diff --git a/lib/Slic3r.pm b/lib/Slic3r.pm
index 0bf56a08..f72dd1ea 100644
--- a/lib/Slic3r.pm
+++ b/lib/Slic3r.pm
@@ -3,6 +3,7 @@ package Slic3r;
 use strict;
 use warnings;
 
+use Slic3r::ExtrusionPath;
 use Slic3r::Layer;
 use Slic3r::Line;
 use Slic3r::Perimeter;
diff --git a/lib/Slic3r/ExtrusionPath.pm b/lib/Slic3r/ExtrusionPath.pm
new file mode 100644
index 00000000..e462956f
--- /dev/null
+++ b/lib/Slic3r/ExtrusionPath.pm
@@ -0,0 +1,6 @@
+package Slic3r::ExtrusionPath;
+use Moose;
+
+extends 'Slic3r::Polyline';
+
+1;
diff --git a/lib/Slic3r/Layer.pm b/lib/Slic3r/Layer.pm
index 733caa4b..933c5e6b 100644
--- a/lib/Slic3r/Layer.pm
+++ b/lib/Slic3r/Layer.pm
@@ -3,12 +3,16 @@ use Moose;
 
 use XXX;
 
+# a sequential number of layer, starting at 0
 has 'id' => (
     is          => 'ro',
     isa         => 'Int',
     required    => 1,
 );
 
+# index of points generated by slicing the original geometry
+# keys are stringified coordinates (example: "0,0")
+# each points connects exactly two segments
 has 'pointmap' => (
     traits      => ['Hash'],
     is          => 'rw',
@@ -19,12 +23,15 @@ has 'pointmap' => (
     },
 );
 
+# collection of segments generated by slicing the original geometry
+# each segment is part of a closed polyline
 has 'lines' => (
     is      => 'rw',
     isa     => 'ArrayRef[Slic3r::Line]',
     default => sub { [] },
 );
 
+# collection of surfaces generated by slicing the original geometry
 has 'surfaces' => (
     traits  => ['Array'],
     is      => 'rw',
@@ -32,9 +39,19 @@ has 'surfaces' => (
     default => sub { [] },
 );
 
+# ordered collection of extrusion paths to build all perimeters
 has 'perimeters' => (
     is      => 'rw',
-    isa     => 'ArrayRef[Slic3r::Polyline]',
+    isa     => 'ArrayRef[Slic3r::ExtrusionPath]',
+    default => sub { [] },
+);
+
+# collection of surfaces generated by offsetting the innermost perimeter(s)
+# they represent boundaries of areas to fill
+has 'fill_surfaces' => (
+    traits  => ['Array'],
+    is      => 'rw',
+    isa     => 'ArrayRef[Slic3r::Surface]',
     default => sub { [] },
 );
 
diff --git a/lib/Slic3r/Perimeter.pm b/lib/Slic3r/Perimeter.pm
index 8d6beda7..ce6a8409 100644
--- a/lib/Slic3r/Perimeter.pm
+++ b/lib/Slic3r/Perimeter.pm
@@ -29,34 +29,22 @@ sub make_perimeter {
         
         # create other offsets
         for (my $loop = 1; $loop < $Slic3r::perimeter_offsets; $loop++) {
-            my ($contour_p, @holes_p) = map $self->_mgp_from_points_ref($_), @{ $perimeters[-1]->polygons };
             
-            # generate offsets
-            my $contour_offsets = $contour_p->offset_polygon($Slic3r::flow_width / $Slic3r::resolution);
-            my @hole_offsets = map @$_, map $_->offset_polygon(- $Slic3r::flow_width / $Slic3r::resolution), @holes_p;
+            # offsetting a polygon can result in one or many offset polygons
+            my @offsets = $self->offset_polygon($perimeters[-1]);
             
-            # now we subtract perimeter offsets from the contour offset polygon
-            # this will generate a single polygon with correct holes and also
-            # will take care of collisions between contour offset and holes
-            foreach my $contour_points (@$contour_offsets) {
-                my $tmp = $self->_mgp_from_points_ref($contour_points)->convert2gpc;
-                foreach my $hole_points (@hole_offsets) {
-                    $hole_points = $self->_mgp_from_points_ref($hole_points)->convert2gpc;
-                    $tmp = GpcClip('DIFFERENCE', $tmp, $hole_points);
-                }
+            foreach my $offset_polygon (@offsets) {
+                my ($contour_p, @holes_p) = @{ $offset_polygon->polygons };
                 
-                my ($result) = Gpc2Polygons($tmp);
-                # now we've got $result, which is a Math::Geometry::Planar
-                # representing the inner surface including hole perimeters
-                
-                my $result_polylines = $result->polygons;
-                
-                ($contour_p, @holes_p) = @$result_polylines;
                 push @{ $contours{$surface} }, $contour_p;
                 push @{ $holes{$surface} }, @holes_p;
-                push @perimeters, $result;
+                push @perimeters, $offset_polygon;
             }
         }
+        
+        # create one more offset to be used as boundary for fill
+        push @{ $layer->fill_surfaces }, 
+            map Slic3r::Surface->new_from_mgp($_), $self->offset_polygon($perimeters[-1]);
     }
     
     # generate paths for holes
@@ -82,10 +70,42 @@ sub make_perimeter {
             # away from it to avoid the extruder to get two times there
             push @path_points, @$points, $points->[0];
         }
-        push @{ $layer->perimeters }, Slic3r::Polyline->new_from_points(reverse @path_points);
+        push @{ $layer->perimeters }, Slic3r::ExtrusionPath->new_from_points(reverse @path_points);
     }
 }
 
+sub offset_polygon {
+    my $self = shift;
+    my ($polygon) = @_;
+    
+    # $polygon holds a Math::Geometry::Planar object representing 
+    # a polygon and its holes
+    my ($contour_p, @holes_p) = map $self->_mgp_from_points_ref($_), @{ $polygon->polygons };
+            
+    # generate offsets
+    my $contour_offsets = $contour_p->offset_polygon($Slic3r::flow_width / $Slic3r::resolution);
+    my @hole_offsets = map @$_, map $_->offset_polygon(- $Slic3r::flow_width / $Slic3r::resolution), @holes_p;
+    
+    # now we subtract perimeter offsets from the contour offset polygon
+    # this will generate a single polygon with correct holes and also
+    # will take care of collisions between contour offset and holes
+    my @resulting_offsets = ();
+    foreach my $contour_points (@$contour_offsets) {
+        my $tmp = $self->_mgp_from_points_ref($contour_points)->convert2gpc;
+        foreach my $hole_points (@hole_offsets) {
+            $hole_points = $self->_mgp_from_points_ref($hole_points)->convert2gpc;
+            $tmp = GpcClip('DIFFERENCE', $tmp, $hole_points);
+        }
+        
+        my ($result) = Gpc2Polygons($tmp);
+        # now we've got $result, which is a Math::Geometry::Planar
+        # representing the inner surface including hole perimeters
+        push @resulting_offsets, $result;
+    }
+    
+    return @resulting_offsets;
+}
+
 sub _mgp_from_points_ref {
     my $self = shift;
     my ($points) = @_;
diff --git a/lib/Slic3r/Polyline.pm b/lib/Slic3r/Polyline.pm
index 27c1e543..592e5d31 100644
--- a/lib/Slic3r/Polyline.pm
+++ b/lib/Slic3r/Polyline.pm
@@ -40,7 +40,7 @@ sub new_from_points {
             : $_
     } @points;
     
-    my $polyline = __PACKAGE__->new;
+    my $polyline = $class->new;
     my $previous_point;
     $previous_point = $points[-1] if $class eq 'Slic3r::Polyline::Closed';
     foreach my $point (@points) {
diff --git a/lib/Slic3r/Surface.pm b/lib/Slic3r/Surface.pm
index d8ab0ddc..5333a7eb 100644
--- a/lib/Slic3r/Surface.pm
+++ b/lib/Slic3r/Surface.pm
@@ -42,6 +42,20 @@ sub BUILD {
     $_->hole_of($self) for @{ $self->holes };
 }
 
+sub new_from_mgp {
+    my $self = shift;
+    my ($polygon) = @_;
+    
+    my ($contour_p, @holes_p) = @{ $polygon->polygons };
+    
+    return __PACKAGE__->new(
+        contour => Slic3r::Polyline::Closed->new_from_points(@$contour_p),
+        holes   => [
+            map Slic3r::Polyline::Closed->new_from_points(@$_), @holes_p
+        ],
+    );
+}
+
 sub id {
     my $self = shift;
     return $self->contour->id;