diff --git a/src/libnest2d/include/libnest2d/backends/clipper/CMakeLists.txt b/src/libnest2d/include/libnest2d/backends/clipper/CMakeLists.txt
index 995afcc76..462d1dd06 100644
--- a/src/libnest2d/include/libnest2d/backends/clipper/CMakeLists.txt
+++ b/src/libnest2d/include/libnest2d/backends/clipper/CMakeLists.txt
@@ -64,6 +64,7 @@ endif()
 target_include_directories(ClipperBackend INTERFACE ${Boost_INCLUDE_DIRS} )
 target_sources(ClipperBackend INTERFACE
     ${CMAKE_CURRENT_SOURCE_DIR}/geometries.hpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/clipper_polygon.hpp
     ${SRC_DIR}/libnest2d/utils/boost_alg.hpp )
 
 target_compile_definitions(ClipperBackend INTERFACE LIBNEST2D_BACKEND_CLIPPER)
diff --git a/src/libnest2d/include/libnest2d/backends/clipper/clipper_polygon.hpp b/src/libnest2d/include/libnest2d/backends/clipper/clipper_polygon.hpp
new file mode 100644
index 000000000..e9fbfbd18
--- /dev/null
+++ b/src/libnest2d/include/libnest2d/backends/clipper/clipper_polygon.hpp
@@ -0,0 +1,72 @@
+#ifndef CLIPPER_POLYGON_HPP
+#define CLIPPER_POLYGON_HPP
+
+#include <clipper.hpp>
+
+namespace ClipperLib {
+
+struct Polygon {
+    Path Contour;
+    Paths Holes;
+
+    inline Polygon() = default;
+
+    inline explicit Polygon(const Path& cont): Contour(cont) {}
+    inline explicit Polygon(const Paths& holes):
+        Holes(holes) {}
+    inline Polygon(const Path& cont, const Paths& holes):
+        Contour(cont), Holes(holes) {}
+
+    inline explicit Polygon(Path&& cont): Contour(std::move(cont)) {}
+    inline explicit Polygon(Paths&& holes): Holes(std::move(holes)) {}
+    inline Polygon(Path&& cont, Paths&& holes):
+        Contour(std::move(cont)), Holes(std::move(holes)) {}
+};
+
+inline IntPoint& operator +=(IntPoint& p, const IntPoint& pa ) {
+    // This could be done with SIMD
+    p.X += pa.X;
+    p.Y += pa.Y;
+    return p;
+}
+
+inline IntPoint operator+(const IntPoint& p1, const IntPoint& p2) {
+    IntPoint ret = p1;
+    ret += p2;
+    return ret;
+}
+
+inline IntPoint& operator -=(IntPoint& p, const IntPoint& pa ) {
+    p.X -= pa.X;
+    p.Y -= pa.Y;
+    return p;
+}
+
+inline IntPoint operator -(IntPoint& p ) {
+    IntPoint ret = p;
+    ret.X = -ret.X;
+    ret.Y = -ret.Y;
+    return ret;
+}
+
+inline IntPoint operator-(const IntPoint& p1, const IntPoint& p2) {
+    IntPoint ret = p1;
+    ret -= p2;
+    return ret;
+}
+
+inline IntPoint& operator *=(IntPoint& p, const IntPoint& pa ) {
+    p.X *= pa.X;
+    p.Y *= pa.Y;
+    return p;
+}
+
+inline IntPoint operator*(const IntPoint& p1, const IntPoint& p2) {
+    IntPoint ret = p1;
+    ret *= p2;
+    return ret;
+}
+
+}
+
+#endif // CLIPPER_POLYGON_HPP
diff --git a/src/libnest2d/include/libnest2d/backends/clipper/geometries.hpp b/src/libnest2d/include/libnest2d/backends/clipper/geometries.hpp
index 9f881e7e0..232668f61 100644
--- a/src/libnest2d/include/libnest2d/backends/clipper/geometries.hpp
+++ b/src/libnest2d/include/libnest2d/backends/clipper/geometries.hpp
@@ -10,84 +10,15 @@
 #include <libnest2d/geometry_traits.hpp>
 #include <libnest2d/geometry_traits_nfp.hpp>
 
-#include <clipper.hpp>
-
-namespace ClipperLib {
-using PointImpl = IntPoint;
-using PathImpl = Path;
-using HoleStore = std::vector<PathImpl>;
-
-struct PolygonImpl {
-    PathImpl Contour;
-    HoleStore Holes;
-
-    inline PolygonImpl() = default;
-
-    inline explicit PolygonImpl(const PathImpl& cont): Contour(cont) {}
-    inline explicit PolygonImpl(const HoleStore& holes):
-        Holes(holes) {}
-    inline PolygonImpl(const Path& cont, const HoleStore& holes):
-        Contour(cont), Holes(holes) {}
-
-    inline explicit PolygonImpl(PathImpl&& cont): Contour(std::move(cont)) {}
-    inline explicit PolygonImpl(HoleStore&& holes): Holes(std::move(holes)) {}
-    inline PolygonImpl(Path&& cont, HoleStore&& holes):
-        Contour(std::move(cont)), Holes(std::move(holes)) {}
-};
-
-inline PointImpl& operator +=(PointImpl& p, const PointImpl& pa ) {
-    // This could be done with SIMD
-    p.X += pa.X;
-    p.Y += pa.Y;
-    return p;
-}
-
-inline PointImpl operator+(const PointImpl& p1, const PointImpl& p2) {
-    PointImpl ret = p1;
-    ret += p2;
-    return ret;
-}
-
-inline PointImpl& operator -=(PointImpl& p, const PointImpl& pa ) {
-    p.X -= pa.X;
-    p.Y -= pa.Y;
-    return p;
-}
-
-inline PointImpl operator -(PointImpl& p ) {
-    PointImpl ret = p;
-    ret.X = -ret.X;
-    ret.Y = -ret.Y;
-    return ret;
-}
-
-inline PointImpl operator-(const PointImpl& p1, const PointImpl& p2) {
-    PointImpl ret = p1;
-    ret -= p2;
-    return ret;
-}
-
-inline PointImpl& operator *=(PointImpl& p, const PointImpl& pa ) {
-    p.X *= pa.X;
-    p.Y *= pa.Y;
-    return p;
-}
-
-inline PointImpl operator*(const PointImpl& p1, const PointImpl& p2) {
-    PointImpl ret = p1;
-    ret *= p2;
-    return ret;
-}
-
-}
+#include "clipper_polygon.hpp"
 
 namespace libnest2d {
 
 // Aliases for convinience
-using ClipperLib::PointImpl;
-using ClipperLib::PathImpl;
-using ClipperLib::PolygonImpl;
-using ClipperLib::HoleStore;
+using PointImpl = ClipperLib::IntPoint;
+using PathImpl  = ClipperLib::Path;
+using HoleStore = ClipperLib::Paths;
+using PolygonImpl = ClipperLib::Polygon;
 
 // Type of coordinate units used by Clipper
 template<> struct CoordType<PointImpl> {
@@ -158,33 +89,24 @@ template<> inline TCoord<PointImpl>& y(PointImpl& p)
 #define DISABLE_BOOST_AREA
 
 namespace _smartarea {
+
 template<Orientation o>
 inline double area(const PolygonImpl& /*sh*/) {
     return std::nan("");
 }
 
 template<>
-inline double area<Orientation::CLOCKWISE>(const PolygonImpl& sh) {
-    double a = 0;
-
-    std::for_each(sh.Holes.begin(), sh.Holes.end(), [&a](const PathImpl& h)
-    {
-        a -= ClipperLib::Area(h);
+inline double area<Orientation::COUNTER_CLOCKWISE>(const PolygonImpl& sh) {
+    return std::accumulate(sh.Holes.begin(), sh.Holes.end(),
+                           ClipperLib::Area(sh.Contour),
+                           [](double a, const ClipperLib::Path& pt){
+        return a + ClipperLib::Area(pt);
     });
-
-    return -ClipperLib::Area(sh.Contour) + a;
 }
 
 template<>
-inline double area<Orientation::COUNTER_CLOCKWISE>(const PolygonImpl& sh) {
-    double a = 0;
-
-    std::for_each(sh.Holes.begin(), sh.Holes.end(), [&a](const PathImpl& h)
-    {
-        a += ClipperLib::Area(h);
-    });
-
-    return ClipperLib::Area(sh.Contour) + a;
+inline double area<Orientation::CLOCKWISE>(const PolygonImpl& sh) {
+    return -area<Orientation::COUNTER_CLOCKWISE>(sh);
 }
 
 }
@@ -228,9 +150,10 @@ template<> inline void offset(PolygonImpl& sh, TCoord<PointImpl> distance)
             // but throwing would be an overkill. Instead, we should warn the
             // caller about the inability to create correct geometries
             if(!found_the_contour) {
-                sh.Contour = r;
+                sh.Contour = std::move(r);
                 ClipperLib::ReversePath(sh.Contour);
-                sh.Contour.push_back(sh.Contour.front());
+                auto front_p = sh.Contour.front();
+                sh.Contour.emplace_back(std::move(front_p));
                 found_the_contour = true;
             } else {
                 dout() << "Warning: offsetting result is invalid!";
@@ -240,9 +163,10 @@ template<> inline void offset(PolygonImpl& sh, TCoord<PointImpl> distance)
             // TODO If there are multiple contours we can't be sure which hole
             // belongs to the first contour. (But in this case the situation is
             // bad enough to let it go...)
-            sh.Holes.push_back(r);
+            sh.Holes.emplace_back(std::move(r));
             ClipperLib::ReversePath(sh.Holes.back());
-            sh.Holes.back().push_back(sh.Holes.back().front());
+            auto front_p = sh.Holes.back().front();
+            sh.Holes.back().emplace_back(std::move(front_p));
         }
     }
 }
@@ -390,34 +314,53 @@ inline void rotate(PolygonImpl& sh, const Radians& rads)
 } // namespace shapelike
 
 #define DISABLE_BOOST_NFP_MERGE
-inline std::vector<PolygonImpl> _merge(ClipperLib::Clipper& clipper) {
+inline std::vector<PolygonImpl> clipper_execute(
+        ClipperLib::Clipper& clipper,
+        ClipperLib::ClipType clipType,
+        ClipperLib::PolyFillType subjFillType = ClipperLib::pftEvenOdd,
+        ClipperLib::PolyFillType clipFillType = ClipperLib::pftEvenOdd)
+{
     shapelike::Shapes<PolygonImpl> retv;
 
     ClipperLib::PolyTree result;
-    clipper.Execute(ClipperLib::ctUnion, result, ClipperLib::pftNegative);
+    clipper.Execute(clipType, result, subjFillType, clipFillType);
+
     retv.reserve(static_cast<size_t>(result.Total()));
 
     std::function<void(ClipperLib::PolyNode*, PolygonImpl&)> processHole;
 
     auto processPoly = [&retv, &processHole](ClipperLib::PolyNode *pptr) {
-        PolygonImpl poly(pptr->Contour);
-        poly.Contour.push_back(poly.Contour.front());
+        PolygonImpl poly;
+        poly.Contour.swap(pptr->Contour);
+
+        assert(!pptr->IsHole());
+
+        if(pptr->IsOpen()) {
+            auto front_p = poly.Contour.front();
+            poly.Contour.emplace_back(front_p);
+        }
+
         for(auto h : pptr->Childs) { processHole(h, poly); }
         retv.push_back(poly);
     };
 
     processHole = [&processPoly](ClipperLib::PolyNode *pptr, PolygonImpl& poly)
     {
-        poly.Holes.push_back(pptr->Contour);
-        poly.Holes.back().push_back(poly.Holes.back().front());
+        poly.Holes.emplace_back(std::move(pptr->Contour));
+
+        assert(pptr->IsHole());
+
+        if(pptr->IsOpen()) {
+            auto front_p = poly.Holes.back().front();
+            poly.Holes.back().emplace_back(front_p);
+        }
+
         for(auto c : pptr->Childs) processPoly(c);
     };
 
     auto traverse = [&processPoly] (ClipperLib::PolyNode *node)
     {
-        for(auto ch : node->Childs) {
-            processPoly(ch);
-        }
+        for(auto ch : node->Childs) processPoly(ch);
     };
 
     traverse(&result);
@@ -438,14 +381,13 @@ merge(const std::vector<PolygonImpl>& shapes)
     for(auto& path : shapes) {
         valid &= clipper.AddPath(path.Contour, ClipperLib::ptSubject, closed);
 
-        for(auto& hole : path.Holes) {
-            valid &= clipper.AddPath(hole, ClipperLib::ptSubject, closed);
-        }
+        for(auto& h : path.Holes)
+            valid &= clipper.AddPath(h, ClipperLib::ptSubject, closed);
     }
 
     if(!valid) throw GeometryException(GeomErr::MERGE);
 
-    return _merge(clipper);
+    return clipper_execute(clipper, ClipperLib::ctUnion, ClipperLib::pftNegative);
 }
 
 }
diff --git a/src/libnest2d/include/libnest2d/libnest2d.hpp b/src/libnest2d/include/libnest2d/libnest2d.hpp
index 49baa65f2..c7b252e5d 100644
--- a/src/libnest2d/include/libnest2d/libnest2d.hpp
+++ b/src/libnest2d/include/libnest2d/libnest2d.hpp
@@ -966,7 +966,7 @@ private:
 
         for(size_t i = 0; i < pckgrp.size(); i++) {
             auto items = pckgrp[i];
-            pg.push_back({});
+            pg.emplace_back();
             pg[i].reserve(items.size());
 
             for(Item& itemA : items) {
diff --git a/src/libnest2d/include/libnest2d/placers/nfpplacer.hpp b/src/libnest2d/include/libnest2d/placers/nfpplacer.hpp
index 6fb717a7a..91affe978 100644
--- a/src/libnest2d/include/libnest2d/placers/nfpplacer.hpp
+++ b/src/libnest2d/include/libnest2d/placers/nfpplacer.hpp
@@ -261,7 +261,7 @@ template<class RawShape> class EdgeCache {
             while(next != endit) {
                 contour_.emap.emplace_back(*(first++), *(next++));
                 contour_.full_distance += contour_.emap.back().length();
-                contour_.distances.push_back(contour_.full_distance);
+                contour_.distances.emplace_back(contour_.full_distance);
             }
         }
 
@@ -276,10 +276,10 @@ template<class RawShape> class EdgeCache {
             while(next != endit) {
                 hc.emap.emplace_back(*(first++), *(next++));
                 hc.full_distance += hc.emap.back().length();
-                hc.distances.push_back(hc.full_distance);
+                hc.distances.emplace_back(hc.full_distance);
             }
 
-            holes_.push_back(hc);
+            holes_.emplace_back(std::move(hc));
         }
     }
 
diff --git a/src/libnest2d/include/libnest2d/placers/placer_boilerplate.hpp b/src/libnest2d/include/libnest2d/placers/placer_boilerplate.hpp
index 309a5007d..abcd86183 100644
--- a/src/libnest2d/include/libnest2d/placers/placer_boilerplate.hpp
+++ b/src/libnest2d/include/libnest2d/placers/placer_boilerplate.hpp
@@ -63,7 +63,7 @@ public:
     bool pack(Item& item, const Range& rem = Range()) {
         auto&& r = static_cast<Subclass*>(this)->trypack(item, rem);
         if(r) {
-            items_.push_back(*(r.item_ptr_));
+            items_.emplace_back(*(r.item_ptr_));
             farea_valid_ = false;
         }
         return r;
@@ -78,7 +78,7 @@ public:
         if(r) {
             r.item_ptr_->translation(r.move_);
             r.item_ptr_->rotation(r.rot_);
-            items_.push_back(*(r.item_ptr_));
+            items_.emplace_back(*(r.item_ptr_));
             farea_valid_ = false;
         }
     }
diff --git a/src/libnest2d/include/libnest2d/selections/djd_heuristic.hpp b/src/libnest2d/include/libnest2d/selections/djd_heuristic.hpp
index b03534dc4..25007e580 100644
--- a/src/libnest2d/include/libnest2d/selections/djd_heuristic.hpp
+++ b/src/libnest2d/include/libnest2d/selections/djd_heuristic.hpp
@@ -667,7 +667,7 @@ public:
                 addBin();
                 ItemList& not_packed = not_packeds[b];
                 for(unsigned idx = b; idx < store_.size(); idx+=bincount_guess) {
-                    not_packed.push_back(store_[idx]);
+                    not_packed.emplace_back(store_[idx]);
                 }
             }
 
diff --git a/src/libnest2d/include/libnest2d/utils/boost_alg.hpp b/src/libnest2d/include/libnest2d/utils/boost_alg.hpp
index a6988ca00..baf1c6a10 100644
--- a/src/libnest2d/include/libnest2d/utils/boost_alg.hpp
+++ b/src/libnest2d/include/libnest2d/utils/boost_alg.hpp
@@ -463,7 +463,7 @@ template<> inline std::string serialize<libnest2d::Formats::SVG>(
             auto& v = *it;
             hf.emplace_back(getX(v)*scale, getY(v)*scale);
         };
-        holes.push_back(hf);
+        holes.emplace_back(std::move(hf));
     }
 
     Polygonf poly;
diff --git a/src/libnest2d/tests/printer_parts.h b/src/libnest2d/tests/printer_parts.h
index b9a4eb8fa..1e65826bd 100644
--- a/src/libnest2d/tests/printer_parts.h
+++ b/src/libnest2d/tests/printer_parts.h
@@ -2,36 +2,10 @@
 #define PRINTER_PARTS_H
 
 #include <vector>
-#include <clipper.hpp>
-
-#ifndef CLIPPER_BACKEND_HPP
-namespace ClipperLib {
-using PointImpl = IntPoint;
-using PathImpl = Path;
-using HoleStore = std::vector<PathImpl>;
-
-struct PolygonImpl {
-    PathImpl Contour;
-    HoleStore Holes;
-
-    inline PolygonImpl() {}
-
-    inline explicit PolygonImpl(const PathImpl& cont): Contour(cont) {}
-    inline explicit PolygonImpl(const HoleStore& holes):
-        Holes(holes) {}
-    inline PolygonImpl(const Path& cont, const HoleStore& holes):
-        Contour(cont), Holes(holes) {}
-
-    inline explicit PolygonImpl(PathImpl&& cont): Contour(std::move(cont)) {}
-    inline explicit PolygonImpl(HoleStore&& holes): Holes(std::move(holes)) {}
-    inline PolygonImpl(Path&& cont, HoleStore&& holes):
-        Contour(std::move(cont)), Holes(std::move(holes)) {}
-};
-}
-#endif
+#include <libnest2d/backends/clipper/clipper_polygon.hpp>
 
 using TestData = std::vector<ClipperLib::Path>;
-using TestDataEx = std::vector<ClipperLib::PolygonImpl>;
+using TestDataEx = std::vector<ClipperLib::Polygon>;
 
 extern const TestData PRINTER_PART_POLYGONS;
 extern const TestData STEGOSAUR_POLYGONS;
diff --git a/src/libslic3r/Geometry.hpp b/src/libslic3r/Geometry.hpp
index 380245b5f..d556f664c 100644
--- a/src/libslic3r/Geometry.hpp
+++ b/src/libslic3r/Geometry.hpp
@@ -246,6 +246,7 @@ public:
 
     const Vec3d& get_mirror() const { return m_mirror; }
     double get_mirror(Axis axis) const { return m_mirror(axis); }
+    bool is_left_handed() const { return m_mirror.x() * m_mirror.y() * m_mirror.z() < 0.; }
 
     void set_mirror(const Vec3d& mirror);
     void set_mirror(Axis axis, double mirror);
diff --git a/src/libslic3r/LayerRegion.cpp b/src/libslic3r/LayerRegion.cpp
index 913ba76a6..19fbb3bb6 100644
--- a/src/libslic3r/LayerRegion.cpp
+++ b/src/libslic3r/LayerRegion.cpp
@@ -258,13 +258,18 @@ void LayerRegion::process_external_surfaces(const Layer* lower_layer)
                 #ifdef SLIC3R_DEBUG
                 printf("Processing bridge at layer " PRINTF_ZU ":\n", this->layer()->id());
                 #endif
-                if (bd.detect_angle(Geometry::deg2rad(this->region()->config().bridge_angle.value))) {
+				double custom_angle = Geometry::deg2rad(this->region()->config().bridge_angle.value);
+				if (bd.detect_angle(custom_angle)) {
                     bridges[idx_last].bridge_angle = bd.angle;
                     if (this->layer()->object()->config().support_material) {
                         polygons_append(this->bridged, bd.coverage());
                         this->unsupported_bridge_edges.append(bd.unsupported_edges()); 
                     }
-                }
+				} else if (custom_angle > 0) {
+					// Bridge was not detected (likely it is only supported at one side). Still it is a surface filled in
+					// using a bridging flow, therefore it makes sense to respect the custom bridging direction.
+					bridges[idx_last].bridge_angle = custom_angle;
+				}
                 // without safety offset, artifacts are generated (GH #2494)
                 surfaces_append(bottom, union_ex(grown, true), bridges[idx_last]);
             }
diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index f9db9fea0..b5b9a008d 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -61,7 +61,7 @@ Model& Model::assign_copy(Model &&rhs)
 	this->objects = std::move(rhs.objects);
     for (ModelObject *model_object : this->objects)
         model_object->set_model(this);
-	rhs.objects.clear();
+    rhs.objects.clear();
     return *this;
 }
 
@@ -651,7 +651,7 @@ ModelObject& ModelObject::assign_copy(ModelObject &&rhs)
     for (ModelInstance *model_instance : this->instances)
         model_instance->set_model_object(this);
 
-	return *this;
+    return *this;
 }
 
 void ModelObject::assign_new_unique_ids_recursive()
@@ -970,8 +970,8 @@ Polygon ModelObject::convex_hull_2d(const Transform3d &trafo_instance)
                 }
             }
         }
-	std::sort(pts.begin(), pts.end(), [](const Point& a, const Point& b) { return a(0) < b(0) || (a(0) == b(0) && a(1) < b(1)); });
-	pts.erase(std::unique(pts.begin(), pts.end(), [](const Point& a, const Point& b) { return a(0) == b(0) && a(1) == b(1); }), pts.end());
+    std::sort(pts.begin(), pts.end(), [](const Point& a, const Point& b) { return a(0) < b(0) || (a(0) == b(0) && a(1) < b(1)); });
+    pts.erase(std::unique(pts.begin(), pts.end(), [](const Point& a, const Point& b) { return a(0) == b(0) && a(1) == b(1); }), pts.end());
 
     Polygon hull;
     int n = (int)pts.size();
@@ -1291,11 +1291,11 @@ void ModelObject::split(ModelObjectPtrs* new_objects)
         
         // XXX: this seems to be the only real usage of m_model, maybe refactor this so that it's not needed?
         ModelObject* new_object = m_model->add_object();    
-		new_object->name   = this->name;
-		new_object->config = this->config;
-		new_object->instances.reserve(this->instances.size());
-		for (const ModelInstance *model_instance : this->instances)
-			new_object->add_instance(*model_instance);
+        new_object->name   = this->name;
+        new_object->config = this->config;
+        new_object->instances.reserve(this->instances.size());
+        for (const ModelInstance *model_instance : this->instances)
+            new_object->add_instance(*model_instance);
         ModelVolume* new_vol = new_object->add_volume(*volume, std::move(*mesh));
 #if !ENABLE_VOLUMES_CENTERING_FIXES
         new_vol->center_geometry();
@@ -1467,9 +1467,9 @@ int ModelVolume::extruder_id() const
 
 bool ModelVolume::is_splittable() const
 {
-    // the call mesh.has_multiple_patches() is expensive, so cache the value to calculate it only once
+    // the call mesh.is_splittable() is expensive, so cache the value to calculate it only once
     if (m_is_splittable == -1)
-        m_is_splittable = (int)mesh.has_multiple_patches();
+        m_is_splittable = (int)mesh.is_splittable();
 
     return m_is_splittable == 1;
 }
@@ -1609,6 +1609,7 @@ void ModelVolume::rotate(double angle, Axis axis)
     case X: { rotate(angle, Vec3d::UnitX()); break; }
     case Y: { rotate(angle, Vec3d::UnitY()); break; }
     case Z: { rotate(angle, Vec3d::UnitZ()); break; }
+    default: break;
     }
 }
 
@@ -1625,6 +1626,7 @@ void ModelVolume::mirror(Axis axis)
     case X: { mirror(0) *= -1.0; break; }
     case Y: { mirror(1) *= -1.0; break; }
     case Z: { mirror(2) *= -1.0; break; }
+    default: break;
     }
     set_mirror(mirror);
 }
@@ -1711,7 +1713,6 @@ bool model_object_list_extended(const Model &model_old, const Model &model_new)
 
 bool model_volume_list_changed(const ModelObject &model_object_old, const ModelObject &model_object_new, const ModelVolumeType type)
 {
-    bool modifiers_differ = false;
     size_t i_old, i_new;
     for (i_old = 0, i_new = 0; i_old < model_object_old.volumes.size() && i_new < model_object_new.volumes.size();) {
         const ModelVolume &mv_old = *model_object_old.volumes[i_old];
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index 8a48f8ee9..5cf7f49ca 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -394,6 +394,7 @@ public:
 
     const Vec3d& get_mirror() const { return m_transformation.get_mirror(); }
     double get_mirror(Axis axis) const { return m_transformation.get_mirror(axis); }
+    bool is_left_handed() const { return m_transformation.is_left_handed(); }
 
     void set_mirror(const Vec3d& mirror) { m_transformation.set_mirror(mirror); }
     void set_mirror(Axis axis, double mirror) { m_transformation.set_mirror(axis, mirror); }
@@ -498,6 +499,7 @@ public:
 
     const Vec3d& get_mirror() const { return m_transformation.get_mirror(); }
     double get_mirror(Axis axis) const { return m_transformation.get_mirror(axis); }
+	bool is_left_handed() const { return m_transformation.is_left_handed(); }
 
     void set_mirror(const Vec3d& mirror) { m_transformation.set_mirror(mirror); }
     void set_mirror(Axis axis, double mirror) { m_transformation.set_mirror(axis, mirror); }
diff --git a/src/libslic3r/ModelArrange.cpp b/src/libslic3r/ModelArrange.cpp
index 4942e35b6..54627ba86 100644
--- a/src/libslic3r/ModelArrange.cpp
+++ b/src/libslic3r/ModelArrange.cpp
@@ -574,7 +574,7 @@ ShapeData2D projectModelFromTop(const Slic3r::Model &model) {
 
             for(ModelInstance* objinst : objptr->instances) {
                 if(objinst) {
-                    ClipperLib::PolygonImpl pn;
+                    ClipperLib::Polygon pn;
                     pn.Contour = clpath;
 
                     // Efficient conversion to item.
diff --git a/src/libslic3r/PrintExport.hpp b/src/libslic3r/PrintExport.hpp
index cdb2cc008..04b993a52 100644
--- a/src/libslic3r/PrintExport.hpp
+++ b/src/libslic3r/PrintExport.hpp
@@ -42,8 +42,9 @@ template<FilePrinterFormat format>
 class FilePrinter {
 public:
 
-    // Draw an ExPolygon which is a polygon inside a slice on the specified layer.
+    // Draw a polygon which is a polygon inside a slice on the specified layer.
     void draw_polygon(const ExPolygon& p, unsigned lyr);
+    void draw_polygon(const ClipperLib::Polygon& p, unsigned lyr);
 
     // Tell the printer how many layers should it consider.
     void layers(unsigned layernum);
@@ -221,6 +222,11 @@ public:
         m_layers_rst[lyr].raster.draw(p);
     }
 
+    inline void draw_polygon(const ClipperLib::Polygon& p, unsigned lyr) {
+        assert(lyr < m_layers_rst.size());
+        m_layers_rst[lyr].raster.draw(p);
+    }
+
     inline void begin_layer(unsigned lyr) {
         if(m_layers_rst.size() <= lyr) m_layers_rst.resize(lyr+1);
         m_layers_rst[lyr].raster.reset(m_res, m_pxdim, m_o);
diff --git a/src/libslic3r/Rasterizer/Rasterizer.cpp b/src/libslic3r/Rasterizer/Rasterizer.cpp
index c28e11352..496a584a2 100644
--- a/src/libslic3r/Rasterizer/Rasterizer.cpp
+++ b/src/libslic3r/Rasterizer/Rasterizer.cpp
@@ -1,5 +1,6 @@
 #include "Rasterizer.hpp"
 #include <ExPolygon.hpp>
+#include <libnest2d/backends/clipper/clipper_polygon.hpp>
 
 // For rasterizing
 #include <agg/agg_basics.h>
@@ -89,6 +90,25 @@ public:
         agg::render_scanlines(ras, scanlines, m_renderer);
     }
 
+    void draw(const ClipperLib::Polygon &poly) {
+        agg::rasterizer_scanline_aa<> ras;
+        agg::scanline_p8 scanlines;
+
+        auto&& path = to_path(poly.Contour);
+
+        if(m_o == Origin::TOP_LEFT) flipy(path);
+
+        ras.add_path(path);
+
+        for(auto h : poly.Holes) {
+            auto&& holepath = to_path(h);
+            if(m_o == Origin::TOP_LEFT) flipy(holepath);
+            ras.add_path(holepath);
+        }
+
+        agg::render_scanlines(ras, scanlines, m_renderer);
+    }
+
     inline void clear() {
         m_raw_renderer.clear(ColorBlack);
     }
@@ -108,14 +128,36 @@ private:
         return p(1) * SCALING_FACTOR/m_pxdim.h_mm;
     }
 
-    agg::path_storage to_path(const Polygon& poly) {
+    agg::path_storage to_path(const Polygon& poly)
+    {
         agg::path_storage path;
+
         auto it = poly.points.begin();
         path.move_to(getPx(*it), getPy(*it));
-        while(++it != poly.points.end())
+        while(++it != poly.points.end()) path.line_to(getPx(*it), getPy(*it));
+        path.line_to(getPx(poly.points.front()), getPy(poly.points.front()));
+
+        return path;
+    }
+
+
+    double getPx(const ClipperLib::IntPoint& p) {
+        return p.X * SCALING_FACTOR/m_pxdim.w_mm;
+    }
+
+    double getPy(const ClipperLib::IntPoint& p) {
+        return p.Y * SCALING_FACTOR/m_pxdim.h_mm;
+    }
+
+    agg::path_storage to_path(const ClipperLib::Path& poly)
+    {
+        agg::path_storage path;
+        auto it = poly.begin();
+        path.move_to(getPx(*it), getPy(*it));
+        while(++it != poly.end())
             path.line_to(getPx(*it), getPy(*it));
 
-        path.line_to(getPx(poly.points.front()), getPy(poly.points.front()));
+        path.line_to(getPx(poly.front()), getPy(poly.front()));
         return path;
     }
 
@@ -167,9 +209,13 @@ void Raster::clear()
     m_impl->clear();
 }
 
-void Raster::draw(const ExPolygon &poly)
+void Raster::draw(const ExPolygon &expoly)
+{
+    m_impl->draw(expoly);
+}
+
+void Raster::draw(const ClipperLib::Polygon &poly)
 {
-    assert(m_impl);
     m_impl->draw(poly);
 }
 
diff --git a/src/libslic3r/Rasterizer/Rasterizer.hpp b/src/libslic3r/Rasterizer/Rasterizer.hpp
index 768488adc..671dcbb3d 100644
--- a/src/libslic3r/Rasterizer/Rasterizer.hpp
+++ b/src/libslic3r/Rasterizer/Rasterizer.hpp
@@ -6,6 +6,8 @@
 #include <vector>
 #include <cstdint>
 
+namespace ClipperLib { struct Polygon; }
+
 namespace Slic3r {
 
 class ExPolygon;
@@ -123,6 +125,7 @@ public:
 
     /// Draw a polygon with holes.
     void draw(const ExPolygon& poly);
+    void draw(const ClipperLib::Polygon& poly);
 
     /// Save the raster on the specified stream.
     void save(std::ostream& stream, Compression comp = Compression::RAW);
diff --git a/src/libslic3r/SLA/SLAAutoSupports.cpp b/src/libslic3r/SLA/SLAAutoSupports.cpp
index 9e9f07b6c..0a2537b91 100644
--- a/src/libslic3r/SLA/SLAAutoSupports.cpp
+++ b/src/libslic3r/SLA/SLAAutoSupports.cpp
@@ -49,8 +49,8 @@ float SLAAutoSupports::distance_limit(float angle) const
 }*/
 
 SLAAutoSupports::SLAAutoSupports(const TriangleMesh& mesh, const sla::EigenMesh3D& emesh, const std::vector<ExPolygons>& slices, const std::vector<float>& heights,
-                                   const Config& config, std::function<void(void)> throw_on_cancel)
-: m_config(config), m_emesh(emesh), m_throw_on_cancel(throw_on_cancel)
+                                   const Config& config, std::function<void(void)> throw_on_cancel, std::function<void(int)> statusfn)
+: m_config(config), m_emesh(emesh), m_throw_on_cancel(throw_on_cancel), m_statusfn(statusfn)
 {
     process(slices, heights);
     project_onto_mesh(m_output);
@@ -197,6 +197,9 @@ void SLAAutoSupports::process(const std::vector<ExPolygons>& slices, const std::
     PointGrid3D point_grid;
     point_grid.cell_size = Vec3f(10.f, 10.f, 10.f);
 
+    double increment = 100.0 / layers.size();
+    double status    = 0;
+
     for (unsigned int layer_id = 0; layer_id < layers.size(); ++ layer_id) {
         SLAAutoSupports::MyLayer *layer_top     = &layers[layer_id];
         SLAAutoSupports::MyLayer *layer_bottom  = (layer_id > 0) ? &layers[layer_id - 1] : nullptr;
@@ -252,6 +255,9 @@ void SLAAutoSupports::process(const std::vector<ExPolygons>& slices, const std::
 
         m_throw_on_cancel();
 
+        status += increment;
+        m_statusfn(int(std::round(status)));
+
 #ifdef SLA_AUTOSUPPORTS_DEBUG
         /*std::string layer_num_str = std::string((i<10 ? "0" : "")) + std::string((i<100 ? "0" : "")) + std::to_string(i);
         output_expolygons(expolys_top, "top" + layer_num_str + ".svg");
diff --git a/src/libslic3r/SLA/SLAAutoSupports.hpp b/src/libslic3r/SLA/SLAAutoSupports.hpp
index 038b505da..d32d182bc 100644
--- a/src/libslic3r/SLA/SLAAutoSupports.hpp
+++ b/src/libslic3r/SLA/SLAAutoSupports.hpp
@@ -24,7 +24,7 @@ public:
         };
 
     SLAAutoSupports(const TriangleMesh& mesh, const sla::EigenMesh3D& emesh, const std::vector<ExPolygons>& slices,
-                     const std::vector<float>& heights, const Config& config, std::function<void(void)> throw_on_cancel);
+                     const std::vector<float>& heights, const Config& config, std::function<void(void)> throw_on_cancel, std::function<void(int)> statusfn);
     const std::vector<sla::SupportPoint>& output() { return m_output; }
 
 	struct MyLayer;
@@ -196,12 +196,13 @@ private:
     static void output_structures(const std::vector<Structure> &structures);
 #endif // SLA_AUTOSUPPORTS_DEBUG
 
-    std::function<void(void)> m_throw_on_cancel;
     const sla::EigenMesh3D& m_emesh;
+    std::function<void(void)> m_throw_on_cancel;
+    std::function<void(int)>  m_statusfn;
 };
 
 
 } // namespace Slic3r
 
 
-#endif // SLAAUTOSUPPORTS_HPP_
\ No newline at end of file
+#endif // SLAAUTOSUPPORTS_HPP_
diff --git a/src/libslic3r/SLAPrint.cpp b/src/libslic3r/SLAPrint.cpp
index ee24cf3ec..7dc920517 100644
--- a/src/libslic3r/SLAPrint.cpp
+++ b/src/libslic3r/SLAPrint.cpp
@@ -12,6 +12,9 @@
 #include <boost/filesystem/path.hpp>
 #include <boost/log/trivial.hpp>
 
+// For geometry algorithms with native Clipper types (no copies and conversions)
+#include <libnest2d/backends/clipper/geometries.hpp>
+
 //#include <tbb/spin_mutex.h>//#include "tbb/mutex.h"
 
 #include "I18N.hpp"
@@ -39,37 +42,33 @@ namespace {
 // should add up to 100 (%)
 const std::array<unsigned, slaposCount>     OBJ_STEP_LEVELS =
 {
-    10,     // slaposObjectSlice,
-    30,     // slaposSupportPoints,
-    25,     // slaposSupportTree,
-    25,     // slaposBasePool,
-    5,      // slaposSliceSupports,
-    5       // slaposIndexSlices
+    30,     // slaposObjectSlice,
+    20,     // slaposSupportPoints,
+    10,     // slaposSupportTree,
+    10,     // slaposBasePool,
+    30,     // slaposSliceSupports,
 };
 
 const std::array<std::string, slaposCount> OBJ_STEP_LABELS =
 {
     L("Slicing model"),                 // slaposObjectSlice,
-    L("Generating support points"),      // slaposSupportPoints,
+    L("Generating support points"),     // slaposSupportPoints,
     L("Generating support tree"),       // slaposSupportTree,
     L("Generating pad"),                // slaposBasePool,
     L("Slicing supports"),              // slaposSliceSupports,
-    L("Slicing supports")               // slaposIndexSlices,
 };
 
 // Should also add up to 100 (%)
 const std::array<unsigned, slapsCount> PRINT_STEP_LEVELS =
 {
-    5,      // slapsStats
-    94,     // slapsRasterize
-    1,      // slapsValidate
+    10,      // slapsMergeSlicesAndEval
+    90,      // slapsRasterize
 };
 
 const std::array<std::string, slapsCount> PRINT_STEP_LABELS =
 {
-    L("Calculating statistics"),     // slapsStats
+    L("Merging slices and calculating statistics"),     // slapsStats
     L("Rasterizing layers"),         // slapsRasterize
-    L("Validating"),                 // slapsValidate
 };
 
 }
@@ -94,7 +93,10 @@ static Transform3d sla_trafo(const ModelObject &model_object)
     offset(0) = 0.;
     offset(1) = 0.;
     rotation(2) = 0.;
-    return Geometry::assemble_transform(offset, rotation, model_instance.get_scaling_factor(), model_instance.get_mirror());
+    Transform3d trafo = Geometry::assemble_transform(offset, rotation, model_instance.get_scaling_factor(), model_instance.get_mirror());
+	if (model_instance.is_left_handed())
+		trafo = Eigen::Scaling(Vec3d(-1., 1., 1.)) * trafo;
+    return trafo;
 }
 
 // List of instances, where the ModelInstance transformation is a composite of sla_trafo and the transformation defined by SLAPrintObject::Instance.
@@ -103,10 +105,10 @@ static std::vector<SLAPrintObject::Instance> sla_instances(const ModelObject &mo
     std::vector<SLAPrintObject::Instance> instances;
     for (ModelInstance *model_instance : model_object.instances)
         if (model_instance->is_printable()) {
-            instances.emplace_back(SLAPrintObject::Instance(
+            instances.emplace_back(
                 model_instance->id(),
                 Point::new_scale(model_instance->get_offset(X), model_instance->get_offset(Y)),
-                float(model_instance->get_rotation(Z))));
+                float(model_instance->get_rotation(Z)));
         }
     return instances;
 }
@@ -206,7 +208,7 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
                 model_object_status.emplace(model_object->id(), ModelObjectStatus::Old);
         } else if (model_object_list_extended(m_model, model)) {
             // Add new objects. Their volumes and configs will be synchronized later.
-            update_apply_status(this->invalidate_step(slapsRasterize));
+            update_apply_status(this->invalidate_step(slapsMergeSlicesAndEval));
             for (const ModelObject *model_object : m_model.objects)
                 model_object_status.emplace(model_object->id(), ModelObjectStatus::Old);
             for (size_t i = m_model.objects.size(); i < model.objects.size(); ++ i) {
@@ -218,7 +220,7 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
             // Reorder the objects, add new objects.
             // First stop background processing before shuffling or deleting the PrintObjects in the object list.
             this->call_cancel_callback();
-            update_apply_status(this->invalidate_step(slapsRasterize));
+            update_apply_status(this->invalidate_step(slapsMergeSlicesAndEval));
             // Second create a new list of objects.
             std::vector<ModelObject*> model_objects_old(std::move(m_model.objects));
             m_model.objects.clear();
@@ -315,8 +317,11 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
 				it_print_object_status = print_object_status.end();
 			// Check whether a model part volume was added or removed, their transformations or order changed.
 			bool model_parts_differ = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::MODEL_PART);
-			bool sla_trafo_differs  = model_object.instances.empty() != model_object_new.instances.empty() ||
-				(! model_object.instances.empty() && ! sla_trafo(model_object).isApprox(sla_trafo(model_object_new)));
+			bool sla_trafo_differs  = 
+				model_object.instances.empty() != model_object_new.instances.empty() ||
+				(! model_object.instances.empty() && 
+				  (! sla_trafo(model_object).isApprox(sla_trafo(model_object_new)) || 
+				    model_object.instances.front()->is_left_handed() != model_object_new.instances.front()->is_left_handed()));
 			if (model_parts_differ || sla_trafo_differs) {
 				// The very first step (the slicing step) is invalidated. One may freely remove all associated PrintObjects.
 				if (it_print_object_status != print_object_status.end()) {
@@ -390,7 +395,7 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
 				if (new_instances != it_print_object_status->print_object->instances()) {
 					// Instances changed.
 					it_print_object_status->print_object->set_instances(new_instances);
-					update_apply_status(this->invalidate_step(slapsRasterize));
+                    update_apply_status(this->invalidate_step(slapsMergeSlicesAndEval));
 				}
 				print_objects_new.emplace_back(it_print_object_status->print_object);
 				const_cast<PrintObjectStatus&>(*it_print_object_status).status = PrintObjectStatus::Reused;
@@ -400,9 +405,9 @@ SLAPrint::ApplyStatus SLAPrint::apply(const Model &model, const DynamicPrintConf
 
             // FIXME: this invalidates the transformed mesh in SLAPrintObject
             // which is expensive to calculate (especially the raw_mesh() call)
-            print_object->set_trafo(sla_trafo(model_object));
+            print_object->set_trafo(sla_trafo(model_object), model_object.instances.front()->is_left_handed());
 
-            print_object->set_instances(new_instances);
+            print_object->set_instances(std::move(new_instances));
             print_object->config_apply(config, true);
             print_objects_new.emplace_back(print_object);
             new_objects = true;
@@ -579,11 +584,6 @@ sla::PoolConfig make_pool_config(const SLAPrintObjectConfig& c) {
 
     return pcfg;
 }
-
-void swapXY(ExPolygon& expoly) {
-    for(auto& p : expoly.contour.points) std::swap(p(X), p(Y));
-    for(auto& h : expoly.holes) for(auto& p : h.points) std::swap(p(X), p(Y));
-}
 }
 
 std::string SLAPrint::validate() const
@@ -613,13 +613,17 @@ std::string SLAPrint::validate() const
     return "";
 }
 
-template<class...Args>
-void report_status(SLAPrint& p, int st, const std::string& msg, Args&&...args)
+bool SLAPrint::invalidate_step(SLAPrintStep step)
 {
-    BOOST_LOG_TRIVIAL(info) << st << "% " << msg;
-    p.set_status(st, msg, std::forward<Args>(args)...);
-}
+    bool invalidated = Inherited::invalidate_step(step);
 
+    // propagate to dependent steps
+    if (step == slapsMergeSlicesAndEval) {
+        invalidated |= this->invalidate_all_steps();
+    }
+
+    return invalidated;
+}
 
 void SLAPrint::process()
 {
@@ -639,7 +643,7 @@ void SLAPrint::process()
     const size_t objcount = m_objects.size();
 
     const unsigned min_objstatus = 0;   // where the per object operations start
-    const unsigned max_objstatus = PRINT_STEP_LEVELS[slapsRasterize];  // where the per object operations end
+    const unsigned max_objstatus = 50;  // where the per object operations end
 
     // the coefficient that multiplies the per object status values which
     // are set up for <0, 100>. They need to be scaled into the whole process
@@ -714,7 +718,7 @@ void SLAPrint::process()
 
     // In this step we check the slices, identify island and cover them with
     // support points. Then we sprinkle the rest of the mesh.
-    auto support_points = [this](SLAPrintObject& po) {
+    auto support_points = [this, ostepd](SLAPrintObject& po) {
         const ModelObject& mo = *po.m_model_object;
         po.m_supportdata.reset(
                     new SLAPrintObject::SupportData(po.transformed_mesh()) );
@@ -748,6 +752,19 @@ void SLAPrint::process()
             config.minimal_distance = float(cfg.support_points_minimal_distance);
             config.head_diameter    = float(cfg.support_head_front_diameter);
 
+            // scaling for the sub operations
+            double d = ostepd * OBJ_STEP_LEVELS[slaposSupportPoints] / 100.0;
+            double init = m_report_status.status();
+
+            auto statuscb = [this, d, init](unsigned st)
+            {
+                double current = init + st * d;
+                if(std::round(m_report_status.status()) < std::round(current))
+                    m_report_status(*this, current,
+                                    OBJ_STEP_LABELS[slaposSupportPoints]);
+
+            };
+
             // Construction of this object does the calculation.
             this->throw_if_canceled();
             SLAAutoSupports auto_supports(po.transformed_mesh(),
@@ -755,7 +772,8 @@ void SLAPrint::process()
                                           po.get_model_slices(),
                                           heights,
                                           config, 
-                                          [this]() { throw_if_canceled(); });
+                                          [this]() { throw_if_canceled(); },
+                                          statuscb);
 
             // Now let's extract the result.
             const std::vector<sla::SupportPoint>& points = auto_supports.output();
@@ -766,7 +784,7 @@ void SLAPrint::process()
                                      << po.m_supportdata->support_points.size();
 
             // Using RELOAD_SLA_SUPPORT_POINTS to tell the Plater to pass the update status to GLGizmoSlaSupports
-            report_status(*this, -1, L("Generating support points"), SlicingStatus::RELOAD_SLA_SUPPORT_POINTS);
+            m_report_status(*this, -1, L("Generating support points"), SlicingStatus::RELOAD_SLA_SUPPORT_POINTS);
         }
         else {
             // There are either some points on the front-end, or the user removed them on purpose. No calculation will be done.
@@ -775,7 +793,8 @@ void SLAPrint::process()
     };
 
     // In this step we create the supports
-    auto support_tree = [this, objcount, ostepd](SLAPrintObject& po) {
+    auto support_tree = [this, ostepd](SLAPrintObject& po)
+    {
         if(!po.m_supportdata) return;
 
         if(!po.m_config.supports_enable.getBool()) {
@@ -787,22 +806,17 @@ void SLAPrint::process()
         sla::SupportConfig scfg = make_support_cfg(po.m_config);
         sla::Controller ctl;
 
-        // some magic to scale the status values coming from the support
-        // tree creation into the whole print process
-        auto stfirst = OBJ_STEP_LEVELS.begin();
-        auto stthis = stfirst + slaposSupportTree;
-        // we need to add up the status portions until this operation
-        int init = std::accumulate(stfirst, stthis, 0);
-        init = int(init * ostepd);     // scale the init portion
-
         // scaling for the sub operations
-        double d = *stthis / (objcount * 100.0);
+        double d = ostepd * OBJ_STEP_LEVELS[slaposSupportTree] / 100.0;
+        double init = m_report_status.status();
 
-        ctl.statuscb = [this, init, d](unsigned st, const std::string& msg)
+        ctl.statuscb = [this, d, init](unsigned st, const std::string&)
         {
-            //FIXME this status line scaling does not seem to be correct.
-            // How does it account for an increasing object index?
-            report_status(*this, int(init + st*d), msg);
+            double current = init + st * d;
+            if(std::round(m_report_status.status()) < std::round(current))
+                m_report_status(*this, current,
+                                OBJ_STEP_LABELS[slaposSupportTree]);
+
         };
 
         ctl.stopcondition = [this](){ return canceled(); };
@@ -818,7 +832,7 @@ void SLAPrint::process()
         auto rc = SlicingStatus::RELOAD_SCENE;
 
         // This is to prevent "Done." being displayed during merged_mesh()
-        report_status(*this, -1, L("Visualizing supports"));
+        m_report_status(*this, -1, L("Visualizing supports"));
         po.m_supportdata->support_tree_ptr->merged_mesh();
 
         BOOST_LOG_TRIVIAL(debug) << "Processed support point count "
@@ -828,8 +842,7 @@ void SLAPrint::process()
         if(po.support_mesh().empty())
             BOOST_LOG_TRIVIAL(warning) << "Support mesh is empty";
 
-        report_status(*this, -1, L("Visualizing supports"), rc);
-
+        m_report_status(*this, -1, L("Visualizing supports"), rc);
     };
 
     // This step generates the sla base pad
@@ -877,13 +890,13 @@ void SLAPrint::process()
 
         po.throw_if_canceled();
         auto rc = SlicingStatus::RELOAD_SCENE;
-        report_status(*this, -1, L("Visualizing supports"), rc);
+        m_report_status(*this, -1, L("Visualizing supports"), rc);
     };
 
     // Slicing the support geometries similarly to the model slicing procedure.
     // If the pad had been added previously (see step "base_pool" than it will
     // be part of the slices)
-    auto slice_supports = [](SLAPrintObject& po) {
+    auto slice_supports = [this](SLAPrintObject& po) {
         auto& sd = po.m_supportdata;
 
         if(sd) sd->support_slices.clear();
@@ -906,28 +919,14 @@ void SLAPrint::process()
         {
             po.m_slice_index[i].set_support_slice_idx(po, i);
         }
-    };
 
-    // We have the layer polygon collection but we need to unite them into
-    // an index where the key is the height level in discrete levels (clipper)
-    auto index_slices = [this/*, ilhd*/](SLAPrintObject& /*po*/) {
         // Using RELOAD_SLA_PREVIEW to tell the Plater to pass the update status to the 3D preview to load the SLA slices.
-        report_status(*this, -2, "", SlicingStatus::RELOAD_SLA_PREVIEW);
+        m_report_status(*this, -2, "", SlicingStatus::RELOAD_SLA_PREVIEW);
     };
 
-    auto fillstats = [this]() {
-
-        m_print_statistics.clear();
-
-        // Fill statistics
-        fill_statistics();
-
-        report_status(*this, -2, "", SlicingStatus::RELOAD_SLA_PREVIEW);
-    };
-
-    // Rasterizing the model objects, and their supports
-    auto rasterize = [this, max_objstatus, ilhs]() {
-        if(canceled()) return;
+    // Merging the slices from all the print objects into one slice grid and
+    // calculating print statistics from the merge result.
+    auto merge_slices_and_eval_stats = [this, ilhs]() {
 
         // clear the rasterizer input
         m_printer_input.clear();
@@ -962,6 +961,284 @@ void SLAPrint::process()
             }
         }
 
+        m_print_statistics.clear();
+
+        using ClipperPoint  = ClipperLib::IntPoint;
+        using ClipperPolygon = ClipperLib::Polygon; // see clipper_polygon.hpp in libnest2d
+        using ClipperPolygons = std::vector<ClipperPolygon>;
+        namespace sl = libnest2d::shapelike;    // For algorithms
+
+        // If the raster has vertical orientation, we will flip the coordinates
+        bool flpXY = m_printer_config.display_orientation.getInt() == SLADisplayOrientation::sladoPortrait;
+
+        // Set up custom union and diff functions for clipper polygons
+        auto polyunion = [] (const ClipperPolygons& subjects)
+        {
+            ClipperLib::Clipper clipper;
+
+            bool closed = true;
+
+            for(auto& path : subjects) {
+                clipper.AddPath(path.Contour, ClipperLib::ptSubject, closed);
+                clipper.AddPaths(path.Holes, ClipperLib::ptSubject, closed);
+            }
+
+            auto mode = ClipperLib::pftPositive;
+
+            return libnest2d::clipper_execute(clipper, ClipperLib::ctUnion, mode, mode);
+        };
+
+        auto polydiff = [](const ClipperPolygons& subjects, const ClipperPolygons& clips)
+        {
+            ClipperLib::Clipper clipper;
+
+            bool closed = true;
+
+            for(auto& path : subjects) {
+                clipper.AddPath(path.Contour, ClipperLib::ptSubject, closed);
+                clipper.AddPaths(path.Holes, ClipperLib::ptSubject, closed);
+            }
+
+            for(auto& path : clips) {
+                clipper.AddPath(path.Contour, ClipperLib::ptClip, closed);
+                clipper.AddPaths(path.Holes, ClipperLib::ptClip, closed);
+            }
+
+            auto mode = ClipperLib::pftPositive;
+
+            return libnest2d::clipper_execute(clipper, ClipperLib::ctDifference, mode, mode);
+        };
+
+        // libnest calculates positive area for clockwise polygons, Slic3r is in counter-clockwise
+        auto areafn = [](const ClipperPolygon& poly) { return - sl::area(poly); };
+
+        const double area_fill          = m_printer_config.area_fill.getFloat()*0.01;// 0.5 (50%);
+        const double fast_tilt          = m_printer_config.fast_tilt_time.getFloat();// 5.0;
+        const double slow_tilt          = m_printer_config.slow_tilt_time.getFloat();// 8.0;
+
+        const double init_exp_time      = m_material_config.initial_exposure_time.getFloat();
+        const double exp_time           = m_material_config.exposure_time.getFloat();
+
+        const int    fade_layers_cnt    = m_default_object_config.faded_layers.getInt();// 10 // [3;20]
+
+        const double width              = m_printer_config.display_width.getFloat() / SCALING_FACTOR;
+        const double height             = m_printer_config.display_height.getFloat() / SCALING_FACTOR;
+        const double display_area       = width*height;
+
+        // get polygons for all instances in the object
+        auto get_all_polygons =
+                [flpXY](const ExPolygons& input_polygons,
+                        const std::vector<SLAPrintObject::Instance>& instances,
+                        bool is_lefthanded)
+        {
+            ClipperPolygons polygons;
+            polygons.reserve(input_polygons.size() * instances.size());
+
+            for (const ExPolygon& polygon : input_polygons) {
+                if(polygon.contour.empty()) continue;
+
+                for (size_t i = 0; i < instances.size(); ++i)
+                {
+                    ClipperPolygon poly;
+
+                    // should be a move
+                    poly.Contour.reserve(polygon.contour.size() + 1);
+
+                    for(auto& p : polygon.contour.points)
+                        poly.Contour.emplace_back(p.x(), p.y());
+
+                    auto pfirst = poly.Contour.front();
+                    poly.Contour.emplace_back(pfirst);
+
+                    for(auto& h : polygon.holes) {
+                        poly.Holes.emplace_back();
+                        auto& hole = poly.Holes.back();
+                        hole.reserve(h.points.size() + 1);
+
+                        for(auto& p : h.points) hole.emplace_back(p.x(), p.y());
+                        auto pfirst = hole.front(); hole.emplace_back(pfirst);
+                    }
+
+                    if(is_lefthanded) {
+                        for(auto& p : poly.Contour) p.X = -p.X;
+                        std::reverse(poly.Contour.begin(), poly.Contour.end());
+                        for(auto& h : poly.Holes) {
+                            for(auto& p : h) p.X = -p.X;
+                            std::reverse(h.begin(), h.end());
+                        }
+                    }
+
+                    sl::rotate(poly, double(instances[i].rotation));
+                    sl::translate(poly, ClipperPoint{instances[i].shift(X),
+                                                     instances[i].shift(Y)});
+
+                    if (flpXY) {
+                        for(auto& p : poly.Contour) std::swap(p.X, p.Y);
+                        std::reverse(poly.Contour.begin(), poly.Contour.end());
+
+                        for(auto& h : poly.Holes) {
+                            for(auto& p : h) std::swap(p.X, p.Y);
+                            std::reverse(h.begin(), h.end());
+                        }
+                    }
+
+                    polygons.emplace_back(std::move(poly));
+                }
+            }
+            return polygons;
+        };
+
+        double supports_volume(0.0);
+        double models_volume(0.0);
+
+        double estim_time(0.0);
+
+        size_t slow_layers = 0;
+        size_t fast_layers = 0;
+
+        const double delta_fade_time = (init_exp_time - exp_time) / (fade_layers_cnt + 1);
+        double fade_layer_time = init_exp_time;
+
+        SpinMutex mutex;
+        using Lock = std::lock_guard<SpinMutex>;
+
+        // Going to parallel:
+        auto printlayerfn = [this,
+                // functions and read only vars
+                get_all_polygons, polyunion, polydiff, areafn,
+                area_fill, display_area, exp_time, init_exp_time, fast_tilt, slow_tilt, delta_fade_time,
+
+                // write vars
+                &mutex, &models_volume, &supports_volume, &estim_time, &slow_layers,
+                &fast_layers, &fade_layer_time](size_t sliced_layer_cnt)
+        {
+            PrintLayer& layer = m_printer_input[sliced_layer_cnt];
+
+            // vector of slice record references
+            auto& slicerecord_references = layer.slices();
+
+            if(slicerecord_references.empty()) return;
+
+            // Layer height should match for all object slices for a given level.
+            const auto l_height = double(slicerecord_references.front().get().layer_height());
+
+            // Calculation of the consumed material
+
+            ClipperPolygons model_polygons;
+            ClipperPolygons supports_polygons;
+
+            size_t c = std::accumulate(layer.slices().begin(), layer.slices().end(), 0u, [](size_t a, const SliceRecord& sr) {
+                                           return a + sr.get_slice(soModel).size();
+                                       });
+
+            model_polygons.reserve(c);
+
+            c = std::accumulate(layer.slices().begin(), layer.slices().end(), 0u, [](size_t a, const SliceRecord& sr) {
+                                    return a + sr.get_slice(soModel).size();
+                                });
+
+            supports_polygons.reserve(c);
+
+            for(const SliceRecord& record : layer.slices()) {
+                const SLAPrintObject *po = record.print_obj();
+
+                const ExPolygons &modelslices = record.get_slice(soModel);
+                bool is_lefth = record.print_obj()->is_left_handed();
+                if (!modelslices.empty()) {
+                    ClipperPolygons v = get_all_polygons(modelslices, po->instances(), is_lefth);
+                    for(ClipperPolygon& p_tmp : v) model_polygons.emplace_back(std::move(p_tmp));
+                }
+
+                const ExPolygons &supportslices = record.get_slice(soSupport);
+                if (!supportslices.empty()) {
+                    ClipperPolygons v = get_all_polygons(supportslices, po->instances(), is_lefth);
+                    for(ClipperPolygon& p_tmp : v) supports_polygons.emplace_back(std::move(p_tmp));
+                }
+            }
+
+            model_polygons = polyunion(model_polygons);
+            double layer_model_area = 0;
+            for (const ClipperPolygon& polygon : model_polygons)
+                layer_model_area += areafn(polygon);
+
+            if (layer_model_area < 0 || layer_model_area > 0) {
+                Lock lck(mutex); models_volume += layer_model_area * l_height;
+            }
+
+            if(!supports_polygons.empty()) {
+                if(model_polygons.empty()) supports_polygons = polyunion(supports_polygons);
+                else supports_polygons = polydiff(supports_polygons, model_polygons);
+                // allegedly, union of subject is done withing the diff according to the pftPositive polyFillType
+            }
+
+            double layer_support_area = 0;
+            for (const ClipperPolygon& polygon : supports_polygons)
+                layer_support_area += areafn(polygon);
+
+            if (layer_support_area < 0 || layer_support_area > 0) {
+                Lock lck(mutex); supports_volume += layer_support_area * l_height;
+            }
+
+            // Here we can save the expensively calculated polygons for printing
+            ClipperPolygons trslices;
+            trslices.reserve(model_polygons.size() + supports_polygons.size());
+            for(ClipperPolygon& poly : model_polygons) trslices.emplace_back(std::move(poly));
+            for(ClipperPolygon& poly : supports_polygons) trslices.emplace_back(std::move(poly));
+
+            layer.transformed_slices(polyunion(trslices));
+
+            // Calculation of the slow and fast layers to the future controlling those values on FW
+
+            const bool is_fast_layer = (layer_model_area + layer_support_area) <= display_area*area_fill;
+            const double tilt_time = is_fast_layer ? fast_tilt : slow_tilt;
+
+            { Lock lck(mutex);
+                if (is_fast_layer)
+                    fast_layers++;
+                else
+                    slow_layers++;
+
+
+                // Calculation of the printing time
+
+                if (sliced_layer_cnt < 3)
+                    estim_time += init_exp_time;
+                else if (fade_layer_time > exp_time)
+                {
+                    fade_layer_time -= delta_fade_time;
+                    estim_time += fade_layer_time;
+                }
+                else
+                    estim_time += exp_time;
+
+                estim_time += tilt_time;
+            }
+        };
+
+        // sequential version for debugging:
+        // for(size_t i = 0; i < m_printer_input.size(); ++i) printlayerfn(i);
+        tbb::parallel_for<size_t, decltype(printlayerfn)>(0, m_printer_input.size(), printlayerfn);
+
+        m_print_statistics.support_used_material = supports_volume * SCALING_FACTOR * SCALING_FACTOR;
+        m_print_statistics.objects_used_material = models_volume  * SCALING_FACTOR * SCALING_FACTOR;
+
+        // Estimated printing time
+        // A layers count o the highest object
+        if (m_printer_input.size() == 0)
+            m_print_statistics.estimated_print_time = "N/A";
+        else
+            m_print_statistics.estimated_print_time = get_time_dhms(float(estim_time));
+
+        m_print_statistics.fast_layers_count = fast_layers;
+        m_print_statistics.slow_layers_count = slow_layers;
+
+        m_report_status(*this, -2, "", SlicingStatus::RELOAD_SLA_PREVIEW);
+    };
+
+    // Rasterizing the model objects, and their supports
+    auto rasterize = [this, max_objstatus]() {
+        if(canceled()) return;
+
         // collect all the keys
 
         // If the raster has vertical orientation, we will flip the coordinates
@@ -994,18 +1271,24 @@ void SLAPrint::process()
         auto lvlcnt = unsigned(m_printer_input.size());
         printer.layers(lvlcnt);
 
-        // slot is the portion of 100% that is realted to rasterization
-        unsigned slot = PRINT_STEP_LEVELS[slapsRasterize];
-        // ist: initial state; pst: previous state
-        unsigned ist = max_objstatus, pst = ist;
         // coefficient to map the rasterization state (0-99) to the allocated
         // portion (slot) of the process state
-        double sd = (100 - ist) / 100.0;
+        double sd = (100 - max_objstatus) / 100.0;
+
+        // slot is the portion of 100% that is realted to rasterization
+        unsigned slot = PRINT_STEP_LEVELS[slapsRasterize];
+
+        // pst: previous state
+        double pst = m_report_status.status();
+
+        double increment = (slot * sd) / m_printer_input.size();
+        double dstatus = m_report_status.status();
+
         SpinMutex slck;
 
         // procedure to process one height level. This will run in parallel
         auto lvlfn =
-        [this, &slck, &printer, slot, sd, ist, &pst, flpXY]
+        [this, &slck, &printer, increment, &dstatus, &pst]
             (unsigned level_id)
         {
             if(canceled()) return;
@@ -1015,39 +1298,20 @@ void SLAPrint::process()
             // Switch to the appropriate layer in the printer
             printer.begin_layer(level_id);
 
-            using Instance = SLAPrintObject::Instance;
-
-            auto draw =
-                [&printer, flpXY, level_id](ExPolygon& poly, const Instance& tr)
-            {
-                poly.rotate(double(tr.rotation));
-                poly.translate(tr.shift(X), tr.shift(Y));
-                if(flpXY) swapXY(poly);
+            for(const ClipperLib::Polygon& poly : printlayer.transformed_slices())
                 printer.draw_polygon(poly, level_id);
-            };
-
-            for(const SliceRecord& sr : printlayer.slices()) {
-                if(! sr.print_obj()) continue;
-
-                for(const Instance& inst : sr.print_obj()->instances()) {
-                    ExPolygons objsl = sr.get_slice(soModel);
-                    for(ExPolygon& poly : objsl) draw(poly, inst);
-
-                    ExPolygons supsl = sr.get_slice(soSupport);
-                    for(ExPolygon& poly : supsl) draw(poly, inst);
-                }
-            }
 
             // Finish the layer for later saving it.
             printer.finish_layer(level_id);
 
             // Status indication guarded with the spinlock
-            auto st = ist + unsigned(sd*level_id*slot/m_printer_input.size());
             {
                 std::lock_guard<SpinMutex> lck(slck);
-                if( st > pst) {
-                    report_status(*this, int(st),
-                                  PRINT_STEP_LABELS[slapsRasterize]);
+                dstatus += increment;
+                double st = std::round(dstatus);
+                if(st > pst) {
+                    m_report_status(*this, st,
+                                    PRINT_STEP_LABELS[slapsRasterize]);
                     pst = st;
                 }
             }
@@ -1079,18 +1343,16 @@ void SLAPrint::process()
         support_points,
         support_tree,
         base_pool,
-        slice_supports,
-        index_slices
+        slice_supports
     };
 
     std::array<slapsFn, slapsCount> print_program =
     {
-        fillstats,
-        rasterize,
-        [](){}  // validate
+        merge_slices_and_eval_stats,
+        rasterize
     };
 
-    unsigned st = min_objstatus;
+    double st = min_objstatus;
     unsigned incr = 0;
 
     BOOST_LOG_TRIVIAL(info) << "Start slicing process.";
@@ -1104,18 +1366,18 @@ void SLAPrint::process()
 
             BOOST_LOG_TRIVIAL(info) << "Slicing object " << po->model_object()->name;
 
-            for (int s = (int)step_ranges[idx_range]; s < (int)step_ranges[idx_range + 1]; ++s) {
-                auto currentstep = (SLAPrintObjectStep)s;
+            for (int s = int(step_ranges[idx_range]); s < int(step_ranges[idx_range + 1]); ++s) {
+                auto currentstep = static_cast<SLAPrintObjectStep>(s);
 
                 // Cancellation checking. Each step will check for cancellation
                 // on its own and return earlier gracefully. Just after it returns
                 // execution gets to this point and throws the canceled signal.
                 throw_if_canceled();
 
-                st += unsigned(incr * ostepd);
+                st += incr * ostepd;
 
                 if(po->m_stepmask[currentstep] && po->set_started(currentstep)) {
-                    report_status(*this, int(st), OBJ_STEP_LABELS[currentstep]);
+                    m_report_status(*this, st, OBJ_STEP_LABELS[currentstep]);
                     pobj_program[currentstep](*po);
                     throw_if_canceled();
                     po->set_done(currentstep);
@@ -1127,7 +1389,7 @@ void SLAPrint::process()
     }
 
     std::array<SLAPrintStep, slapsCount> printsteps = {
-        slapsStats, slapsRasterize, slapsValidate
+        slapsMergeSlicesAndEval, slapsRasterize
     };
 
     // this would disable the rasterization step
@@ -1142,17 +1404,17 @@ void SLAPrint::process()
 
         if(m_stepmask[currentstep] && set_started(currentstep))
         {
-            report_status(*this, int(st), PRINT_STEP_LABELS[currentstep]);
+            m_report_status(*this, st, PRINT_STEP_LABELS[currentstep]);
             print_program[currentstep]();
             throw_if_canceled();
             set_done(currentstep);
         }
 
-        st += unsigned(PRINT_STEP_LEVELS[currentstep] * pstd);
+        st += PRINT_STEP_LEVELS[currentstep] * pstd;
     }
 
     // If everything vent well
-    report_status(*this, 100, L("Slicing done"));
+    m_report_status(*this, 100, L("Slicing done"));
 }
 
 bool SLAPrint::invalidate_state_by_config_options(const std::vector<t_config_option_key> &opt_keys)
@@ -1193,11 +1455,11 @@ bool SLAPrint::invalidate_state_by_config_options(const std::vector<t_config_opt
         if (steps_rasterize.find(opt_key) != steps_rasterize.end()) {
             // These options only affect the final rasterization, or they are just notes without influence on the output,
             // so there is nothing to invalidate.
-            steps.emplace_back(slapsRasterize);
+            steps.emplace_back(slapsMergeSlicesAndEval);
         } else if (steps_ignore.find(opt_key) != steps_ignore.end()) {
             // These steps have no influence on the output. Just ignore them.
         } else if (opt_key == "initial_layer_height") {
-            steps.emplace_back(slapsRasterize);
+            steps.emplace_back(slapsMergeSlicesAndEval);
             osteps.emplace_back(slaposObjectSlice);
         } else {
             // All values should be covered.
@@ -1215,165 +1477,6 @@ bool SLAPrint::invalidate_state_by_config_options(const std::vector<t_config_opt
     return invalidated;
 }
 
-void SLAPrint::fill_statistics()
-{
-    const double init_layer_height  = m_material_config.initial_layer_height.getFloat();
-    const double layer_height       = m_default_object_config.layer_height.getFloat();
-
-    const double area_fill          = m_printer_config.area_fill.getFloat()*0.01;// 0.5 (50%);
-    const double fast_tilt          = m_printer_config.fast_tilt_time.getFloat();// 5.0;
-    const double slow_tilt          = m_printer_config.slow_tilt_time.getFloat();// 8.0;
-
-    const double init_exp_time      = m_material_config.initial_exposure_time.getFloat();
-    const double exp_time           = m_material_config.exposure_time.getFloat();
-
-    const int    fade_layers_cnt    = m_default_object_config.faded_layers.getInt();// 10 // [3;20]
-
-    const double width              = m_printer_config.display_width.getFloat() / SCALING_FACTOR;
-    const double height             = m_printer_config.display_height.getFloat() / SCALING_FACTOR;
-    const double display_area       = width*height;
-
-    // get polygons for all instances in the object
-    auto get_all_polygons = [](const ExPolygons& input_polygons, const std::vector<SLAPrintObject::Instance>& instances) {
-        const size_t inst_cnt = instances.size();
-
-        size_t polygon_cnt = 0;
-        for (const ExPolygon& polygon : input_polygons)
-			polygon_cnt += polygon.holes.size() + 1;
-
-        Polygons polygons;
-        polygons.reserve(polygon_cnt * inst_cnt);
-        for (const ExPolygon& polygon : input_polygons) {
-            for (size_t i = 0; i < inst_cnt; ++i)
-            {
-                ExPolygon tmp = polygon;
-                tmp.rotate(double(instances[i].rotation));
-                tmp.translate(instances[i].shift.x(), instances[i].shift.y());
-                polygons_append(polygons, to_polygons(std::move(tmp)));
-            }
-        }
-        return polygons;
-    };
-
-    double supports_volume = 0.0;
-    double models_volume = 0.0;
-
-    double estim_time = 0.0;
-
-    size_t slow_layers = 0;
-    size_t fast_layers = 0;
-
-    // find highest object
-    // Which is a better bet? To compare by max_z or by number of layers in the index?
-    // float max_z = 0.;
-	size_t max_layers_cnt = 0;
-    size_t highest_obj_idx = 0;
-	for (SLAPrintObject *&po : m_objects) {
-        auto& slice_index = po->get_slice_index();
-        if (! slice_index.empty()) {
-            // float z = (-- slice_index.end())->slice_level();
-            size_t cnt = slice_index.size();
-            //if (z > max_z) {
-            if (cnt > max_layers_cnt) {
-                max_layers_cnt = cnt;
-                // max_z = z;
-                highest_obj_idx = &po - &m_objects.front();
-            }
-        }
-    }
-
-    const SLAPrintObject * highest_obj = m_objects[highest_obj_idx];
-    auto& highest_obj_slice_index = highest_obj->get_slice_index();
-
-    const double delta_fade_time = (init_exp_time - exp_time) / (fade_layers_cnt + 1);
-    double fade_layer_time = init_exp_time;
-
-    int sliced_layer_cnt = 0;
-    for (const SliceRecord& layer : highest_obj_slice_index)
-    {
-        const auto l_height = double(layer.layer_height());
-
-        // Calculation of the consumed material 
-
-        Polygons model_polygons;
-        Polygons supports_polygons;
-
-        for (SLAPrintObject * po : m_objects)
-        {
-            const SliceRecord *record = nullptr;
-            {
-                const SliceRecord& slr = po->closest_slice_to_slice_level(layer.slice_level(), float(EPSILON));
-                if (!slr.is_valid()) continue;
-                record = &slr;
-            }
-
-            const ExPolygons &modelslices = record->get_slice(soModel);
-            if (!modelslices.empty())
-                append(model_polygons, get_all_polygons(modelslices, po->instances()));
-
-            const ExPolygons &supportslices = record->get_slice(soSupport);
-            if (!supportslices.empty())
-                append(supports_polygons, get_all_polygons(supportslices, po->instances()));
-        }
-        
-        model_polygons = union_(model_polygons);
-        double layer_model_area = 0;
-        for (const Polygon& polygon : model_polygons)
-            layer_model_area += polygon.area();
-
-        if (layer_model_area != 0)
-            models_volume += layer_model_area * l_height;
-
-        if (!supports_polygons.empty() && !model_polygons.empty())
-            supports_polygons = diff(supports_polygons, model_polygons);
-        double layer_support_area = 0;
-        for (const Polygon& polygon : supports_polygons)
-            layer_support_area += polygon.area();
-
-        if (layer_support_area != 0)
-            supports_volume += layer_support_area * l_height;
-
-        // Calculation of the slow and fast layers to the future controlling those values on FW
-
-        const bool is_fast_layer = (layer_model_area + layer_support_area) <= display_area*area_fill;
-        const double tilt_time = is_fast_layer ? fast_tilt : slow_tilt;
-        if (is_fast_layer)
-            fast_layers++;
-        else
-            slow_layers++;
-
-
-        // Calculation of the printing time
-
-        if (sliced_layer_cnt < 3)
-            estim_time += init_exp_time;
-        else if (fade_layer_time > exp_time)
-        {
-            fade_layer_time -= delta_fade_time;
-            estim_time += fade_layer_time;
-        }
-        else
-            estim_time += exp_time;
-
-        estim_time += tilt_time;
-
-        sliced_layer_cnt++;
-    }
-
-    m_print_statistics.support_used_material = supports_volume * SCALING_FACTOR * SCALING_FACTOR; 
-    m_print_statistics.objects_used_material = models_volume  * SCALING_FACTOR * SCALING_FACTOR;
-
-    // Estimated printing time
-    // A layers count o the highest object 
-    if (max_layers_cnt == 0)
-        m_print_statistics.estimated_print_time = "N/A";
-    else
-        m_print_statistics.estimated_print_time = get_time_dhms(float(estim_time));
-
-    m_print_statistics.fast_layers_count = fast_layers;
-    m_print_statistics.slow_layers_count = slow_layers;
-}
-
 // Returns true if an object step is done on all objects and there's at least one object.
 bool SLAPrint::is_step_done(SLAPrintObjectStep step) const
 {
@@ -1459,19 +1562,16 @@ bool SLAPrintObject::invalidate_step(SLAPrintObjectStep step)
     if (step == slaposObjectSlice) {
         invalidated |= this->invalidate_all_steps();
     } else if (step == slaposSupportPoints) {
-        invalidated |= this->invalidate_steps({ slaposSupportTree, slaposBasePool, slaposSliceSupports, slaposIndexSlices });
-        invalidated |= m_print->invalidate_step(slapsRasterize);
+        invalidated |= this->invalidate_steps({ slaposSupportTree, slaposBasePool, slaposSliceSupports });
+        invalidated |= m_print->invalidate_step(slapsMergeSlicesAndEval);
     } else if (step == slaposSupportTree) {
-        invalidated |= this->invalidate_steps({ slaposBasePool, slaposSliceSupports, slaposIndexSlices });
-        invalidated |= m_print->invalidate_step(slapsRasterize);
+        invalidated |= this->invalidate_steps({ slaposBasePool, slaposSliceSupports });
+        invalidated |= m_print->invalidate_step(slapsMergeSlicesAndEval);
     } else if (step == slaposBasePool) {
-        invalidated |= this->invalidate_steps({slaposSliceSupports, slaposIndexSlices});
-        invalidated |= m_print->invalidate_step(slapsRasterize);
+        invalidated |= this->invalidate_steps({slaposSliceSupports});
+        invalidated |= m_print->invalidate_step(slapsMergeSlicesAndEval);
     } else if (step == slaposSliceSupports) {
-        invalidated |= this->invalidate_step(slaposIndexSlices);
-        invalidated |= m_print->invalidate_step(slapsRasterize);
-    } else if(step == slaposIndexSlices) {
-        invalidated |= m_print->invalidate_step(slapsRasterize);
+        invalidated |= m_print->invalidate_step(slapsMergeSlicesAndEval);
     }
     return invalidated;
 }
@@ -1547,18 +1647,6 @@ const ExPolygons &SliceRecord::get_slice(SliceOrigin o) const
     return idx >= v.size() ? EMPTY_SLICE : v[idx];
 }
 
-const std::vector<SliceRecord> & SLAPrintObject::get_slice_index() const
-{
-    // assert(is_step_done(slaposIndexSlices));
-    return m_slice_index;
-}
-
-const std::vector<ExPolygons> &SLAPrintObject::get_model_slices() const
-{
-    // assert(is_step_done(slaposObjectSlice));
-    return m_model_slices;
-}
-
 bool SLAPrintObject::has_mesh(SLAPrintObjectStep step) const
 {
     switch (step) {
@@ -1650,7 +1738,8 @@ DynamicConfig SLAPrintStatistics::placeholders()
         "print_time", "total_cost", "total_weight",
         "objects_used_material", "support_used_material" })
         config.set_key_value(key, new ConfigOptionString(std::string("{") + key + "}"));
-        return config;
+
+    return config;
 }
 
 std::string SLAPrintStatistics::finalize_output_path(const std::string &path_in) const
@@ -1670,4 +1759,12 @@ std::string SLAPrintStatistics::finalize_output_path(const std::string &path_in)
     return final_path;
 }
 
+void SLAPrint::StatusReporter::operator()(
+        SLAPrint &p, double st, const std::string &msg, unsigned flags)
+{
+    m_st = st;
+    BOOST_LOG_TRIVIAL(info) << st << "% " << msg;
+    p.set_status(int(std::round(st)), msg, flags);
+}
+
 } // namespace Slic3r
diff --git a/src/libslic3r/SLAPrint.hpp b/src/libslic3r/SLAPrint.hpp
index d831908c7..a1e382acb 100644
--- a/src/libslic3r/SLAPrint.hpp
+++ b/src/libslic3r/SLAPrint.hpp
@@ -6,14 +6,14 @@
 #include "PrintExport.hpp"
 #include "Point.hpp"
 #include "MTUtils.hpp"
+#include <libnest2d/backends/clipper/clipper_polygon.hpp>
 #include "Zipper.hpp"
 
 namespace Slic3r {
 
 enum SLAPrintStep : unsigned int {
-    slapsStats,
-	slapsRasterize,
-	slapsValidate,
+    slapsMergeSlicesAndEval,
+    slapsRasterize,
 	slapsCount
 };
 
@@ -22,8 +22,7 @@ enum SLAPrintObjectStep : unsigned int {
 	slaposSupportPoints,
 	slaposSupportTree,
 	slaposBasePool,
-	slaposSliceSupports,
-    slaposIndexSlices,
+    slaposSliceSupports,
 	slaposCount
 };
 
@@ -52,6 +51,7 @@ public:
 
     const SLAPrintObjectConfig& config() const { return m_config; }
     const Transform3d&          trafo()  const { return m_trafo; }
+    bool                        is_left_handed() const { return m_left_handed; }
 
     struct Instance {
     	Instance(ModelID instance_id, const Point &shift, float rotation) : instance_id(instance_id), shift(shift), rotation(rotation) {}
@@ -127,7 +127,7 @@ public:
 
         bool is_valid() const { return ! std::isnan(m_slice_z); }
 
-        const SLAPrintObject* print_obj() const { return m_po; }
+        const SLAPrintObject* print_obj() const { assert(m_po); return m_po; }
 
         // Methods for setting the indices into the slice vectors.
         void set_model_slice_idx(const SLAPrintObject &po, size_t id) {
@@ -190,7 +190,7 @@ private:
         return it;
     }
 
-    const std::vector<ExPolygons>& get_model_slices() const;
+    const std::vector<ExPolygons>& get_model_slices() const { return m_model_slices; }
     const std::vector<ExPolygons>& get_support_slices() const;
 
 public:
@@ -205,7 +205,9 @@ public:
     // /////////////////////////////////////////////////////////////////////////
 
     // Retrieve the slice index.
-    const std::vector<SliceRecord>& get_slice_index() const;
+    const std::vector<SliceRecord>& get_slice_index() const {
+        return m_slice_index;
+    }
 
     // Search slice index for the closest slice to given print_level.
     // max_epsilon gives the allowable deviation of the returned slice record's
@@ -240,11 +242,12 @@ protected:
     void                    config_apply_only(const ConfigBase &other, const t_config_option_keys &keys, bool ignore_nonexistent = false) 
     	{ this->m_config.apply_only(other, keys, ignore_nonexistent); }
 
-    void                    set_trafo(const Transform3d& trafo) {
-        m_transformed_rmesh.invalidate([this, &trafo](){ m_trafo = trafo; });
+    void                    set_trafo(const Transform3d& trafo, bool left_handed) {
+		m_transformed_rmesh.invalidate([this, &trafo, left_handed](){ m_trafo = trafo; m_left_handed = left_handed; });
     }
 
-    void                    set_instances(const std::vector<Instance> &instances) { m_instances = instances; }
+    template<class InstVec> inline void set_instances(InstVec&& instances) { m_instances = std::forward<InstVec>(instances); }
+
     // Invalidates the step, and its depending steps in SLAPrintObject and SLAPrint.
     bool                    invalidate_step(SLAPrintObjectStep step);
     bool                    invalidate_all_steps();
@@ -261,6 +264,8 @@ private:
 
     // Translation in Z + Rotation by Y and Z + Scaling / Mirroring.
     Transform3d                             m_trafo = Transform3d::Identity();
+    // m_trafo is left handed -> 3x3 affine transformation has negative determinant.
+    bool                                    m_left_handed = false;
 
     std::vector<Instance> 					m_instances;
 
@@ -367,31 +372,6 @@ private: // Prevents erroneous use by other classes.
 
 public:
 
-    // An aggregation of SliceRecord-s from all the print objects for each
-    // occupied layer. Slice record levels dont have to match exactly.
-    // They are unified if the level difference is within +/- SCALED_EPSILON
-    class PrintLayer {
-        coord_t m_level;
-
-        // The collection of slice records for the current level.
-        std::vector<std::reference_wrapper<const SliceRecord>> m_slices;
-
-    public:
-
-        explicit PrintLayer(coord_t lvl) : m_level(lvl) {}
-
-        // for being sorted in their container (see m_printer_input)
-        bool operator<(const PrintLayer& other) const {
-            return m_level < other.m_level;
-        }
-
-        void add(const SliceRecord& sr) { m_slices.emplace_back(sr); }
-
-        coord_t level() const { return m_level; }
-
-        auto slices() const -> const decltype (m_slices)& { return m_slices; }
-    };
-
     SLAPrint(): m_stepmask(slapsCount, true) {}
 
     virtual ~SLAPrint() override { this->clear(); }
@@ -407,7 +387,7 @@ public:
     // Returns true if an object step is done on all objects and there's at least one object.    
     bool                is_step_done(SLAPrintObjectStep step) const;
     // Returns true if the last step was finished with success.
-	bool                finished() const override { return this->is_step_done(slaposIndexSlices) && this->Inherited::is_step_done(slapsRasterize); }
+    bool                finished() const override { return this->is_step_done(slaposSliceSupports) && this->Inherited::is_step_done(slapsRasterize); }
 
     template<class Fmt = SLAminzZipper>
     void export_raster(const std::string& fname) {
@@ -427,6 +407,43 @@ public:
 
     std::string validate() const override;
 
+    // An aggregation of SliceRecord-s from all the print objects for each
+    // occupied layer. Slice record levels dont have to match exactly.
+    // They are unified if the level difference is within +/- SCALED_EPSILON
+    class PrintLayer {
+        coord_t m_level;
+
+        // The collection of slice records for the current level.
+        std::vector<std::reference_wrapper<const SliceRecord>> m_slices;
+
+        std::vector<ClipperLib::Polygon> m_transformed_slices;
+
+        template<class Container> void transformed_slices(Container&& c) {
+            m_transformed_slices = std::forward<Container>(c);
+        }
+
+        friend void SLAPrint::process();
+
+    public:
+
+        explicit PrintLayer(coord_t lvl) : m_level(lvl) {}
+
+        // for being sorted in their container (see m_printer_input)
+        bool operator<(const PrintLayer& other) const {
+            return m_level < other.m_level;
+        }
+
+        void add(const SliceRecord& sr) { m_slices.emplace_back(sr); }
+
+        coord_t level() const { return m_level; }
+
+        auto slices() const -> const decltype (m_slices)& { return m_slices; }
+
+        const std::vector<ClipperLib::Polygon> & transformed_slices() const {
+            return m_transformed_slices;
+        }
+    };
+
     // The aggregated and leveled print records from various objects.
     // TODO: use this structure for the preview in the future.
     const std::vector<PrintLayer>& print_layers() const { return m_printer_input; }
@@ -435,11 +452,12 @@ private:
     using SLAPrinter = FilePrinter<FilePrinterFormat::SLA_PNGZIP>;
     using SLAPrinterPtr = std::unique_ptr<SLAPrinter>;
 
+    // Implement same logic as in SLAPrintObject
+    bool invalidate_step(SLAPrintStep st);
+
     // Invalidate steps based on a set of parameters changed.
     bool invalidate_state_by_config_options(const std::vector<t_config_option_key> &opt_keys);
 
-    void fill_statistics();
-
     SLAPrintConfig                  m_print_config;
     SLAPrinterConfig                m_printer_config;
     SLAMaterialConfig               m_material_config;
@@ -457,6 +475,15 @@ private:
     // Estimated print time, material consumed.
     SLAPrintStatistics                      m_print_statistics;
 
+    class StatusReporter {
+        double m_st = 0;
+    public:
+        void operator() (SLAPrint& p, double st, const std::string& msg,
+                         unsigned flags = SlicingStatus::DEFAULT);
+        double status() const { return m_st; }
+    } m_report_status;
+
+
 	friend SLAPrintObject;
 };
 
diff --git a/src/libslic3r/TriangleMesh.cpp b/src/libslic3r/TriangleMesh.cpp
index eaa11b738..c145380c9 100644
--- a/src/libslic3r/TriangleMesh.cpp
+++ b/src/libslic3r/TriangleMesh.cpp
@@ -55,7 +55,7 @@ TriangleMesh::TriangleMesh(const Pointf3s &points, const std::vector<Vec3crd>& f
     stl.stats.original_num_facets = stl.stats.number_of_facets;
     stl_allocate(&stl);
 
-    for (int i = 0; i < stl.stats.number_of_facets; i++) {
+    for (uint32_t i = 0; i < stl.stats.number_of_facets; i++) {
         stl_facet facet;
         facet.vertex[0] = points[facets[i](0)].cast<float>();
         facet.vertex[1] = points[facets[i](1)].cast<float>();
@@ -125,9 +125,9 @@ void TriangleMesh::repair()
 	float tolerance = stl.stats.shortest_edge;
     float increment = stl.stats.bounding_diameter / 10000.0;
     int iterations = 2;
-    if (stl.stats.connected_facets_3_edge < stl.stats.number_of_facets) {
+    if (stl.stats.connected_facets_3_edge < (int)stl.stats.number_of_facets) {
         for (int i = 0; i < iterations; i++) {
-            if (stl.stats.connected_facets_3_edge < stl.stats.number_of_facets) {
+            if (stl.stats.connected_facets_3_edge < (int)stl.stats.number_of_facets) {
                 //printf("Checking nearby. Tolerance= %f Iteration=%d of %d...", tolerance, i + 1, iterations);
 #ifdef SLIC3R_TRACE_REPAIR
 				BOOST_LOG_TRIVIAL(trace) << "\tstl_check_faces_nearby";
@@ -143,7 +143,7 @@ void TriangleMesh::repair()
     }
     
     // remove_unconnected
-    if (stl.stats.connected_facets_3_edge <  stl.stats.number_of_facets) {
+    if (stl.stats.connected_facets_3_edge < (int)stl.stats.number_of_facets) {
 #ifdef SLIC3R_TRACE_REPAIR
         BOOST_LOG_TRIVIAL(trace) << "\tstl_remove_unconnected_facets";
 #endif /* SLIC3R_TRACE_REPAIR */
@@ -212,9 +212,9 @@ void TriangleMesh::check_topology()
     float tolerance = stl.stats.shortest_edge;
     float increment = stl.stats.bounding_diameter / 10000.0;
     int iterations = 2;
-    if (stl.stats.connected_facets_3_edge < stl.stats.number_of_facets) {
+    if (stl.stats.connected_facets_3_edge < (int)stl.stats.number_of_facets) {
         for (int i = 0; i < iterations; i++) {
-            if (stl.stats.connected_facets_3_edge < stl.stats.number_of_facets) {
+            if (stl.stats.connected_facets_3_edge < (int)stl.stats.number_of_facets) {
                 //printf("Checking nearby. Tolerance= %f Iteration=%d of %d...", tolerance, i + 1, iterations);
                 stl_check_facets_nearby(&stl, tolerance);
                 //printf("  Fixed %d edges.\n", stl.stats.edges_fixed - last_edges_fixed);
@@ -338,113 +338,79 @@ void TriangleMesh::rotate(double angle, Point* center)
     this->translate(c(0), c(1), 0);
 }
 
-bool TriangleMesh::has_multiple_patches() const
+/**
+ * Calculates whether or not the mesh is splittable.
+ */
+bool TriangleMesh::is_splittable() const
 {
-    // we need neighbors
-    if (!this->repaired)
-        throw std::runtime_error("split() requires repair()");
-    
-    if (this->stl.stats.number_of_facets == 0)
-        return false;
+    std::vector<unsigned char> visited;
+    find_unvisited_neighbors(visited);
 
-    std::vector<int>  facet_queue(this->stl.stats.number_of_facets, 0);
-    std::vector<char> facet_visited(this->stl.stats.number_of_facets, false);
-    int               facet_queue_cnt = 1;
-    facet_queue[0] = 0;
-    facet_visited[0] = true;
-    while (facet_queue_cnt > 0) {
-        int facet_idx = facet_queue[-- facet_queue_cnt];
-        facet_visited[facet_idx] = true;
-        for (int j = 0; j < 3; ++ j) {
-            int neighbor_idx = this->stl.neighbors_start[facet_idx].neighbor[j];
-            if (neighbor_idx != -1 && ! facet_visited[neighbor_idx])
-                facet_queue[facet_queue_cnt ++] = neighbor_idx;
-        }
-    }
-
-    // If any of the face was not visited at the first time, return "multiple bodies".
-    for (int facet_idx = 0; facet_idx < this->stl.stats.number_of_facets; ++ facet_idx)
-        if (! facet_visited[facet_idx])
-            return true;
-    return false;
+    // Try finding an unvisited facet. If there are none, the mesh is not splittable.
+    auto it = std::find(visited.begin(), visited.end(), false);
+    return it != visited.end();
 }
 
-size_t TriangleMesh::number_of_patches() const
+/**
+ * Visit all unvisited neighboring facets that are reachable from the first unvisited facet,
+ * and return them.
+ * 
+ * @param facet_visited A reference to a vector of booleans. Contains whether or not a
+ *                      facet with the same index has been visited.
+ * @return A deque with all newly visited facets.
+ */
+std::deque<uint32_t> TriangleMesh::find_unvisited_neighbors(std::vector<unsigned char> &facet_visited) const
 {
-    // we need neighbors
+    // Make sure we're not operating on a broken mesh.
     if (!this->repaired)
-        throw std::runtime_error("split() requires repair()");
-    
-    if (this->stl.stats.number_of_facets == 0)
-        return false;
+        throw std::runtime_error("find_unvisited_neighbors() requires repair()");
 
-    std::vector<int>  facet_queue(this->stl.stats.number_of_facets, 0);
-    std::vector<char> facet_visited(this->stl.stats.number_of_facets, false);
-    int               facet_queue_cnt = 0;
-    size_t            num_bodies = 0;
-    for (;;) {
-        // Find a seeding triangle for a new body.
-        int facet_idx = 0;
-        for (; facet_idx < this->stl.stats.number_of_facets; ++ facet_idx)
-            if (! facet_visited[facet_idx]) {
-                // A seed triangle was found.
-                facet_queue[facet_queue_cnt ++] = facet_idx;
-                facet_visited[facet_idx] = true;
-                break;
-            }
-        if (facet_idx == this->stl.stats.number_of_facets)
-            // No seed found.
-            break;
-        ++ num_bodies;
-        while (facet_queue_cnt > 0) {
-            int facet_idx = facet_queue[-- facet_queue_cnt];
-            facet_visited[facet_idx] = true;
-            for (int j = 0; j < 3; ++ j) {
-                int neighbor_idx = this->stl.neighbors_start[facet_idx].neighbor[j];
-                if (neighbor_idx != -1 && ! facet_visited[neighbor_idx])
-                    facet_queue[facet_queue_cnt ++] = neighbor_idx;
-            }
-        }
+    // If the visited list is empty, populate it with false for every facet.
+    if (facet_visited.empty())
+        facet_visited = std::vector<unsigned char>(this->stl.stats.number_of_facets, false);
+
+    // Find the first unvisited facet.
+    std::queue<uint32_t> facet_queue;
+    std::deque<uint32_t> facets;
+    auto facet = std::find(facet_visited.begin(), facet_visited.end(), false);
+    if (facet != facet_visited.end()) {
+        uint32_t idx = uint32_t(facet - facet_visited.begin());
+        facet_queue.push(idx);
+        facet_visited[idx] = true;
+        facets.emplace_back(idx);
     }
 
-    return num_bodies;
+    // Traverse all reachable neighbors and mark them as visited.
+    while (! facet_queue.empty()) {
+        uint32_t facet_idx = facet_queue.front();
+        facet_queue.pop();
+        for (int neighbor_idx : this->stl.neighbors_start[facet_idx].neighbor)
+            if (neighbor_idx != -1 && ! facet_visited[neighbor_idx]) {
+                facet_queue.push(uint32_t(neighbor_idx));
+                facet_visited[neighbor_idx] = true;
+                facets.emplace_back(uint32_t(neighbor_idx));
+            }
+    }
+
+    return facets;
 }
 
+/**
+ * Splits a mesh into multiple meshes when possible.
+ * 
+ * @return A TriangleMeshPtrs with the newly created meshes.
+ */
 TriangleMeshPtrs TriangleMesh::split() const
 {
-    TriangleMeshPtrs            meshes;
-    std::vector<unsigned char>  facet_visited(this->stl.stats.number_of_facets, false);
-    
-    // we need neighbors
-    if (!this->repaired)
-        throw std::runtime_error("split() requires repair()");
-    
-    // loop while we have remaining facets
+    // Loop while we have remaining facets.
+    std::vector<unsigned char> facet_visited;
+    TriangleMeshPtrs meshes;
     for (;;) {
-        // get the first facet
-        std::queue<int> facet_queue;
-        std::deque<int> facets;
-        for (int facet_idx = 0; facet_idx < this->stl.stats.number_of_facets; ++ facet_idx) {
-            if (! facet_visited[facet_idx]) {
-                // if facet was not seen put it into queue and start searching
-                facet_queue.push(facet_idx);
-                break;
-            }
-        }
-        if (facet_queue.empty())
+        std::deque<uint32_t> facets = find_unvisited_neighbors(facet_visited);
+        if (facets.empty())
             break;
 
-        while (! facet_queue.empty()) {
-            int facet_idx = facet_queue.front();
-            facet_queue.pop();
-            if (! facet_visited[facet_idx]) {
-                facets.emplace_back(facet_idx);
-                for (int j = 0; j < 3; ++ j)
-                    facet_queue.push(this->stl.neighbors_start[facet_idx].neighbor[j]);
-                facet_visited[facet_idx] = true;
-            }
-        }
-
+        // Create a new mesh for the part that was just split off.
         TriangleMesh* mesh = new TriangleMesh;
         meshes.emplace_back(mesh);
         mesh->stl.stats.type = inmemory;
@@ -452,14 +418,15 @@ TriangleMeshPtrs TriangleMesh::split() const
         mesh->stl.stats.original_num_facets = mesh->stl.stats.number_of_facets;
         stl_clear_error(&mesh->stl);
         stl_allocate(&mesh->stl);
-        
+
+        // Assign the facets to the new mesh.
         bool first = true;
-        for (std::deque<int>::const_iterator facet = facets.begin(); facet != facets.end(); ++ facet) {
+        for (auto facet = facets.begin(); facet != facets.end(); ++ facet) {
             mesh->stl.facet_start[facet - facets.begin()] = this->stl.facet_start[*facet];
             stl_facet_stats(&mesh->stl, this->stl.facet_start[*facet], first);
         }
     }
-    
+
     return meshes;
 }
 
@@ -476,7 +443,7 @@ void TriangleMesh::merge(const TriangleMesh &mesh)
     stl_reallocate(&this->stl);
     
     // copy facets
-    for (int i = 0; i < mesh.stl.stats.number_of_facets; ++ i)
+    for (uint32_t i = 0; i < mesh.stl.stats.number_of_facets; ++ i)
         this->stl.facet_start[number_of_facets + i] = mesh.stl.facet_start[i];
     
     // update size
@@ -489,7 +456,7 @@ ExPolygons TriangleMesh::horizontal_projection() const
 {
     Polygons pp;
     pp.reserve(this->stl.stats.number_of_facets);
-    for (int i = 0; i < this->stl.stats.number_of_facets; ++ i) {
+    for (uint32_t i = 0; i < this->stl.stats.number_of_facets; ++ i) {
         stl_facet* facet = &this->stl.facet_start[i];
         Polygon p;
         p.points.resize(3);
@@ -531,7 +498,7 @@ BoundingBoxf3 TriangleMesh::transformed_bounding_box(const Transform3d &trafo) c
     BoundingBoxf3 bbox;
     if (stl.v_shared == nullptr) {
         // Using the STL faces.
-        for (int i = 0; i < this->facets_count(); ++ i) {
+        for (size_t i = 0; i < this->facets_count(); ++ i) {
             const stl_facet &facet = this->stl.facet_start[i];
             for (size_t j = 0; j < 3; ++ j)
                 bbox.merge(trafo * facet.vertex[j].cast<double>());
@@ -656,7 +623,7 @@ void TriangleMeshSlicer::init(TriangleMesh *_mesh, throw_on_cancel_callback_type
     };
     std::vector<EdgeToFace> edges_map;
     edges_map.assign(this->mesh->stl.stats.number_of_facets * 3, EdgeToFace());
-    for (int facet_idx = 0; facet_idx < this->mesh->stl.stats.number_of_facets; ++ facet_idx)
+    for (uint32_t facet_idx = 0; facet_idx < this->mesh->stl.stats.number_of_facets; ++ facet_idx)
         for (int i = 0; i < 3; ++ i) {
             EdgeToFace &e2f = edges_map[facet_idx*3+i];
             e2f.vertex_low  = this->mesh->stl.v_indices[facet_idx].vertex[i];
@@ -905,7 +872,6 @@ TriangleMeshSlicer::FacetSliceType TriangleMeshSlicer::slice_facet(
             const stl_normal &normal = this->mesh->stl.facet_start[facet_idx].normal;
             // We may ignore this edge for slicing purposes, but we may still use it for object cutting.
             FacetSliceType    result = Slicing;
-            const stl_neighbors &nbr = this->mesh->stl.neighbors_start[facet_idx];
             if (min_z == max_z) {
                 // All three vertices are aligned with slice_z.
                 line_out->edge_type = feHorizontal;
@@ -917,8 +883,6 @@ TriangleMeshSlicer::FacetSliceType TriangleMeshSlicer::slice_facet(
                 }
             } else {
                 // Two vertices are aligned with the cutting plane, the third vertex is below or above the cutting plane.
-                int  nbr_idx     = j % 3;
-                int  nbr_face    = nbr.neighbor[nbr_idx];
                 // Is the third vertex below the cutting plane?
                 bool third_below = v0.z() < slice_z || v1.z() < slice_z || v2.z() < slice_z;
                 // Two vertices on the cutting plane, the third vertex is below the plane. Consider the edge to be part of the slice
@@ -1697,7 +1661,7 @@ void TriangleMeshSlicer::cut(float z, TriangleMesh* upper, TriangleMesh* lower)
     
     BOOST_LOG_TRIVIAL(trace) << "TriangleMeshSlicer::cut - slicing object";
     float scaled_z = scale_(z);
-    for (int facet_idx = 0; facet_idx < this->mesh->stl.stats.number_of_facets; ++ facet_idx) {
+    for (uint32_t facet_idx = 0; facet_idx < this->mesh->stl.stats.number_of_facets; ++ facet_idx) {
         stl_facet* facet = &this->mesh->stl.facet_start[facet_idx];
         
         // find facet extents
diff --git a/src/libslic3r/TriangleMesh.hpp b/src/libslic3r/TriangleMesh.hpp
index a4387e5c1..a65a4be75 100644
--- a/src/libslic3r/TriangleMesh.hpp
+++ b/src/libslic3r/TriangleMesh.hpp
@@ -68,18 +68,14 @@ public:
     size_t facets_count() const { return this->stl.stats.number_of_facets; }
     bool   empty() const { return this->facets_count() == 0; }
 
-    // Returns true, if there are two and more connected patches in the mesh.
-    // Returns false, if one or zero connected patch is in the mesh.
-    bool has_multiple_patches() const;
-
-    // Count disconnected triangle patches.
-    size_t number_of_patches() const;
+    bool is_splittable() const;
 
     stl_file stl;
     bool repaired;
     
 private:
     void require_shared_vertices();
+    std::deque<uint32_t> find_unvisited_neighbors(std::vector<unsigned char> &facet_visited) const;
     friend class TriangleMeshSlicer;
 };
 
diff --git a/src/libslic3r/Utils.hpp b/src/libslic3r/Utils.hpp
index c13df4546..dfd72b7a9 100644
--- a/src/libslic3r/Utils.hpp
+++ b/src/libslic3r/Utils.hpp
@@ -208,7 +208,7 @@ public:
 
 // Shorten the dhms time by removing the seconds, rounding the dhm to full minutes
 // and removing spaces.
-static std::string short_time(const std::string &time)
+inline std::string short_time(const std::string &time)
 {
     // Parse the dhms time format.
     int days = 0;
@@ -247,7 +247,7 @@ static std::string short_time(const std::string &time)
 }
 
 // Returns the given time is seconds in format DDd HHh MMm SSs
-static std::string get_time_dhms(float time_in_secs)
+inline std::string get_time_dhms(float time_in_secs)
 {
     int days = (int)(time_in_secs / 86400.0f);
     time_in_secs -= (float)days * 86400.0f;
diff --git a/src/slic3r.cpp b/src/slic3r.cpp
index 5198eeaa3..958b66305 100644
--- a/src/slic3r.cpp
+++ b/src/slic3r.cpp
@@ -361,6 +361,14 @@ int CLI::run(int argc, char **argv)
                 std::string outfile = m_config.opt_string("output");
                 Print       fff_print;
                 SLAPrint    sla_print;
+
+                sla_print.set_status_callback(
+                            [](const PrintBase::SlicingStatus& s)
+                {
+                    if(s.percent >= 0) // FIXME: is this sufficient?
+                        printf("%3d%s %s\n", s.percent, "% =>", s.text.c_str());
+                });
+
                 PrintBase  *print = (printer_technology == ptFFF) ? static_cast<PrintBase*>(&fff_print) : static_cast<PrintBase*>(&sla_print);
                 if (! m_config.opt_bool("dont_arrange")) {
                     //FIXME make the min_object_distance configurable.
diff --git a/src/slic3r/GUI/3DScene.cpp b/src/slic3r/GUI/3DScene.cpp
index 58011730b..7ba61bdb6 100644
--- a/src/slic3r/GUI/3DScene.cpp
+++ b/src/slic3r/GUI/3DScene.cpp
@@ -333,6 +333,13 @@ Transform3d GLVolume::world_matrix() const
     return m;
 }
 
+bool GLVolume::is_left_handed() const
+{
+    const Vec3d &m1 = m_instance_transformation.get_mirror();
+    const Vec3d &m2 = m_volume_transformation.get_mirror();
+    return m1.x() * m1.y() * m1.z() * m2.x() * m2.y() * m2.z() < 0.;
+}
+
 const BoundingBoxf3& GLVolume::transformed_bounding_box() const
 {
 	assert(bounding_box.defined || bounding_box.min(0) >= bounding_box.max(0) || bounding_box.min(1) >= bounding_box.max(1) || bounding_box.min(2) >= bounding_box.max(2));
@@ -401,6 +408,8 @@ void GLVolume::render() const
     if (!is_active)
         return;
 
+    if (this->is_left_handed())
+        glFrontFace(GL_CW);
     glsafe(::glCullFace(GL_BACK));
     glsafe(::glPushMatrix());
 
@@ -410,6 +419,8 @@ void GLVolume::render() const
     else
         this->indexed_vertex_array.render();
     glsafe(::glPopMatrix());
+    if (this->is_left_handed())
+        glFrontFace(GL_CCW);
 }
 
 void GLVolume::render_VBOs(int color_id, int detection_id, int worldmatrix_id) const
@@ -420,6 +431,9 @@ void GLVolume::render_VBOs(int color_id, int detection_id, int worldmatrix_id) c
     if (!indexed_vertex_array.vertices_and_normals_interleaved_VBO_id)
         return;
 
+    if (this->is_left_handed())
+        glFrontFace(GL_CW);
+
     GLsizei n_triangles = GLsizei(std::min(indexed_vertex_array.triangle_indices_size, tverts_range.second - tverts_range.first));
     GLsizei n_quads = GLsizei(std::min(indexed_vertex_array.quad_indices_size, qverts_range.second - qverts_range.first));
     if (n_triangles + n_quads == 0)
@@ -481,6 +495,9 @@ void GLVolume::render_VBOs(int color_id, int detection_id, int worldmatrix_id) c
     }
 
     glsafe(::glPopMatrix());
+
+    if (this->is_left_handed())
+        glFrontFace(GL_CCW);
 }
 
 void GLVolume::render_legacy() const
@@ -489,6 +506,9 @@ void GLVolume::render_legacy() const
     if (!is_active)
         return;
 
+    if (this->is_left_handed())
+        glFrontFace(GL_CW);
+
     GLsizei n_triangles = GLsizei(std::min(indexed_vertex_array.triangle_indices_size, tverts_range.second - tverts_range.first));
     GLsizei n_quads = GLsizei(std::min(indexed_vertex_array.quad_indices_size, qverts_range.second - qverts_range.first));
     if (n_triangles + n_quads == 0)
@@ -520,6 +540,9 @@ void GLVolume::render_legacy() const
         glsafe(::glDrawElements(GL_QUADS, n_quads, GL_UNSIGNED_INT, indexed_vertex_array.quad_indices.data() + qverts_range.first));
 
     glsafe(::glPopMatrix());
+
+    if (this->is_left_handed())
+        glFrontFace(GL_CCW);
 }
 
 std::vector<int> GLVolumeCollection::load_object(
diff --git a/src/slic3r/GUI/3DScene.hpp b/src/slic3r/GUI/3DScene.hpp
index e421997e5..5cc301a39 100644
--- a/src/slic3r/GUI/3DScene.hpp
+++ b/src/slic3r/GUI/3DScene.hpp
@@ -388,6 +388,7 @@ public:
     int                 instance_idx() const { return this->composite_id.instance_id; }
 
     Transform3d         world_matrix() const;
+    bool                is_left_handed() const;
 
     const BoundingBoxf3& transformed_bounding_box() const;
     const BoundingBoxf3& transformed_convex_hull_bounding_box() const;
diff --git a/src/slic3r/GUI/FirmwareDialog.cpp b/src/slic3r/GUI/FirmwareDialog.cpp
index 1a294d210..8095a3237 100644
--- a/src/slic3r/GUI/FirmwareDialog.cpp
+++ b/src/slic3r/GUI/FirmwareDialog.cpp
@@ -59,6 +59,8 @@ enum {
 	USB_PID_MK3      = 2,
 	USB_PID_MMU_BOOT = 3,
 	USB_PID_MMU_APP  = 4,
+	USB_PID_CW1_BOOT = 7,
+	USB_PID_CW1_APP  = 8,
 };
 
 // This enum discriminates the kind of information in EVT_AVRDUDE,
@@ -77,6 +79,13 @@ wxDEFINE_EVENT(EVT_AVRDUDE, wxCommandEvent);
 wxDECLARE_EVENT(EVT_ASYNC_DIALOG, wxCommandEvent);
 wxDEFINE_EVENT(EVT_ASYNC_DIALOG, wxCommandEvent);
 
+struct Avr109Pid
+{
+	unsigned boot;
+	unsigned app;
+
+	Avr109Pid(unsigned boot, unsigned app) : boot(boot), app(app) {}
+};
 
 // Private
 
@@ -146,24 +155,40 @@ struct FirmwareDialog::priv
 	void flashing_done(AvrDudeComplete complete);
 	void enable_port_picker(bool enable);
 	void load_hex_file(const wxString &path);
-	void queue_status(wxString message);
-	void queue_error(const wxString &message);
+	void queue_event(AvrdudeEvent aevt, wxString message);
 
 	bool ask_model_id_mismatch(const std::string &printer_model);
 	bool check_model_id();
-	void wait_for_mmu_bootloader(unsigned retries);
-	void mmu_reboot(const SerialPortInfo &port);
-	void lookup_port_mmu();
+	void avr109_wait_for_bootloader(Avr109Pid usb_pid, unsigned retries);
+	void avr109_reboot(const SerialPortInfo &port);
+	void avr109_lookup_port(Avr109Pid usb_pid);
 	void prepare_common();
 	void prepare_mk2();
 	void prepare_mk3();
-	void prepare_mm_control();
+	void prepare_avr109(Avr109Pid usb_pid);
 	void perform_upload();
 
 	void user_cancel();
 	void on_avrdude(const wxCommandEvent &evt);
 	void on_async_dialog(const wxCommandEvent &evt);
 	void ensure_joined();
+
+	void queue_status(wxString message) { queue_event(AE_STATUS, std::move(message)); }
+
+	template<class ...Args> void queue_message(const wxString &format, Args... args) {
+		auto message = wxString::Format(format, args...);
+		BOOST_LOG_TRIVIAL(info) << message;
+		message.Append('\n');
+		queue_event(AE_MESSAGE, std::move(message));
+	}
+
+	template<class ...Args> void queue_error(const wxString &format, Args... args) {
+		queue_message(format, args...);
+		queue_event(AE_STATUS, _(L("Flashing failed: ")) + wxString::Format(format, args...));
+		avrdude->cancel();
+	}
+
+	static const char* avr109_dev_name(Avr109Pid usb_pid);
 };
 
 void FirmwareDialog::priv::find_serial_ports()
@@ -259,26 +284,18 @@ void FirmwareDialog::priv::enable_port_picker(bool enable)
 void FirmwareDialog::priv::load_hex_file(const wxString &path)
 {
 	hex_file = HexFile(path.wx_str());
-	enable_port_picker(hex_file.device != HexFile::DEV_MM_CONTROL);
+	const bool auto_lookup = hex_file.device == HexFile::DEV_MM_CONTROL || hex_file.device == HexFile::DEV_CW1;
+	enable_port_picker(! auto_lookup);
 }
 
-void FirmwareDialog::priv::queue_status(wxString message)
+void FirmwareDialog::priv::queue_event(AvrdudeEvent aevt, wxString message)
 {
 	auto evt = new wxCommandEvent(EVT_AVRDUDE, this->q->GetId());
-	evt->SetExtraLong(AE_STATUS);
+	evt->SetExtraLong(aevt);
 	evt->SetString(std::move(message));
 	wxQueueEvent(this->q, evt);
 }
 
-void FirmwareDialog::priv::queue_error(const wxString &message)
-{
-	auto evt = new wxCommandEvent(EVT_AVRDUDE, this->q->GetId());
-	evt->SetExtraLong(AE_STATUS);
-	evt->SetString(wxString::Format(_(L("Flashing failed: %s")), message));
-
-	wxQueueEvent(this->q, evt);	avrdude->cancel();
-}
-
 bool FirmwareDialog::priv::ask_model_id_mismatch(const std::string &printer_model)
 {
 	// model_id in the hex file doesn't match what the printer repoted.
@@ -356,7 +373,7 @@ bool FirmwareDialog::priv::check_model_id()
 	// return false;
 }
 
-void FirmwareDialog::priv::wait_for_mmu_bootloader(unsigned retries)
+void FirmwareDialog::priv::avr109_wait_for_bootloader(Avr109Pid usb_pid, unsigned retries)
 {
 	enum {
 		SLEEP_MS = 500,
@@ -367,61 +384,63 @@ void FirmwareDialog::priv::wait_for_mmu_bootloader(unsigned retries)
 
 		auto ports = Utils::scan_serial_ports_extended();
 		ports.erase(std::remove_if(ports.begin(), ports.end(), [=](const SerialPortInfo &port ) {
-			return port.id_vendor != USB_VID_PRUSA || port.id_product != USB_PID_MMU_BOOT;
+			return port.id_vendor != USB_VID_PRUSA || port.id_product != usb_pid.boot;
 		}), ports.end());
 
 		if (ports.size() == 1) {
 			port = ports[0];
 			return;
 		} else if (ports.size() > 1) {
-			BOOST_LOG_TRIVIAL(error) << "Several VID/PID 0x2c99/3 devices found";
-			queue_error(_(L("Multiple Original Prusa i3 MMU 2.0 devices found. Please only connect one at a time for flashing.")));
+			queue_message("Several VID/PID 0x2c99/%u devices found", usb_pid.boot);
+			queue_error(_(L("Multiple %s devices found. Please only connect one at a time for flashing.")), avr109_dev_name(usb_pid));
 			return;
 		}
 	}
 }
 
-void FirmwareDialog::priv::mmu_reboot(const SerialPortInfo &port)
+void FirmwareDialog::priv::avr109_reboot(const SerialPortInfo &port)
 {
 	asio::io_service io;
 	Serial serial(io, port.port, 1200);
 	std::this_thread::sleep_for(std::chrono::milliseconds(50));
 }
 
-void FirmwareDialog::priv::lookup_port_mmu()
+void FirmwareDialog::priv::avr109_lookup_port(Avr109Pid usb_pid)
 {
-	static const auto msg_not_found =
-		"The Multi Material Control device was not found.\n"
-		"If the device is connected, please press the Reset button next to the USB connector ...";
+	const char *dev_name = avr109_dev_name(usb_pid);
+	const wxString msg_not_found = wxString::Format(
+		_(L("The %s device was not found.\n"
+			"If the device is connected, please press the Reset button next to the USB connector ...")),
+		dev_name);
 
-	BOOST_LOG_TRIVIAL(info) << "Flashing MMU 2.0, looking for VID/PID 0x2c99/3 or 0x2c99/4 ...";
+	queue_message("Flashing %s, looking for VID/PID 0x2c99/%u or 0x2c99/%u ...", dev_name, usb_pid.boot, usb_pid.app);
 
 	auto ports = Utils::scan_serial_ports_extended();
 	ports.erase(std::remove_if(ports.begin(), ports.end(), [=](const SerialPortInfo &port ) {
 		return port.id_vendor != USB_VID_PRUSA ||
-			port.id_product != USB_PID_MMU_BOOT &&
-			port.id_product != USB_PID_MMU_APP;
+			port.id_product != usb_pid.boot &&
+			port.id_product != usb_pid.app;
 	}), ports.end());
 
 	if (ports.size() == 0) {
-		BOOST_LOG_TRIVIAL(info) << "MMU 2.0 device not found, asking the user to press Reset and waiting for the device to show up ...";
-		queue_status(_(L(msg_not_found)));
-		wait_for_mmu_bootloader(30);
+		queue_message("The %s device was not found.", dev_name);
+		queue_status(msg_not_found);
+		avr109_wait_for_bootloader(usb_pid, 30);
 	} else if (ports.size() > 1) {
-		BOOST_LOG_TRIVIAL(error) << "Several VID/PID 0x2c99/3 devices found";
-		queue_error(_(L("Multiple Original Prusa i3 MMU 2.0 devices found. Please only connect one at a time for flashing.")));
+		queue_message("Several VID/PID 0x2c99/%u devices found", usb_pid.boot);
+		queue_error(_(L("Multiple %s devices found. Please only connect one at a time for flashing.")), dev_name);
 	} else {
-		if (ports[0].id_product == USB_PID_MMU_APP) {
+		if (ports[0].id_product == usb_pid.app) {
 			// The device needs to be rebooted into the bootloader mode
-			BOOST_LOG_TRIVIAL(info) << boost::format("Found VID/PID 0x2c99/4 at `%1%`, rebooting the device ...") % ports[0].port;
-			mmu_reboot(ports[0]);
-			wait_for_mmu_bootloader(10);
+			queue_message("Found VID/PID 0x2c99/%u at `%s`, rebooting the device ...", usb_pid.app, ports[0].port);
+			avr109_reboot(ports[0]);
+			avr109_wait_for_bootloader(usb_pid, 10);
 
 			if (! port) {
 				// The device in bootloader mode was not found, inform the user and wait some more...
-				BOOST_LOG_TRIVIAL(info) << "MMU 2.0 bootloader device not found after reboot, asking the user to press Reset and waiting for the device to show up ...";
-				queue_status(_(L(msg_not_found)));
-				wait_for_mmu_bootloader(30);
+				queue_message("%s device not found after reboot", dev_name);
+				queue_status(msg_not_found);
+				avr109_wait_for_bootloader(usb_pid, 30);
 			}
 		} else {
 			port = ports[0];
@@ -498,16 +517,16 @@ void FirmwareDialog::priv::prepare_mk3()
 	avrdude->push_args(std::move(args));
 }
 
-void FirmwareDialog::priv::prepare_mm_control()
+void FirmwareDialog::priv::prepare_avr109(Avr109Pid usb_pid)
 {
 	port = boost::none;
-	lookup_port_mmu();
+	avr109_lookup_port(usb_pid);
 	if (! port) {
-		queue_error(_(L("The device could not have been found")));
+		queue_error(_(L("The %s device could not have been found")), avr109_dev_name(usb_pid));
 		return;
 	}
 
-	BOOST_LOG_TRIVIAL(info) << boost::format("Found VID/PID 0x2c99/3 at `%1%`, flashing ...") % port->port;
+	queue_message("Found VID/PID 0x2c99/%u at `%s`, flashing ...", usb_pid.boot, port->port);
 	queue_status(label_status_flashing);
 
 	std::vector<std::string> args {{
@@ -568,7 +587,11 @@ void FirmwareDialog::priv::perform_upload()
 					break;
 
 				case HexFile::DEV_MM_CONTROL:
-					this->prepare_mm_control();
+					this->prepare_avr109(Avr109Pid(USB_PID_MMU_BOOT, USB_PID_MMU_APP));
+					break;
+
+				case HexFile::DEV_CW1:
+					this->prepare_avr109(Avr109Pid(USB_PID_CW1_BOOT, USB_PID_CW1_APP));
 					break;
 
 				default:
@@ -576,7 +599,11 @@ void FirmwareDialog::priv::perform_upload()
 					break;
 				}
 			} catch (const std::exception &ex) {
-				queue_error(wxString::Format(_(L("Error accessing port at %s: %s")), port->port, ex.what()));
+				if (port) {
+					queue_error(_(L("Error accessing port at %s: %s")), port->port, ex.what());
+				} else {
+					queue_error(_(L("Error: %s")), ex.what());
+				}
 			}
 		})
 		.on_message(std::move([q, extra_verbose](const char *msg, unsigned /* size */) {
@@ -688,6 +715,19 @@ void FirmwareDialog::priv::ensure_joined()
 	avrdude.reset();
 }
 
+const char* FirmwareDialog::priv::avr109_dev_name(Avr109Pid usb_pid) {
+	switch (usb_pid.boot) {
+		case USB_PID_MMU_BOOT:
+			return "Prusa MMU 2.0 Control";
+		break;
+		case USB_PID_CW1_BOOT:
+			return "Prusa CurWa";
+		break;
+
+		default: throw std::runtime_error((boost::format("Invalid avr109 device USB PID: %1%") % usb_pid.boot).str());
+	}
+}
+
 
 // Public
 
@@ -757,7 +797,7 @@ FirmwareDialog::FirmwareDialog(wxWindow *parent) :
 
 	vsizer->Add(grid, 0, wxEXPAND | wxTOP | wxBOTTOM, SPACING);
 
-	p->spoiler = new wxCollapsiblePane(panel, wxID_ANY, _(L("Advanced: avrdude output log")), wxDefaultPosition, wxDefaultSize, wxCP_DEFAULT_STYLE | wxCP_NO_TLW_RESIZE);
+	p->spoiler = new wxCollapsiblePane(panel, wxID_ANY, _(L("Advanced: Output log")), wxDefaultPosition, wxDefaultSize, wxCP_DEFAULT_STYLE | wxCP_NO_TLW_RESIZE);
 	auto *spoiler_pane = p->spoiler->GetPane();
 	auto *spoiler_sizer = new wxBoxSizer(wxVERTICAL);
 	p->txt_stdout = new wxTextCtrl(spoiler_pane, wxID_ANY, wxEmptyString, wxDefaultPosition, wxDefaultSize, wxTE_MULTILINE | wxTE_READONLY);
diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index a25b7e7c1..79a3684ef 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -380,7 +380,7 @@ void GLCanvas3D::LayersEditing::render_overlay(const GLCanvas3D& canvas) const
 
 float GLCanvas3D::LayersEditing::get_cursor_z_relative(const GLCanvas3D& canvas)
 {
-    const Point& mouse_pos = canvas.get_local_mouse_position();
+    const Vec2d mouse_pos = canvas.get_local_mouse_position();
     const Rect& rect = get_bar_rect_screen(canvas);
     float x = (float)mouse_pos(0);
     float y = (float)mouse_pos(1);
@@ -3915,19 +3915,25 @@ Size GLCanvas3D::get_canvas_size() const
     w *= factor;
     h *= factor;
 #else
-    const float factor = 1.0;
+    const float factor = 1.0f;
 #endif
 
     return Size(w, h, factor);
 }
 
-Point GLCanvas3D::get_local_mouse_position() const
+Vec2d GLCanvas3D::get_local_mouse_position() const
 {
     if (m_canvas == nullptr)
-        return Point();
+		return Vec2d::Zero();
 
     wxPoint mouse_pos = m_canvas->ScreenToClient(wxGetMousePosition());
-    return Point(mouse_pos.x, mouse_pos.y);
+    const double factor = 
+#if ENABLE_RETINA_GL
+        m_retina_helper->get_scale_factor();
+#else
+        1.0;
+#endif
+    return Vec2d(factor * mouse_pos.x, factor * mouse_pos.y);
 }
 
 void GLCanvas3D::reset_legend_texture()
@@ -4397,11 +4403,13 @@ void GLCanvas3D::_resize(unsigned int w, unsigned int h)
     if ((m_canvas == nullptr) && (m_context == nullptr))
         return;
 
-    wxGetApp().imgui()->set_display_size((float)w, (float)h);
+    auto *imgui = wxGetApp().imgui();
+    imgui->set_display_size((float)w, (float)h);
+    const float font_size = 1.5f * wxGetApp().em_unit();
 #if ENABLE_RETINA_GL
-    wxGetApp().imgui()->set_style_scaling(m_retina_helper->get_scale_factor());
+    imgui->set_scaling(font_size, 1.0f, m_retina_helper->get_scale_factor());
 #else
-    wxGetApp().imgui()->set_style_scaling(m_canvas->GetContentScaleFactor());
+    imgui->set_scaling(font_size, m_canvas->GetContentScaleFactor(), 1.0f);
 #endif
 
     // ensures that this canvas is current
@@ -4979,6 +4987,9 @@ void GLCanvas3D::_render_sla_slices() const
     {
         const SLAPrintObject* obj = print_objects[i];
 
+        if (!obj->is_step_done(slaposSliceSupports))
+            continue;
+
         SlaCap::ObjectIdToTrianglesMap::iterator it_caps_bottom = m_sla_caps[0].triangles.find(i);
         SlaCap::ObjectIdToTrianglesMap::iterator it_caps_top    = m_sla_caps[1].triangles.find(i);
         {
@@ -5002,24 +5013,12 @@ void GLCanvas3D::_render_sla_slices() const
         Pointf3s &top_obj_triangles    = it_caps_top->second.object;
         Pointf3s &top_sup_triangles    = it_caps_top->second.supports;
 
-        const std::vector<SLAPrintObject::Instance>& instances = obj->instances();
-        struct InstanceTransform
-        {
-            Vec3d offset;
-            float rotation;
-        };
-
-        std::vector<InstanceTransform> instance_transforms;
-        for (const SLAPrintObject::Instance& inst : instances)
-        {
-			instance_transforms.push_back({ to_3d(unscale(inst.shift), 0.), Geometry::rad2deg(inst.rotation) });
-        }
-
         if ((bottom_obj_triangles.empty() || bottom_sup_triangles.empty() || top_obj_triangles.empty() || top_sup_triangles.empty()) &&
-            obj->is_step_done(slaposIndexSlices) && !obj->get_slice_index().empty())
+            !obj->get_slice_index().empty())
         {
             double layer_height         = print->default_object_config().layer_height.value;
             double initial_layer_height = print->material_config().initial_layer_height.value;
+            bool   left_handed          = obj->is_left_handed();
 
             coord_t key_zero = obj->get_slice_index().front().print_level();
             // Slice at the center of the slab starting at clip_min_z will be rendered for the lower plane.
@@ -5038,10 +5037,10 @@ void GLCanvas3D::_render_sla_slices() const
                 const ExPolygons& sup_bottom = slice_low.get_slice(soSupport);
                 // calculate model bottom cap
                 if (bottom_obj_triangles.empty() && !obj_bottom.empty())
-                    bottom_obj_triangles = triangulate_expolygons_3d(obj_bottom, clip_min_z - plane_shift_z, true);
+                    bottom_obj_triangles = triangulate_expolygons_3d(obj_bottom, clip_min_z - plane_shift_z, ! left_handed);
                 // calculate support bottom cap
                 if (bottom_sup_triangles.empty() && !sup_bottom.empty())
-                    bottom_sup_triangles = triangulate_expolygons_3d(sup_bottom, clip_min_z - plane_shift_z, true);
+                    bottom_sup_triangles = triangulate_expolygons_3d(sup_bottom, clip_min_z - plane_shift_z, ! left_handed);
             }
 
             if (slice_high.is_valid()) {
@@ -5049,49 +5048,43 @@ void GLCanvas3D::_render_sla_slices() const
                 const ExPolygons& sup_top = slice_high.get_slice(soSupport);
                 // calculate model top cap
                 if (top_obj_triangles.empty() && !obj_top.empty())
-                    top_obj_triangles = triangulate_expolygons_3d(obj_top, clip_max_z + plane_shift_z, false);
+                    top_obj_triangles = triangulate_expolygons_3d(obj_top, clip_max_z + plane_shift_z, left_handed);
                 // calculate support top cap
                 if (top_sup_triangles.empty() && !sup_top.empty())
-                    top_sup_triangles = triangulate_expolygons_3d(sup_top, clip_max_z + plane_shift_z, false);
+                    top_sup_triangles = triangulate_expolygons_3d(sup_top, clip_max_z + plane_shift_z, left_handed);
             }
         }
 
         if (!bottom_obj_triangles.empty() || !top_obj_triangles.empty() || !bottom_sup_triangles.empty() || !top_sup_triangles.empty())
         {
-            for (const InstanceTransform& inst : instance_transforms)
+			for (const SLAPrintObject::Instance& inst : obj->instances())
             {
                 ::glPushMatrix();
-                ::glTranslated(inst.offset(0), inst.offset(1), inst.offset(2));
-                ::glRotatef(inst.rotation, 0.0, 0.0, 1.0);
-
-                ::glBegin(GL_TRIANGLES);
-
-                ::glColor3f(1.0f, 0.37f, 0.0f);
-
-                for (const Vec3d& v : bottom_obj_triangles)
-                {
-                    ::glVertex3dv((GLdouble*)v.data());
-                }
-
-                for (const Vec3d& v : top_obj_triangles)
-                {
-                    ::glVertex3dv((GLdouble*)v.data());
-                }
-
-                ::glColor3f(1.0f, 0.0f, 0.37f);
-
-                for (const Vec3d& v : bottom_sup_triangles)
-                {
-                    ::glVertex3dv((GLdouble*)v.data());
-                }
-
-                for (const Vec3d& v : top_sup_triangles)
-                {
-                    ::glVertex3dv((GLdouble*)v.data());
-                }
-
-                ::glEnd();
-
+				::glTranslated(unscale<double>(inst.shift.x()), unscale<double>(inst.shift.y()), 0);
+				::glRotatef(Geometry::rad2deg(inst.rotation), 0.0, 0.0, 1.0);
+				if (obj->is_left_handed())
+                    // The polygons are mirrored by X.
+                    ::glScalef(-1.0, 1.0, 1.0);
+				::glEnableClientState(GL_VERTEX_ARRAY);
+				::glColor3f(1.0f, 0.37f, 0.0f);
+				if (!bottom_obj_triangles.empty()) {
+					::glVertexPointer(3, GL_DOUBLE, 0, (GLdouble*)bottom_obj_triangles.front().data());
+					::glDrawArrays(GL_TRIANGLES, 0, bottom_obj_triangles.size());
+				}
+				if (! top_obj_triangles.empty()) {
+					::glVertexPointer(3, GL_DOUBLE, 0, (GLdouble*)top_obj_triangles.front().data());
+					::glDrawArrays(GL_TRIANGLES, 0, top_obj_triangles.size());
+				}
+				::glColor3f(1.0f, 0.0f, 0.37f);
+				if (! bottom_sup_triangles.empty()) {
+					::glVertexPointer(3, GL_DOUBLE, 0, (GLdouble*)bottom_sup_triangles.front().data());
+					::glDrawArrays(GL_TRIANGLES, 0, bottom_sup_triangles.size());
+				}
+				if (! top_sup_triangles.empty()) {
+					::glVertexPointer(3, GL_DOUBLE, 0, (GLdouble*)top_sup_triangles.front().data());
+					::glDrawArrays(GL_TRIANGLES, 0, top_sup_triangles.size());
+				}
+				::glDisableClientState(GL_VERTEX_ARRAY);
                 ::glPopMatrix();
             }
         }
@@ -6209,6 +6202,8 @@ void GLCanvas3D::_load_shells_fff()
 
 void GLCanvas3D::_load_shells_sla()
 {
+    //FIXME use reload_scene
+#if 1
     const SLAPrint* print = this->sla_print();
     if (print->objects().empty())
         // nothing to render, return
@@ -6218,23 +6213,30 @@ void GLCanvas3D::_load_shells_sla()
     int obj_idx = 0;
     for (const SLAPrintObject* obj : print->objects())
     {
-        if (!obj->is_step_done(slaposIndexSlices))
+        if (!obj->is_step_done(slaposSliceSupports))
             continue;
 
         unsigned int initial_volumes_count = (unsigned int)m_volumes.volumes.size();
 
+        // selects only instances which were sliced
         const ModelObject* model_obj = obj->model_object();
-        std::vector<int> instance_idxs(model_obj->instances.size());
-        for (int i = 0; i < (int)model_obj->instances.size(); ++i)
+        const std::vector<SLAPrintObject::Instance>& sla_instances = obj->instances();
+        std::vector<int> instances_model_idxs(sla_instances.size());
+        for (int i = 0; i < (int)sla_instances.size(); ++i)
         {
-            instance_idxs[i] = i;
+            instances_model_idxs[i] = (int)sla_instances[i].instance_id.id;
         }
 
-        m_volumes.load_object(model_obj, obj_idx, instance_idxs, "object", m_use_VBOs && m_initialized);
+        std::vector<int> sliced_instance_idxs;
+        for (int i = 0; i < (int)model_obj->instances.size(); ++i)
+        {
+            if (std::find(instances_model_idxs.begin(), instances_model_idxs.end(), (int)model_obj->instances[i]->id().id) != instances_model_idxs.end())
+                sliced_instance_idxs.push_back(i);
+        }
 
-        const std::vector<SLAPrintObject::Instance>& instances = obj->instances();
+        m_volumes.load_object(model_obj, obj_idx, sliced_instance_idxs, "object", m_use_VBOs && m_initialized);
 
-        for (const SLAPrintObject::Instance& instance : instances)
+        for (const SLAPrintObject::Instance& instance : sla_instances)
         {
             Vec3d offset = unscale(instance.shift(0), instance.shift(1), 0);
             Vec3d rotation(0.0, 0.0, (double)instance.rotation);
@@ -6257,6 +6259,7 @@ void GLCanvas3D::_load_shells_sla()
                 v.composite_id.volume_id = -1;
                 v.set_instance_offset(offset);
                 v.set_instance_rotation(rotation);
+                v.set_instance_mirror(X, obj->is_left_handed() ? -1. : 1.);
             }
 
             // add pad
@@ -6275,6 +6278,7 @@ void GLCanvas3D::_load_shells_sla()
                 v.composite_id.volume_id = -1;
                 v.set_instance_offset(offset);
                 v.set_instance_rotation(rotation);
+                v.set_instance_mirror(X, obj->is_left_handed() ? -1. : 1.);
             }
 
             // finalize volumes and sends geometry to gpu
@@ -6297,6 +6301,9 @@ void GLCanvas3D::_load_shells_sla()
     }
 
     update_volumes_colors_by_extruder();
+#else
+    this->reload_scene(true, true);
+#endif
 }
 
 void GLCanvas3D::_update_gcode_volumes_visibility(const GCodePreviewData& preview_data)
diff --git a/src/slic3r/GUI/GLCanvas3D.hpp b/src/slic3r/GUI/GLCanvas3D.hpp
index cc69117bf..7e414d52a 100644
--- a/src/slic3r/GUI/GLCanvas3D.hpp
+++ b/src/slic3r/GUI/GLCanvas3D.hpp
@@ -634,6 +634,7 @@ public:
             m_sla_caps[id].reset();
         }
     }
+    void reset_clipping_planes_cache() { m_sla_caps[0].triangles.clear(); m_sla_caps[1].triangles.clear(); }
     void set_use_clipping_planes(bool use) { m_use_clipping_planes = use; }
 
     void set_color_by(const std::string& value);
@@ -699,7 +700,7 @@ public:
     void on_paint(wxPaintEvent& evt);
 
     Size get_canvas_size() const;
-    Point get_local_mouse_position() const;
+    Vec2d get_local_mouse_position() const;
 
     void reset_legend_texture();
 
diff --git a/src/slic3r/GUI/GUI_App.cpp b/src/slic3r/GUI/GUI_App.cpp
index bdfd2fc26..f1a7d9263 100644
--- a/src/slic3r/GUI/GUI_App.cpp
+++ b/src/slic3r/GUI/GUI_App.cpp
@@ -90,7 +90,6 @@ bool GUI_App::OnInit()
     const wxString resources_dir = from_u8(Slic3r::resources_dir());
     wxCHECK_MSG(wxDirExists(resources_dir), false,
         wxString::Format("Resources path does not exist or is not a directory: %s", resources_dir));
-    wxCHECK_MSG(m_imgui->init(), false, "Failed to initialize ImGui");
 
     SetAppName("Slic3rPE-beta");
     SetAppDisplayName("Slic3r Prusa Edition");
@@ -136,6 +135,10 @@ bool GUI_App::OnInit()
         app_config->save();
     });
 
+    // initialize label colors and fonts
+    init_label_colours();
+    init_fonts();
+
     load_language();
 
     // Suppress the '- default -' presets.
@@ -148,9 +151,6 @@ bool GUI_App::OnInit()
 
     // Let the libslic3r know the callback, which will translate messages on demand.
     Slic3r::I18N::set_translate_callback(libslic3r_translate_callback);
-    // initialize label colors and fonts
-    init_label_colours();
-    init_fonts();
 
     // application frame
     if (wxImage::FindHandler(wxBITMAP_TYPE_PNG) == nullptr)
diff --git a/src/slic3r/GUI/GUI_Preview.cpp b/src/slic3r/GUI/GUI_Preview.cpp
index f41d148de..438e9d236 100644
--- a/src/slic3r/GUI/GUI_Preview.cpp
+++ b/src/slic3r/GUI/GUI_Preview.cpp
@@ -27,7 +27,7 @@
 namespace Slic3r {
 namespace GUI {
 
-    View3D::View3D(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, Model* model, DynamicPrintConfig* config, BackgroundSlicingProcess* process)
+View3D::View3D(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, Model* model, DynamicPrintConfig* config, BackgroundSlicingProcess* process)
     : m_canvas_widget(nullptr)
     , m_canvas(nullptr)
 {
@@ -155,7 +155,9 @@ void View3D::render()
         m_canvas->set_as_dirty();
 }
 
-Preview::Preview(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, DynamicPrintConfig* config, BackgroundSlicingProcess* process, GCodePreviewData* gcode_preview_data, std::function<void()> schedule_background_process_func)
+Preview::Preview(
+    wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, Model* model, DynamicPrintConfig* config, 
+    BackgroundSlicingProcess* process, GCodePreviewData* gcode_preview_data, std::function<void()> schedule_background_process_func)
     : m_canvas_widget(nullptr)
     , m_canvas(nullptr)
     , m_double_slider_sizer(nullptr)
@@ -179,14 +181,14 @@ Preview::Preview(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_t
     , m_volumes_cleanup_required(false)
 #endif // __linux__
 {
-    if (init(parent, bed, camera, view_toolbar))
+    if (init(parent, bed, camera, view_toolbar, model))
     {
         show_hide_ui_elements("none");
         load_print();
     }
 }
 
-bool Preview::init(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar)
+bool Preview::init(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, Model* model)
 {
     if (!Create(parent, wxID_ANY, wxDefaultPosition, wxDefaultSize, 0 /* disable wxTAB_TRAVERSAL */))
         return false;
@@ -196,6 +198,7 @@ bool Preview::init(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view
     m_canvas = _3DScene::get_canvas(this->m_canvas_widget);
     m_canvas->allow_multisample(GLCanvas3DManager::can_multisample());
     m_canvas->set_config(m_config);
+    m_canvas->set_model(model);
     m_canvas->set_process(m_process);
     m_canvas->enable_legend_texture(true);
     m_canvas->enable_dynamic_background(true);
@@ -773,7 +776,7 @@ void Preview::load_print_as_sla()
     std::vector<double> zs;
     double initial_layer_height = print->material_config().initial_layer_height.value;
     for (const SLAPrintObject* obj : print->objects())
-        if (obj->is_step_done(slaposIndexSlices) && !obj->get_slice_index().empty())
+        if (obj->is_step_done(slaposSliceSupports) && !obj->get_slice_index().empty())
         {
             auto low_coord = obj->get_slice_index().front().print_level();
             for (auto& rec : obj->get_slice_index())
@@ -781,6 +784,8 @@ void Preview::load_print_as_sla()
         }
     sort_remove_duplicates(zs);
 
+    m_canvas->reset_clipping_planes_cache();
+
     n_layers = (unsigned int)zs.size();
     if (n_layers == 0)
     {
diff --git a/src/slic3r/GUI/GUI_Preview.hpp b/src/slic3r/GUI/GUI_Preview.hpp
index 96c49e54f..a2929f2e6 100644
--- a/src/slic3r/GUI/GUI_Preview.hpp
+++ b/src/slic3r/GUI/GUI_Preview.hpp
@@ -102,7 +102,8 @@ class Preview : public wxPanel
     PrusaDoubleSlider* m_slider {nullptr};
 
 public:
-    Preview(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, DynamicPrintConfig* config, BackgroundSlicingProcess* process, GCodePreviewData* gcode_preview_data, std::function<void()> schedule_background_process = [](){});
+    Preview(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, Model* model, DynamicPrintConfig* config, 
+        BackgroundSlicingProcess* process, GCodePreviewData* gcode_preview_data, std::function<void()> schedule_background_process = [](){});
     virtual ~Preview();
 
     wxGLCanvas* get_wxglcanvas() { return m_canvas_widget; }
@@ -120,7 +121,7 @@ public:
     void refresh_print();
 
 private:
-    bool init(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar);
+    bool init(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, Model* model);
 
     void bind_event_handlers();
     void unbind_event_handlers();
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp b/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp
index 566090504..02d663e93 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp
@@ -185,7 +185,10 @@ void GLGizmoCut::on_render_for_picking(const Selection& selection) const
 
 void GLGizmoCut::on_render_input_window(float x, float y, float bottom_limit, const Selection& selection)
 {
+    const float approx_height = m_imgui->scaled(11.0f);
+    y = std::min(y, bottom_limit - approx_height);
     m_imgui->set_next_window_pos(x, y, ImGuiCond_Always);
+
     m_imgui->set_next_window_bg_alpha(0.5f);
     m_imgui->begin(_(L("Cut")), ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoCollapse);
 
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
index d83ef9ed8..75f13cdcf 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
@@ -565,8 +565,7 @@ void GLGizmoSlaSupports::on_render_input_window(float x, float y, float bottom_l
 RENDER_AGAIN:
     m_imgui->set_next_window_pos(x, y, ImGuiCond_Always);
 
-    const float scaling = m_imgui->get_style_scaling();
-    const ImVec2 window_size(285.f * scaling, 300.f * scaling);
+    const ImVec2 window_size(m_imgui->scaled(15.f, 16.5f));
     ImGui::SetNextWindowPos(ImVec2(x, y - std::max(0.f, y+window_size.y-bottom_limit) ));
     ImGui::SetNextWindowSize(ImVec2(window_size));
 
@@ -817,7 +816,7 @@ void GLGizmoSlaSupports::editing_mode_apply_changes()
         // Recalculate support structures once the editing mode is left.
         // m_parent.post_event(SimpleEvent(EVT_GLCANVAS_SCHEDULE_BACKGROUND_PROCESS));
         // m_parent.post_event(SimpleEvent(EVT_GLCANVAS_SCHEDULE_BACKGROUND_PROCESS));
-        wxGetApp().plater()->reslice_SLA_supports(*m_model_object);
+        wxGetApp().CallAfter([this]() { wxGetApp().plater()->reslice_SLA_supports(*m_model_object); });
     }
     m_editing_mode = false;
     m_unsaved_changes = false;
@@ -870,7 +869,7 @@ void GLGizmoSlaSupports::auto_generate()
         m_model_object->sla_support_points.clear();
         m_model_object->sla_points_status = sla::PointsStatus::Generating;
         m_editing_mode_cache.clear();
-        wxGetApp().plater()->reslice_SLA_supports(*m_model_object);
+        wxGetApp().CallAfter([this]() { wxGetApp().plater()->reslice_SLA_supports(*m_model_object); });
     }
 }
 
diff --git a/src/slic3r/GUI/ImGuiWrapper.cpp b/src/slic3r/GUI/ImGuiWrapper.cpp
index 0932c8ce9..1b4d4edf9 100644
--- a/src/slic3r/GUI/ImGuiWrapper.cpp
+++ b/src/slic3r/GUI/ImGuiWrapper.cpp
@@ -27,31 +27,25 @@ namespace GUI {
 
 ImGuiWrapper::ImGuiWrapper()
     : m_glyph_ranges(nullptr)
+    , m_font_size(18.0)
     , m_font_texture(0)
     , m_style_scaling(1.0)
     , m_mouse_buttons(0)
     , m_disabled(false)
     , m_new_frame_open(false)
-{
-}
-
-ImGuiWrapper::~ImGuiWrapper()
-{
-    destroy_device_objects();
-    ImGui::DestroyContext();
-}
-
-bool ImGuiWrapper::init()
 {
     ImGui::CreateContext();
 
-    init_default_font(m_style_scaling);
     init_input();
     init_style();
 
     ImGui::GetIO().IniFilename = nullptr;
+}
 
-    return true;
+ImGuiWrapper::~ImGuiWrapper()
+{
+    destroy_font();
+    ImGui::DestroyContext();
 }
 
 void ImGuiWrapper::set_language(const std::string &language)
@@ -87,7 +81,7 @@ void ImGuiWrapper::set_language(const std::string &language)
 
     if (ranges != m_glyph_ranges) {
         m_glyph_ranges = ranges;
-        init_default_font(m_style_scaling);
+        destroy_font();
     }
 }
 
@@ -98,13 +92,21 @@ void ImGuiWrapper::set_display_size(float w, float h)
     io.DisplayFramebufferScale = ImVec2(1.0f, 1.0f);
 }
 
-void ImGuiWrapper::set_style_scaling(float scaling)
+void ImGuiWrapper::set_scaling(float font_size, float scale_style, float scale_both)
 {
-    if (!std::isnan(scaling) && !std::isinf(scaling) && scaling != m_style_scaling) {
-        ImGui::GetStyle().ScaleAllSizes(scaling / m_style_scaling);
-        init_default_font(scaling);
-        m_style_scaling = scaling;
+    font_size *= scale_both;
+    scale_style *= scale_both;
+
+    if (m_font_size == font_size && m_style_scaling == scale_style) {
+        return;
     }
+
+    m_font_size = font_size;
+
+    ImGui::GetStyle().ScaleAllSizes(scale_style / m_style_scaling);
+    m_style_scaling = scale_style;
+
+    destroy_font();
 }
 
 bool ImGuiWrapper::update_mouse_data(wxMouseEvent& evt)
@@ -165,8 +167,9 @@ void ImGuiWrapper::new_frame()
         return;
     }
 
-    if (m_font_texture == 0)
-        create_device_objects();
+    if (m_font_texture == 0) {
+        init_font();
+    }
 
     ImGui::NewFrame();
     m_new_frame_open = true;
@@ -179,6 +182,12 @@ void ImGuiWrapper::render()
     m_new_frame_open = false;
 }
 
+ImVec2 ImGuiWrapper::calc_text_size(const wxString &text)
+{
+    auto text_utf8 = into_u8(text);
+    return ImGui::CalcTextSize(text_utf8.c_str());
+}
+
 void ImGuiWrapper::set_next_window_pos(float x, float y, int flag)
 {
     ImGui::SetNextWindowPos(ImVec2(x, y), (ImGuiCond)flag);
@@ -259,7 +268,8 @@ void ImGuiWrapper::text(const std::string &label)
 
 void ImGuiWrapper::text(const wxString &label)
 {
-    this->text(into_u8(label).c_str());
+    auto label_utf8 = into_u8(label);
+    this->text(label_utf8.c_str());
 }
 
 bool ImGuiWrapper::combo(const wxString& label, const std::vector<std::string>& options, int& selection)
@@ -328,32 +338,23 @@ bool ImGuiWrapper::want_any_input() const
     return io.WantCaptureMouse || io.WantCaptureKeyboard || io.WantTextInput;
 }
 
-void ImGuiWrapper::init_default_font(float scaling)
+void ImGuiWrapper::init_font()
 {
-    static const float font_size = 18.0f;
+    const float font_size = m_font_size * m_style_scaling;
 
-    destroy_fonts_texture();
+    destroy_font();
 
     ImGuiIO& io = ImGui::GetIO();
     io.Fonts->Clear();
-    ImFont* font = io.Fonts->AddFontFromFileTTF((Slic3r::resources_dir() + "/fonts/NotoSans-Regular.ttf").c_str(), font_size * scaling, nullptr, m_glyph_ranges);
+    ImFont* font = io.Fonts->AddFontFromFileTTF((Slic3r::resources_dir() + "/fonts/NotoSans-Regular.ttf").c_str(), font_size, nullptr, m_glyph_ranges);
     if (font == nullptr) {
         font = io.Fonts->AddFontDefault();
         if (font == nullptr) {
             throw std::runtime_error("ImGui: Could not load deafult font");
         }
     }
-}
 
-void ImGuiWrapper::create_device_objects()
-{
-    create_fonts_texture();
-}
-
-void ImGuiWrapper::create_fonts_texture()
-{
     // Build texture atlas
-    ImGuiIO& io = ImGui::GetIO();
     unsigned char* pixels;
     int width, height;
     io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);   // Load as RGBA 32-bits (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.
@@ -559,14 +560,9 @@ bool ImGuiWrapper::display_initialized() const
     return io.DisplaySize.x >= 0.0f && io.DisplaySize.y >= 0.0f;
 }
 
-void ImGuiWrapper::destroy_device_objects()
+void ImGuiWrapper::destroy_font()
 {
-    destroy_fonts_texture();
-}
-
-void ImGuiWrapper::destroy_fonts_texture()
-{
-    if (m_font_texture) {
+    if (m_font_texture != 0) {
         ImGuiIO& io = ImGui::GetIO();
         io.Fonts->TexID = 0;
         glDeleteTextures(1, &m_font_texture);
diff --git a/src/slic3r/GUI/ImGuiWrapper.hpp b/src/slic3r/GUI/ImGuiWrapper.hpp
index 35d0b5636..c1bf491e1 100644
--- a/src/slic3r/GUI/ImGuiWrapper.hpp
+++ b/src/slic3r/GUI/ImGuiWrapper.hpp
@@ -18,10 +18,8 @@ namespace GUI {
 
 class ImGuiWrapper
 {
-    typedef std::map<std::string, ImFont*> FontsMap;
-
-    FontsMap m_fonts;
     const ImWchar *m_glyph_ranges;
+    float m_font_size;
     unsigned m_font_texture;
     float m_style_scaling;
     unsigned m_mouse_buttons;
@@ -33,20 +31,24 @@ public:
     ImGuiWrapper();
     ~ImGuiWrapper();
 
-    bool init();
     void read_glsl_version();
 
     void set_language(const std::string &language);
     void set_display_size(float w, float h);
-    void set_style_scaling(float scaling);
+    void set_scaling(float font_size, float scale_style, float scale_both);
     bool update_mouse_data(wxMouseEvent &evt);
     bool update_key_data(wxKeyEvent &evt);
 
+    float get_font_size() const { return m_font_size; }
     float get_style_scaling() const { return m_style_scaling; }
 
     void new_frame();
     void render();
 
+    float scaled(float x) const { return x * m_font_size * m_style_scaling; }
+    ImVec2 scaled(float x, float y) const { return ImVec2(x * m_font_size * m_style_scaling, y * m_font_size * m_style_scaling); }
+    ImVec2 calc_text_size(const wxString &text);
+
     void set_next_window_pos(float x, float y, int flag);
     void set_next_window_bg_alpha(float alpha);
 
@@ -73,15 +75,12 @@ public:
     bool want_any_input() const;
 
 private:
-    void init_default_font(float scaling);
-    void create_device_objects();
-    void create_fonts_texture();
+    void init_font();
     void init_input();
     void init_style();
     void render_draw_data(ImDrawData *draw_data);
     bool display_initialized() const;
-    void destroy_device_objects();
-    void destroy_fonts_texture();
+    void destroy_font();
 
     static const char* clipboard_get(void* user_data);
     static void clipboard_set(void* user_data, const char* text);
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index c92c22c50..435d9548f 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -1350,7 +1350,7 @@ Plater::priv::priv(Plater *q, MainFrame *main_frame)
     this->q->Bind(EVT_SLICING_UPDATE, &priv::on_slicing_update, this);
 
     view3D = new View3D(q, bed, camera, view_toolbar, &model, config, &background_process);
-    preview = new Preview(q, bed, camera, view_toolbar, config, &background_process, &gcode_preview_data, [this](){ schedule_background_process(); });
+    preview = new Preview(q, bed, camera, view_toolbar, &model, config, &background_process, &gcode_preview_data, [this](){ schedule_background_process(); });
 
     panels.push_back(view3D);
     panels.push_back(preview);
diff --git a/src/slic3r/GUI/Selection.cpp b/src/slic3r/GUI/Selection.cpp
index fb35b500e..7103ca12d 100644
--- a/src/slic3r/GUI/Selection.cpp
+++ b/src/slic3r/GUI/Selection.cpp
@@ -118,17 +118,17 @@ void Selection::add(unsigned int volume_idx, bool as_single_selection)
     if (needs_reset)
         clear();
 
-    if (volume->is_modifier)
-        m_mode = Volume;
-    else if (!contains_volume(volume_idx))
-        m_mode = Instance;
-    // else -> keep current mode
+    if (!contains_volume(volume_idx))
+        m_mode = volume->is_modifier ? Volume : Instance;
+    else
+        // keep current mode
+        return;
 
     switch (m_mode)
     {
     case Volume:
     {
-        if (volume->volume_idx() >= 0 && (is_empty() || (volume->instance_idx() == get_instance_idx())))
+        if ((volume->volume_idx() >= 0) && (is_empty() || (volume->instance_idx() == get_instance_idx())))
             _add_volume(volume_idx);
 
         break;
@@ -439,6 +439,8 @@ void Selection::translate(const Vec3d& displacement, bool local)
     if (!m_valid)
         return;
 
+    EMode translation_type = m_mode;
+
     for (unsigned int i : m_list)
     {
         if ((m_mode == Volume) || (*m_volumes)[i]->is_wipe_tower)
@@ -452,13 +454,22 @@ void Selection::translate(const Vec3d& displacement, bool local)
             }
         }
         else if (m_mode == Instance)
-            (*m_volumes)[i]->set_instance_offset(m_cache.volumes_data[i].get_instance_position() + displacement);
+        {
+            if (_is_from_fully_selected_instance(i))
+                (*m_volumes)[i]->set_instance_offset(m_cache.volumes_data[i].get_instance_position() + displacement);
+            else
+            {
+                Vec3d local_displacement = (m_cache.volumes_data[i].get_instance_rotation_matrix() * m_cache.volumes_data[i].get_instance_scale_matrix() * m_cache.volumes_data[i].get_instance_mirror_matrix()).inverse() * displacement;
+                (*m_volumes)[i]->set_volume_offset(m_cache.volumes_data[i].get_volume_position() + local_displacement);
+                translation_type = Volume;
+            }
+        }
     }
 
 #if !DISABLE_INSTANCES_SYNCH
-    if (m_mode == Instance)
+    if (translation_type == Instance)
         _synchronize_unselected_instances(SYNC_ROTATION_NONE);
-    else if (m_mode == Volume)
+    else if (translation_type == Volume)
         _synchronize_unselected_volumes();
 #endif // !DISABLE_INSTANCES_SYNCH
 
@@ -970,7 +981,23 @@ void Selection::render_sidebar_hints(const std::string& sidebar_field) const
         ::glTranslated(center(0), center(1), center(2));
         if (!boost::starts_with(sidebar_field, "position"))
         {
-            Transform3d orient_matrix = (*m_volumes)[*m_list.begin()]->get_instance_transformation().get_matrix(true, false, true, true);
+            Transform3d orient_matrix = Transform3d::Identity();
+            if (boost::starts_with(sidebar_field, "scale"))
+                orient_matrix = (*m_volumes)[*m_list.begin()]->get_instance_transformation().get_matrix(true, false, true, true);
+            else if (boost::starts_with(sidebar_field, "rotation"))
+            {
+                if (boost::ends_with(sidebar_field, "x"))
+                    orient_matrix = (*m_volumes)[*m_list.begin()]->get_instance_transformation().get_matrix(true, false, true, true);
+                else if (boost::ends_with(sidebar_field, "y"))
+                {
+                    const Vec3d& rotation = (*m_volumes)[*m_list.begin()]->get_instance_transformation().get_rotation();
+                    if (rotation(0) == 0.0)
+                        orient_matrix = (*m_volumes)[*m_list.begin()]->get_instance_transformation().get_matrix(true, false, true, true);
+                    else
+                        orient_matrix.rotate(Eigen::AngleAxisd(rotation(2), Vec3d::UnitZ()));
+                }
+            }
+
             ::glMultMatrixd(orient_matrix.data());
         }
     }
@@ -1667,5 +1694,29 @@ void Selection::_ensure_on_bed()
     }
 }
 
+bool Selection::_is_from_fully_selected_instance(unsigned int volume_idx) const
+{
+    struct SameInstance
+    {
+        int obj_idx;
+        int inst_idx;
+        GLVolumePtrs& volumes;
+
+        SameInstance(int obj_idx, int inst_idx, GLVolumePtrs& volumes) : obj_idx(obj_idx), inst_idx(inst_idx), volumes(volumes) {}
+        bool operator () (unsigned int i) { return (volumes[i]->volume_idx() >= 0) && (volumes[i]->object_idx() == obj_idx) && (volumes[i]->instance_idx() == inst_idx); }
+    };
+
+    if ((unsigned int)m_volumes->size() <= volume_idx)
+        return false;
+
+    GLVolume* volume = (*m_volumes)[volume_idx];
+    int object_idx = volume->object_idx();
+    if ((int)m_model->objects.size() <= object_idx)
+        return false;
+
+    unsigned int count = (unsigned int)std::count_if(m_list.begin(), m_list.end(), SameInstance(object_idx, volume->instance_idx(), *m_volumes));
+    return count == (unsigned int)m_model->objects[object_idx]->volumes.size();
+}
+
 } // namespace GUI
 } // namespace Slic3r
diff --git a/src/slic3r/GUI/Selection.hpp b/src/slic3r/GUI/Selection.hpp
index 6390214cd..883fb5400 100644
--- a/src/slic3r/GUI/Selection.hpp
+++ b/src/slic3r/GUI/Selection.hpp
@@ -299,6 +299,7 @@ private:
     void _synchronize_unselected_instances(SyncRotationType sync_rotation_type);
     void _synchronize_unselected_volumes();
     void _ensure_on_bed();
+    bool _is_from_fully_selected_instance(unsigned int volume_idx) const;
 };
 
 } // namespace GUI
diff --git a/src/slic3r/Utils/HexFile.cpp b/src/slic3r/Utils/HexFile.cpp
index 9e0803325..26596f629 100644
--- a/src/slic3r/Utils/HexFile.cpp
+++ b/src/slic3r/Utils/HexFile.cpp
@@ -18,6 +18,7 @@ static HexFile::DeviceKind parse_device_kind(const std::string &str)
 	     if (str == "mk2") { return HexFile::DEV_MK2; }
 	else if (str == "mk3") { return HexFile::DEV_MK3; }
 	else if (str == "mm-control") { return HexFile::DEV_MM_CONTROL; }
+	else if (str == "cw1") { return HexFile::DEV_CW1; }
 	else { return HexFile::DEV_GENERIC; }
 }
 
diff --git a/src/slic3r/Utils/HexFile.hpp b/src/slic3r/Utils/HexFile.hpp
index 1201d23a4..742ae00e6 100644
--- a/src/slic3r/Utils/HexFile.hpp
+++ b/src/slic3r/Utils/HexFile.hpp
@@ -16,6 +16,7 @@ struct HexFile
 		DEV_MK2,
 		DEV_MK3,
 		DEV_MM_CONTROL,
+		DEV_CW1,
 	};
 
 	boost::filesystem::path path;