diff --git a/lib/Slic3r/Fill/Concentric.pm b/lib/Slic3r/Fill/Concentric.pm
index 3c47de489..311bfa1f5 100644
--- a/lib/Slic3r/Fill/Concentric.pm
+++ b/lib/Slic3r/Fill/Concentric.pm
@@ -37,7 +37,7 @@ sub fill_surface {
     # generate paths from the outermost to the innermost, to avoid 
     # adhesion problems of the first central tiny loops
     @loops = map Slic3r::Polygon->new(@$_),
-        reverse traverse_pt( union_pt(\@loops, PFT_EVENODD) );
+        reverse traverse_pt( union_pt(\@loops) );
     
     # order paths using a nearest neighbor search
     my @paths = ();
diff --git a/lib/Slic3r/Geometry/Clipper.pm b/lib/Slic3r/Geometry/Clipper.pm
index 40f1c7d35..362569ff7 100644
--- a/lib/Slic3r/Geometry/Clipper.pm
+++ b/lib/Slic3r/Geometry/Clipper.pm
@@ -13,20 +13,6 @@ use Math::Clipper 1.22 qw(:cliptypes :polyfilltypes :jointypes is_counter_clockw
 use Slic3r::Geometry qw(scale);
 our $clipper = Math::Clipper->new;
 
-sub _safety_offset {
-    my ($polygons, $factor) = @_;
-    return [ map Slic3r::Polygon->new(@$_),
-        @{Math::Clipper::int_offset(_convert($polygons), $factor // (scale 1e-05), 100000, JT_MITER, 2)} ];
-}
-
-sub union_pt {
-    my ($polygons, $jointype, $safety_offset) = @_;
-    $jointype = PFT_NONZERO unless defined $jointype;
-    $clipper->clear;
-    $clipper->add_subject_polygons($safety_offset ? _convert(_safety_offset($polygons)) : _convert($polygons));
-    return $clipper->pt_execute(CT_UNION, $jointype, $jointype);
-}
-
 sub traverse_pt {
     my ($polynodes) = @_;
     
@@ -45,10 +31,4 @@ sub traverse_pt {
     return @polygons;
 }
 
-sub _convert {
-    my $p = shift;
-    $p = $p->pp if ref($p) ne 'ARRAY' && $p->can('pp');
-    return [ map { (ref($_) ne 'ARRAY' && $_->can('pp')) ? $_->pp : $_ } @$p ];
-}
-
 1;
diff --git a/lib/Slic3r/Layer/Region.pm b/lib/Slic3r/Layer/Region.pm
index b642f30c1..2c896bc07 100644
--- a/lib/Slic3r/Layer/Region.pm
+++ b/lib/Slic3r/Layer/Region.pm
@@ -239,8 +239,8 @@ sub make_perimeters {
     $self->_fill_gaps(\@gaps);
     
     # find nesting hierarchies separately for contours and holes
-    my $contours_pt = union_pt(\@contours, PFT_EVENODD);
-    my $holes_pt    = union_pt(\@holes, PFT_EVENODD);
+    my $contours_pt = union_pt(\@contours);
+    my $holes_pt    = union_pt(\@holes);
     
     # prepare a coderef for traversing the PolyTree object
     # external contours are root items of $contours_pt
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index 30e57b251..e40b1eb84 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -681,7 +681,7 @@ sub make_brim {
         polygon         => Slic3r::Polygon->new(@$_),
         role            => EXTR_ROLE_SKIRT,
         flow_spacing    => $flow->spacing,
-    ), reverse traverse_pt( union_pt(\@loops, PFT_EVENODD) );
+    ), reverse traverse_pt( union_pt(\@loops) );
 }
 
 sub write_gcode {
diff --git a/xs/src/ClipperUtils.cpp b/xs/src/ClipperUtils.cpp
index c398d3154..4327406bb 100644
--- a/xs/src/ClipperUtils.cpp
+++ b/xs/src/ClipperUtils.cpp
@@ -28,19 +28,19 @@ void PolyTreeToExPolygons(ClipperLib::PolyTree& polytree, Slic3r::ExPolygons& ex
 //-----------------------------------------------------------
 
 void
-ClipperPolygon_to_Slic3rPolygon(ClipperLib::Polygon &input, Slic3r::Polygon &output)
+ClipperPolygon_to_Slic3rPolygon(const ClipperLib::Polygon &input, Slic3r::Polygon &output)
 {
     output.points.clear();
-    for (ClipperLib::Polygon::iterator pit = input.begin(); pit != input.end(); ++pit) {
+    for (ClipperLib::Polygon::const_iterator pit = input.begin(); pit != input.end(); ++pit) {
         output.points.push_back(Slic3r::Point( (*pit).X, (*pit).Y ));
     }
 }
 
 void
-ClipperPolygons_to_Slic3rPolygons(ClipperLib::Polygons &input, Slic3r::Polygons &output)
+ClipperPolygons_to_Slic3rPolygons(const ClipperLib::Polygons &input, Slic3r::Polygons &output)
 {
     output.clear();
-    for (ClipperLib::Polygons::iterator it = input.begin(); it != input.end(); ++it) {
+    for (ClipperLib::Polygons::const_iterator it = input.begin(); it != input.end(); ++it) {
         Slic3r::Polygon p;
         ClipperPolygon_to_Slic3rPolygon(*it, p);
         output.push_back(p);
@@ -48,7 +48,7 @@ ClipperPolygons_to_Slic3rPolygons(ClipperLib::Polygons &input, Slic3r::Polygons
 }
 
 void
-ClipperPolygons_to_Slic3rExPolygons(ClipperLib::Polygons &input, Slic3r::ExPolygons &output)
+ClipperPolygons_to_Slic3rExPolygons(const ClipperLib::Polygons &input, Slic3r::ExPolygons &output)
 {
     // init Clipper
     ClipperLib::Clipper clipper;
@@ -67,19 +67,19 @@ ClipperPolygons_to_Slic3rExPolygons(ClipperLib::Polygons &input, Slic3r::ExPolyg
 }
 
 void
-Slic3rPolygon_to_ClipperPolygon(Slic3r::Polygon &input, ClipperLib::Polygon &output)
+Slic3rPolygon_to_ClipperPolygon(const Slic3r::Polygon &input, ClipperLib::Polygon &output)
 {
     output.clear();
-    for (Slic3r::Points::iterator pit = input.points.begin(); pit != input.points.end(); ++pit) {
+    for (Slic3r::Points::const_iterator pit = input.points.begin(); pit != input.points.end(); ++pit) {
         output.push_back(ClipperLib::IntPoint( (*pit).x, (*pit).y ));
     }
 }
 
 void
-Slic3rPolygons_to_ClipperPolygons(Slic3r::Polygons &input, ClipperLib::Polygons &output)
+Slic3rPolygons_to_ClipperPolygons(const Slic3r::Polygons &input, ClipperLib::Polygons &output)
 {
     output.clear();
-    for (Slic3r::Polygons::iterator it = input.begin(); it != input.end(); ++it) {
+    for (Slic3r::Polygons::const_iterator it = input.begin(); it != input.end(); ++it) {
         ClipperLib::Polygon p;
         Slic3rPolygon_to_ClipperPolygon(*it, p);
         output.push_back(p);
@@ -194,7 +194,7 @@ offset2_ex(Slic3r::Polygons &polygons, Slic3r::ExPolygons &retval, const float d
 
 template <class T>
 void _clipper_do(const ClipperLib::ClipType clipType, Slic3r::Polygons &subject, 
-    Slic3r::Polygons &clip, T &retval, const bool safety_offset_)
+    Slic3r::Polygons &clip, T &retval, const ClipperLib::PolyFillType fillType, const bool safety_offset_)
 {
     // read input
     ClipperLib::Polygons* input_subject = new ClipperLib::Polygons();
@@ -222,7 +222,7 @@ void _clipper_do(const ClipperLib::ClipType clipType, Slic3r::Polygons &subject,
     delete input_clip;
     
     // perform operation
-    clipper.Execute(clipType, retval, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
+    clipper.Execute(clipType, retval, fillType, fillType);
 }
 
 void _clipper(ClipperLib::ClipType clipType, Slic3r::Polygons &subject, 
@@ -230,7 +230,7 @@ void _clipper(ClipperLib::ClipType clipType, Slic3r::Polygons &subject,
 {
     // perform operation
     ClipperLib::Polygons* output = new ClipperLib::Polygons();
-    _clipper_do<ClipperLib::Polygons>(clipType, subject, clip, *output, safety_offset_);
+    _clipper_do<ClipperLib::Polygons>(clipType, subject, clip, *output, ClipperLib::pftNonZero, safety_offset_);
     
     // convert into Polygons
     ClipperPolygons_to_Slic3rPolygons(*output, retval);
@@ -242,7 +242,7 @@ void _clipper(ClipperLib::ClipType clipType, Slic3r::Polygons &subject,
 {
     // perform operation
     ClipperLib::PolyTree* polytree = new ClipperLib::PolyTree();
-    _clipper_do<ClipperLib::PolyTree>(clipType, subject, clip, *polytree, safety_offset_);
+    _clipper_do<ClipperLib::PolyTree>(clipType, subject, clip, *polytree, ClipperLib::pftNonZero, safety_offset_);
     
     // convert into ExPolygons
     PolyTreeToExPolygons(*polytree, retval);
@@ -280,6 +280,12 @@ void union_(Slic3r::Polygons &subject, T &retval, bool safety_offset_)
 template void union_<Slic3r::ExPolygons>(Slic3r::Polygons &subject, Slic3r::ExPolygons &retval, bool safety_offset_);
 template void union_<Slic3r::Polygons>(Slic3r::Polygons &subject, Slic3r::Polygons &retval, bool safety_offset_);
 
+void union_pt(Slic3r::Polygons &subject, ClipperLib::PolyTree &retval, bool safety_offset_)
+{
+    Slic3r::Polygons clip;
+    _clipper_do<ClipperLib::PolyTree>(ClipperLib::ctUnion, subject, clip, retval, ClipperLib::pftEvenOdd, safety_offset_);
+}
+
 void simplify_polygons(Slic3r::Polygons &subject, Slic3r::Polygons &retval)
 {
     // convert into Clipper polygons
@@ -312,4 +318,33 @@ void safety_offset(ClipperLib::Polygons* &subject)
     subject = retval;
 }
 
+///////////////////////
+
+SV*
+polynode_children_2_perl(const ClipperLib::PolyNode& node)
+{
+    AV* av = newAV();
+    const unsigned int len = node.ChildCount();
+    av_extend(av, len-1);
+    for (int i = 0; i < len; ++i) {
+        av_store(av, i, polynode2perl(*node.Childs[i]));
+    }
+    return (SV*)newRV_noinc((SV*)av);
+}
+
+SV*
+polynode2perl(const ClipperLib::PolyNode& node)
+{
+    HV* hv = newHV();
+    Slic3r::Polygon p;
+    ClipperPolygon_to_Slic3rPolygon(node.Contour, p);
+    if (node.IsHole()) {
+        (void)hv_stores( hv, "hole", p.to_SV() );
+    } else {
+        (void)hv_stores( hv, "outer", p.to_SV() );
+    }
+    (void)hv_stores( hv, "children", polynode_children_2_perl(node) );
+    return (SV*)newRV_noinc((SV*)hv);
+}
+
 }
diff --git a/xs/src/ClipperUtils.hpp b/xs/src/ClipperUtils.hpp
index 77214bd2c..c907bbcd7 100644
--- a/xs/src/ClipperUtils.hpp
+++ b/xs/src/ClipperUtils.hpp
@@ -16,11 +16,11 @@ void AddOuterPolyNodeToExPolygons(ClipperLib::PolyNode& polynode, Slic3r::ExPoly
 void PolyTreeToExPolygons(ClipperLib::PolyTree& polytree, Slic3r::ExPolygons& expolygons);
 //-----------------------------------------------------------
 
-void Slic3rPolygon_to_ClipperPolygon(Slic3r::Polygon &input, ClipperLib::Polygon &output);
-void Slic3rPolygons_to_ClipperPolygons(Slic3r::Polygons &input, ClipperLib::Polygons &output);
-void ClipperPolygon_to_Slic3rPolygon(ClipperLib::Polygon &input, Slic3r::Polygon &output);
-void ClipperPolygons_to_Slic3rPolygons(ClipperLib::Polygons &input, Slic3r::Polygons &output);
-void ClipperPolygons_to_Slic3rExPolygons(ClipperLib::Polygons &input, Slic3r::ExPolygons &output);
+void Slic3rPolygon_to_ClipperPolygon(const Slic3r::Polygon &input, ClipperLib::Polygon &output);
+void Slic3rPolygons_to_ClipperPolygons(const Slic3r::Polygons &input, ClipperLib::Polygons &output);
+void ClipperPolygon_to_Slic3rPolygon(const ClipperLib::Polygon &input, Slic3r::Polygon &output);
+void ClipperPolygons_to_Slic3rPolygons(const ClipperLib::Polygons &input, Slic3r::Polygons &output);
+void ClipperPolygons_to_Slic3rExPolygons(const ClipperLib::Polygons &input, Slic3r::ExPolygons &output);
 
 void scaleClipperPolygons(ClipperLib::Polygons &polygons, const double scale);
 
@@ -64,10 +64,18 @@ void xor_ex(Slic3r::Polygons &subject, Slic3r::Polygons &clip, Slic3r::ExPolygon
 template <class T>
 void union_(Slic3r::Polygons &subject, T &retval, bool safety_offset_ = false);
 
+void union_pt(Slic3r::Polygons &subject, ClipperLib::PolyTree &retval, bool safety_offset_ = false);
+
 void simplify_polygons(Slic3r::Polygons &subject, Slic3r::Polygons &retval);
 
 void safety_offset(ClipperLib::Polygons* &subject);
 
+/////////////////
+
+SV* polynode_children_2_perl(const ClipperLib::PolyNode& node);
+SV* polynode2perl(const ClipperLib::PolyNode& node);
+
+
 }
 
 #endif
diff --git a/xs/xsp/Clipper.xsp b/xs/xsp/Clipper.xsp
index 150a31166..e69873e07 100644
--- a/xs/xsp/Clipper.xsp
+++ b/xs/xsp/Clipper.xsp
@@ -128,6 +128,19 @@ union_ex(subject, safety_offset = false)
     OUTPUT:
         RETVAL
 
+SV*
+union_pt(subject, safety_offset = false)
+    Polygons                    subject
+    bool                        safety_offset
+    CODE:
+        // perform operation
+        ClipperLib::PolyTree polytree;
+        union_pt(subject, polytree, safety_offset);
+        
+        RETVAL = polynode_children_2_perl(polytree);
+    OUTPUT:
+        RETVAL
+
 Polygons
 simplify_polygons(subject)
     Polygons                    subject