.idx_polyline_outter << "\n";
+            //PerimeterGeneratorLoops less_childs = childs;
+            //less_childs.erase(less_childs.begin() + nearest.idx_children);
+            //create new node with recursive ask for the inner perimeter & COPY of the points, ready to be cut
+            const bool cut_path_is_ccw = path_is_ccw[nearest.idx_polyline_outter];
+            my_loop.paths.insert(my_loop.paths.begin() + nearest.idx_polyline_outter + 1, my_loop.paths[nearest.idx_polyline_outter]);
+            path_is_ccw.insert(path_is_ccw.begin() + nearest.idx_polyline_outter + 1, cut_path_is_ccw);
+
+            ExtrusionPath *outer_start = &my_loop.paths[nearest.idx_polyline_outter];
+            ExtrusionPath *outer_end = &my_loop.paths[nearest.idx_polyline_outter + 1];
+            Line deletedSection;
+
+            //cut our polyline
+            //separate them
+            size_t nearest_idx_outter = outer_start->polyline.closest_point_index(nearest.outter_best);
+            if (outer_start->polyline.points[nearest_idx_outter].coincides_with_epsilon(nearest.outter_best)) {
+                if (nearest_idx_outter < outer_start->polyline.points.size() - 1) {
+                    outer_start->polyline.points.erase(outer_start->polyline.points.begin() + nearest_idx_outter + 1, outer_start->polyline.points.end());
+                }
+                if (nearest_idx_outter > 0) {
+                    outer_end->polyline.points.erase(outer_end->polyline.points.begin(), outer_end->polyline.points.begin() + nearest_idx_outter);
+                }
+            } else {
+                //get first point
+                size_t idx_before = -1;
+                for (size_t idx_p_a = 0; idx_p_a < outer_start->polyline.points.size() - 1; ++idx_p_a) {
+                    Line l(outer_start->polyline.points[idx_p_a], outer_start->polyline.points[idx_p_a + 1]);
+                    if (nearest.outter_best.distance_to(l) < SCALED_EPSILON) {
+                        idx_before = idx_p_a;
+                        break;
+                    }
+                }
+                if (idx_before == (size_t)-1) std::cout << "ERROR: idx_before can't be finded\n";
+
+                Points &my_polyline_points = outer_start->polyline.points;
+                my_polyline_points.erase(my_polyline_points.begin() + idx_before + 1, my_polyline_points.end());
+                my_polyline_points.push_back(nearest.outter_best);
+
+                if (idx_before < outer_end->polyline.points.size()-1)
+                    outer_end->polyline.points.erase(outer_end->polyline.points.begin(), outer_end->polyline.points.begin() + idx_before + 1);
+                else
+                    outer_end->polyline.points.erase(outer_end->polyline.points.begin()+1, outer_end->polyline.points.end());
+                outer_end->polyline.points.insert(outer_end->polyline.points.begin(), nearest.outter_best);
+            }
+            log_bef << "dist travel before child loop get is : " << unscale(outer_start->polyline.points.back().distance_to(nearest.child_best))
+                << " from " << unscale(outer_start->polyline.points.back().x) << ":" << unscale(outer_start->polyline.points.back().y)
+                << " to " << unscale(nearest.child_best.x) << ":" << unscale(nearest.child_best.y)
+                << "\n";
+            Polyline to_reduce = outer_start->polyline;
+            if (to_reduce.points.size()>1) to_reduce.clip_end(SCALED_RESOLUTION);
+            deletedSection.a = to_reduce.points.back();
+            to_reduce = outer_end->polyline;
+            if (to_reduce.points.size()>1) to_reduce.clip_start(SCALED_RESOLUTION);
+            deletedSection.b = to_reduce.points.front();
+            
+            //get the inner loop to connect to us.
+            ExtrusionLoop child_loop = _extrude_and_cut_loop(child, nearest.child_best, deletedSection);
+
+            //FIXME: if child_loophas no point or 1 point or not enough space !!!!!!!
+            const size_t child_paths_size = child_loop.paths.size();
+            my_loop.paths.insert(my_loop.paths.begin() + nearest.idx_polyline_outter + 1, child_loop.paths.begin(), child_loop.paths.end());
+            for (size_t i = 0; i < child_paths_size; i++)  path_is_ccw.insert(path_is_ccw.begin() + nearest.idx_polyline_outter + 1, !cut_path_is_ccw);
+            
+            //add paths into my_loop => need to re-get the refs
+            outer_start = &my_loop.paths[nearest.idx_polyline_outter];
+            outer_end = &my_loop.paths[nearest.idx_polyline_outter + child_paths_size + 1];
+            ExtrusionPath *inner_start = &my_loop.paths[nearest.idx_polyline_outter+1];
+            ExtrusionPath *inner_end = &my_loop.paths[nearest.idx_polyline_outter + child_paths_size];
+            log_bef << "dist travel before trim is : " << unscale(outer_start->polyline.points.back().distance_to(inner_start->polyline.points.front()))
+                << " from " << unscale(outer_start->polyline.points.back().x) << ":" << unscale(outer_start->polyline.points.back().y)
+                << " to " << unscale(inner_start->polyline.points.front().x) << ":" << unscale(inner_start->polyline.points.front().y)
+                << "\n";
+            //TRIM
+            //choose trim direction
+            if (outer_start->polyline.points.size() == 1) {
+                outer_end->polyline.clip_start(dist_cut);
+                my_loop.paths[nearest.idx_polyline_outter + child_paths_size ].polyline.clip_end(dist_cut);
+            } else if (outer_end->polyline.points.size() == 1) {
+                outer_start->polyline.clip_end(dist_cut);
+                inner_start->polyline.clip_start(dist_cut);
+            } else {
+                coord_t length_poly_1 = outer_start->polyline.length();
+                coord_t length_poly_2 = outer_end->polyline.length();
+                coord_t length_trim_1 = dist_cut / 2;
+                coord_t length_trim_2 = dist_cut / 2;
+                if (length_poly_1 < length_trim_1) {
+                    length_trim_2 = length_trim_1 + length_trim_2 - length_poly_1;
+                }
+                if (length_poly_2 < length_trim_1) {
+                    length_trim_1 = length_trim_1 + length_trim_2 - length_poly_2;
+                }
+                if (length_poly_1 > length_trim_1) {
+                    outer_start->polyline.clip_end(length_trim_1);
+                } else {
+                    outer_start->polyline.points.erase(outer_start->polyline.points.begin() + 1, outer_start->polyline.points.end());
+                }
+                if (length_poly_2 > length_trim_2) {
+                    outer_end->polyline.clip_start(length_trim_2);
+                } else {
+                    outer_end->polyline.points.erase(outer_end->polyline.points.begin(), outer_end->polyline.points.end() - 1);
+                }
+                
+                length_poly_1 = inner_start->polyline.length();
+                length_poly_2 = inner_end->polyline.length();
+                length_trim_1 = dist_cut / 2;
+                length_trim_2 = dist_cut / 2;
+                if (length_poly_1 < length_trim_1) {
+                    length_trim_2 = length_trim_1 + length_trim_2 - length_poly_1;
+                }
+                if (length_poly_2 < length_trim_1) {
+                    length_trim_1 = length_trim_1 + length_trim_2 - length_poly_2;
+                }
+                if (length_poly_1 > length_trim_1) {
+                    inner_start->polyline.clip_start(length_trim_1);
+                } else {
+                    inner_start->polyline.points.erase(
+                        inner_start->polyline.points.begin(), 
+                        inner_start->polyline.points.end() - 1);
+                }
+                if (length_poly_2 > length_trim_2) {
+                    inner_end->polyline.clip_end(length_trim_2);
+                } else {
+                    inner_end->polyline.points.erase(
+                        inner_end->polyline.points.begin() + 1,
+                        inner_end->polyline.points.end());
+                }
+            }
+
+            //last check to see if we need a reverse
+            {
+                log_bef << "dist travel before swap is : " << unscale(outer_start->polyline.points.back().distance_to(inner_start->polyline.points.front()))
+                    << " from " << unscale(outer_start->polyline.points.back().x) << ":" << unscale(outer_start->polyline.points.back().y)
+                    << " to " << unscale(inner_start->polyline.points.front().x) << ":" << unscale(inner_start->polyline.points.front().y)
+                    << "\n";
+                Line l1(outer_start->polyline.points.back(), inner_start->polyline.points.front());
+                Line l2(inner_end->polyline.points.back(), outer_end->polyline.points.front());
+                Point p_inter(0, 0);
+                bool is_interect = l1.intersection(l2, &p_inter);
+                if (is_interect && p_inter.distance_to(l1) < SCALED_EPSILON && p_inter.distance_to(l2) < SCALED_EPSILON) {
+                    //intersection! need to reverse!
+                    std::reverse(my_loop.paths.begin() + nearest.idx_polyline_outter + 1, my_loop.paths.begin() + nearest.idx_polyline_outter + child_paths_size + 1);
+                    for (size_t idx = nearest.idx_polyline_outter + 1; idx < nearest.idx_polyline_outter + child_paths_size + 1; idx++) {
+                        my_loop.paths[idx].reverse();
+                    }
+                    outer_start = &my_loop.paths[nearest.idx_polyline_outter];
+                    outer_end = &my_loop.paths[nearest.idx_polyline_outter + child_paths_size + 1];
+                    inner_start = &my_loop.paths[nearest.idx_polyline_outter + 1];
+                    inner_end = &my_loop.paths[nearest.idx_polyline_outter + child_paths_size];
+                }
+
+            }
+
+            //now add extrusionPAths to connect the two loops
+            ExtrusionPaths travel_path_begin;// (ExtrusionRole::erNone, 0, outer_start->width, outer_start->height);
+            //travel_path_begin.extruder_id = -1;
+            ExtrusionPaths travel_path_end;// (ExtrusionRole::erNone, 0, outer_end->width, outer_end->height);
+            //travel_path_end.extruder_id = -1;
+            double dist_travel = outer_start->polyline.points.back().distance_to(inner_start->polyline.points.front());
+            if (dist_travel > max_width_extrusion * 10) {
+                std::cout << "ERROR: dist travel is to high : " << unscale(dist_travel)
+                    << " from " << unscale(outer_start->polyline.points.back().x) << ":" << unscale(outer_start->polyline.points.back().y)
+                    << " to " << unscale(inner_start->polyline.points.front().x) << ":" << unscale(inner_start->polyline.points.front().y)
+                    << "\n";
+                std::cout << log_bef.str();
+                //std::cout << log.str();
+            }
+            if (dist_travel > max_width_extrusion*1.5) {
+                travel_path_begin.emplace_back(ExtrusionRole::erPerimeter, outer_start->mm3_per_mm, outer_start->width, outer_start->height);
+                travel_path_begin.emplace_back(ExtrusionRole::erNone, 0, outer_start->width, outer_start->height);
+                travel_path_begin.emplace_back(ExtrusionRole::erPerimeter, outer_start->mm3_per_mm, outer_start->width, outer_start->height);
+                travel_path_begin[0].extruder_id = -1;
+                travel_path_begin[1].extruder_id = -1;
+                travel_path_begin[2].extruder_id = -1;
+                Line line(outer_start->polyline.points.back(), inner_start->polyline.points.front());
+                Point p_dist_cut_extrude = (line.b - line.a);
+                p_dist_cut_extrude.x = (coord_t)(p_dist_cut_extrude.x * ((double)max_width_extrusion) / (line.length() * 2));
+                p_dist_cut_extrude.y = (coord_t)(p_dist_cut_extrude.y * ((double)max_width_extrusion) / (line.length() * 2));
+                //extrude a bit after the turn, to close the loop
+                Point p_start_travel = line.a;
+                p_start_travel += p_dist_cut_extrude;
+                travel_path_begin[0].polyline.append(outer_start->polyline.points.back());
+                travel_path_begin[0].polyline.append(p_start_travel);
+                //extrude a bit before the final turn, to close the loop
+                Point p_end_travel = line.b;
+                p_end_travel -= p_dist_cut_extrude;
+                travel_path_begin[2].polyline.append(p_end_travel);
+                travel_path_begin[2].polyline.append(inner_start->polyline.points.front());
+                //fake travel in the middle
+                travel_path_begin[1].polyline.append(p_start_travel);
+                travel_path_begin[1].polyline.append(p_end_travel);
+            } else {
+                // the path is small enough to extrude all along.
+                double flow_mult = 1;
+                if (dist_travel > max_width_extrusion) {
+                    // the path is a bit too long, reduce the extrusion flow.
+                    flow_mult = max_width_extrusion / dist_travel;
+                }
+                travel_path_begin.emplace_back(ExtrusionRole::erPerimeter, outer_start->mm3_per_mm * flow_mult, (float)(outer_start->width * flow_mult), outer_start->height);
+                travel_path_begin[0].extruder_id = -1;
+                travel_path_begin[0].polyline.append(outer_start->polyline.points.back());
+                travel_path_begin[0].polyline.append(inner_start->polyline.points.front());
+            }
+            dist_travel = inner_end->polyline.points.back().distance_to(outer_end->polyline.points.front());
+            if (dist_travel > max_width_extrusion*1.5) {
+                travel_path_end.emplace_back(ExtrusionRole::erPerimeter, outer_end->mm3_per_mm, outer_end->width, outer_end->height);
+                travel_path_end.emplace_back(ExtrusionRole::erNone, 0, outer_end->width, outer_end->height);
+                travel_path_end.emplace_back(ExtrusionRole::erPerimeter, outer_end->mm3_per_mm, outer_end->width, outer_end->height);
+                travel_path_end[0].extruder_id = -1;
+                travel_path_end[1].extruder_id = -1;
+                travel_path_end[2].extruder_id = -1;
+                Line line(inner_end->polyline.points.back(), outer_end->polyline.points.front());
+                Point p_dist_cut_extrude = (line.b - line.a);
+                p_dist_cut_extrude.x = (coord_t)(p_dist_cut_extrude.x * ((double)max_width_extrusion) / (line.length() * 2));
+                p_dist_cut_extrude.y = (coord_t)(p_dist_cut_extrude.y * ((double)max_width_extrusion) / (line.length() * 2));
+                //extrude a bit after the turn, to close the loop
+                Point p_start_travel_2 = line.a;
+                p_start_travel_2 += p_dist_cut_extrude;
+                travel_path_end[0].polyline.append(inner_end->polyline.points.back());
+                travel_path_end[0].polyline.append(p_start_travel_2);
+                //extrude a bit before the final turn, to close the loop
+                Point p_end_travel_2 = line.b;
+                p_end_travel_2 -= p_dist_cut_extrude;
+                travel_path_end[2].polyline.append(p_end_travel_2);
+                travel_path_end[2].polyline.append(outer_end->polyline.points.front());
+                //fake travel in the middle
+                travel_path_end[1].polyline.append(p_start_travel_2);
+                travel_path_end[1].polyline.append(p_end_travel_2);
+            } else {
+                // the path is small enough to extrude all along.
+                double flow_mult = 1;
+                if (dist_travel > max_width_extrusion) {
+                    // the path is a bit too long, reduce the extrusion flow.
+                    flow_mult = max_width_extrusion / dist_travel;
+                }
+                travel_path_end.emplace_back(ExtrusionRole::erPerimeter, outer_end->mm3_per_mm * flow_mult, (float)(outer_end->width * flow_mult), outer_end->height);
+                travel_path_end[0].extruder_id = -1;
+                travel_path_end[0].polyline.append(inner_end->polyline.points.back());
+                travel_path_end[0].polyline.append(outer_end->polyline.points.front());
+            }
+            //check if we add path or reuse bits
+            if (outer_start->polyline.points.size() == 1) {
+                outer_start->polyline = travel_path_begin.front().polyline;
+                travel_path_begin.erase(travel_path_begin.begin());
+                outer_start->extruder_id = -1;
+            } else if (outer_end->polyline.points.size() == 1) {
+                outer_end->polyline = travel_path_end.back().polyline;
+                travel_path_end.erase(travel_path_end.end() - 1);
+                outer_end->extruder_id = -1;
+            }
+            //add paths into my_loop => after that all ref are wrong!
+            for (int i = travel_path_end.size() - 1; i >= 0; i--) {
+                my_loop.paths.insert(my_loop.paths.begin() + nearest.idx_polyline_outter + child_paths_size + 1, travel_path_end[i]);
+                path_is_ccw.insert(path_is_ccw.begin() + nearest.idx_polyline_outter + child_paths_size + 1, cut_path_is_ccw);
+            }
+            for (int i = travel_path_begin.size() - 1; i >= 0; i--) {
+                my_loop.paths.insert(my_loop.paths.begin() + nearest.idx_polyline_outter + 1, travel_path_begin[i]);
+                path_is_ccw.insert(path_is_ccw.begin() + nearest.idx_polyline_outter + 1, cut_path_is_ccw);
+            }
+        }
+
+        //update for next loop
+        childs.erase(childs.begin() + nearest.idx_children);
+    }
+
+    return my_loop;
+}
+
+
 ExtrusionEntityCollection PerimeterGenerator::_variable_width(const ThickPolylines &polylines, ExtrusionRole role, Flow flow) const
 {
     // this value determines granularity of adaptive width, as G-code does not allow
diff --git a/xs/src/libslic3r/PerimeterGenerator.hpp b/xs/src/libslic3r/PerimeterGenerator.hpp
index f89311c19..57d5f7d13 100644
--- a/xs/src/libslic3r/PerimeterGenerator.hpp
+++ b/xs/src/libslic3r/PerimeterGenerator.hpp
@@ -8,9 +8,18 @@
 #include "Polygon.hpp"
 #include "PrintConfig.hpp"
 #include "SurfaceCollection.hpp"
+#include "ExtrusionEntityCollection.hpp"
 
 namespace Slic3r {
 
+struct PerimeterIntersectionPoint {
+    size_t idx_children;
+    Point child_best;
+    Point outter_best;
+    size_t idx_polyline_outter;
+    coord_t distance;
+};
+
 // Hierarchy of perimeters.
 class PerimeterGeneratorLoop {
 public:
@@ -89,9 +98,11 @@ private:
     double _mm3_per_mm;
     double _mm3_per_mm_overhang;
     Polygons _lower_slices_p;
-    
+
     ExtrusionEntityCollection _traverse_loops(const PerimeterGeneratorLoops &loops,
         ThickPolylines &thin_walls) const;
+    ExtrusionLoop _traverse_and_join_loops(const PerimeterGeneratorLoop &loop, const PerimeterGeneratorLoops &childs, const Point entryPoint) const;
+    ExtrusionLoop _extrude_and_cut_loop(const PerimeterGeneratorLoop &loop, const Point entryPoint, const Line &direction = Line(Point(0,0),Point(0,0))) const;
     ExtrusionEntityCollection _variable_width
         (const ThickPolylines &polylines, ExtrusionRole role, Flow flow) const;
 };
diff --git a/xs/src/libslic3r/Point.hpp b/xs/src/libslic3r/Point.hpp
index 347966c03..ff1f3ecc9 100644
--- a/xs/src/libslic3r/Point.hpp
+++ b/xs/src/libslic3r/Point.hpp
@@ -46,6 +46,8 @@ public:
     Point& operator+=(const Point& rhs) { this->x += rhs.x; this->y += rhs.y; return *this; }
     Point& operator-=(const Point& rhs) { this->x -= rhs.x; this->y -= rhs.y; return *this; }
     Point& operator*=(const coord_t& rhs) { this->x *= rhs; this->y *= rhs;   return *this; }
+    //Point& operator=(const Point& p) { this->x = p.x; this->y = p.y;          return *this; }
+    //Point& operator=(Point&& p) { this->x = p.x; this->y = p.y;               return *this; }
 
     std::string wkt() const;
     std::string dump_perl() const;
diff --git a/xs/src/libslic3r/PrintConfig.cpp b/xs/src/libslic3r/PrintConfig.cpp
index 2c8d78882..463dc7eeb 100644
--- a/xs/src/libslic3r/PrintConfig.cpp
+++ b/xs/src/libslic3r/PrintConfig.cpp
@@ -395,10 +395,18 @@ PrintConfigDef::PrintConfigDef()
     def->label = L("External perimeters first");
     def->category = L("Layers and Perimeters");
     def->tooltip = L("Print contour perimeters from the outermost one to the innermost one "
-                   "instead of the default inverse order.");
+        "instead of the default inverse order.");
     def->cli = "external-perimeters-first!";
     def->default_value = new ConfigOptionBool(false);
 
+    def = this->add("perimeter_loop", coBool);
+    def->label = L("Looping perimeters");
+    def->category = L("Layers and Perimeters");
+    def->tooltip = L("Join the perimeters to create only one continuous extrusion without any z-hop."
+        " Long inside travel (from external to holes) are not extruded to give some place to the infill.");
+    def->cli = "loop-perimeter!";
+    def->default_value = new ConfigOptionBool(false);
+
     def = this->add("extra_perimeters", coBool);
     def->label = L("Extra perimeters if needed");
     def->category = L("Layers and Perimeters");
diff --git a/xs/src/libslic3r/PrintConfig.hpp b/xs/src/libslic3r/PrintConfig.hpp
index 3aadd523c..95a21a89c 100644
--- a/xs/src/libslic3r/PrintConfig.hpp
+++ b/xs/src/libslic3r/PrintConfig.hpp
@@ -433,6 +433,7 @@ public:
     ConfigOptionFloatOrPercent      external_perimeter_extrusion_width;
     ConfigOptionFloatOrPercent      external_perimeter_speed;
     ConfigOptionBool                external_perimeters_first;
+    ConfigOptionBool                perimeter_loop;
     ConfigOptionBool                extra_perimeters;
     ConfigOptionBool                only_one_perimeter_top;
     ConfigOptionFloat               fill_angle;
@@ -485,6 +486,7 @@ protected:
         OPT_PTR(external_perimeter_extrusion_width);
         OPT_PTR(external_perimeter_speed);
         OPT_PTR(external_perimeters_first);
+        OPT_PTR(perimeter_loop);
         OPT_PTR(extra_perimeters);
         OPT_PTR(only_one_perimeter_top);
         OPT_PTR(fill_angle);
diff --git a/xs/src/libslic3r/PrintObject.cpp b/xs/src/libslic3r/PrintObject.cpp
index eba8d19cb..3a3423645 100644
--- a/xs/src/libslic3r/PrintObject.cpp
+++ b/xs/src/libslic3r/PrintObject.cpp
@@ -157,6 +157,7 @@ bool PrintObject::invalidate_state_by_config_options(const std::vector<t_config_
             || opt_key == "infill_overlap"
             || opt_key == "thin_walls"
             || opt_key == "external_perimeters_first"
+            || opt_key == "perimeter_loop"
             || opt_key == "no_perimeter_unsupported"
             || opt_key == "min_perimeter_unsupported"
             || opt_key == "noperi_bridge_only") {
diff --git a/xs/src/libslic3r/SupportMaterial.cpp b/xs/src/libslic3r/SupportMaterial.cpp
index 2dcf30481..15d39fadb 100644
--- a/xs/src/libslic3r/SupportMaterial.cpp
+++ b/xs/src/libslic3r/SupportMaterial.cpp
@@ -1938,8 +1938,8 @@ struct MyLayerExtruded
             *this->m_polygons_to_extrude = union_(*this->m_polygons_to_extrude, true);
         }
         // 2) Merge the extrusions.
-        this->extrusions.insert(this->extrusions.end(), other.extrusions.begin(), other.extrusions.end());
-        other.extrusions.clear();
+        this->extrusions.entities.insert(this->extrusions.entities.end(), other.extrusions.entities.begin(), other.extrusions.entities.end());
+        other.extrusions.entities.clear();
         // 3) Merge the infill polygons.
         Slic3r::polygons_append(this->layer->polygons, std::move(other.layer->polygons));
         this->layer->polygons = union_(this->layer->polygons, true);
@@ -1954,7 +1954,7 @@ struct MyLayerExtruded
     // The source layer. It carries the height and extrusion type (bridging / non bridging, extrusion height).
     PrintObjectSupportMaterial::MyLayer  *layer;
     // Collect extrusions. They will be exported sorted by the bottom height.
-    ExtrusionEntitiesPtr                  extrusions;
+    ExtrusionEntityCollection            extrusions;
     // In case the extrusions are non-empty, m_polygons_to_extrude may contain the rest areas yet to be filled by additional support.
     // This is useful mainly for the loop interfaces, which are generated before the zig-zag infills.
     Polygons                             *m_polygons_to_extrude;
@@ -2188,7 +2188,7 @@ void LoopInterfaceProcessor::generate(MyLayerExtruded &top_contact_layer, const
 
     // Transform loops into ExtrusionPath objects.
     extrusion_entities_append_paths(
-        top_contact_layer.extrusions,
+        top_contact_layer.extrusions.entities,
         STDMOVE(loop_lines),
         erSupportMaterialInterface, flow.mm3_per_mm(), flow.width, flow.height);
 }
@@ -2215,7 +2215,7 @@ static std::string dbg_index_to_color(int idx)
 // to stick too firmly to the object.
 void modulate_extrusion_by_overlapping_layers(
     // Extrusions generated for this_layer.
-    ExtrusionEntitiesPtr                               &extrusions_in_out,
+    ExtrusionEntityCollection                          &extrusions_in_out,
     const PrintObjectSupportMaterial::MyLayer          &this_layer,
     // Multiple layers overlapping with this_layer, sorted bottom up.
     const PrintObjectSupportMaterial::MyLayersPtr      &overlapping_layers)
@@ -2225,10 +2225,12 @@ void modulate_extrusion_by_overlapping_layers(
         // The extrusions do not overlap with any other extrusion.
         return;
 
+    ExtrusionEntityCollection flatten_extrusions_in_out = extrusions_in_out.flatten();
+
     // Get the initial extrusion parameters.
-    ExtrusionPath *extrusion_path_template = dynamic_cast<ExtrusionPath*>(extrusions_in_out.front());
+    ExtrusionPath *extrusion_path_template = dynamic_cast<ExtrusionPath*>(flatten_extrusions_in_out.entities.front());
     assert(extrusion_path_template != nullptr);
-    ExtrusionRole extrusion_role  = extrusion_path_template->role();
+    ExtrusionRole extrusion_role = extrusion_path_template->role();
     float         extrusion_width = extrusion_path_template->width;
 
     struct ExtrusionPathFragment
@@ -2301,7 +2303,7 @@ void modulate_extrusion_by_overlapping_layers(
     // Collect the paths of this_layer.
     {
         Polylines &polylines = path_fragments.back().polylines;
-        for (ExtrusionEntitiesPtr::const_iterator it = extrusions_in_out.begin(); it != extrusions_in_out.end(); ++ it) {
+        for (ExtrusionEntitiesPtr::const_iterator it = flatten_extrusions_in_out.entities.begin(); it != flatten_extrusions_in_out.entities.end(); ++it) {
             ExtrusionPath *path = dynamic_cast<ExtrusionPath*>(*it);
             assert(path != nullptr);
             polylines.emplace_back(Polyline(std::move(path->polyline)));
@@ -2436,18 +2438,18 @@ void modulate_extrusion_by_overlapping_layers(
         if (!multipath.paths.empty()) {
             if (multipath.paths.size() == 1) {
                 // This path was not fragmented.
-                extrusions_in_out.push_back(new ExtrusionPath(std::move(multipath.paths.front())));
+                extrusions_in_out.entities.push_back(new ExtrusionPath(std::move(multipath.paths.front())));
             } else {
                 // This path was fragmented. Copy the collection as a whole object, so the order inside the collection will not be changed
                 // during the chaining of extrusions_in_out.
-                extrusions_in_out.push_back(new ExtrusionMultiPath(std::move(multipath)));
+                extrusions_in_out.entities.push_back(new ExtrusionMultiPath(std::move(multipath)));
             }
         }
     }
     // If there are any non-consumed fragments, add them separately.
     //FIXME this shall not happen, if the Clipper works as expected and all paths split to fragments could be re-connected.
     for (auto it_fragment = path_fragments.begin(); it_fragment != path_fragments.end(); ++ it_fragment)
-        extrusion_entities_append_paths(extrusions_in_out, std::move(it_fragment->polylines), extrusion_role, it_fragment->mm3_per_mm, it_fragment->width, it_fragment->height);
+        extrusion_entities_append_paths(extrusions_in_out.entities, std::move(it_fragment->polylines), extrusion_role, it_fragment->mm3_per_mm, it_fragment->width, it_fragment->height);
 }
 
 void PrintObjectSupportMaterial::generate_toolpaths(
@@ -2742,7 +2744,7 @@ void PrintObjectSupportMaterial::generate_toolpaths(
                 }
                 fill_expolygons_generate_paths(
                     // Destination
-                    layer_ex.extrusions, 
+                    layer_ex.extrusions.entities, 
                     // Regions to fill
                     union_ex(layer_ex.polygons_to_extrude(), true),
                     // Filler and its parameters
@@ -2794,13 +2796,13 @@ void PrintObjectSupportMaterial::generate_toolpaths(
                     // TODO: use offset2_ex()
                     to_infill = offset_ex(to_infill, - 0.4 * float(flow.scaled_spacing()));
                     extrusion_entities_append_paths(
-                        base_layer.extrusions, 
+                        base_layer.extrusions.entities,
                         to_polylines(STDMOVE(to_infill_polygons)),
                         erSupportMaterial, flow.mm3_per_mm(), flow.width, flow.height);
                 }
                 fill_expolygons_generate_paths(
                     // Destination
-                    base_layer.extrusions, 
+                    base_layer.extrusions.entities,
                     // Regions to fill
                     STDMOVE(to_infill), 
                     // Filler and its parameters
diff --git a/xs/src/slic3r/GUI/Preset.cpp b/xs/src/slic3r/GUI/Preset.cpp
index 043118473..5c1463f8a 100644
--- a/xs/src/slic3r/GUI/Preset.cpp
+++ b/xs/src/slic3r/GUI/Preset.cpp
@@ -307,7 +307,7 @@ const std::vector<std::string>& Preset::print_options()
         "wipe_tower", "wipe_tower_x", "wipe_tower_y", "wipe_tower_width", "wipe_tower_rotation_angle", "wipe_tower_bridging",
         "only_one_perimeter_top", "single_extruder_multi_material_priming", "compatible_printers", "compatible_printers_condition", "inherits", 
         "infill_dense", "infill_dense_algo", "no_perimeter_unsupported", "min_perimeter_unsupported", "noperi_bridge_only",
-        "support_material_solid_first_layer", "exact_last_layer_height"
+        "support_material_solid_first_layer", "exact_last_layer_height", "perimeter_loop"
     };
     return s_opts;
 }
diff --git a/xs/src/slic3r/GUI/Tab.cpp b/xs/src/slic3r/GUI/Tab.cpp
index aa29d774f..e1ce5ecb5 100644
--- a/xs/src/slic3r/GUI/Tab.cpp
+++ b/xs/src/slic3r/GUI/Tab.cpp
@@ -821,8 +821,9 @@ void TabPrint::build()
         optgroup->append_line(line);
 
 		optgroup = page->new_optgroup(_(L("Advanced")));
-		optgroup->append_single_option_line("seam_position");
-		optgroup->append_single_option_line("external_perimeters_first");
+        optgroup->append_single_option_line("seam_position");
+        optgroup->append_single_option_line("external_perimeters_first");
+        optgroup->append_single_option_line("perimeter_loop");
 
 	page = add_options_page(_(L("Infill")), "infill.png");
 		optgroup = page->new_optgroup(_(L("Infill")));
@@ -1194,7 +1195,7 @@ void TabPrint::update()
 	bool have_perimeters = m_config->opt_int("perimeters") > 0;
 	for (auto el : {"extra_perimeters", "only_one_perimeter_top", "ensure_vertical_shell_thickness", "thin_walls", "overhangs",
 					"seam_position", "external_perimeters_first", "external_perimeter_extrusion_width",
-					"perimeter_speed", "small_perimeter_speed", "external_perimeter_speed" })
+					"perimeter_speed", "small_perimeter_speed", "external_perimeter_speed", "perimeter_loop" })
 		get_field(el)->toggle(have_perimeters);
 
     bool have_no_perimeter_unsupported = have_perimeters && m_config->opt_bool("no_perimeter_unsupported");