diff --git a/lib/Slic3r.pm b/lib/Slic3r.pm
index e052240a1..bcd337dec 100644
--- a/lib/Slic3r.pm
+++ b/lib/Slic3r.pm
@@ -54,7 +54,6 @@ use Slic3r::GCode::VibrationLimit;
 use Slic3r::Geometry qw(PI);
 use Slic3r::Geometry::Clipper;
 use Slic3r::Layer;
-use Slic3r::Layer::PerimeterGenerator;
 use Slic3r::Layer::Region;
 use Slic3r::Line;
 use Slic3r::Model;
@@ -79,7 +78,6 @@ use constant SCALED_RESOLUTION      => RESOLUTION / SCALING_FACTOR;
 use constant LOOP_CLIPPING_LENGTH_OVER_NOZZLE_DIAMETER => 0.15;
 use constant INFILL_OVERLAP_OVER_SPACING  => 0.3;
 use constant EXTERNAL_INFILL_MARGIN => 3;
-use constant INSET_OVERLAP_TOLERANCE => 0.4;
 
 # keep track of threads we created
 my @my_threads = ();
@@ -201,6 +199,7 @@ sub thread_cleanup {
     *Slic3r::Geometry::BoundingBox::DESTROY = sub {};
     *Slic3r::Geometry::BoundingBoxf::DESTROY = sub {};
     *Slic3r::Geometry::BoundingBoxf3::DESTROY = sub {};
+    *Slic3r::Layer::PerimeterGenerator::DESTROY = sub {};
     *Slic3r::Line::DESTROY                  = sub {};
     *Slic3r::Linef3::DESTROY                = sub {};
     *Slic3r::Model::DESTROY                 = sub {};
diff --git a/lib/Slic3r/Layer/PerimeterGenerator.pm b/lib/Slic3r/Layer/PerimeterGenerator.pm
deleted file mode 100644
index daf2ba8f8..000000000
--- a/lib/Slic3r/Layer/PerimeterGenerator.pm
+++ /dev/null
@@ -1,533 +0,0 @@
-package Slic3r::Layer::PerimeterGenerator;
-use Moo;
-
-use Slic3r::ExtrusionLoop ':roles';
-use Slic3r::ExtrusionPath ':roles';
-use Slic3r::Geometry qw(scale unscale chained_path);
-use Slic3r::Geometry::Clipper qw(union_ex diff diff_ex intersection_ex offset offset2
-    offset_ex offset2_ex intersection_ppl diff_ppl);
-use Slic3r::Surface ':types';
-
-has 'slices'                => (is => 'ro', required => 1);  # SurfaceCollection
-has 'lower_slices'          => (is => 'ro', required => 0);
-has 'layer_height'          => (is => 'ro', required => 1);
-has 'layer_id'              => (is => 'ro', required => 0, default => sub { -1 });
-has 'perimeter_flow'        => (is => 'ro', required => 1);
-has 'ext_perimeter_flow'    => (is => 'ro', required => 1);
-has 'overhang_flow'         => (is => 'ro', required => 1);
-has 'solid_infill_flow'     => (is => 'ro', required => 1);
-has 'config'                => (is => 'ro', default => sub { Slic3r::Config::PrintRegion->new });
-has 'object_config'         => (is => 'ro', default => sub { Slic3r::Config::PrintObject->new });
-has 'print_config'          => (is => 'ro', default => sub { Slic3r::Config::Print->new });
-has '_lower_slices_p'       => (is => 'rw', default => sub { [] });
-has '_holes_pt'             => (is => 'rw');
-has '_ext_mm3_per_mm'       => (is => 'rw');
-has '_mm3_per_mm'           => (is => 'rw');
-has '_mm3_per_mm_overhang'  => (is => 'rw');
-
-# generated loops will be put here
-has 'loops'         => (is => 'ro', default => sub { Slic3r::ExtrusionPath::Collection->new });
-
-# generated gap fills will be put here
-has 'gap_fill'      => (is => 'ro', default => sub { Slic3r::ExtrusionPath::Collection->new });
-
-# generated fill surfaces will be put here
-has 'fill_surfaces' => (is => 'ro', default => sub { Slic3r::Surface::Collection->new });
-
-sub BUILDARGS {
-    my ($class, %args) = @_;
-    
-    if (my $flow = delete $args{flow}) {
-        $args{perimeter_flow}       //= $flow;
-        $args{ext_perimeter_flow}   //= $flow;
-        $args{overhang_flow}        //= $flow;
-        $args{solid_infill_flow}    //= $flow;
-    }
-    
-    return { %args };
-}
-
-sub process {
-    my ($self) = @_;
-    
-    # other perimeters
-    $self->_mm3_per_mm($self->perimeter_flow->mm3_per_mm);
-    my $pwidth              = $self->perimeter_flow->scaled_width;
-    my $pspacing            = $self->perimeter_flow->scaled_spacing;
-    
-    # external perimeters
-    $self->_ext_mm3_per_mm($self->ext_perimeter_flow->mm3_per_mm);
-    my $ext_pwidth          = $self->ext_perimeter_flow->scaled_width;
-    my $ext_pspacing        = scale($self->ext_perimeter_flow->spacing_to($self->perimeter_flow));
-    
-    # overhang perimeters
-    $self->_mm3_per_mm_overhang($self->overhang_flow->mm3_per_mm);
-    
-    # solid infill
-    my $ispacing            = $self->solid_infill_flow->scaled_spacing;
-    my $gap_area_threshold  = $pwidth ** 2;
-    
-    # Calculate the minimum required spacing between two adjacent traces.
-    # This should be equal to the nominal flow spacing but we experiment
-    # with some tolerance in order to avoid triggering medial axis when
-    # some squishing might work. Loops are still spaced by the entire
-    # flow spacing; this only applies to collapsing parts.
-    my $min_spacing         = $pspacing * (1 - &Slic3r::INSET_OVERLAP_TOLERANCE);
-    my $ext_min_spacing     = $ext_pspacing * (1 - &Slic3r::INSET_OVERLAP_TOLERANCE);
-    
-    # prepare grown lower layer slices for overhang detection
-    if ($self->lower_slices && $self->config->overhangs) {
-        # We consider overhang any part where the entire nozzle diameter is not supported by the
-        # lower layer, so we take lower slices and offset them by half the nozzle diameter used 
-        # in the current layer
-        my $nozzle_diameter = $self->print_config->get_at('nozzle_diameter', $self->config->perimeter_extruder-1);
-        
-        $self->_lower_slices_p(
-            offset([ map @$_, @{$self->lower_slices} ], scale +$nozzle_diameter/2)
-        );
-    }
-    
-    # we need to process each island separately because we might have different
-    # extra perimeters for each one
-    foreach my $surface (@{$self->slices}) {
-        # detect how many perimeters must be generated for this island
-        my $loop_number = $self->config->perimeters + ($surface->extra_perimeters || 0);
-        $loop_number--;  # 0-indexed loops
-        
-        my @gaps = ();   # Polygons
-        
-        my @last = @{$surface->expolygon->simplify_p(&Slic3r::SCALED_RESOLUTION)};
-        if ($loop_number >= 0) {  # no loops = -1
-        
-            my @contours    = ();   # depth => [ Polygon, Polygon ... ]
-            my @holes       = ();   # depth => [ Polygon, Polygon ... ]
-            my @thin_walls  = ();   # Polylines
-        
-            # we loop one time more than needed in order to find gaps after the last perimeter was applied
-            for my $i (0..($loop_number+1)) {  # outer loop is 0
-                my @offsets = ();
-                if ($i == 0) {
-                    # the minimum thickness of a single loop is:
-                    # ext_width/2 + ext_spacing/2 + spacing/2 + width/2
-                    if ($self->config->thin_walls) {
-                        @offsets = @{offset2(
-                            \@last,
-                            -(0.5*$ext_pwidth + 0.5*$ext_min_spacing - 1),
-                            +(0.5*$ext_min_spacing - 1),
-                        )};
-                    } else {
-                        @offsets = @{offset(
-                            \@last,
-                            -0.5*$ext_pwidth,
-                        )};
-                    }
-                    
-                    # look for thin walls
-                    if ($self->config->thin_walls) {
-                        my $diff = diff(
-                            \@last,
-                            offset(\@offsets, +0.5*$ext_pwidth),
-                            1,  # medial axis requires non-overlapping geometry
-                        );
-                        
-                        # the following offset2 ensures almost nothing in @thin_walls is narrower than $min_width
-                        # (actually, something larger than that still may exist due to mitering or other causes)
-                        my $min_width = $ext_pwidth / 2;
-                        @thin_walls = @{offset2_ex($diff, -$min_width/2, +$min_width/2)};
-                        
-                        # the maximum thickness of our thin wall area is equal to the minimum thickness of a single loop
-                        @thin_walls = grep $_->length > $ext_pwidth*2,
-                            map @{$_->medial_axis($ext_pwidth + $ext_pspacing, $min_width)}, @thin_walls;
-                        Slic3r::debugf "  %d thin walls detected\n", scalar(@thin_walls) if $Slic3r::debug;
-        
-                        if (0) {
-                            require "Slic3r/SVG.pm";
-                            Slic3r::SVG::output(
-                                "medial_axis.svg",
-                                no_arrows       => 1,
-                                #expolygons      => \@expp,
-                                polylines       => \@thin_walls,
-                            );
-                        }
-                    }
-                } else {
-                    my $distance = ($i == 1) ? $ext_pspacing : $pspacing;
-                    
-                    if ($self->config->thin_walls) {
-                        @offsets = @{offset2(
-                            \@last,
-                            -($distance + 0.5*$min_spacing - 1),
-                            +(0.5*$min_spacing - 1),
-                        )};
-                    } else {
-                        @offsets = @{offset(
-                            \@last,
-                            -$distance,
-                        )};
-                    }
-                    
-                    # look for gaps
-                    if ($self->config->gap_fill_speed > 0 && $self->config->fill_density > 0) {
-                        # not using safety offset here would "detect" very narrow gaps
-                        # (but still long enough to escape the area threshold) that gap fill
-                        # won't be able to fill but we'd still remove from infill area
-                        my $diff = diff_ex(
-                            offset(\@last, -0.5*$distance),
-                            offset(\@offsets, +0.5*$distance + 10),  # safety offset
-                        );
-                        push @gaps, map $_->clone, map @$_, grep abs($_->area) >= $gap_area_threshold, @$diff;
-                    }
-                }
-            
-                last if !@offsets;
-                last if $i > $loop_number; # we were only looking for gaps this time
-                
-                @last = @offsets;
-                
-                $contours[$i]   = [];
-                $holes[$i]      = [];
-                foreach my $polygon (@offsets) {
-                    my $loop = Slic3r::Layer::PerimeterGenerator::Loop->new(
-                        polygon     => $polygon,
-                        is_contour  => $polygon->is_counter_clockwise,
-                        depth       => $i,
-                    );
-                    if ($loop->is_contour) {
-                        push @{$contours[$i]}, $loop;
-                    } else {
-                        push @{$holes[$i]}, $loop;
-                    }
-                }
-            }
-            
-            # nest loops: holes first
-            for my $d (0..$loop_number) {
-                # loop through all holes having depth $d
-                LOOP: for (my $i = 0; $i <= $#{$holes[$d]}; ++$i) {
-                    my $loop = $holes[$d][$i];
-                
-                    # find the hole loop that contains this one, if any
-                    for my $t (($d+1)..$loop_number) {
-                        for (my $j = 0; $j <= $#{$holes[$t]}; ++$j) {
-                            my $candidate_parent = $holes[$t][$j];
-                            if ($candidate_parent->polygon->contains_point($loop->polygon->first_point)) {
-                                $candidate_parent->add_child($loop);
-                                splice @{$holes[$d]}, $i, 1;
-                                --$i;
-                                next LOOP;
-                            }
-                        }
-                    }
-                
-                    # if no hole contains this hole, find the contour loop that contains it
-                    for my $t (reverse 0..$loop_number) {
-                        for (my $j = 0; $j <= $#{$contours[$t]}; ++$j) {
-                            my $candidate_parent = $contours[$t][$j];
-                            if ($candidate_parent->polygon->contains_point($loop->polygon->first_point)) {
-                                $candidate_parent->add_child($loop);
-                                splice @{$holes[$d]}, $i, 1;
-                                --$i;
-                                next LOOP;
-                            }
-                        }
-                    }
-                }
-            }
-        
-            # nest contour loops
-            for my $d (reverse 1..$loop_number) {
-                # loop through all contours having depth $d
-                LOOP: for (my $i = 0; $i <= $#{$contours[$d]}; ++$i) {
-                    my $loop = $contours[$d][$i];
-                
-                    # find the contour loop that contains it
-                    for my $t (reverse 0..($d-1)) {
-                        for (my $j = 0; $j <= $#{$contours[$t]}; ++$j) {
-                            my $candidate_parent = $contours[$t][$j];
-                            if ($candidate_parent->polygon->contains_point($loop->polygon->first_point)) {
-                                $candidate_parent->add_child($loop);
-                                splice @{$contours[$d]}, $i, 1;
-                                --$i;
-                                next LOOP;
-                            }
-                        }
-                    }
-                }
-            }
-        
-            # at this point, all loops should be in $contours[0]
-            my @entities = $self->_traverse_loops($contours[0], \@thin_walls);
-            
-            # if brim will be printed, reverse the order of perimeters so that
-            # we continue inwards after having finished the brim
-            # TODO: add test for perimeter order
-            @entities = reverse @entities
-                if $self->config->external_perimeters_first
-                    || ($self->layer_id == 0 && $self->print_config->brim_width > 0);
-        
-            # append perimeters for this slice as a collection
-            $self->loops->append(Slic3r::ExtrusionPath::Collection->new(@entities))
-                if @entities;
-        }
-        
-        # fill gaps
-        if (@gaps) {
-            if (0) {
-                require "Slic3r/SVG.pm";
-                Slic3r::SVG::output(
-                    "gaps.svg",
-                    expolygons => union_ex(\@gaps),
-                );
-            }
-            
-            # where $pwidth < thickness < 2*$pspacing, infill with width = 2*$pwidth
-            # where 0.1*$pwidth < thickness < $pwidth, infill with width = 1*$pwidth
-            my @gap_sizes = (
-                [ $pwidth, 2*$pspacing, unscale 2*$pwidth ],
-                [ 0.1*$pwidth, $pwidth, unscale 1*$pwidth ],
-            );
-            foreach my $gap_size (@gap_sizes) {
-                my @gap_fill = $self->_fill_gaps(@$gap_size, \@gaps);
-                $self->gap_fill->append($_) for @gap_fill;
-                
-                # Make sure we don't infill narrow parts that are already gap-filled
-                # (we only consider this surface's gaps to reduce the diff() complexity).
-                # Growing actual extrusions ensures that gaps not filled by medial axis
-                # are not subtracted from fill surfaces (they might be too short gaps
-                # that medial axis skips but infill might join with other infill regions
-                # and use zigzag).
-                my $w = $gap_size->[2];
-                my @filled = map {
-                    @{($_->isa('Slic3r::ExtrusionLoop') ? $_->polygon->split_at_first_point : $_->polyline)
-                        ->grow(scale $w/2)};
-                } @gap_fill;
-                @last = @{diff(\@last, \@filled)};
-                @gaps = @{diff(\@gaps, \@filled)};  # prevent more gap fill here
-            }
-        }
-        
-        # create one more offset to be used as boundary for fill
-        # we offset by half the perimeter spacing (to get to the actual infill boundary)
-        # and then we offset back and forth by half the infill spacing to only consider the
-        # non-collapsing regions
-        my $inset = 0;
-        if ($loop_number == 0) {
-            # one loop
-            $inset += $ext_pspacing/2;
-        } elsif ($loop_number > 0) {
-            # two or more loops
-            $inset += $pspacing/2;
-        }
-        
-        # only apply infill overlap if we actually have one perimeter
-        $inset -= $self->config->get_abs_value_over('infill_overlap', $inset + $ispacing/2)
-            if $inset > 0;
-        
-        my $min_perimeter_infill_spacing = $ispacing * (1 - &Slic3r::INSET_OVERLAP_TOLERANCE);
-        $self->fill_surfaces->append($_)
-            for map Slic3r::Surface->new(expolygon => $_, surface_type => S_TYPE_INTERNAL),  # use a bogus surface type
-                @{offset2_ex(
-                    [ map @{$_->simplify_p(&Slic3r::SCALED_RESOLUTION)}, @{union_ex(\@last)} ],
-                    -$inset -$min_perimeter_infill_spacing/2,
-                    +$min_perimeter_infill_spacing/2,
-                )};
-    }
-}
-
-sub _traverse_loops {
-    my ($self, $loops, $thin_walls) = @_;
-    
-    # loops is an arrayref of ::Loop objects
-    # turn each one into an ExtrusionLoop object
-    my $coll = Slic3r::ExtrusionPath::Collection->new;
-    foreach my $loop (@$loops) {
-        my $is_external = $loop->is_external;
-        
-        my ($role, $loop_role);
-        if ($is_external) {
-            $role = EXTR_ROLE_EXTERNAL_PERIMETER;
-        } else {
-            $role = EXTR_ROLE_PERIMETER;
-        }
-        if ($loop->is_internal_contour) {
-            # Note that we set loop role to ContourInternalPerimeter
-            # also when loop is both internal and external (i.e.
-            # there's only one contour loop).
-            $loop_role = EXTRL_ROLE_CONTOUR_INTERNAL_PERIMETER;
-        } else {
-            $loop_role = EXTRL_ROLE_DEFAULT;
-        }
-        
-        # detect overhanging/bridging perimeters
-        my @paths = ();
-        if ($self->config->overhangs && $self->layer_id > 0
-            && !($self->object_config->support_material && $self->object_config->support_material_contact_distance == 0)) {
-            # get non-overhang paths by intersecting this loop with the grown lower slices
-            foreach my $polyline (@{ intersection_ppl([ $loop->polygon ], $self->_lower_slices_p) }) {
-                push @paths, Slic3r::ExtrusionPath->new(
-                    polyline        => $polyline,
-                    role            => $role,
-                    mm3_per_mm      => ($is_external ? $self->_ext_mm3_per_mm : $self->_mm3_per_mm),
-                    width           => ($is_external ? $self->ext_perimeter_flow->width : $self->perimeter_flow->width),
-                    height          => $self->layer_height,
-                );
-            }
-            
-            # get overhang paths by checking what parts of this loop fall 
-            # outside the grown lower slices (thus where the distance between
-            # the loop centerline and original lower slices is >= half nozzle diameter
-            foreach my $polyline (@{ diff_ppl([ $loop->polygon ], $self->_lower_slices_p) }) {
-                push @paths, Slic3r::ExtrusionPath->new(
-                    polyline        => $polyline,
-                    role            => EXTR_ROLE_OVERHANG_PERIMETER,
-                    mm3_per_mm      => $self->_mm3_per_mm_overhang,
-                    width           => $self->overhang_flow->width,
-                    height          => $self->overhang_flow->height,
-                );
-            }
-            
-            # reapply the nearest point search for starting point
-            # (clone because the collection gets DESTROY'ed)
-            # We allow polyline reversal because Clipper may have randomly
-            # reversed polylines during clipping.
-            my $collection = Slic3r::ExtrusionPath::Collection->new(@paths); # temporary collection
-            @paths = map $_->clone, @{$collection->chained_path(0)};
-        } else {
-            push @paths, Slic3r::ExtrusionPath->new(
-                polyline        => $loop->polygon->split_at_first_point,
-                role            => $role,
-                mm3_per_mm      => ($is_external ? $self->_ext_mm3_per_mm : $self->_mm3_per_mm),
-                width           => ($is_external ? $self->ext_perimeter_flow->width : $self->perimeter_flow->width),
-                height          => $self->layer_height,
-            );
-        }
-        my $eloop = Slic3r::ExtrusionLoop->new_from_paths(@paths);
-        $eloop->role($loop_role);
-        $coll->append($eloop);
-    }
-    
-    # append thin walls to the nearest-neighbor search (only for first iteration)
-    if (@$thin_walls) {
-        foreach my $polyline (@$thin_walls) {
-            $coll->append(Slic3r::ExtrusionPath->new(
-                polyline        => $polyline,
-                role            => EXTR_ROLE_EXTERNAL_PERIMETER,
-                mm3_per_mm      => $self->_mm3_per_mm,
-                width           => $self->perimeter_flow->width,
-                height          => $self->layer_height,
-            ));
-        }
-        
-        @$thin_walls = ();
-    }
-    
-    # sort entities
-    my $sorted_coll = $coll->chained_path_indices(0);
-    my @indices = @{$sorted_coll->orig_indices};
-    
-    # traverse children
-    my @entities = ();
-    for my $i (0..$#indices) {
-        my $idx = $indices[$i];
-        if ($idx > $#$loops) {
-            # this is a thin wall
-            # let's get it from the sorted collection as it might have been reversed
-            push @entities, $sorted_coll->[$i]->clone;
-        } else {
-            my $loop = $loops->[$idx];
-            my $eloop = $coll->[$idx]->clone;
-        
-            my @children = $self->_traverse_loops($loop->children, $thin_walls);
-            if ($loop->is_contour) {
-                $eloop->make_counter_clockwise;
-                push @entities, @children, $eloop;
-            } else {
-                $eloop->make_clockwise;
-                push @entities, $eloop, @children;
-            }
-        }
-    }
-    return @entities;
-}
-
-sub _fill_gaps {
-    my ($self, $min, $max, $w, $gaps) = @_;
-    
-    $min *= (1 - &Slic3r::INSET_OVERLAP_TOLERANCE);
-    
-    my $this = diff_ex(
-        offset2($gaps, -$min/2, +$min/2),
-        offset2($gaps, -$max/2, +$max/2),
-        1,
-    );
-    
-    my @polylines = map @{$_->medial_axis($max, $min/2)}, @$this;
-    return if !@polylines;
-    
-    Slic3r::debugf "  %d gaps filled with extrusion width = %s\n", scalar @$this, $w
-        if @$this;
-
-    #my $flow = $layerm->flow(FLOW_ROLE_SOLID_INFILL, 0, $w);
-    my $flow = Slic3r::Flow->new(
-        width           => $w,
-        height          => $self->layer_height,
-        nozzle_diameter => $self->solid_infill_flow->nozzle_diameter,
-    );
-    
-    my %path_args = (
-        role        => EXTR_ROLE_GAPFILL,
-        mm3_per_mm  => $flow->mm3_per_mm,
-        width       => $flow->width,
-        height      => $self->layer_height,
-    );
-    
-    my @entities = ();
-    foreach my $polyline (@polylines) {
-        #if ($polylines[$i]->isa('Slic3r::Polygon')) {
-        #    my $loop = Slic3r::ExtrusionLoop->new;
-        #    $loop->append(Slic3r::ExtrusionPath->new(polyline => $polylines[$i]->split_at_first_point, %path_args));
-        #    $polylines[$i] = $loop;
-        if ($polyline->is_valid && $polyline->first_point->coincides_with($polyline->last_point)) {
-            # since medial_axis() now returns only Polyline objects, detect loops here
-            push @entities, my $loop = Slic3r::ExtrusionLoop->new;
-            $loop->append(Slic3r::ExtrusionPath->new(polyline => $polyline, %path_args));
-        } else {
-            push @entities, Slic3r::ExtrusionPath->new(polyline => $polyline, %path_args);
-        }
-    }
-    
-    return @entities;
-}
-
-
-package Slic3r::Layer::PerimeterGenerator::Loop;
-use Moo;
-
-has 'polygon'       => (is => 'ro', required => 1);
-has 'is_contour'    => (is => 'ro', required => 1);
-has 'depth'         => (is => 'ro', required => 1);
-has 'children'      => (is => 'ro', default => sub { [] });
-
-use List::Util qw(first);
-
-sub add_child {
-    my ($self, $child) = @_;
-    push @{$self->children}, $child;
-}
-
-sub is_external {
-    my ($self) = @_;
-    return $self->depth == 0;
-}
-
-sub is_internal_contour {
-    my ($self) = @_;
-    
-    if ($self->is_contour) {
-        # an internal contour is a contour containing no other contours
-        return !defined first { $_->is_contour } @{$self->children};
-    }
-    return 0;
-}
-
-1;
diff --git a/lib/Slic3r/Layer/Region.pm b/lib/Slic3r/Layer/Region.pm
index f65e90129..51648c3ed 100644
--- a/lib/Slic3r/Layer/Region.pm
+++ b/lib/Slic3r/Layer/Region.pm
@@ -33,23 +33,25 @@ sub make_perimeters {
     
     my $generator = Slic3r::Layer::PerimeterGenerator->new(
         # input:
-        config              => $self->config,
-        object_config       => $self->layer->object->config,
-        print_config        => $self->layer->print->config,
-        layer_height        => $self->height,
-        layer_id            => $self->layer->id,
-        slices              => $slices,
-        lower_slices        => defined($self->layer->lower_layer) ? $self->layer->lower_layer->slices : undef,
-        perimeter_flow      => $self->flow(FLOW_ROLE_PERIMETER),
-        ext_perimeter_flow  => $self->flow(FLOW_ROLE_EXTERNAL_PERIMETER),
-        overhang_flow       => $self->region->flow(FLOW_ROLE_PERIMETER, -1, 1, 0, -1, $self->layer->object),
-        solid_infill_flow   => $self->flow(FLOW_ROLE_SOLID_INFILL),
+        $slices,
+        $self->height,
+        $self->flow(FLOW_ROLE_PERIMETER),
+        $self->config,
+        $self->layer->object->config,
+        $self->layer->print->config,
         
         # output:
-        loops               => $self->perimeters,
-        gap_fill            => $self->thin_fills,
-        fill_surfaces       => $fill_surfaces,
+        $self->perimeters,
+        $self->thin_fills,
+        $fill_surfaces,
     );
+    $generator->set_lower_slices($self->layer->lower_layer->slices)
+        if defined($self->layer->lower_layer);
+    $generator->set_layer_id($self->id);
+    $generator->set_ext_perimeter_flow($self->flow(FLOW_ROLE_EXTERNAL_PERIMETER));
+    $generator->set_overhang_flow($self->region->flow(FLOW_ROLE_PERIMETER, -1, 1, 0, -1, $self->layer->object));
+    $generator->set_solid_infill_flow($self->flow(FLOW_ROLE_SOLID_INFILL));
+    
     $generator->process;
 }
 
diff --git a/t/perimeters.t b/t/perimeters.t
index d103eb3f2..1e47b51f0 100644
--- a/t/perimeters.t
+++ b/t/perimeters.t
@@ -17,6 +17,101 @@ use Slic3r::Geometry::Clipper qw(union_ex diff union offset);
 use Slic3r::Surface ':types';
 use Slic3r::Test;
 
+{
+    my $flow = Slic3r::Flow->new(
+        width           => 1,
+        height          => 1,
+        nozzle_diameter => 1,
+    );
+    
+    my $config = Slic3r::Config->new;
+    my $test = sub {
+        my ($expolygons, %expected) = @_;
+        
+        my $slices = Slic3r::Surface::Collection->new;
+        $slices->append(Slic3r::Surface->new(
+            surface_type => S_TYPE_INTERNAL,
+            expolygon => $_,
+        )) for @$expolygons;
+        
+        my ($region_config, $object_config, $print_config, $loops, $gap_fill, $fill_surfaces);
+        my $g = Slic3r::Layer::PerimeterGenerator->new(
+            # input:
+            $slices,
+            1,  # layer height
+            $flow,
+            ($region_config = Slic3r::Config::PrintRegion->new),
+            ($object_config = Slic3r::Config::PrintObject->new),
+            ($print_config  = Slic3r::Config::Print->new),
+            
+            # output:
+            ($loops         = Slic3r::ExtrusionPath::Collection->new),
+            ($gap_fill      = Slic3r::ExtrusionPath::Collection->new),
+            ($fill_surfaces = Slic3r::Surface::Collection->new),
+        );
+        $g->config->apply_dynamic($config);
+        $g->process;
+        
+        is scalar(@$loops),
+            scalar(@$expolygons), 'expected number of collections';
+        ok !defined(first { !$_->isa('Slic3r::ExtrusionPath::Collection') } @$loops),
+            'everything is returned as collections';
+        
+        my $flattened_loops = $loops->flatten;
+        my @loops = @$flattened_loops;
+        is scalar(@loops),
+            $expected{total}, 'expected number of loops';
+        is scalar(grep $_->role == EXTR_ROLE_EXTERNAL_PERIMETER, map @$_, @loops),
+            $expected{external}, 'expected number of external loops';
+        is scalar(grep $_->role == EXTRL_ROLE_CONTOUR_INTERNAL_PERIMETER, @loops),
+            $expected{cinternal}, 'expected number of internal contour loops';
+        is scalar(grep $_->polygon->is_counter_clockwise, @loops),
+            $expected{ccw}, 'expected number of ccw loops';
+    };
+    
+    $config->set('perimeters', 3);
+    $test->(
+        [
+            Slic3r::ExPolygon->new(
+                Slic3r::Polygon->new_scale([0,0], [100,0], [100,100], [0,100]),
+            ),
+        ],
+        total       => 3,
+        external    => 1,
+        cinternal   => 1,
+        ccw         => 3,
+    );
+    $test->(
+        [
+            Slic3r::ExPolygon->new(
+                Slic3r::Polygon->new_scale([0,0], [100,0], [100,100], [0,100]),
+                Slic3r::Polygon->new_scale([40,40], [40,60], [60,60], [60,40]),
+            ),
+        ],
+        total       => 6,
+        external    => 2,
+        cinternal   => 1,
+        ccw         => 3,
+    );
+    $test->(
+        [
+            Slic3r::ExPolygon->new(
+                Slic3r::Polygon->new_scale([0,0], [200,0], [200,200], [0,200]),
+                Slic3r::Polygon->new_scale([20,20], [20,180], [180,180], [180,20]),
+            ),
+            # nested:
+            Slic3r::ExPolygon->new(
+                Slic3r::Polygon->new_scale([50,50], [150,50], [150,150], [50,150]),
+                Slic3r::Polygon->new_scale([80,80], [80,120], [120,120], [120,80]),
+            ),
+        ],
+        total       => 4*3,
+        external    => 4,
+        cinternal   => 2,
+        ccw         => 2*3,
+    );
+}
+
 {
     my $config = Slic3r::Config->new_from_defaults;
     $config->set('skirts', 0);
@@ -215,7 +310,7 @@ use Slic3r::Test;
         [ map @$_, (@$covered_by_perimeters, @$covered_by_infill) ],
     );
     
-    if (0) {
+    if (1) {
         printf "max non covered = %f\n", List::Util::max(map unscale unscale $_->area, @$non_covered);
         require "Slic3r/SVG.pm";
         Slic3r::SVG::output(
@@ -223,9 +318,12 @@ use Slic3r::Test;
             expolygons          => [ map $_->expolygon, @{$layerm->slices} ],
             red_expolygons      => union_ex([ map @$_, (@$covered_by_perimeters, @$covered_by_infill) ]),
             green_expolygons    => union_ex($non_covered),
+            no_arrows           => 1,
+            polylines           => [
+                map $_->polygon->split_at_first_point, map @$_, @{$layerm->perimeters},
+            ],
         );
     }
-    
     ok !(defined first { $_->area > ($iflow->scaled_width**2) } @$non_covered), 'no gap between perimeters and infill';
 }
 
@@ -299,92 +397,4 @@ use Slic3r::Test;
     $test->('small_dorito');
 }
 
-{
-    my $flow = Slic3r::Flow->new(
-        width           => 1,
-        height          => 1,
-        nozzle_diameter => 1,
-    );
-    
-    my $config = Slic3r::Config->new;
-    my $test = sub {
-        my ($expolygons, %expected) = @_;
-        
-        my $slices = Slic3r::Surface::Collection->new;
-        $slices->append(Slic3r::Surface->new(
-            surface_type => S_TYPE_INTERNAL,
-            expolygon => $_,
-        )) for @$expolygons;
-    
-        my $g = Slic3r::Layer::PerimeterGenerator->new(
-            # input:
-            layer_height    => 1,
-            slices          => $slices,
-            flow            => $flow,
-        );
-        $g->config->apply_dynamic($config);
-        $g->process;
-        
-        is scalar(@{$g->loops}),
-            scalar(@$expolygons), 'expected number of collections';
-        ok !defined(first { !$_->isa('Slic3r::ExtrusionPath::Collection') } @{$g->loops}),
-            'everything is returned as collections';
-        
-        my $flattened_loops = $g->loops->flatten;
-        my @loops = @$flattened_loops;
-        is scalar(@loops),
-            $expected{total}, 'expected number of loops';
-        is scalar(grep $_->role == EXTR_ROLE_EXTERNAL_PERIMETER, map @$_, @loops),
-            $expected{external}, 'expected number of external loops';
-        is scalar(grep $_->role == EXTRL_ROLE_CONTOUR_INTERNAL_PERIMETER, @loops),
-            $expected{cinternal}, 'expected number of internal contour loops';
-        is scalar(grep $_->polygon->is_counter_clockwise, @loops),
-            $expected{ccw}, 'expected number of ccw loops';
-        
-        return $g;
-    };
-    
-    $config->set('perimeters', 3);
-    $test->(
-        [
-            Slic3r::ExPolygon->new(
-                Slic3r::Polygon->new_scale([0,0], [100,0], [100,100], [0,100]),
-            ),
-        ],
-        total       => 3,
-        external    => 1,
-        cinternal   => 1,
-        ccw         => 3,
-    );
-    $test->(
-        [
-            Slic3r::ExPolygon->new(
-                Slic3r::Polygon->new_scale([0,0], [100,0], [100,100], [0,100]),
-                Slic3r::Polygon->new_scale([40,40], [40,60], [60,60], [60,40]),
-            ),
-        ],
-        total       => 6,
-        external    => 2,
-        cinternal   => 1,
-        ccw         => 3,
-    );
-    $test->(
-        [
-            Slic3r::ExPolygon->new(
-                Slic3r::Polygon->new_scale([0,0], [200,0], [200,200], [0,200]),
-                Slic3r::Polygon->new_scale([20,20], [20,180], [180,180], [180,20]),
-            ),
-            # nested:
-            Slic3r::ExPolygon->new(
-                Slic3r::Polygon->new_scale([50,50], [150,50], [150,150], [50,150]),
-                Slic3r::Polygon->new_scale([80,80], [80,120], [120,120], [120,80]),
-            ),
-        ],
-        total       => 4*3,
-        external    => 4,
-        cinternal   => 2,
-        ccw         => 2*3,
-    );
-}
-
 __END__
diff --git a/xs/MANIFEST b/xs/MANIFEST
index 2011b9cf3..36ac111f6 100644
--- a/xs/MANIFEST
+++ b/xs/MANIFEST
@@ -1690,6 +1690,8 @@ src/libslic3r/MotionPlanner.cpp
 src/libslic3r/MotionPlanner.hpp
 src/libslic3r/MultiPoint.cpp
 src/libslic3r/MultiPoint.hpp
+src/libslic3r/PerimeterGenerator.cpp
+src/libslic3r/PerimeterGenerator.hpp
 src/libslic3r/PlaceholderParser.cpp
 src/libslic3r/PlaceholderParser.hpp
 src/libslic3r/Point.cpp
@@ -1774,6 +1776,7 @@ xsp/Model.xsp
 xsp/MotionPlanner.xsp
 xsp/my.map
 xsp/mytype.map
+xsp/PerimeterGenerator.xsp
 xsp/PlaceholderParser.xsp
 xsp/Point.xsp
 xsp/Polygon.xsp
diff --git a/xs/src/libslic3r/ClipperUtils.cpp b/xs/src/libslic3r/ClipperUtils.cpp
index ba243ee82..baddd8f45 100644
--- a/xs/src/libslic3r/ClipperUtils.cpp
+++ b/xs/src/libslic3r/ClipperUtils.cpp
@@ -136,6 +136,15 @@ offset(const Slic3r::Polygons &polygons, Slic3r::Polygons* retval, const float d
     ClipperPaths_to_Slic3rMultiPoints(output, retval);
 }
 
+Slic3r::Polygons
+offset(const Slic3r::Polygons &polygons, const float delta,
+    double scale, ClipperLib::JoinType joinType, double miterLimit)
+{
+    Slic3r::Polygons pp;
+    offset(polygons, &pp, delta, scale, joinType, miterLimit);
+    return pp;
+}
+
 void
 offset(const Slic3r::Polylines &polylines, ClipperLib::Paths* retval, const float delta,
     double scale, ClipperLib::JoinType joinType, double miterLimit)
@@ -248,6 +257,15 @@ offset2(const Slic3r::Polygons &polygons, Slic3r::Polygons* retval, const float
     ClipperPaths_to_Slic3rMultiPoints(output, retval);
 }
 
+Slic3r::Polygons
+offset2(const Slic3r::Polygons &polygons, const float delta1,
+    const float delta2, const double scale, const ClipperLib::JoinType joinType, const double miterLimit)
+{
+    Slic3r::Polygons pp;
+    offset2(polygons, &pp, delta1, delta2, scale, joinType, miterLimit);
+    return pp;
+}
+
 void
 offset2(const Slic3r::Polygons &polygons, Slic3r::ExPolygons* retval, const float delta1,
     const float delta2, const double scale, const ClipperLib::JoinType joinType, const double miterLimit)
@@ -260,6 +278,15 @@ offset2(const Slic3r::Polygons &polygons, Slic3r::ExPolygons* retval, const floa
     ClipperPaths_to_Slic3rExPolygons(output, retval);
 }
 
+Slic3r::ExPolygons
+offset2_ex(const Slic3r::Polygons &polygons, const float delta1,
+    const float delta2, const double scale, const ClipperLib::JoinType joinType, const double miterLimit)
+{
+    Slic3r::ExPolygons expp;
+    offset2(polygons, &expp, delta1, delta2, scale, joinType, miterLimit);
+    return expp;
+}
+
 template <class T>
 void _clipper_do(const ClipperLib::ClipType clipType, const Slic3r::Polygons &subject, 
     const Slic3r::Polygons &clip, T* retval, const ClipperLib::PolyFillType fillType, const bool safety_offset_)
@@ -437,6 +464,22 @@ void diff(const SubjectType &subject, const Slic3r::ExPolygons &clip, ResultType
 }
 template void diff<Slic3r::Polygons, Slic3r::ExPolygons>(const Slic3r::Polygons &subject, const Slic3r::ExPolygons &clip, Slic3r::ExPolygons* retval, bool safety_offset_);
 
+Slic3r::Polygons
+diff(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, bool safety_offset_)
+{
+    Slic3r::Polygons pp;
+    diff(subject, clip, &pp, safety_offset_);
+    return pp;
+}
+
+Slic3r::ExPolygons
+diff_ex(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, bool safety_offset_)
+{
+    Slic3r::ExPolygons expp;
+    diff(subject, clip, &expp, safety_offset_);
+    return expp;
+}
+
 template <class SubjectType, class ResultType>
 void intersection(const SubjectType &subject, const Slic3r::Polygons &clip, ResultType* retval, bool safety_offset_)
 {
@@ -448,6 +491,22 @@ template void intersection<Slic3r::Polygons, Slic3r::Polylines>(const Slic3r::Po
 template void intersection<Slic3r::Polylines, Slic3r::Polylines>(const Slic3r::Polylines &subject, const Slic3r::Polygons &clip, Slic3r::Polylines* retval, bool safety_offset_);
 template void intersection<Slic3r::Lines, Slic3r::Lines>(const Slic3r::Lines &subject, const Slic3r::Polygons &clip, Slic3r::Lines* retval, bool safety_offset_);
 
+Slic3r::Polygons
+intersection(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, bool safety_offset_)
+{
+    Slic3r::Polygons pp;
+    intersection(subject, clip, &pp, safety_offset_);
+    return pp;
+}
+
+Slic3r::Polylines
+intersection(const Slic3r::Polylines &subject, const Slic3r::Polygons &clip, bool safety_offset_)
+{
+    Slic3r::Polylines pp;
+    intersection(subject, clip, &pp, safety_offset_);
+    return pp;
+}
+
 template <class SubjectType>
 bool intersects(const SubjectType &subject, const Slic3r::Polygons &clip, bool safety_offset_)
 {
@@ -474,6 +533,22 @@ void union_(const Slic3r::Polygons &subject, T* retval, bool safety_offset_)
 template void union_<Slic3r::ExPolygons>(const Slic3r::Polygons &subject, Slic3r::ExPolygons* retval, bool safety_offset_);
 template void union_<Slic3r::Polygons>(const Slic3r::Polygons &subject, Slic3r::Polygons* retval, bool safety_offset_);
 
+Slic3r::Polygons
+union_(const Slic3r::Polygons &subject, bool safety_offset)
+{
+    Polygons pp;
+    union_(subject, &pp, safety_offset);
+    return pp;
+}
+
+Slic3r::ExPolygons
+union_ex(const Slic3r::Polygons &subject, bool safety_offset)
+{
+    ExPolygons expp;
+    union_(subject, &expp, safety_offset);
+    return expp;
+}
+
 void union_(const Slic3r::Polygons &subject1, const Slic3r::Polygons &subject2, Slic3r::Polygons* retval, bool safety_offset)
 {
     Polygons pp = subject1;
diff --git a/xs/src/libslic3r/ClipperUtils.hpp b/xs/src/libslic3r/ClipperUtils.hpp
index ab144f202..4a3ba2e5c 100644
--- a/xs/src/libslic3r/ClipperUtils.hpp
+++ b/xs/src/libslic3r/ClipperUtils.hpp
@@ -40,6 +40,9 @@ void offset(const Slic3r::Polygons &polygons, ClipperLib::Paths* retval, const f
 void offset(const Slic3r::Polygons &polygons, Slic3r::Polygons* retval, const float delta,
     double scale = 100000, ClipperLib::JoinType joinType = ClipperLib::jtMiter, 
     double miterLimit = 3);
+Slic3r::Polygons offset(const Slic3r::Polygons &polygons, const float delta,
+    double scale = 100000, ClipperLib::JoinType joinType = ClipperLib::jtMiter, 
+    double miterLimit = 3);
 
 // offset Polylines
 void offset(const Slic3r::Polylines &polylines, ClipperLib::Paths* retval, const float delta,
@@ -62,9 +65,15 @@ void offset2(const Slic3r::Polygons &polygons, ClipperLib::Paths* retval, const
 void offset2(const Slic3r::Polygons &polygons, Slic3r::Polygons* retval, const float delta1,
     const float delta2, double scale = 100000, ClipperLib::JoinType joinType = ClipperLib::jtMiter, 
     double miterLimit = 3);
+Slic3r::Polygons offset2(const Slic3r::Polygons &polygons, const float delta1,
+    const float delta2, double scale = 100000, ClipperLib::JoinType joinType = ClipperLib::jtMiter, 
+    double miterLimit = 3);
 void offset2(const Slic3r::Polygons &polygons, Slic3r::ExPolygons* retval, const float delta1,
     const float delta2, double scale = 100000, ClipperLib::JoinType joinType = ClipperLib::jtMiter, 
     double miterLimit = 3);
+Slic3r::ExPolygons offset2_ex(const Slic3r::Polygons &polygons, const float delta1,
+    const float delta2, double scale = 100000, ClipperLib::JoinType joinType = ClipperLib::jtMiter, 
+    double miterLimit = 3);
 
 template <class T>
 void _clipper_do(ClipperLib::ClipType clipType, const Slic3r::Polygons &subject, 
@@ -86,9 +95,15 @@ void diff(const SubjectType &subject, const Slic3r::Polygons &clip, ResultType*
 template <class SubjectType, class ResultType>
 void diff(const SubjectType &subject, const Slic3r::ExPolygons &clip, ResultType* retval, bool safety_offset_ = false);
 
+Slic3r::Polygons diff(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, bool safety_offset_ = false);
+Slic3r::ExPolygons diff_ex(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, bool safety_offset_ = false);
+
 template <class SubjectType, class ResultType>
 void intersection(const SubjectType &subject, const Slic3r::Polygons &clip, ResultType* retval, bool safety_offset_ = false);
 
+Slic3r::Polygons intersection(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, bool safety_offset_ = false);
+Slic3r::Polylines intersection(const Slic3r::Polylines &subject, const Slic3r::Polygons &clip, bool safety_offset_ = false);
+
 template <class SubjectType>
 bool intersects(const SubjectType &subject, const Slic3r::Polygons &clip, bool safety_offset_ = false);
 
@@ -98,6 +113,9 @@ void xor_(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, Slic3r:
 template <class T>
 void union_(const Slic3r::Polygons &subject, T* retval, bool safety_offset_ = false);
 
+Slic3r::Polygons union_(const Slic3r::Polygons &subject, bool safety_offset = false);
+Slic3r::ExPolygons union_ex(const Slic3r::Polygons &subject, bool safety_offset = false);
+
 void union_(const Slic3r::Polygons &subject1, const Slic3r::Polygons &subject2, Slic3r::Polygons* retval, bool safety_offset = false);
 
 void union_pt(const Slic3r::Polygons &subject, ClipperLib::PolyTree* retval, bool safety_offset_ = false);
diff --git a/xs/src/libslic3r/ExPolygon.cpp b/xs/src/libslic3r/ExPolygon.cpp
index 53a1e9333..ee0473656 100644
--- a/xs/src/libslic3r/ExPolygon.cpp
+++ b/xs/src/libslic3r/ExPolygon.cpp
@@ -122,6 +122,13 @@ ExPolygon::has_boundary_point(const Point &point) const
     return false;
 }
 
+void
+ExPolygon::simplify_p(double tolerance, Polygons* polygons) const
+{
+    Polygons pp = this->simplify_p(tolerance);
+    polygons->insert(polygons->end(), pp.begin(), pp.end());
+}
+
 Polygons
 ExPolygon::simplify_p(double tolerance) const
 {
@@ -180,16 +187,17 @@ ExPolygon::medial_axis(double max_width, double min_width, Polylines* polylines)
     }
     
     // compute the Voronoi diagram
-    ma.build(polylines);
+    Polylines pp;
+    ma.build(&pp);
     
     // clip segments to our expolygon area
     // (do this before extending endpoints as external segments coule be extended into
     // expolygon, this leaving wrong things inside)
-    intersection(*polylines, *this, polylines);
+    pp = intersection(pp, *this);
     
     // extend initial and final segments of each polyline (they will be clipped)
     // unless they represent closed loops
-    for (Polylines::iterator polyline = polylines->begin(); polyline != polylines->end(); ++polyline) {
+    for (Polylines::iterator polyline = pp.begin(); polyline != pp.end(); ++polyline) {
         if (polyline->points.front().distance_to(polyline->points.back()) < min_width) continue;
         // TODO: we should *not* extend endpoints where other polylines start/end
         // (such as T joints, which are returned as three polylines by MedialAxis)
@@ -198,18 +206,20 @@ ExPolygon::medial_axis(double max_width, double min_width, Polylines* polylines)
     }
     
     // clip again after extending endpoints to prevent them from exceeding the expolygon boundaries
-    intersection(*polylines, *this, polylines);
+    pp = intersection(pp, *this);
     
     // remove too short polylines
     // (we can't do this check before endpoints extension and clipping because we don't
     // know how long will the endpoints be extended since it depends on polygon thickness
     // which is variable - extension will be <= max_width/2 on each side)
-    for (size_t i = 0; i < polylines->size(); ++i) {
-        if ((*polylines)[i].length() < max_width) {
-            polylines->erase(polylines->begin() + i);
+    for (size_t i = 0; i < pp.size(); ++i) {
+        if (pp[i].length() < max_width) {
+            pp.erase(pp.begin() + i);
             --i;
         }
     }
+    
+    polylines->insert(polylines->end(), pp.begin(), pp.end());
 }
 
 void
diff --git a/xs/src/libslic3r/ExPolygon.hpp b/xs/src/libslic3r/ExPolygon.hpp
index 3d7cd3540..7b7b0b760 100644
--- a/xs/src/libslic3r/ExPolygon.hpp
+++ b/xs/src/libslic3r/ExPolygon.hpp
@@ -27,6 +27,7 @@ class ExPolygon
     bool contains(const Point &point) const;
     bool contains_b(const Point &point) const;
     bool has_boundary_point(const Point &point) const;
+    void simplify_p(double tolerance, Polygons* polygons) const;
     Polygons simplify_p(double tolerance) const;
     ExPolygons simplify(double tolerance) const;
     void simplify(double tolerance, ExPolygons &expolygons) const;
diff --git a/xs/src/libslic3r/ExtrusionEntity.hpp b/xs/src/libslic3r/ExtrusionEntity.hpp
index bcb50155a..c1eef6af3 100644
--- a/xs/src/libslic3r/ExtrusionEntity.hpp
+++ b/xs/src/libslic3r/ExtrusionEntity.hpp
@@ -52,6 +52,7 @@ class ExtrusionEntity
     virtual Point last_point() const = 0;
     virtual Polygons grow() const = 0;
     virtual double min_mm3_per_mm() const = 0;
+    virtual Polyline as_polyline() const = 0;
 };
 
 typedef std::vector<ExtrusionEntity*> ExtrusionEntitiesPtr;
@@ -83,6 +84,9 @@ class ExtrusionPath : public ExtrusionEntity
     double min_mm3_per_mm() const {
         return this->mm3_per_mm;
     };
+    Polyline as_polyline() const {
+        return this->polyline;
+    };
 
     private:
     void _inflate_collection(const Polylines &polylines, ExtrusionEntityCollection* collection) const;
@@ -97,6 +101,8 @@ class ExtrusionLoop : public ExtrusionEntity
     ExtrusionLoopRole role;
     
     ExtrusionLoop(ExtrusionLoopRole role = elrDefault) : role(role) {};
+    ExtrusionLoop(const ExtrusionPaths &paths, ExtrusionLoopRole role = elrDefault)
+        : paths(paths), role(role) {};
     bool is_loop() const {
         return true;
     };
@@ -120,6 +126,9 @@ class ExtrusionLoop : public ExtrusionEntity
     bool is_solid_infill() const;
     Polygons grow() const;
     double min_mm3_per_mm() const;
+    Polyline as_polyline() const {
+        return this->polygon().split_at_first_point();
+    };
 };
 
 }
diff --git a/xs/src/libslic3r/ExtrusionEntityCollection.cpp b/xs/src/libslic3r/ExtrusionEntityCollection.cpp
index 79736cbcb..eb77aaede 100644
--- a/xs/src/libslic3r/ExtrusionEntityCollection.cpp
+++ b/xs/src/libslic3r/ExtrusionEntityCollection.cpp
@@ -8,9 +8,13 @@ namespace Slic3r {
 ExtrusionEntityCollection::ExtrusionEntityCollection(const ExtrusionEntityCollection& collection)
     : no_sort(collection.no_sort), orig_indices(collection.orig_indices)
 {
-    this->entities.reserve(collection.entities.size());
-    for (ExtrusionEntitiesPtr::const_iterator it = collection.entities.begin(); it != collection.entities.end(); ++it)
-        this->entities.push_back((*it)->clone());
+    this->append(collection.entities);
+}
+
+ExtrusionEntityCollection::ExtrusionEntityCollection(const ExtrusionPaths &paths)
+    : no_sort(false)
+{
+    this->append(paths);
 }
 
 ExtrusionEntityCollection& ExtrusionEntityCollection::operator= (const ExtrusionEntityCollection &other)
@@ -28,10 +32,30 @@ ExtrusionEntityCollection::swap (ExtrusionEntityCollection &c)
     std::swap(this->no_sort, c.no_sort);
 }
 
+ExtrusionEntityCollection::~ExtrusionEntityCollection()
+{
+    for (ExtrusionEntitiesPtr::iterator it = this->entities.begin(); it != this->entities.end(); ++it)
+        delete *it;
+}
+
+ExtrusionEntityCollection::operator ExtrusionPaths() const
+{
+    ExtrusionPaths paths;
+    for (ExtrusionEntitiesPtr::const_iterator it = this->entities.begin(); it != this->entities.end(); ++it) {
+        if (const ExtrusionPath* path = dynamic_cast<const ExtrusionPath*>(*it))
+            paths.push_back(*path);
+    }
+    return paths;
+}
+
 ExtrusionEntityCollection*
 ExtrusionEntityCollection::clone() const
 {
-    return new ExtrusionEntityCollection(*this);
+    ExtrusionEntityCollection* coll = new ExtrusionEntityCollection(*this);
+    for (size_t i = 0; i < coll->entities.size(); ++i) {
+        coll->entities[i] = this->entities[i]->clone();
+    }
+    return coll;
 }
 
 void
@@ -57,6 +81,34 @@ ExtrusionEntityCollection::last_point() const
     return this->entities.back()->last_point();
 }
 
+void
+ExtrusionEntityCollection::append(const ExtrusionEntity &entity)
+{
+    this->entities.push_back(entity.clone());
+}
+
+void
+ExtrusionEntityCollection::append(const ExtrusionEntitiesPtr &entities)
+{
+    for (ExtrusionEntitiesPtr::const_iterator ptr = entities.begin(); ptr != entities.end(); ++ptr)
+        this->append(**ptr);
+}
+
+void
+ExtrusionEntityCollection::append(const ExtrusionPaths &paths)
+{
+    for (ExtrusionPaths::const_iterator path = paths.begin(); path != paths.end(); ++path)
+        this->append(*path);
+}
+
+ExtrusionEntityCollection
+ExtrusionEntityCollection::chained_path(bool no_reverse, std::vector<size_t>* orig_indices) const
+{
+    ExtrusionEntityCollection coll;
+    this->chained_path(&coll, no_reverse, orig_indices);
+    return coll;
+}
+
 void
 ExtrusionEntityCollection::chained_path(ExtrusionEntityCollection* retval, bool no_reverse, std::vector<size_t>* orig_indices) const
 {
@@ -145,15 +197,21 @@ ExtrusionEntityCollection::flatten(ExtrusionEntityCollection* retval) const
     for (ExtrusionEntitiesPtr::const_iterator it = this->entities.begin(); it != this->entities.end(); ++it) {
         if ((*it)->is_collection()) {
             ExtrusionEntityCollection* collection = dynamic_cast<ExtrusionEntityCollection*>(*it);
-            ExtrusionEntityCollection contents;
-            collection->flatten(&contents);
-            retval->entities.insert(retval->entities.end(), contents.entities.begin(), contents.entities.end());
+            retval->append(collection->flatten().entities);
         } else {
-            retval->entities.push_back((*it)->clone());
+            retval->append(**it);
         }
     }
 }
 
+ExtrusionEntityCollection
+ExtrusionEntityCollection::flatten() const
+{
+    ExtrusionEntityCollection coll;
+    this->flatten(&coll);
+    return coll;
+}
+
 double
 ExtrusionEntityCollection::min_mm3_per_mm() const
 {
diff --git a/xs/src/libslic3r/ExtrusionEntityCollection.hpp b/xs/src/libslic3r/ExtrusionEntityCollection.hpp
index 24016d638..504c82ae1 100644
--- a/xs/src/libslic3r/ExtrusionEntityCollection.hpp
+++ b/xs/src/libslic3r/ExtrusionEntityCollection.hpp
@@ -10,19 +10,30 @@ class ExtrusionEntityCollection : public ExtrusionEntity
 {
     public:
     ExtrusionEntityCollection* clone() const;
-    ExtrusionEntitiesPtr entities;
+    ExtrusionEntitiesPtr entities;     // we own these entities
     std::vector<size_t> orig_indices;  // handy for XS
     bool no_sort;
     ExtrusionEntityCollection(): no_sort(false) {};
     ExtrusionEntityCollection(const ExtrusionEntityCollection &collection);
+    ExtrusionEntityCollection(const ExtrusionPaths &paths);
     ExtrusionEntityCollection& operator= (const ExtrusionEntityCollection &other);
+    ~ExtrusionEntityCollection();
+    operator ExtrusionPaths() const;
+    
     bool is_collection() const {
         return true;
     };
     bool can_reverse() const {
         return !this->no_sort;
     };
+    bool empty() const {
+        return this->entities.empty();
+    };
     void swap (ExtrusionEntityCollection &c);
+    void append(const ExtrusionEntity &entity);
+    void append(const ExtrusionEntitiesPtr &entities);
+    void append(const ExtrusionPaths &paths);
+    ExtrusionEntityCollection chained_path(bool no_reverse = false, std::vector<size_t>* orig_indices = NULL) const;
     void chained_path(ExtrusionEntityCollection* retval, bool no_reverse = false, std::vector<size_t>* orig_indices = NULL) const;
     void chained_path_from(Point start_near, ExtrusionEntityCollection* retval, bool no_reverse = false, std::vector<size_t>* orig_indices = NULL) const;
     void reverse();
@@ -31,7 +42,12 @@ class ExtrusionEntityCollection : public ExtrusionEntity
     Polygons grow() const;
     size_t items_count() const;
     void flatten(ExtrusionEntityCollection* retval) const;
+    ExtrusionEntityCollection flatten() const;
     double min_mm3_per_mm() const;
+    Polyline as_polyline() const {
+        CONFESS("Calling as_polyline() on a ExtrusionEntityCollection");
+        return Polyline();
+    };
 };
 
 }
diff --git a/xs/src/libslic3r/PerimeterGenerator.cpp b/xs/src/libslic3r/PerimeterGenerator.cpp
new file mode 100644
index 000000000..f95930e2d
--- /dev/null
+++ b/xs/src/libslic3r/PerimeterGenerator.cpp
@@ -0,0 +1,525 @@
+#include "PerimeterGenerator.hpp"
+#include "ClipperUtils.hpp"
+#include "ExtrusionEntityCollection.hpp"
+
+namespace Slic3r {
+
+void
+PerimeterGenerator::process()
+{
+    // other perimeters
+    this->_mm3_per_mm           = this->perimeter_flow.mm3_per_mm();
+    coord_t pwidth              = this->perimeter_flow.scaled_width();
+    coord_t pspacing            = this->perimeter_flow.scaled_spacing();
+    
+    // external perimeters
+    this->_ext_mm3_per_mm       = this->ext_perimeter_flow.mm3_per_mm();
+    coord_t ext_pwidth        = this->ext_perimeter_flow.scaled_width();
+    coord_t ext_pspacing      = scale_(this->ext_perimeter_flow.spacing(this->perimeter_flow));
+    
+    // overhang perimeters
+    this->_mm3_per_mm_overhang  = this->overhang_flow.mm3_per_mm();
+    
+    // solid infill
+    coord_t ispacing            = this->solid_infill_flow.scaled_spacing();
+    coord_t gap_area_threshold  = pwidth * pwidth;
+    
+    // Calculate the minimum required spacing between two adjacent traces.
+    // This should be equal to the nominal flow spacing but we experiment
+    // with some tolerance in order to avoid triggering medial axis when
+    // some squishing might work. Loops are still spaced by the entire
+    // flow spacing; this only applies to collapsing parts.
+    coord_t min_spacing         = pspacing      * (1 - INSET_OVERLAP_TOLERANCE);
+    coord_t ext_min_spacing     = ext_pspacing  * (1 - INSET_OVERLAP_TOLERANCE);
+    
+    // prepare grown lower layer slices for overhang detection
+    if (this->lower_slices != NULL && this->config->overhangs) {
+        // We consider overhang any part where the entire nozzle diameter is not supported by the
+        // lower layer, so we take lower slices and offset them by half the nozzle diameter used 
+        // in the current layer
+        double nozzle_diameter = this->print_config->nozzle_diameter.get_at(this->config->perimeter_extruder-1);
+        
+        this->_lower_slices_p = offset(*this->lower_slices, scale_(+nozzle_diameter/2));
+    }
+    
+    // we need to process each island separately because we might have different
+    // extra perimeters for each one
+    for (Surfaces::const_iterator surface = this->slices->surfaces.begin();
+        surface != this->slices->surfaces.end(); ++surface) {
+        // detect how many perimeters must be generated for this island
+        unsigned short loop_number = this->config->perimeters + surface->extra_perimeters;
+        loop_number--;  // 0-indexed loops
+        
+        Polygons gaps;
+        
+        Polygons last = surface->expolygon.simplify_p(SCALED_RESOLUTION);
+        if (loop_number >= 0) {  // no loops = -1
+            
+            std::vector<PerimeterGeneratorLoops> contours(loop_number+1);    // depth => loops
+            std::vector<PerimeterGeneratorLoops> holes(loop_number+1);       // depth => loops
+            Polylines thin_walls;
+            
+            // we loop one time more than needed in order to find gaps after the last perimeter was applied
+            for (unsigned short i = 0; i <= loop_number+1; ++i) {  // outer loop is 0
+                Polygons offsets;
+                if (i == 0) {
+                    // the minimum thickness of a single loop is:
+                    // ext_width/2 + ext_spacing/2 + spacing/2 + width/2
+                    if (this->config->thin_walls) {
+                        offsets = offset2(
+                            last,
+                            -(0.5*ext_pwidth + 0.5*ext_min_spacing - 1),
+                            +(0.5*ext_min_spacing - 1)
+                        );
+                    } else {
+                        offsets = offset(last, -0.5*ext_pwidth);
+                    }
+                    
+                    // look for thin walls
+                    if (this->config->thin_walls) {
+                        Polygons diffpp = diff(
+                            last,
+                            offset(offsets, +0.5*ext_pwidth),
+                            true  // medial axis requires non-overlapping geometry
+                        );
+                        
+                        // the following offset2 ensures almost nothing in @thin_walls is narrower than $min_width
+                        // (actually, something larger than that still may exist due to mitering or other causes)
+                        coord_t min_width = ext_pwidth / 2;
+                        ExPolygons expp = offset2_ex(diffpp, -min_width/2, +min_width/2);
+                        
+                        // the maximum thickness of our thin wall area is equal to the minimum thickness of a single loop
+                        Polylines pp;
+                        for (ExPolygons::const_iterator ex = expp.begin(); ex != expp.end(); ++ex)
+                            ex->medial_axis(ext_pwidth + ext_pspacing, min_width, &pp);
+                        
+                        double threshold = ext_pwidth * ext_pwidth;
+                        for (Polylines::const_iterator p = pp.begin(); p != pp.end(); ++p) {
+                            if (p->length() > threshold) {
+                                thin_walls.push_back(*p);
+                            }
+                        }
+                        
+                        #ifdef DEBUG
+                        printf("  %zu thin walls detected\n", thin_walls.size());
+                        #endif
+                        
+                        /*
+                        if (false) {
+                            require "Slic3r/SVG.pm";
+                            Slic3r::SVG::output(
+                                "medial_axis.svg",
+                                no_arrows       => 1,
+                                #expolygons      => \@expp,
+                                polylines       => \@thin_walls,
+                            );
+                        }
+                        */
+                    }
+                } else {
+                    coord_t distance = (i == 1) ? ext_pspacing : pspacing;
+                    
+                    if (this->config->thin_walls) {
+                        offsets = offset2(
+                            last,
+                            -(distance + 0.5*min_spacing - 1),
+                            +(0.5*min_spacing - 1)
+                        );
+                    } else {
+                        offsets = offset(
+                            last,
+                            -distance
+                        );
+                    }
+                    
+                    // look for gaps
+                    if (this->config->gap_fill_speed.value > 0 && this->config->fill_density.value > 0) {
+                        // not using safety offset here would "detect" very narrow gaps
+                        // (but still long enough to escape the area threshold) that gap fill
+                        // won't be able to fill but we'd still remove from infill area
+                        ExPolygons diff_expp = diff_ex(
+                            offset(last, -0.5*distance),
+                            offset(offsets, +0.5*distance + 10)  // safety offset
+                        );
+                        for (ExPolygons::const_iterator ex = diff_expp.begin(); ex != diff_expp.end(); ++ex) {
+                            if (fabs(ex->area()) >= gap_area_threshold) {
+                                Polygons pp = *ex;
+                                gaps.insert(gaps.end(), pp.begin(), pp.end());
+                            }
+                        }
+                    }
+                }
+                
+                if (offsets.empty()) break;
+                if (i > loop_number) break; // we were only looking for gaps this time
+                
+                last = offsets;
+                for (Polygons::const_iterator polygon = offsets.begin(); polygon != offsets.end(); ++polygon) {
+                    PerimeterGeneratorLoop loop(*polygon, i);
+                    loop.is_contour = polygon->is_counter_clockwise();
+                    if (loop.is_contour) {
+                        contours[i].push_back(loop);
+                    } else {
+                        holes[i].push_back(loop);
+                    }
+                }
+            }
+            
+            // nest loops: holes first
+            for (unsigned short d = 0; d <= loop_number; ++d) {
+                PerimeterGeneratorLoops &holes_d = holes[d];
+                
+                // loop through all holes having depth == d
+                for (unsigned short i = 0; i < holes_d.size(); ++i) {
+                    const PerimeterGeneratorLoop &loop = holes_d[i];
+                    
+                    // find the hole loop that contains this one, if any
+                    for (unsigned short t = d+1; t <= loop_number; ++t) {
+                        for (unsigned short j = 0; j < holes[t].size(); ++j) {
+                            PerimeterGeneratorLoop &candidate_parent = holes[t][j];
+                            if (candidate_parent.polygon.contains(loop.polygon.first_point())) {
+                                candidate_parent.children.push_back(loop);
+                                holes_d.erase(holes_d.begin() + i);
+                                --i;
+                                goto NEXT_LOOP;
+                            }
+                        }
+                    }
+                
+                    // if no hole contains this hole, find the contour loop that contains it
+                    for (unsigned short t = loop_number; t >= 0; --t) {
+                        for (unsigned short j = 0; j < contours[t].size(); ++j) {
+                            PerimeterGeneratorLoop &candidate_parent = contours[t][j];
+                            if (candidate_parent.polygon.contains(loop.polygon.first_point())) {
+                                candidate_parent.children.push_back(loop);
+                                holes_d.erase(holes_d.begin() + i);
+                                --i;
+                                goto NEXT_LOOP;
+                            }
+                        }
+                    }
+                    NEXT_LOOP: ;
+                }
+            }
+        
+            // nest contour loops
+            for (unsigned short d = loop_number; d >= 1; --d) {
+                PerimeterGeneratorLoops &contours_d = contours[d];
+                
+                // loop through all contours having depth == d
+                for (unsigned short i = 0; i < contours_d.size(); ++i) {
+                    const PerimeterGeneratorLoop &loop = contours_d[i];
+                
+                    // find the contour loop that contains it
+                    for (unsigned short t = d-1; t >= 0; --t) {
+                        for (unsigned short j = 0; j < contours[t].size(); ++j) {
+                            PerimeterGeneratorLoop &candidate_parent = contours[t][j];
+                            if (candidate_parent.polygon.contains(loop.polygon.first_point())) {
+                                candidate_parent.children.push_back(loop);
+                                contours_d.erase(contours_d.begin() + i);
+                                --i;
+                                goto NEXT_CONTOUR;
+                            }
+                        }
+                    }
+                    
+                    NEXT_CONTOUR: ;
+                }
+            }
+        
+            // at this point, all loops should be in contours[0]
+            
+            ExtrusionEntityCollection entities = this->_traverse_loops(contours.front(), thin_walls);
+            
+            // if brim will be printed, reverse the order of perimeters so that
+            // we continue inwards after having finished the brim
+            // TODO: add test for perimeter order
+            if (this->config->external_perimeters_first
+                || (this->layer_id == 0 && this->print_config->brim_width.value > 0))
+                    entities.reverse();
+        
+            // append perimeters for this slice as a collection
+            if (!entities.empty())
+                this->loops->append(entities);
+        }
+        
+        // fill gaps
+        if (!gaps.empty()) {
+            /*
+            if (false) {
+                require "Slic3r/SVG.pm";
+                Slic3r::SVG::output(
+                    "gaps.svg",
+                    expolygons => union_ex(\@gaps),
+                );
+            }
+            */
+            
+            // where $pwidth < thickness < 2*$pspacing, infill with width = 2*$pwidth
+            // where 0.1*$pwidth < thickness < $pwidth, infill with width = 1*$pwidth
+            std::vector<PerimeterGeneratorGapSize> gap_sizes;
+            gap_sizes.push_back(PerimeterGeneratorGapSize(pwidth, 2*pspacing, unscale(2*pwidth)));
+            gap_sizes.push_back(PerimeterGeneratorGapSize(0.1*pwidth, pwidth, unscale(1*pwidth)));
+            
+            for (std::vector<PerimeterGeneratorGapSize>::const_iterator gap_size = gap_sizes.begin();
+                gap_size != gap_sizes.end(); ++gap_size) {
+                ExtrusionEntityCollection gap_fill = this->_fill_gaps(gap_size->min, 
+                    gap_size->max, gap_size->width, gaps);
+                this->gap_fill->append(gap_fill.entities);
+                
+                // Make sure we don't infill narrow parts that are already gap-filled
+                // (we only consider this surface's gaps to reduce the diff() complexity).
+                // Growing actual extrusions ensures that gaps not filled by medial axis
+                // are not subtracted from fill surfaces (they might be too short gaps
+                // that medial axis skips but infill might join with other infill regions
+                // and use zigzag).
+                double dist = scale_(gap_size->width/2);
+                Polygons filled;
+                for (ExtrusionEntitiesPtr::const_iterator it = gap_fill.entities.begin();
+                    it != gap_fill.entities.end(); ++it)
+                    offset((*it)->as_polyline(), &filled, dist);
+                
+                last = diff(last, filled);
+                gaps = diff(gaps, filled);  // prevent more gap fill here
+            }
+        }
+        
+        // create one more offset to be used as boundary for fill
+        // we offset by half the perimeter spacing (to get to the actual infill boundary)
+        // and then we offset back and forth by half the infill spacing to only consider the
+        // non-collapsing regions
+        coord_t inset = 0;
+        if (loop_number == 0) {
+            // one loop
+            inset += ext_pspacing/2;
+        } else if (loop_number > 0) {
+            // two or more loops
+            inset += pspacing/2;
+        }
+        
+        // only apply infill overlap if we actually have one perimeter
+        if (inset > 0)
+            inset -= this->config->get_abs_value("infill_overlap", inset + ispacing/2);
+        
+        {
+            ExPolygons expp = union_ex(last);
+            
+            // simplify infill contours according to resolution
+            Polygons pp;
+            for (ExPolygons::const_iterator ex = expp.begin(); ex != expp.end(); ++ex)
+                ex->simplify_p(SCALED_RESOLUTION, &pp);
+            
+            // collapse too narrow infill areas
+            coord_t min_perimeter_infill_spacing = ispacing * (1 - INSET_OVERLAP_TOLERANCE);
+            expp = offset2_ex(
+                pp,
+                -inset -min_perimeter_infill_spacing/2,
+                +min_perimeter_infill_spacing/2
+            );
+            
+            // append infill areas to fill_surfaces
+            for (ExPolygons::const_iterator ex = expp.begin(); ex != expp.end(); ++ex)
+                this->fill_surfaces->surfaces.push_back(Surface(stInternal, *ex));  // use a bogus surface type
+        }
+    }
+}
+
+ExtrusionEntityCollection
+PerimeterGenerator::_traverse_loops(const PerimeterGeneratorLoops &loops,
+    Polylines &thin_walls) const
+{
+    // loops is an arrayref of ::Loop objects
+    // turn each one into an ExtrusionLoop object
+    ExtrusionEntityCollection coll;
+    for (PerimeterGeneratorLoops::const_iterator loop = loops.begin();
+        loop != loops.end(); ++loop) {
+        bool is_external = loop->is_external();
+        
+        ExtrusionRole role;
+        ExtrusionLoopRole loop_role;
+        role = is_external ? erExternalPerimeter : erPerimeter;
+        if (loop->is_internal_contour()) {
+            // Note that we set loop role to ContourInternalPerimeter
+            // also when loop is both internal and external (i.e.
+            // there's only one contour loop).
+            loop_role = elrContourInternalPerimeter;
+        } else {
+            loop_role = elrDefault;
+        }
+        
+        // detect overhanging/bridging perimeters
+        ExtrusionPaths paths;
+        if (this->config->overhangs && this->layer_id > 0
+            && !(this->object_config->support_material && this->object_config->support_material_contact_distance.value == 0)) {
+            // get non-overhang paths by intersecting this loop with the grown lower slices
+            {
+                Polylines polylines;
+                intersection((Polygons)loop->polygon, this->_lower_slices_p, &polylines);
+                
+                for (Polylines::const_iterator polyline = polylines.begin(); polyline != polylines.end(); ++polyline) {
+                    ExtrusionPath path(role);
+                    path.polyline   = *polyline;
+                    path.mm3_per_mm = is_external ? this->_ext_mm3_per_mm           : this->_mm3_per_mm;
+                    path.width      = is_external ? this->ext_perimeter_flow.width  : this->perimeter_flow.width;
+                    path.height     = this->layer_height;
+                    paths.push_back(path);
+                }
+            }
+            
+            // get overhang paths by checking what parts of this loop fall 
+            // outside the grown lower slices (thus where the distance between
+            // the loop centerline and original lower slices is >= half nozzle diameter
+            {
+                Polylines polylines;
+                diff((Polygons)loop->polygon, this->_lower_slices_p, &polylines);
+                
+                for (Polylines::const_iterator polyline = polylines.begin(); polyline != polylines.end(); ++polyline) {
+                    ExtrusionPath path(erOverhangPerimeter);
+                    path.polyline   = *polyline;
+                    path.mm3_per_mm = this->_mm3_per_mm_overhang;
+                    path.width      = this->overhang_flow.width;
+                    path.height     = this->overhang_flow.height;
+                    paths.push_back(path);
+                }
+            }
+            
+            // reapply the nearest point search for starting point
+            // We allow polyline reversal because Clipper may have randomly
+            // reversed polylines during clipping.
+            paths = ExtrusionEntityCollection(paths).chained_path();
+        } else {
+            ExtrusionPath path(role);
+            path.polyline   = loop->polygon.split_at_first_point();
+            path.mm3_per_mm = is_external ? this->_ext_mm3_per_mm           : this->_mm3_per_mm;
+            path.width      = is_external ? this->ext_perimeter_flow.width  : this->perimeter_flow.width;
+            path.height     = this->layer_height;
+            paths.push_back(path);
+        }
+        
+        coll.append(ExtrusionLoop(paths, loop_role));
+    }
+    
+    // append thin walls to the nearest-neighbor search (only for first iteration)
+    if (!thin_walls.empty()) {
+        for (Polylines::const_iterator polyline = thin_walls.begin(); polyline != thin_walls.end(); ++polyline) {
+            ExtrusionPath path(erExternalPerimeter);
+            path.polyline   = *polyline;
+            path.mm3_per_mm = this->_mm3_per_mm;
+            path.width      = this->perimeter_flow.width;
+            path.height     = this->layer_height;
+            coll.append(path);
+        }
+        
+        thin_walls.clear();
+    }
+    
+    // sort entities
+    ExtrusionEntityCollection sorted_coll;
+    coll.chained_path(&sorted_coll, false, &sorted_coll.orig_indices);
+    
+    // traverse children
+    ExtrusionEntityCollection entities;
+    for (unsigned short i = 0; i < sorted_coll.orig_indices.size(); ++i) {
+        size_t idx = sorted_coll.orig_indices[i];
+        if (idx >= loops.size()) {
+            // this is a thin wall
+            // let's get it from the sorted collection as it might have been reversed
+            entities.append(*sorted_coll.entities[i]);
+        } else {
+            const PerimeterGeneratorLoop &loop = loops[i];
+            ExtrusionLoop eloop = *dynamic_cast<ExtrusionLoop*>(coll.entities[idx]);
+            
+            ExtrusionEntityCollection children = this->_traverse_loops(loop.children, thin_walls);
+            if (loop.is_contour) {
+                eloop.make_counter_clockwise();
+                entities.append(children.entities);
+                entities.append(eloop);
+            } else {
+                eloop.make_clockwise();
+                entities.append(eloop);
+                entities.append(children.entities);
+            }
+        }
+    }
+    return entities;
+}
+
+ExtrusionEntityCollection
+PerimeterGenerator::_fill_gaps(double min, double max, double w,
+    const Polygons &gaps) const
+{
+    ExtrusionEntityCollection coll;
+    
+    min *= (1 - INSET_OVERLAP_TOLERANCE);
+    
+    ExPolygons curr = diff_ex(
+        offset2(gaps, -min/2, +min/2),
+        offset2(gaps, -max/2, +max/2),
+        true
+    );
+    
+    Polylines polylines;
+    for (ExPolygons::const_iterator ex = curr.begin(); ex != curr.end(); ++ex)
+        ex->medial_axis(max, min/2, &polylines);
+    if (polylines.empty())
+        return coll;
+    
+    #ifdef SLIC3R_DEBUG
+    if (!curr.empty())
+        printf("  %zu gaps filled with extrusion width = %f\n", curr.size(), w);
+    #endif
+    
+    //my $flow = $layerm->flow(FLOW_ROLE_SOLID_INFILL, 0, $w);
+    Flow flow(
+        w, this->layer_height, this->solid_infill_flow.nozzle_diameter
+    );
+    
+    double mm3_per_mm = flow.mm3_per_mm();
+    
+    for (Polylines::const_iterator p = polylines.begin(); p != polylines.end(); ++p) {
+        ExtrusionPath path(erGapFill);
+        path.polyline   = *p;
+        path.mm3_per_mm = mm3_per_mm;
+        path.width      = flow.width;
+        path.height     = this->layer_height;
+        
+        if (p->is_valid() && p->first_point().coincides_with(p->last_point())) {
+            // since medial_axis() now returns only Polyline objects, detect loops here
+            ExtrusionLoop loop;
+            loop.paths.push_back(path);
+            coll.append(loop);
+        } else {
+            coll.append(path);
+        }
+    }
+    
+    return coll;
+}
+
+#ifdef SLIC3RXS
+REGISTER_CLASS(PerimeterGenerator, "Layer::PerimeterGenerator");
+#endif
+
+bool
+PerimeterGeneratorLoop::is_external() const
+{
+    return this->depth == 0;
+}
+
+bool
+PerimeterGeneratorLoop::is_internal_contour() const
+{
+    if (this->is_contour) {
+        // an internal contour is a contour containing no other contours
+        for (std::vector<PerimeterGeneratorLoop>::const_iterator loop = this->children.begin();
+            loop != this->children.end(); ++loop) {
+            if (loop->is_contour) {
+                return false;
+            }
+        }
+        return true;
+    }
+    return false;
+}
+
+}
diff --git a/xs/src/libslic3r/PerimeterGenerator.hpp b/xs/src/libslic3r/PerimeterGenerator.hpp
new file mode 100644
index 000000000..6465d63f9
--- /dev/null
+++ b/xs/src/libslic3r/PerimeterGenerator.hpp
@@ -0,0 +1,84 @@
+#ifndef slic3r_PerimeterGenerator_hpp_
+#define slic3r_PerimeterGenerator_hpp_
+
+#include <myinit.h>
+#include <vector>
+#include "ExPolygonCollection.hpp"
+#include "Flow.hpp"
+#include "Polygon.hpp"
+#include "PrintConfig.hpp"
+#include "SurfaceCollection.hpp"
+
+namespace Slic3r {
+
+class PerimeterGeneratorLoop;
+typedef std::vector<PerimeterGeneratorLoop> PerimeterGeneratorLoops;
+
+class PerimeterGeneratorLoop {
+    public:
+    Polygon polygon;
+    bool is_contour;
+    unsigned short depth;
+    std::vector<PerimeterGeneratorLoop> children;
+    
+    PerimeterGeneratorLoop(Polygon polygon, unsigned short depth)
+        : polygon(polygon), depth(depth), is_contour(false)
+        {};
+    bool is_external() const;
+    bool is_internal_contour() const;
+};
+
+class PerimeterGenerator {
+    public:
+    SurfaceCollection* slices;
+    ExPolygonCollection* lower_slices;
+    double layer_height;
+    int layer_id;
+    Flow perimeter_flow;
+    Flow ext_perimeter_flow;
+    Flow overhang_flow;
+    Flow solid_infill_flow;
+    PrintRegionConfig* config;
+    PrintObjectConfig* object_config;
+    PrintConfig* print_config;
+    ExtrusionEntityCollection* loops;
+    ExtrusionEntityCollection* gap_fill;
+    SurfaceCollection* fill_surfaces;
+    
+    PerimeterGenerator(SurfaceCollection* slices, double layer_height, Flow flow,
+        PrintRegionConfig* config, PrintObjectConfig* object_config, 
+        PrintConfig* print_config, ExtrusionEntityCollection* loops, 
+        ExtrusionEntityCollection* gap_fill, SurfaceCollection* fill_surfaces)
+        : slices(slices), lower_slices(NULL), layer_height(layer_height),
+            perimeter_flow(flow), ext_perimeter_flow(flow), overhang_flow(flow),
+            solid_infill_flow(flow), layer_id(-1),
+            config(config), object_config(object_config), print_config(print_config),
+            loops(loops), gap_fill(gap_fill), fill_surfaces(fill_surfaces),
+            _ext_mm3_per_mm(-1), _mm3_per_mm(-1), _mm3_per_mm_overhang(-1)
+        {};
+    void process();
+    
+    private:
+    double _ext_mm3_per_mm;
+    double _mm3_per_mm;
+    double _mm3_per_mm_overhang;
+    Polygons _lower_slices_p;
+    
+    ExtrusionEntityCollection _traverse_loops(const PerimeterGeneratorLoops &loops,
+        Polylines &thin_walls) const;
+    ExtrusionEntityCollection _fill_gaps(double min, double max, double w,
+        const Polygons &gaps) const;
+};
+
+class PerimeterGeneratorGapSize {
+    public:
+    coord_t min;
+    coord_t max;
+    coord_t width;
+    PerimeterGeneratorGapSize(coord_t min, coord_t max, coord_t width)
+        : min(min), max(max), width(width) {};
+};
+
+}
+
+#endif
diff --git a/xs/src/libslic3r/libslic3r.h b/xs/src/libslic3r/libslic3r.h
index fcf90f133..87d98caf1 100644
--- a/xs/src/libslic3r/libslic3r.h
+++ b/xs/src/libslic3r/libslic3r.h
@@ -15,6 +15,7 @@
 #define PI 3.141592653589793238
 #define LOOP_CLIPPING_LENGTH_OVER_NOZZLE_DIAMETER 0.15
 #define SMALL_PERIMETER_LENGTH (6.5 / SCALING_FACTOR) * 2 * PI
+#define INSET_OVERLAP_TOLERANCE 0.4
 #define scale_(val) (val / SCALING_FACTOR)
 #define unscale(val) (val * SCALING_FACTOR)
 #define SCALED_EPSILON scale_(EPSILON)
diff --git a/xs/xsp/ExtrusionEntityCollection.xsp b/xs/xsp/ExtrusionEntityCollection.xsp
index b7e439479..7570d078a 100644
--- a/xs/xsp/ExtrusionEntityCollection.xsp
+++ b/xs/xsp/ExtrusionEntityCollection.xsp
@@ -7,6 +7,7 @@
 
 %name{Slic3r::ExtrusionPath::Collection} class ExtrusionEntityCollection {
     %name{_new} ExtrusionEntityCollection();
+    ~ExtrusionEntityCollection();
     Clone<ExtrusionEntityCollection> clone()
         %code{% RETVAL = THIS->clone(); %};
     void reverse();
@@ -41,14 +42,6 @@
     Polygons grow();
 %{
 
-void
-ExtrusionEntityCollection::DESTROY()
-    CODE:
-        for (ExtrusionEntitiesPtr::iterator it = THIS->entities.begin(); it != THIS->entities.end(); ++it) {
-            delete *it;
-        }
-        delete THIS;
-
 SV*
 ExtrusionEntityCollection::arrayref()
     CODE:
diff --git a/xs/xsp/PerimeterGenerator.xsp b/xs/xsp/PerimeterGenerator.xsp
new file mode 100644
index 000000000..351c6f4c0
--- /dev/null
+++ b/xs/xsp/PerimeterGenerator.xsp
@@ -0,0 +1,34 @@
+%module{Slic3r::XS};
+
+%{
+#include <myinit.h>
+#include "libslic3r/PerimeterGenerator.hpp"
+%}
+
+%name{Slic3r::Layer::PerimeterGenerator} class PerimeterGenerator {
+    PerimeterGenerator(SurfaceCollection* slices, double layer_height, Flow* flow,
+        PrintRegionConfig* config, PrintObjectConfig* object_config, 
+        PrintConfig* print_config, ExtrusionEntityCollection* loops, 
+        ExtrusionEntityCollection* gap_fill, SurfaceCollection* fill_surfaces)
+        %code{% RETVAL = new PerimeterGenerator(slices, layer_height, *flow,
+            config, object_config, print_config, loops, gap_fill, fill_surfaces); %};
+    ~PerimeterGenerator();
+    
+    void set_lower_slices(ExPolygonCollection* lower_slices)
+        %code{% THIS->lower_slices = lower_slices; %};
+    void set_layer_id(int layer_id)
+        %code{% THIS->layer_id = layer_id; %};
+    void set_perimeter_flow(Flow* flow)
+        %code{% THIS->perimeter_flow = *flow; %};
+    void set_ext_perimeter_flow(Flow* flow)
+        %code{% THIS->ext_perimeter_flow = *flow; %};
+    void set_overhang_flow(Flow* flow)
+        %code{% THIS->overhang_flow = *flow; %};
+    void set_solid_infill_flow(Flow* flow)
+        %code{% THIS->solid_infill_flow = *flow; %};
+    
+    Ref<PrintRegionConfig> config()
+        %code{% RETVAL = THIS->config; %};
+    
+    void process();
+};
diff --git a/xs/xsp/my.map b/xs/xsp/my.map
index af6f9f042..1f59b3fa0 100644
--- a/xs/xsp/my.map
+++ b/xs/xsp/my.map
@@ -198,6 +198,10 @@ BridgeDetector*            O_OBJECT_SLIC3R
 Ref<BridgeDetector>        O_OBJECT_SLIC3R_T
 Clone<BridgeDetector>      O_OBJECT_SLIC3R_T
 
+PerimeterGenerator*         O_OBJECT_SLIC3R
+Ref<PerimeterGenerator>     O_OBJECT_SLIC3R_T
+Clone<PerimeterGenerator>   O_OBJECT_SLIC3R_T
+
 GLVertexArray*             O_OBJECT_SLIC3R
 
 Axis                  T_UV
diff --git a/xs/xsp/typemap.xspt b/xs/xsp/typemap.xspt
index 8b4eb0850..6c7beb17f 100644
--- a/xs/xsp/typemap.xspt
+++ b/xs/xsp/typemap.xspt
@@ -94,6 +94,12 @@
 %typemap{BridgeDetector*};
 %typemap{Ref<BridgeDetector>}{simple};
 %typemap{Clone<BridgeDetector>}{simple};
+%typemap{SurfaceCollection*};
+%typemap{Ref<SurfaceCollection>}{simple};
+%typemap{Clone<SurfaceCollection>}{simple};
+%typemap{PerimeterGenerator*};
+%typemap{Ref<PerimeterGenerator>}{simple};
+%typemap{Clone<PerimeterGenerator>}{simple};
 
 %typemap{Surface*};
 %typemap{Ref<Surface>}{simple};
@@ -153,7 +159,6 @@
 %typemap{Polygons*};
 %typemap{TriangleMesh*};
 %typemap{TriangleMeshPtrs};
-%typemap{Ref<SurfaceCollection>}{simple};
 %typemap{Extruder*};
 %typemap{Ref<Extruder>}{simple};
 %typemap{Clone<Extruder>}{simple};