diff --git a/src/libslic3r/AABBTreeIndirect.hpp b/src/libslic3r/AABBTreeIndirect.hpp
index 76aa36194..217166f8c 100644
--- a/src/libslic3r/AABBTreeIndirect.hpp
+++ b/src/libslic3r/AABBTreeIndirect.hpp
@@ -15,11 +15,6 @@
 
 #include "Utils.hpp" // for next_highest_power_of_2()
 
-extern "C"
-{
-// Ray-Triangle Intersection Test Routines by Tomas Moller, May 2000
-#include <igl/raytri.c>
-}
 // Definition of the ray intersection hit structure.
 #include <igl/Hit.h>
 
@@ -231,6 +226,9 @@ namespace detail {
 		const VectorType					 origin;
 		const VectorType 					 dir;
 		const VectorType					 invdir;
+
+		// epsilon for ray-triangle intersection, see intersect_triangle1()
+		const double  						 eps;
 	};
 
     template<typename VertexType, typename IndexedFaceType, typename TreeType, typename VectorType>
@@ -283,44 +281,91 @@ namespace detail {
         return tmin < t1 && tmax > t0;
 	}
 
+	// The following intersect_triangle() is derived from raytri.c routine intersect_triangle1()
+	// Ray-Triangle Intersection Test Routines
+	// Different optimizations of my and Ben Trumbore's
+	// code from journals of graphics tools (JGT)
+	// http://www.acm.org/jgt/
+	// by Tomas Moller, May 2000
 	template<typename V, typename W>
-    std::enable_if_t<std::is_same<typename V::Scalar, double>::value && std::is_same<typename W::Scalar, double>::value, bool>
-	intersect_triangle(const V &origin, const V &dir, const W &v0, const W &v1, const W &v2, double &t, double &u, double &v) {
-        return intersect_triangle1(const_cast<double*>(origin.data()), const_cast<double*>(dir.data()),
-                                   const_cast<double*>(v0.data()), const_cast<double*>(v1.data()), const_cast<double*>(v2.data()),
-                                   &t, &u, &v);
+	std::enable_if_t<std::is_same<typename V::Scalar, double>::value&& std::is_same<typename W::Scalar, double>::value, bool>
+	intersect_triangle(const V &orig, const V &dir, const W &vert0, const W &vert1, const W &vert2, double &t, double &u, double &v, double eps)
+	{
+	   // find vectors for two edges sharing vert0
+	   const V      edge1 = vert1 - vert0;
+	   const V      edge2 = vert2 - vert0;
+	   // begin calculating determinant - also used to calculate U parameter
+	   const V      pvec  = dir.cross(edge2);
+	   // if determinant is near zero, ray lies in plane of triangle
+	   const double det   = edge1.dot(pvec);
+	   V      	 	qvec;
+
+	   if (det > eps) {
+	      	// calculate distance from vert0 to ray origin
+	      	V tvec = orig - vert0;
+	      	// calculate U parameter and test bounds
+	      	u = tvec.dot(pvec);
+			if (u < 0.0 || u > det)
+				return false;
+	      	// prepare to test V parameter
+	      	qvec = tvec.cross(edge1);
+	      	// calculate V parameter and test bounds
+	      	v = dir.dot(qvec);
+	      	if (v < 0.0 || u + v > det)
+		 		return false;
+	   } else if (det < -eps) {
+	      	// calculate distance from vert0 to ray origin
+	      	V tvec = orig - vert0;
+	      	// calculate U parameter and test bounds
+	      	u = tvec.dot(pvec);
+	      	if (u > 0.0 || u < det)
+		 		return false;
+	      	// prepare to test V parameter
+	      	qvec = tvec.cross(edge1);
+	      	// calculate V parameter and test bounds
+	      	v = dir.dot(qvec);
+	      	if (v > 0.0 || u + v < det)
+		 		return false;
+	   } else 
+	     	// ray is parallel to the plane of the triangle
+		   	return false;
+
+	   double inv_det = 1.0 / det;
+	   // calculate t, ray intersects triangle
+	   t = edge2.dot(qvec) * inv_det;
+	   u *= inv_det;
+	   v *= inv_det;
+	   return true;
 	}
 
 	template<typename V, typename W>
     std::enable_if_t<std::is_same<typename V::Scalar, double>::value && !std::is_same<typename W::Scalar, double>::value, bool>
-	intersect_triangle(const V &origin, const V &dir, const W &v0, const W &v1, const W &v2, double &t, double &u, double &v) {
-        using Vector = Eigen::Matrix<double, 3, 1>;
-        Vector w0 = v0.template cast<double>();
-        Vector w1 = v1.template cast<double>();
-        Vector w2 = v2.template cast<double>();
-        return intersect_triangle1(const_cast<double*>(origin.data()), const_cast<double*>(dir.data()),
-                                   w0.data(), w1.data(), w2.data(), &t, &u, &v);
+	intersect_triangle(const V &origin, const V &dir, const W &v0, const W &v1, const W &v2, double &t, double &u, double &v, double eps) {
+        return intersect_triangle(origin, dir, v0.template cast<double>(), v1.template cast<double>(), v2.template cast<double>(), t, u, v, eps);
 	}
 
 	template<typename V, typename W>
     std::enable_if_t<! std::is_same<typename V::Scalar, double>::value && std::is_same<typename W::Scalar, double>::value, bool>
-	intersect_triangle(const V &origin, const V &dir, const W &v0, const W &v1, const W &v2, double &t, double &u, double &v) {
-        using Vector = Eigen::Matrix<double, 3, 1>;
-        Vector o  = origin.template cast<double>();
-        Vector d  = dir.template cast<double>();
-        return intersect_triangle1(o.data(), d.data(), const_cast<double*>(v0.data()), const_cast<double*>(v1.data()), const_cast<double*>(v2.data()), &t, &u, &v);
+	intersect_triangle(const V &origin, const V &dir, const W &v0, const W &v1, const W &v2, double &t, double &u, double &v, double eps) {
+        return intersect_triangle(origin.template cast<double>(), dir.template cast<double>(), v0, v1, v2, t, u, v, eps);
 	}
 
 	template<typename V, typename W>
     std::enable_if_t<! std::is_same<typename V::Scalar, double>::value && ! std::is_same<typename W::Scalar, double>::value, bool>
-	intersect_triangle(const V &origin, const V &dir, const W &v0, const W &v1, const W &v2, double &t, double &u, double &v) {
-        using Vector = Eigen::Matrix<double, 3, 1>;
-        Vector o  = origin.template cast<double>();
-        Vector d  = dir.template cast<double>();
-        Vector w0 = v0.template cast<double>();
-        Vector w1 = v1.template cast<double>();
-        Vector w2 = v2.template cast<double>();
-	    return intersect_triangle1(o.data(), d.data(), w0.data(), w1.data(), w2.data(), &t, &u, &v);
+	intersect_triangle(const V &origin, const V &dir, const W &v0, const W &v1, const W &v2, double &t, double &u, double &v, double eps) {
+	    return intersect_triangle(origin.template cast<double>(), dir.template cast<double>(), v0.template cast<double>(), v1.template cast<double>(), v2.template cast<double>(), t, u, v, eps);
+	}
+
+	template<typename Tree>
+	double intersect_triangle_epsilon(const Tree &tree) {
+		double eps = 0.000001;
+		if (! tree.empty()) {
+			const typename Tree::BoundingBox &bbox = tree.nodes().front().bbox;
+			double l = (bbox.max() - bbox.min()).cwiseMax();
+			if (l > 0)
+				eps /= (l * l);
+		}
+		return eps;
 	}
 
     template<typename RayIntersectorType, typename Scalar>
@@ -343,7 +388,7 @@ namespace detail {
 		    if (intersect_triangle(
 		    		ray_intersector.origin, ray_intersector.dir, 
 		    		ray_intersector.vertices[face(0)], ray_intersector.vertices[face(1)], ray_intersector.vertices[face(2)], 
-                    t, u, v)
+                    t, u, v, ray_intersector.eps)
 		    	&& t > 0.) {
                 hit = igl::Hit { int(node.idx), -1, float(u), float(v), float(t) };
 				return true;
@@ -388,7 +433,7 @@ namespace detail {
 		    if (intersect_triangle(
 		    		ray_intersector.origin, ray_intersector.dir, 
 		    		ray_intersector.vertices[face(0)], ray_intersector.vertices[face(1)], ray_intersector.vertices[face(2)], 
-                    t, u, v)
+                    t, u, v, ray_intersector.eps)
 		    	&& t > 0.) {
                 ray_intersector.hits.emplace_back(igl::Hit{ int(node.idx), -1, float(u), float(v), float(t) });
 			}
@@ -623,12 +668,15 @@ inline bool intersect_ray_first_hit(
 	// Direction of the ray.
 	const VectorType 					&dir,
 	// First intersection of the ray with the indexed triangle set.
-	igl::Hit 							&hit)
+	igl::Hit 							&hit,
+	// Epsilon for the ray-triangle intersection, it should be proportional to an average triangle edge length.
+	const double 						 eps = 0.000001)
 {
     using Scalar = typename VectorType::Scalar;
-    auto ray_intersector = detail::RayIntersector<VertexType, IndexedFaceType, TreeType, VectorType> {
+	auto ray_intersector = detail::RayIntersector<VertexType, IndexedFaceType, TreeType, VectorType> {
 		vertices, faces, tree,
-        origin, dir, VectorType(dir.cwiseInverse())
+        origin, dir, VectorType(dir.cwiseInverse()),
+        eps
 	};
 	return ! tree.empty() && detail::intersect_ray_recursive_first_hit(
         ray_intersector, size_t(0), std::numeric_limits<Scalar>::infinity(), hit);
@@ -652,11 +700,14 @@ inline bool intersect_ray_all_hits(
 	// Direction of the ray.
 	const VectorType 					&dir,
 	// All intersections of the ray with the indexed triangle set, sorted by parameter t.
-	std::vector<igl::Hit> 				&hits)
+	std::vector<igl::Hit> 				&hits,
+	// Epsilon for the ray-triangle intersection, it should be proportional to an average triangle edge length.
+	const double 						 eps = 0.000001)
 {
     auto ray_intersector = detail::RayIntersectorHits<VertexType, IndexedFaceType, TreeType, VectorType> {
         { vertices, faces, {tree},
-        origin, dir, VectorType(dir.cwiseInverse()) }
+        origin, dir, VectorType(dir.cwiseInverse()),
+        eps }
 	};
 	if (! tree.empty()) {
         ray_intersector.hits.reserve(8);
diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index 254f1d4fd..85e6f810b 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -13,6 +13,7 @@
 #include "ClipperUtils.hpp"
 #include "libslic3r.h"
 #include "LocalesUtils.hpp"
+#include "libslic3r/format.hpp"
 
 #include <algorithm>
 #include <cstdlib>
@@ -512,7 +513,8 @@ std::vector<GCode::LayerToPrint> GCode::collect_layers_to_print(const PrintObjec
         bool has_extrusions = (layer_to_print.object_layer && layer_to_print.object_layer->has_extrusions())
             || (layer_to_print.support_layer && layer_to_print.support_layer->has_extrusions());
 
-        // Check that there are extrusions on the very first layer.
+        // Check that there are extrusions on the very first layer. The case with empty
+        // first layer may result in skirt/brim in the air and maybe other issues.
         if (layers_to_print.size() == 1u) {
             if (!has_extrusions)
                 throw Slic3r::SlicingError(_(L("There is an object with no extrusions in the first layer.")) + "\n" +
@@ -534,11 +536,12 @@ std::vector<GCode::LayerToPrint> GCode::collect_layers_to_print(const PrintObjec
 
             if (has_extrusions && layer_to_print.print_z() > maximal_print_z + 2. * EPSILON) {
                 const_cast<Print*>(object.print())->active_step_add_warning(PrintStateBase::WarningLevel::CRITICAL,
-                    _(L("Empty layers detected. Make sure the object is printable.")) + "\n" +
-                    _(L("Object name")) + ": " + object.model_object()->name + "\n" + _(L("Print z")) + ": " +
-                    std::to_string(layers_to_print.back().print_z()) + "\n\n" + _(L("This is "
-                        "usually caused by negligibly small extrusions or by a faulty model. Try to repair "
-                        "the model or change its orientation on the bed.")));
+                    Slic3r::format(_(L("Empty layer detected between heights %1% and %2%. Make sure the object is printable.")),
+                                   (last_extrusion_layer ? last_extrusion_layer->print_z() : 0.),
+                                   layers_to_print.back().print_z())
+                    + "\n" + Slic3r::format(_(L("Object name: %1%")), object.model_object()->name) + "\n\n"
+                    + _(L("This is usually caused by negligibly small extrusions or by a faulty model. "
+                          "Try to repair the model or change its orientation on the bed.")));
             }
 
             // Remember last layer with extrusions.
diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index ee09e0f5b..d8d26baa6 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -2294,9 +2294,13 @@ void PrintObject::project_and_append_custom_facets(
                     ? mv->seam_facets.get_facets_strict(*mv, type)
                     : mv->supported_facets.get_facets_strict(*mv, type);
             if (! custom_facets.indices.empty())
+#if 0
                 project_triangles_to_slabs(this->layers(), custom_facets, 
                     (this->trafo_centered() * mv->get_matrix()).cast<float>(),
                     seam, out);
+#else
+                slice_mesh_slabs(custom_facets, zs_from_layers(this->layers()), this->trafo_centered() * mv->get_matrix(), nullptr, &out, [](){});
+#endif
         }
 }
 
diff --git a/src/libslic3r/SLA/IndexedMesh.cpp b/src/libslic3r/SLA/IndexedMesh.cpp
index 887ef1555..07c4203ab 100644
--- a/src/libslic3r/SLA/IndexedMesh.cpp
+++ b/src/libslic3r/SLA/IndexedMesh.cpp
@@ -17,10 +17,18 @@ namespace sla {
 class IndexedMesh::AABBImpl {
 private:
     AABBTreeIndirect::Tree3f m_tree;
+    double                   m_triangle_ray_epsilon;
 
 public:
-    void init(const indexed_triangle_set &its)
+    void init(const indexed_triangle_set &its, bool calculate_epsilon)
     {
+        m_triangle_ray_epsilon = 0.000001;
+        if (calculate_epsilon) {
+            // Calculate epsilon from average triangle edge length.
+            double l = its_average_edge_length(its);
+            if (l > 0)
+                m_triangle_ray_epsilon = 0.000001 * l * l;
+        }
         m_tree = AABBTreeIndirect::build_aabb_tree_over_indexed_triangle_set(
             its.vertices, its.indices);
     }
@@ -31,7 +39,7 @@ public:
                        igl::Hit &                  hit)
     {
         AABBTreeIndirect::intersect_ray_first_hit(its.vertices, its.indices,
-                                                  m_tree, s, dir, hit);
+                                                  m_tree, s, dir, hit, m_triangle_ray_epsilon);
     }
 
     void intersect_ray(const indexed_triangle_set &its,
@@ -40,7 +48,7 @@ public:
                        std::vector<igl::Hit> &     hits)
     {
         AABBTreeIndirect::intersect_ray_all_hits(its.vertices, its.indices,
-                                                 m_tree, s, dir, hits);
+                                                 m_tree, s, dir, hits, m_triangle_ray_epsilon);
     }
 
     double squared_distance(const indexed_triangle_set & its,
@@ -60,25 +68,25 @@ public:
     }
 };
 
-template<class M> void IndexedMesh::init(const M &mesh)
+template<class M> void IndexedMesh::init(const M &mesh, bool calculate_epsilon)
 {
     BoundingBoxf3 bb = bounding_box(mesh);
     m_ground_level += bb.min(Z);
 
     // Build the AABB accelaration tree
-    m_aabb->init(*m_tm);
+    m_aabb->init(*m_tm, calculate_epsilon);
 }
 
-IndexedMesh::IndexedMesh(const indexed_triangle_set& tmesh)
+IndexedMesh::IndexedMesh(const indexed_triangle_set& tmesh, bool calculate_epsilon)
     : m_aabb(new AABBImpl()), m_tm(&tmesh)
 {
-    init(tmesh);
+    init(tmesh, calculate_epsilon);
 }
 
-IndexedMesh::IndexedMesh(const TriangleMesh &mesh)
+IndexedMesh::IndexedMesh(const TriangleMesh &mesh, bool calculate_epsilon)
     : m_aabb(new AABBImpl()), m_tm(&mesh.its)
 {
-    init(mesh);
+    init(mesh, calculate_epsilon);
 }
 
 IndexedMesh::~IndexedMesh() {}
diff --git a/src/libslic3r/SLA/IndexedMesh.hpp b/src/libslic3r/SLA/IndexedMesh.hpp
index 25ab75b83..9348a97c9 100644
--- a/src/libslic3r/SLA/IndexedMesh.hpp
+++ b/src/libslic3r/SLA/IndexedMesh.hpp
@@ -42,12 +42,14 @@ class IndexedMesh {
     std::vector<DrainHole> m_holes;
 #endif
 
-    template<class M> void init(const M &mesh);
+    template<class M> void init(const M &mesh, bool calculate_epsilon);
 
 public:
     
-    explicit IndexedMesh(const indexed_triangle_set&);
-    explicit IndexedMesh(const TriangleMesh &mesh);
+    // calculate_epsilon ... calculate epsilon for triangle-ray intersection from an average triangle edge length.
+    // If set to false, a default epsilon is used, which works for "reasonable" meshes.
+    explicit IndexedMesh(const indexed_triangle_set &tmesh, bool calculate_epsilon = false);
+    explicit IndexedMesh(const TriangleMesh &mesh, bool calculate_epsilon = false);
     
     IndexedMesh(const IndexedMesh& other);
     IndexedMesh& operator=(const IndexedMesh&);
diff --git a/src/libslic3r/SupportMaterial.cpp b/src/libslic3r/SupportMaterial.cpp
index e2d7bf199..2e4a47954 100644
--- a/src/libslic3r/SupportMaterial.cpp
+++ b/src/libslic3r/SupportMaterial.cpp
@@ -37,6 +37,7 @@
     #define DEBUG
     #define _DEBUG
     #undef NDEBUG
+    #include "utils.hpp"
     #include "SVG.hpp"
 #endif
 
@@ -429,7 +430,7 @@ void PrintObjectSupportMaterial::generate(PrintObject &object)
     for (const MyLayer *layer : top_contacts)
         Slic3r::SVG::export_expolygons(
             debug_out_path("support-top-contacts-%d-%lf.svg", iRun, layer->print_z), 
-            union_ex(layer->polygons, false));
+            union_ex(layer->polygons));
 #endif /* SLIC3R_DEBUG */
 
     BOOST_LOG_TRIVIAL(info) << "Support generator - Creating bottom contacts";
@@ -447,7 +448,7 @@ void PrintObjectSupportMaterial::generate(PrintObject &object)
     for (size_t layer_id = 0; layer_id < object.layers().size(); ++ layer_id)
         Slic3r::SVG::export_expolygons(
             debug_out_path("support-areas-%d-%lf.svg", iRun, object.layers()[layer_id]->print_z), 
-            union_ex(layer_support_areas[layer_id], false));
+            union_ex(layer_support_areas[layer_id]));
 #endif /* SLIC3R_DEBUG */
 
     BOOST_LOG_TRIVIAL(info) << "Support generator - Creating intermediate layers - indices";
@@ -466,7 +467,7 @@ void PrintObjectSupportMaterial::generate(PrintObject &object)
     for (const MyLayer *layer : top_contacts)
         Slic3r::SVG::export_expolygons(
             debug_out_path("support-top-contacts-trimmed-by-object-%d-%lf.svg", iRun, layer->print_z), 
-            union_ex(layer->polygons, false));
+            union_ex(layer->polygons));
 #endif
 
     BOOST_LOG_TRIVIAL(info) << "Support generator - Creating base layers";
@@ -478,7 +479,7 @@ void PrintObjectSupportMaterial::generate(PrintObject &object)
     for (MyLayersPtr::const_iterator it = intermediate_layers.begin(); it != intermediate_layers.end(); ++ it)
         Slic3r::SVG::export_expolygons(
             debug_out_path("support-base-layers-%d-%lf.svg", iRun, (*it)->print_z), 
-            union_ex((*it)->polygons, false));
+            union_ex((*it)->polygons));
 #endif /* SLIC3R_DEBUG */
 
     BOOST_LOG_TRIVIAL(info) << "Support generator - Trimming top contacts by bottom contacts";
@@ -507,11 +508,11 @@ void PrintObjectSupportMaterial::generate(PrintObject &object)
     for (const MyLayer *l : interface_layers)
         Slic3r::SVG::export_expolygons(
             debug_out_path("support-interface-layers-%d-%lf.svg", iRun, l->print_z), 
-            union_ex(l->polygons, false));
+            union_ex(l->polygons));
     for (const MyLayer *l : base_interface_layers)
         Slic3r::SVG::export_expolygons(
             debug_out_path("support-base-interface-layers-%d-%lf.svg", iRun, l->print_z), 
-            union_ex(l->polygons, false));
+            union_ex(l->polygons));
 #endif // SLIC3R_DEBUG
 
 /*
@@ -1308,9 +1309,9 @@ namespace SupportMaterialInternal {
         #ifdef SLIC3R_DEBUG
             static int iRun = 0;
             SVG::export_expolygons(debug_out_path("support-top-contacts-remove-bridges-run%d.svg", iRun ++),
-                { { { union_ex(offset(layerm->unsupported_bridge_edges, scale_(SUPPORT_MATERIAL_MARGIN), SUPPORT_SURFACES_OFFSET_PARAMETERS), false) }, { "unsupported_bridge_edges", "orange", 0.5f } },
-                  { { union_ex(contact_polygons, false) },            { "contact_polygons",           "blue",   0.5f } },
-                  { { union_ex(bridges, false) },                     { "bridges",                    "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+                { { { union_ex(offset(layerm->unsupported_bridge_edges, scale_(SUPPORT_MATERIAL_MARGIN), SUPPORT_SURFACES_OFFSET_PARAMETERS)) }, { "unsupported_bridge_edges", "orange", 0.5f } },
+                  { { union_ex(contact_polygons) },            { "contact_polygons",           "blue",   0.5f } },
+                  { { union_ex(bridges) },                     { "bridges",                    "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
         #endif /* SLIC3R_DEBUG */
     }
 }
@@ -1416,13 +1417,35 @@ static inline std::tuple<Polygons, Polygons, Polygons, float> detect_overhangs(
         // Generate overhang / contact_polygons for non-raft layers.
         const Layer &lower_layer  = *layer.lower_layer;
         const bool   has_enforcer = ! annotations.enforcers_layers.empty() && ! annotations.enforcers_layers[layer_id].empty();
-        float        fw           = 0;
+
+        // Cache support trimming polygons derived from lower layer polygons, possible merged with "on build plate only" trimming polygons.
+        auto slices_margin_update = 
+            [&slices_margin, &lower_layer, &lower_layer_polygons, buildplate_only, has_enforcer, &annotations, layer_id]
+            (float slices_margin_offset, float no_interface_offset) {
+            if (slices_margin.offset != slices_margin_offset) {
+                slices_margin.offset = slices_margin_offset;
+                slices_margin.polygons = (slices_margin_offset == 0.f) ?
+                    lower_layer_polygons :
+                    offset2(lower_layer.lslices, -no_interface_offset * 0.5f, slices_margin_offset + no_interface_offset * 0.5f, SUPPORT_SURFACES_OFFSET_PARAMETERS);
+                if (buildplate_only && !annotations.buildplate_covered[layer_id].empty()) {
+                    if (has_enforcer)
+                        // Make a backup of trimming polygons before enforcing "on build plate only".
+                        slices_margin.all_polygons = slices_margin.polygons;
+                    // Trim the inflated contact surfaces by the top surfaces as well.
+                    slices_margin.polygons = union_(slices_margin.polygons, annotations.buildplate_covered[layer_id]);
+                }
+            }
+        };
+
+        float fw                  = 0;
+        float lower_layer_offset  = 0;
+        float no_interface_offset = 0;
         for (LayerRegion *layerm : layer.regions()) {
             // Extrusion width accounts for the roundings of the extrudates.
             // It is the maximum widh of the extrudate.
             fw = float(layerm->flow(frExternalPerimeter).scaled_width());
             no_interface_offset = (no_interface_offset == 0.f) ? fw : std::min(no_interface_offset, fw);
-            float lower_layer_offset = 
+            lower_layer_offset  = 
                 (layer_id < (size_t)object_config.support_material_enforce_layers.value) ? 
                     // Enforce a full possible support, ignore the overhang angle.
                     0.f :
@@ -1494,7 +1517,7 @@ static inline std::tuple<Polygons, Polygons, Polygons, float> detect_overhangs(
                     iRun, layer_id, 
                     std::find_if(layer.regions().begin(), layer.regions().end(), [layerm](const LayerRegion* other){return other == layerm;}) - layer.regions().begin()),
                     get_extents(diff_polygons));
-                Slic3r::ExPolygons expolys = union_ex(diff_polygons, false);
+                Slic3r::ExPolygons expolys = union_ex(diff_polygons);
                 svg.draw(expolys);
             }
             #endif /* SLIC3R_DEBUG */
@@ -1512,7 +1535,7 @@ static inline std::tuple<Polygons, Polygons, Polygons, float> detect_overhangs(
                     iRun, layer_id, 
                     std::find_if(layer.regions().begin(), layer.regions().end(), [layerm](const LayerRegion* other){return other == layerm;}) - layer.regions().begin(),
                     layer.print_z),
-                union_ex(diff_polygons, false));
+                union_ex(diff_polygons));
             #endif /* SLIC3R_DEBUG */
 
             //FIXME the overhang_polygons are used to construct the support towers as well.
@@ -1529,20 +1552,7 @@ static inline std::tuple<Polygons, Polygons, Polygons, float> detect_overhangs(
                 //FIXME one should trim with the layer span colliding with the support layer, this layer
                 // may be lower than lower_layer, so the support area needed may need to be actually bigger!
                 // For the same reason, the non-bridging support area may be smaller than the bridging support area!
-                float slices_margin_offset = std::min(lower_layer_offset, float(scale_(gap_xy))); 
-                if (slices_margin.offset != slices_margin_offset) {
-                    slices_margin.offset = slices_margin_offset;
-                    slices_margin.polygons = (slices_margin_offset == 0.f) ?
-                        lower_layer_polygons :
-                        offset2(lower_layer.lslices, - no_interface_offset * 0.5f, slices_margin_offset + no_interface_offset * 0.5f, SUPPORT_SURFACES_OFFSET_PARAMETERS);
-                    if (buildplate_only && ! annotations.buildplate_covered[layer_id].empty()) {
-                        if (has_enforcer)
-                            // Make a backup of trimming polygons before enforcing "on build plate only".
-                            slices_margin.all_polygons = slices_margin.polygons;
-                        // Trim the inflated contact surfaces by the top surfaces as well.
-                        slices_margin.polygons = union_(slices_margin.polygons, annotations.buildplate_covered[layer_id]);
-                    }
-                }
+                slices_margin_update(std::min(lower_layer_offset, float(scale_(gap_xy))), no_interface_offset);
                 // Offset the contact polygons outside.
 #if 0
                 for (size_t i = 0; i < NUM_MARGIN_STEPS; ++ i) {
@@ -1572,12 +1582,13 @@ static inline std::tuple<Polygons, Polygons, Polygons, float> detect_overhangs(
                 offset(lower_layer_polygons, 0.05f * fw, SUPPORT_SURFACES_OFFSET_PARAMETERS));
 #ifdef SLIC3R_DEBUG
             SVG::export_expolygons(debug_out_path("support-top-contacts-enforcers-run%d-layer%d-z%f.svg", iRun, layer_id, layer.print_z),
-                { { layer.lslices,                                       { "layer.lslices",              "gray",   0.2f } },
-                  { { union_ex(lower_layer_polygons, false) },           { "lower_layer_polygons",       "green",  0.5f } },
-                  { enforcers_united,                                    { "enforcers",                  "blue",   0.5f } },
-                  { { union_ex(enforcer_polygons, true) },               { "new_contacts",               "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+                { { layer.lslices,                                 { "layer.lslices",              "gray",   0.2f } },
+                  { { union_ex(lower_layer_polygons) },            { "lower_layer_polygons",       "green",  0.5f } },
+                  { enforcers_united,                              { "enforcers",                  "blue",   0.5f } },
+                  { { union_safety_offset_ex(enforcer_polygons) }, { "new_contacts",               "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
 #endif /* SLIC3R_DEBUG */
             polygons_append(overhang_polygons, enforcer_polygons);
+            slices_margin_update(std::min(lower_layer_offset, float(scale_(gap_xy))), no_interface_offset);
             polygons_append(contact_polygons, diff(enforcer_polygons, slices_margin.all_polygons.empty() ? slices_margin.polygons : slices_margin.all_polygons));
         }
     }
@@ -1738,19 +1749,19 @@ static inline void fill_contact_layer(
 #endif // SLIC3R_DEBUG
                 );
     #ifdef SLIC3R_DEBUG
-            SVG::export_expolygons(debug_out_path("support-top-contacts-final0-run%d-layer%d-z%f.svg", iRun, layer_id, layer.print_z),
-                { { { union_ex(lower_layer_polygons, false) },          { "lower_layer_polygons",       "gray",   0.2f } },
-                    { { union_ex(*new_layer.contact_polygons, false) }, { "new_layer.contact_polygons", "yellow", 0.5f } },
-                    { { union_ex(slices_margin.polygons, false) },      { "slices_margin_cached",       "blue",   0.5f } },
-                    { { union_ex(dense_interface_polygons, false) },    { "dense_interface_polygons",   "green",  0.5f } },
-                    { { union_ex(new_layer.polygons, true) },           { "new_layer.polygons",         "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+            SVG::export_expolygons(debug_out_path("support-top-contacts-final1-run%d-layer%d-z%f.svg", iRun, layer_id, layer.print_z),
+                { { { union_ex(lower_layer_polygons) },               { "lower_layer_polygons",       "gray",   0.2f } },
+                    { { union_ex(*new_layer.contact_polygons) },      { "new_layer.contact_polygons", "yellow", 0.5f } },
+                    { { union_ex(slices_margin.polygons) },           { "slices_margin_cached",       "blue",   0.5f } },
+                    { { union_ex(dense_interface_polygons) },         { "dense_interface_polygons",   "green",  0.5f } },
+                    { { union_safety_offset_ex(new_layer.polygons) }, { "new_layer.polygons",         "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
             //support_grid_pattern.serialize(debug_out_path("support-top-contacts-final-run%d-layer%d-z%f.bin", iRun, layer_id, layer.print_z));
-            SVG::export_expolygons(debug_out_path("support-top-contacts-final0-run%d-layer%d-z%f.svg", iRun, layer_id, layer.print_z),
-                { { { union_ex(lower_layer_polygons, false) },        { "lower_layer_polygons",       "gray",   0.2f } },
-                    { { union_ex(*new_layer.contact_polygons, false) }, { "new_layer.contact_polygons", "yellow", 0.5f } },
-                    { { union_ex(contact_polygons, false) },            { "contact_polygons",           "blue",   0.5f } },
-                    { { union_ex(dense_interface_polygons, false) },    { "dense_interface_polygons",   "green",  0.5f } },
-                    { { union_ex(new_layer.polygons, true) },           { "new_layer.polygons",         "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+            SVG::export_expolygons(debug_out_path("support-top-contacts-final2-run%d-layer%d-z%f.svg", iRun, layer_id, layer.print_z),
+                { { { union_ex(lower_layer_polygons) },               { "lower_layer_polygons",       "gray",   0.2f } },
+                    { { union_ex(*new_layer.contact_polygons) },      { "new_layer.contact_polygons", "yellow", 0.5f } },
+                    { { union_ex(contact_polygons) },                 { "contact_polygons",           "blue",   0.5f } },
+                    { { union_ex(dense_interface_polygons) },         { "dense_interface_polygons",   "green",  0.5f } },
+                    { { union_safety_offset_ex(new_layer.polygons) }, { "new_layer.polygons",         "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
     #endif /* SLIC3R_DEBUG */
         }
     }
@@ -1796,11 +1807,11 @@ static inline void fill_contact_layer(
 
 #ifdef SLIC3R_DEBUG
     SVG::export_expolygons(debug_out_path("support-top-contacts-final0-run%d-layer%d-z%f.svg", iRun, layer_id, layer.print_z),
-        { { { union_ex(lower_layer_polygons, false) },        { "lower_layer_polygons",       "gray",   0.2f } },
-            { { union_ex(*new_layer.contact_polygons, false) }, { "new_layer.contact_polygons", "yellow", 0.5f } },
-            { { union_ex(contact_polygons, false) },            { "contact_polygons",           "blue",   0.5f } },
-            { { union_ex(overhang_polygons, false) },           { "overhang_polygons",          "green",  0.5f } },
-            { { union_ex(new_layer.polygons, true) },           { "new_layer.polygons",         "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+        { { { union_ex(lower_layer_polygons) },               { "lower_layer_polygons",       "gray",   0.2f } },
+            { { union_ex(*new_layer.contact_polygons) },      { "new_layer.contact_polygons", "yellow", 0.5f } },
+            { { union_ex(contact_polygons) },                 { "contact_polygons",           "blue",   0.5f } },
+            { { union_ex(overhang_polygons) },                { "overhang_polygons",          "green",  0.5f } },
+            { { union_safety_offset_ex(new_layer.polygons) }, { "new_layer.polygons",         "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
 #endif /* SLIC3R_DEBUG */
 
     // Even after the contact layer was expanded into a grid, some of the contact islands may be too tiny to be extruded.
@@ -1964,10 +1975,10 @@ static inline PrintObjectSupportMaterial::MyLayer* detect_bottom_contacts(
     Polygons top = collect_region_slices_by_type(layer, stTop);
 #ifdef SLIC3R_DEBUG
     SVG::export_expolygons(debug_out_path("support-bottom-layers-raw-%d-%lf.svg", iRun, layer.print_z),
-        { { { union_ex(top, false) },                  { "top",            "blue",    0.5f } },
-            { { union_ex(supports_projected, true) },  { "overhangs",      "magenta", 0.5f } },
-            { layer.lslices,                           { "layer.lslices",  "green",   0.5f } },
-            { { union_ex(polygons_new, true) },        { "polygons_new",   "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+        { { { union_ex(top) },                                { "top",            "blue",    0.5f } },
+            { { union_safety_offset_ex(supports_projected) }, { "overhangs",      "magenta", 0.5f } },
+            { layer.lslices,                                  { "layer.lslices",  "green",   0.5f } },
+            { { union_safety_offset_ex(polygons_new) },       { "polygons_new",   "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
 #endif /* SLIC3R_DEBUG */
 
     // Now find whether any projection of the contact surfaces above layer.print_z not yet supported by any 
@@ -2037,7 +2048,7 @@ static inline PrintObjectSupportMaterial::MyLayer* detect_bottom_contacts(
 #ifdef SLIC3R_DEBUG
     Slic3r::SVG::export_expolygons(
         debug_out_path("support-bottom-contacts-%d-%lf.svg", iRun, layer_new.print_z),
-        union_ex(layer_new.polygons, false));
+        union_ex(layer_new.polygons));
 #endif /* SLIC3R_DEBUG */
 
     // Trim the already created base layers above the current layer intersecting with the new bottom contacts layer.
@@ -2050,14 +2061,14 @@ static inline PrintObjectSupportMaterial::MyLayer* detect_bottom_contacts(
         if (! layer_support_areas[layer_id_above].empty()) {
 #ifdef SLIC3R_DEBUG
             SVG::export_expolygons(debug_out_path("support-support-areas-raw-before-trimming-%d-with-%f-%lf.svg", iRun, layer.print_z, layer_above.print_z),
-                { { { union_ex(touching, false) },                            { "touching", "blue", 0.5f } },
-                    { { union_ex(layer_support_areas[layer_id_above], true) },  { "above",    "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+                { { { union_ex(touching) },                                            { "touching", "blue", 0.5f } },
+                    { { union_safety_offset_ex(layer_support_areas[layer_id_above]) }, { "above",    "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
 #endif /* SLIC3R_DEBUG */
             layer_support_areas[layer_id_above] = diff(layer_support_areas[layer_id_above], touching);
 #ifdef SLIC3R_DEBUG
             Slic3r::SVG::export_expolygons(
                 debug_out_path("support-support-areas-raw-after-trimming-%d-with-%f-%lf.svg", iRun, layer.print_z, layer_above.print_z),
-                union_ex(layer_support_areas[layer_id_above], false));
+                union_ex(layer_support_areas[layer_id_above]));
 #endif /* SLIC3R_DEBUG */
         }
     }
@@ -2080,8 +2091,8 @@ static inline std::pair<Polygons, Polygons> project_support_to_grid(const Layer
 
 #ifdef SLIC3R_DEBUG
     SVG::export_expolygons(debug_out_path("support-support-areas-%s-raw-%d-%lf.svg", debug_name, iRun, layer.print_z),
-        { { { union_ex(trimming, false) },              { "trimming",               "blue", 0.5f } },
-          { { union_ex(overhangs_projection, true) },   { "overhangs_projection",   "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+        { { { union_ex(trimming) },                           { "trimming",               "blue", 0.5f } },
+          { { union_safety_offset_ex(overhangs_projection) }, { "overhangs_projection",   "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
 #endif /* SLIC3R_DEBUG */
 
     remove_sticks(overhangs_projection);
@@ -2089,8 +2100,8 @@ static inline std::pair<Polygons, Polygons> project_support_to_grid(const Layer
 
 #ifdef SLIC3R_DEBUG
     SVG::export_expolygons(debug_out_path("support-support-areas-%s-raw-cleaned-%d-%lf.svg", debug_name, iRun, layer.print_z),
-        { { { union_ex(trimming, false) },              { "trimming",             "blue", 0.5f } },
-          { { union_ex(overhangs_projection, false) },  { "overhangs_projection", "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+        { { { union_ex(trimming) },              { "trimming",             "blue", 0.5f } },
+          { { union_ex(overhangs_projection) },  { "overhangs_projection", "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
 #endif /* SLIC3R_DEBUG */
 
     SupportGridPattern support_grid_pattern(&overhangs_projection, &trimming, grid_params);
@@ -2113,7 +2124,7 @@ static inline std::pair<Polygons, Polygons> project_support_to_grid(const Layer
 #ifdef SLIC3R_DEBUG
             Slic3r::SVG::export_expolygons(
                 debug_out_path("support-layer_support_area-gridded-%s-%d-%lf.svg", debug_name, iRun, layer.print_z),
-                union_ex(out.first, false));
+                union_ex(out.first));
 #endif /* SLIC3R_DEBUG */
         });
 
@@ -2131,13 +2142,13 @@ static inline std::pair<Polygons, Polygons> project_support_to_grid(const Layer
 #ifdef SLIC3R_DEBUG
             Slic3r::SVG::export_expolygons(
                 debug_out_path("support-projection_new-gridded-%d-%lf.svg", iRun, layer.print_z),
-                union_ex(out.second, false));
+                union_ex(out.second));
 #endif /* SLIC3R_DEBUG */
 #ifdef SLIC3R_DEBUG
             SVG::export_expolygons(debug_out_path("support-projection_new-gridded-%d-%lf.svg", iRun, layer.print_z),
-                { { { union_ex(trimming, false) },                { "trimming",               "gray", 0.5f } },
-                    { { union_ex(overhangs_projection, true) },   { "overhangs_projection",   "blue", 0.5f } },
-                    { { union_ex(out.second, true) },             { "projection_new", "red",  "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+                { { { union_ex(trimming) },                             { "trimming",               "gray", 0.5f } },
+                    { { union_safety_offset_ex(overhangs_projection) }, { "overhangs_projection",   "blue", 0.5f } },
+                    { { union_safety_offset_ex(out.second) },           { "projection_new", "red",  "black", "", scaled<coord_t>(0.1f), 0.5f } } });
 #endif /* SLIC3R_DEBUG */
         });
 
@@ -2667,10 +2678,10 @@ void PrintObjectSupportMaterial::generate_base_layers(
                     BoundingBox bbox = get_extents(polygons_new);
                     bbox.merge(get_extents(polygons_trimming));
                     ::Slic3r::SVG svg(debug_out_path("support-intermediate-layers-raw-%d-%lf.svg", iRun, layer_intermediate.print_z), bbox);
-                    svg.draw(union_ex(polygons_new, false), "blue", 0.5f);
-                    svg.draw(to_polylines(polygons_new), "blue");
-                    svg.draw(union_ex(polygons_trimming, true), "red", 0.5f);
-                    svg.draw(to_polylines(polygons_trimming), "red");
+                    svg.draw(union_ex(polygons_new),                    "blue", 0.5f);
+                    svg.draw(to_polylines(polygons_new),                "blue");
+                    svg.draw(union_safety_offset_ex(polygons_trimming), "red", 0.5f);
+                    svg.draw(to_polylines(polygons_trimming),           "red");
                 }
         #endif /* SLIC3R_DEBUG */
 
@@ -2706,7 +2717,7 @@ void PrintObjectSupportMaterial::generate_base_layers(
     for (MyLayersPtr::const_iterator it = intermediate_layers.begin(); it != intermediate_layers.end(); ++it)
         ::Slic3r::SVG::export_expolygons(
             debug_out_path("support-intermediate-layers-untrimmed-%d-%lf.svg", iRun, (*it)->print_z),
-            union_ex((*it)->polygons, false));
+            union_ex((*it)->polygons));
     ++ iRun;
 #endif /* SLIC3R_DEBUG */
 
diff --git a/src/libslic3r/TriangleMesh.cpp b/src/libslic3r/TriangleMesh.cpp
index d4baabc97..fa8f8bce6 100644
--- a/src/libslic3r/TriangleMesh.cpp
+++ b/src/libslic3r/TriangleMesh.cpp
@@ -1275,6 +1275,21 @@ float its_volume(const indexed_triangle_set &its)
     return volume;
 }
 
+float its_average_edge_length(const indexed_triangle_set &its)
+{
+    if (its.indices.empty())
+        return 0.f;
+
+    double edge_length = 0.f;
+    for (size_t i = 0; i < its.indices.size(); ++ i) {
+        const its_triangle v = its_triangle_vertices(its, i);
+        edge_length += (v[1] - v[0]).cast<double>().norm() + 
+                       (v[2] - v[0]).cast<double>().norm() +
+                       (v[1] - v[2]).cast<double>().norm();
+    }
+    return float(edge_length / (3 * its.indices.size()));
+}
+
 std::vector<indexed_triangle_set> its_split(const indexed_triangle_set &its)
 {
     return its_split<>(its);
diff --git a/src/libslic3r/TriangleMesh.hpp b/src/libslic3r/TriangleMesh.hpp
index b7a1bebb1..c463af5a2 100644
--- a/src/libslic3r/TriangleMesh.hpp
+++ b/src/libslic3r/TriangleMesh.hpp
@@ -199,6 +199,7 @@ inline stl_normal its_unnormalized_normal(const indexed_triangle_set &its,
 }
 
 float its_volume(const indexed_triangle_set &its);
+float its_average_edge_length(const indexed_triangle_set &its);
 
 void its_merge(indexed_triangle_set &A, const indexed_triangle_set &B);
 void its_merge(indexed_triangle_set &A, const std::vector<Vec3f> &triangles);
diff --git a/src/libslic3r/Utils.hpp b/src/libslic3r/Utils.hpp
index 1b02e0331..a01e63166 100644
--- a/src/libslic3r/Utils.hpp
+++ b/src/libslic3r/Utils.hpp
@@ -58,6 +58,11 @@ void set_data_dir(const std::string &path);
 // Return a full path to the GUI resource files.
 const std::string& data_dir();
 
+// Format an output path for debugging purposes.
+// Writes out the output path prefix to the console for the first time the function is called,
+// so the user knows where to search for the debugging output.
+std::string debug_out_path(const char *name, ...);
+
 // A special type for strings encoded in the local Windows 8-bit code page.
 // This type is only needed for Perl bindings to relay to Perl that the string is raw, not UTF-8 encoded.
 typedef std::string local_encoded_string;
diff --git a/src/libslic3r/libslic3r.h b/src/libslic3r/libslic3r.h
index 8d8d15df9..a29436189 100644
--- a/src/libslic3r/libslic3r.h
+++ b/src/libslic3r/libslic3r.h
@@ -65,18 +65,6 @@ static constexpr double EXTERNAL_INFILL_MARGIN = 3.;
 
 #define SCALED_EPSILON scale_(EPSILON)
 
-#define SLIC3R_DEBUG_OUT_PATH_PREFIX "out/"
-
-inline std::string debug_out_path(const char *name, ...)
-{
-	char buffer[2048];
-	va_list args;
-	va_start(args, name);
-	std::vsprintf(buffer, name, args);
-	va_end(args);
-	return std::string(SLIC3R_DEBUG_OUT_PATH_PREFIX) + std::string(buffer);
-}
-
 #ifndef UNUSED
 #define UNUSED(x) (void)(x)
 #endif /* UNUSED */
diff --git a/src/libslic3r/utils.cpp b/src/libslic3r/utils.cpp
index 29f955e92..c330f34b2 100644
--- a/src/libslic3r/utils.cpp
+++ b/src/libslic3r/utils.cpp
@@ -1,6 +1,7 @@
 #include "Utils.hpp"
 #include "I18N.hpp"
 
+#include <atomic>
 #include <locale>
 #include <ctime>
 #include <cstdarg>
@@ -207,6 +208,23 @@ std::string custom_shapes_dir()
     return (boost::filesystem::path(g_data_dir) / "shapes").string();
 }
 
+static std::atomic<bool> debug_out_path_called(false);
+
+std::string debug_out_path(const char *name, ...)
+{
+	static constexpr const char *SLIC3R_DEBUG_OUT_PATH_PREFIX = "out/";
+    if (! debug_out_path_called.exchange(true)) {
+		std::string path = boost::filesystem::system_complete(SLIC3R_DEBUG_OUT_PATH_PREFIX).string();
+        printf("Debugging output files will be written to %s\n", path.c_str());
+    }
+	char buffer[2048];
+	va_list args;
+	va_start(args, name);
+	std::vsprintf(buffer, name, args);
+	va_end(args);
+	return std::string(SLIC3R_DEBUG_OUT_PATH_PREFIX) + std::string(buffer);
+}
+
 #ifdef _WIN32
 // The following helpers are borrowed from the LLVM project https://github.com/llvm
 namespace WindowsSupport
diff --git a/src/slic3r/GUI/DesktopIntegrationDialog.cpp b/src/slic3r/GUI/DesktopIntegrationDialog.cpp
index fb4a62f91..935121935 100644
--- a/src/slic3r/GUI/DesktopIntegrationDialog.cpp
+++ b/src/slic3r/GUI/DesktopIntegrationDialog.cpp
@@ -22,6 +22,95 @@ namespace Slic3r {
 namespace GUI {
 
 namespace {
+
+// escaping of path string according to 
+// https://cgit.freedesktop.org/xdg/xdg-specs/tree/desktop-entry/desktop-entry-spec.xml
+std::string escape_string(const std::string& str)
+{
+    // The buffer needs to be bigger if escaping <,>,&
+    std::vector<char> out(str.size() * 4, 0);
+    char *outptr = out.data();
+    for (size_t i = 0; i < str.size(); ++ i) {
+        char c = str[i];
+        // must be escaped
+        if (c == '\"') { //double quote 
+            (*outptr ++) = '\\';
+            (*outptr ++) = '\"';
+        } else if (c == '`') {  // backtick character
+            (*outptr ++) = '\\';
+            (*outptr ++) = '`';
+        } else if (c == '$') { // dollar sign
+            (*outptr ++) = '\\';
+            (*outptr ++) = '$';
+        } else if (c == '\\') { // backslash character
+            (*outptr ++) = '\\';
+            (*outptr ++) = '\\';
+            (*outptr ++) = '\\';
+            (*outptr ++) = '\\';
+        //  Reserved characters   
+        // At Ubuntu, all these characters must NOT be escaped for desktop integration to work
+        /*
+        } else if (c == ' ') { // space
+            (*outptr ++) = '\\';
+            (*outptr ++) = ' ';
+        } else if (c == '\t') { // tab
+            (*outptr ++) = '\\';
+            (*outptr ++) = '\t';
+        } else if (c == '\n') { // newline
+            (*outptr ++) = '\\';
+            (*outptr ++) = '\n';
+        } else if (c == '\'') { // single quote
+            (*outptr ++) = '\\';
+            (*outptr ++) = '\'';
+        } else if (c == '>') { // greater-than sign
+            (*outptr ++) = '\\';
+            (*outptr ++) = '&';
+            (*outptr ++) = 'g';
+            (*outptr ++) = 't';
+            (*outptr ++) = ';';
+        } else if (c == '<') { //less-than sign
+            (*outptr ++) = '\\';
+            (*outptr ++) = '&';
+            (*outptr ++) = 'l';
+            (*outptr ++) = 't';
+            (*outptr ++) = ';'; 
+        }  else if (c == '~') { // tilde
+            (*outptr ++) = '\\';
+            (*outptr ++) = '~';
+        } else if (c == '|') { // vertical bar 
+            (*outptr ++) = '\\';
+            (*outptr ++) = '|';
+        } else if (c == '&') { // ampersand
+            (*outptr ++) = '\\';
+            (*outptr ++) = '&';
+            (*outptr ++) = 'a';
+            (*outptr ++) = 'm';
+            (*outptr ++) = 'p';
+            (*outptr ++) = ';';
+        } else if (c == ';') { // semicolon
+            (*outptr ++) = '\\';
+            (*outptr ++) = ';';
+        } else if (c == '*') { //asterisk
+            (*outptr ++) = '\\';
+            (*outptr ++) = '*';
+        } else if (c == '?') { // question mark
+            (*outptr ++) = '\\';
+            (*outptr ++) = '?';
+        } else if (c == '#') { // hash mark
+            (*outptr ++) = '\\';
+            (*outptr ++) = '#';
+        } else if (c == '(') { // parenthesis
+            (*outptr ++) = '\\';
+            (*outptr ++) = '(';
+        } else if (c == ')') {
+            (*outptr ++) = '\\';
+            (*outptr ++) = ')';
+        */
+        } else
+            (*outptr ++) = c;
+    }
+    return std::string(out.data(), outptr - out.data());
+}
 // Disects path strings stored in system variable divided by ':' and adds into vector
 void resolve_path_from_var(const std::string& var, std::vector<std::string>& paths)
 {
@@ -157,7 +246,8 @@ void DesktopIntegrationDialog::perform_desktop_integration()
     }
 
     // Escape ' characters in appimage, other special symbols will be esacaped in desktop file by 'excutable_path'
-    boost::replace_all(excutable_path, "'", "'\\''");
+    //boost::replace_all(excutable_path, "'", "'\\''");
+    excutable_path = escape_string(excutable_path);
 
     // Find directories icons and applications
     // $XDG_DATA_HOME defines the base directory relative to which user specific data files should be stored. 
@@ -243,14 +333,14 @@ void DesktopIntegrationDialog::perform_desktop_integration()
                 "Name=PrusaSlicer%1%\n"
                 "GenericName=3D Printing Software\n"
                 "Icon=PrusaSlicer%2%\n"
-                "Exec=\'%3%\' %%F\n"
+                "Exec=\"%3%\" %%F\n"
                 "Terminal=false\n"
                 "Type=Application\n"
                 "MimeType=model/stl;application/vnd.ms-3mfdocument;application/prs.wavefront-obj;application/x-amf;\n"
                 "Categories=Graphics;3DGraphics;Engineering;\n"
                 "Keywords=3D;Printing;Slicer;slice;3D;printer;convert;gcode;stl;obj;amf;SLA\n"
                 "StartupNotify=false\n"
-                "StartupWMClass=prusa-slicer", name_suffix, version_suffix, excutable_path);
+                "StartupWMClass=prusa-slicer\n", name_suffix, version_suffix, excutable_path);
 
             std::string path = GUI::format("%1%/applications/PrusaSlicer%2%.desktop", target_dir_desktop, version_suffix);
             if (create_desktop_file(path, desktop_file)){
@@ -310,13 +400,13 @@ void DesktopIntegrationDialog::perform_desktop_integration()
         "Name=Prusa Gcode Viewer%1%\n"
         "GenericName=3D Printing Software\n"
         "Icon=PrusaSlicer-gcodeviewer%2%\n"
-        "Exec=\'%3%\' --gcodeviwer %%F\n"
+        "Exec=\"%3%\" --gcodeviewer %%F\n"
         "Terminal=false\n"
         "Type=Application\n"
         "MimeType=text/x.gcode;\n"
         "Categories=Graphics;3DGraphics;\n"
         "Keywords=3D;Printing;Slicer;\n"
-        "StartupNotify=false", name_suffix, version_suffix, excutable_path);
+        "StartupNotify=false\n", name_suffix, version_suffix, excutable_path);
 
     std::string desktop_path = GUI::format("%1%/applications/PrusaSlicerGcodeViewer%2%.desktop", target_dir_desktop, version_suffix);
     if (create_desktop_file(desktop_path, desktop_file))
diff --git a/src/slic3r/GUI/GUI_ObjectList.cpp b/src/slic3r/GUI/GUI_ObjectList.cpp
index d4030d41f..b85219c0b 100644
--- a/src/slic3r/GUI/GUI_ObjectList.cpp
+++ b/src/slic3r/GUI/GUI_ObjectList.cpp
@@ -1049,7 +1049,7 @@ void ObjectList::key_event(wxKeyEvent& event)
         || event.GetKeyCode() == WXK_BACK
 #endif //__WXOSX__
         ) {
-        wxGetApp().plater()->remove_selected();
+        remove();
     }
     else if (event.GetKeyCode() == WXK_F5)
         wxGetApp().plater()->reload_all_from_disk();
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
index 5ce0064db..b9e5d111b 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
@@ -199,7 +199,7 @@ void GLGizmoSimplify::on_render_input_window(float x, float y, float bottom_limi
         ImGui::SameLine(m_gui_cfg->bottom_left_width);
         if (m_imgui->button(_L("Preview"))) {
             m_state = State::preview;
-            // simplify but not aply on mesh
+            // simplify but not apply on mesh
             process();
         }
         ImGui::SameLine();
@@ -207,15 +207,12 @@ void GLGizmoSimplify::on_render_input_window(float x, float y, float bottom_limi
             if (!m_is_valid_result) {
                 m_state = State::close_on_end;
                 process();
-            } else {
+            } else if (m_exist_preview) {
                 // use preview and close
-                if (m_exist_preview) {
-                    // fix hollowing, sla support points, modifiers, ...
-                    auto plater = wxGetApp().plater();
-                    plater->changed_mesh(m_obj_index);
-                }
+                after_apply();
+            } else { // no changes made
                 close();
-            }
+            }            
         }
     } else {        
         m_imgui->disabled_begin(m_state == State::canceling);
@@ -237,18 +234,22 @@ void GLGizmoSimplify::on_render_input_window(float x, float y, float bottom_limi
         m_parent.reload_scene(true);
         // set m_state must be before close() !!!
         m_state = State::settings;
-        if (close_on_end) {
-            // fix hollowing, sla support points, modifiers, ...
-            auto plater = wxGetApp().plater();
-            plater->changed_mesh(m_obj_index);
-            close(); 
-        }
+        if (close_on_end) after_apply();
         
         // Fix warning icon in object list
         wxGetApp().obj_list()->update_item_error_icon(m_obj_index, -1);
     }
 }
 
+void GLGizmoSimplify::after_apply() {
+    // set flag to NOT revert changes when switch GLGizmoBase::m_state
+    m_exist_preview = false;
+    // fix hollowing, sla support points, modifiers, ...
+    auto plater = wxGetApp().plater();
+    plater->changed_mesh(m_obj_index);
+    close();
+}
+
 void GLGizmoSimplify::close() {
     // close gizmo == open it again
     GLGizmosManager &gizmos_mgr = m_parent.get_gizmos_manager();
@@ -282,11 +283,11 @@ void GLGizmoSimplify::process()
             }
         };
 
-        std::function<void(int)> statusfn = [this](int percent) {
+        int64_t last = 0;
+        std::function<void(int)> statusfn = [this, &last](int percent) {
             m_progress = percent;
 
             // check max 4fps
-            static int64_t last = 0;
             int64_t now = m_parent.timestamp_now();
             if ((now - last) < 250) return;
             last = now;
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.hpp b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.hpp
index 1b25c4ac9..0f5bd5991 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.hpp
@@ -32,6 +32,7 @@ protected:
     virtual void on_set_state() override;
 
 private:
+    void after_apply();
     void close();
     void process();
     void set_its(indexed_triangle_set &its);
diff --git a/src/slic3r/GUI/MeshUtils.cpp b/src/slic3r/GUI/MeshUtils.cpp
index ba83bdbff..75232c930 100644
--- a/src/slic3r/GUI/MeshUtils.cpp
+++ b/src/slic3r/GUI/MeshUtils.cpp
@@ -106,7 +106,6 @@ void MeshClipper::recalculate_triangles()
     Transform3d tr = Transform3d::Identity();
     tr.rotate(q);
     tr = m_trafo.get_matrix() * tr;
-    height_mesh += 0.001f; // to avoid z-fighting
 
     if (m_limiting_plane != ClippingPlane::ClipsNothing())
     {
@@ -165,6 +164,8 @@ void MeshClipper::recalculate_triangles()
 
     m_triangles2d = triangulate_expolygons_2f(expolys, m_trafo.get_matrix().matrix().determinant() < 0.);
 
+    tr.pretranslate(0.001 * m_plane.get_normal().normalized()); // to avoid z-fighting
+
     m_vertex_array.release_geometry();
     for (auto it=m_triangles2d.cbegin(); it != m_triangles2d.cend(); it=it+3) {
         m_vertex_array.push_geometry(tr * Vec3d((*(it+0))(0), (*(it+0))(1), height_mesh), up);
diff --git a/src/slic3r/GUI/MeshUtils.hpp b/src/slic3r/GUI/MeshUtils.hpp
index ec6c337c0..65c326116 100644
--- a/src/slic3r/GUI/MeshUtils.hpp
+++ b/src/slic3r/GUI/MeshUtils.hpp
@@ -112,7 +112,7 @@ public:
     // The class references extern TriangleMesh, which must stay alive
     // during MeshRaycaster existence.
     MeshRaycaster(const TriangleMesh& mesh)
-        : m_emesh(mesh)
+        : m_emesh(mesh, true) // calculate epsilon for triangle-ray intersection from an average edge length
     {
         m_normals.reserve(mesh.stl.facet_start.size());
         for (const stl_facet& facet : mesh.stl.facet_start)
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index 1841220d5..d315e7734 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -2915,6 +2915,7 @@ void Plater::priv::update_print_volume_state()
     BoundingBox     bed_box_2D = get_extents(Polygon::new_scale(this->config->opt<ConfigOptionPoints>("bed_shape")->values));
     BoundingBoxf3   print_volume(unscale(bed_box_2D.min(0), bed_box_2D.min(1), 0.0), unscale(bed_box_2D.max(0), bed_box_2D.max(1), scale_(this->config->opt_float("max_print_height"))));
     // Allow the objects to protrude below the print bed, only the part of the object above the print bed will be sliced.
+    print_volume.offset(BedEpsilon);
     print_volume.min(2) = -1e10;
     this->q->model().update_print_volume_state(print_volume);
 }
diff --git a/xs/xsp/XS.xsp b/xs/xsp/XS.xsp
index 083d21d38..68ea282bc 100644
--- a/xs/xsp/XS.xsp
+++ b/xs/xsp/XS.xsp
@@ -23,12 +23,6 @@ BUILD()
         RETVAL = newSVpv(SLIC3R_BUILD_ID, 0);
     OUTPUT: RETVAL
 
-SV*
-DEBUG_OUT_PATH_PREFIX()
-    CODE:
-        RETVAL = newSVpv(SLIC3R_DEBUG_OUT_PATH_PREFIX, 0);
-    OUTPUT: RETVAL
-
 SV*
 FORK_NAME()
     CODE: