diff --git a/MANIFEST b/MANIFEST
index 64d93f3687..c4c53288cc 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -35,6 +35,7 @@ lib/Slic3r/GUI/SkeinPanel.pm
 lib/Slic3r/GUI/Tab.pm
 lib/Slic3r/Layer.pm
 lib/Slic3r/Line.pm
+lib/Slic3r/Model.pm
 lib/Slic3r/Point.pm
 lib/Slic3r/Polygon.pm
 lib/Slic3r/Polyline.pm
diff --git a/README.markdown b/README.markdown
index a335f0cb94..1dfe6552b1 100644
--- a/README.markdown
+++ b/README.markdown
@@ -9,8 +9,8 @@ A: Yes.
 Slic3r is a G-code generator for 3D printers. It's compatible with RepRaps,
 Makerbots, Ultimakers and many more machines.
 
-See the [project homepage](http://slic3r.org/) at slic3r.org
-for more information.
+See the [project homepage](http://slic3r.org/) at slic3r.org and the
+[documentation](https://github.com/alexrj/Slic3r/wiki/Documentation) on the Slic3r wiki for more information.
 
 ## What language is it written in?
 
@@ -170,6 +170,9 @@ The author of the Silk icon set is Mark James.
         --layer-gcode       Load layer-change G-code from the supplied file (default: nothing).
         --extra-perimeters  Add more perimeters when needed (default: yes)
         --randomize-start   Randomize starting point across layers (default: yes)
+        --only-retract-when-crossing-perimeters
+                            Disable retraction when travelling between infill paths inside the same island.
+                            (default: no)
         --solid-infill-below-area
                             Force solid infill when a region has a smaller area than this threshold
                             (mm^2, default: 70)
@@ -272,38 +275,3 @@ If you want to change a preset file, just do
 If you want to slice a file overriding an option contained in your preset file:
 
     slic3r.pl --load config.ini --layer-height 0.25 file.stl
-
-## How can I integrate Slic3r with Pronterface?
-
-Put this into *slicecommand*:
-
-    slic3r.pl $s --load config.ini --output $o
-
-And this into *sliceoptscommand*:
-
-    slic3r.pl --load config.ini --ignore-nonexistent-config
-
-Replace `slic3r.pl` with the full path to the slic3r executable and `config.ini`
-with the full path of your config file (put it in your home directory or where
-you like).
-On Mac, the executable has a path like this:
-
-    /Applications/Slic3r.app/Contents/MacOS/slic3r
-
-## How can I specify a custom filename format for output G-code files?
-
-You can specify a filename format by using any of the config options. 
-Just enclose them in square brackets, and Slic3r will replace them upon
-exporting.
-The additional `[input_filename]` and `[input_filename_base]` options will
-be replaced by the input file name (in the second case, the .stl extension 
-is stripped).
-
-The default format is `[input_filename_base].gcode`, meaning that if you slice
-a *foo.stl* file, the output will be saved to *foo.gcode*.
-
-See below for more complex examples:
-
-    [input_filename_base]_h[layer_height]_p[perimeters]_s[solid_layers].gcode
-    [input_filename]_center[print_center]_[layer_height]layers.gcode
-
diff --git a/lib/Slic3r.pm b/lib/Slic3r.pm
index dc97761213..f6bd643c46 100644
--- a/lib/Slic3r.pm
+++ b/lib/Slic3r.pm
@@ -7,7 +7,7 @@ use strict;
 use warnings;
 require v5.10;
 
-our $VERSION = "0.9.2-dev";
+our $VERSION = "0.9.3-dev";
 
 our $debug = 0;
 sub debugf {
@@ -21,6 +21,9 @@ BEGIN {
     $have_threads = $Config{useithreads} && eval "use threads; use Thread::Queue; 1";
 }
 
+warn "Running Slic3r under Perl >= 5.16 is not supported nor recommended\n"
+    if $^V >= v5.16;
+
 use FindBin;
 our $var = "$FindBin::Bin/var";
 
@@ -41,6 +44,7 @@ use Slic3r::GCode;
 use Slic3r::Geometry qw(PI);
 use Slic3r::Layer;
 use Slic3r::Line;
+use Slic3r::Model;
 use Slic3r::Point;
 use Slic3r::Polygon;
 use Slic3r::Polyline;
diff --git a/lib/Slic3r/Config.pm b/lib/Slic3r/Config.pm
index 36aaa5ae75..5ded4a5927 100644
--- a/lib/Slic3r/Config.pm
+++ b/lib/Slic3r/Config.pm
@@ -178,6 +178,7 @@ our $Options = {
     # extruder mapping
     'perimeter_extruder' => {
         label   => 'Perimeter extruder',
+        tooltip => 'The extruder to use when printing perimeters.',
         cli     => 'perimeter-extruder=i',
         type    => 'i',
         aliases => [qw(perimeters_extruder)],
@@ -185,12 +186,14 @@ our $Options = {
     },
     'infill_extruder' => {
         label   => 'Infill extruder',
+        tooltip => 'The extruder to use when printing infill.',
         cli     => 'infill-extruder=i',
         type    => 'i',
         default => 1,
     },
     'support_material_extruder' => {
         label   => 'Support material extruder',
+        tooltip => 'The extruder to use when printing support material. This affects brim too.',
         cli     => 'support-material-extruder=i',
         type    => 'i',
         default => 1,
@@ -470,6 +473,13 @@ our $Options = {
         type    => 'bool',
         default => 1,
     },
+    'only_retract_when_crossing_perimeters' => {
+        label   => 'Only retract when crossing perimeters',
+        tooltip => 'Disables retraction when travelling between infill paths inside the same island.',
+        cli     => 'only-retract-when-crossing-perimeters!',
+        type    => 'bool',
+        default => 0,
+    },
     'support_material' => {
         label   => 'Generate support material',
         tooltip => 'Enable support material generation.',
diff --git a/lib/Slic3r/ExPolygon.pm b/lib/Slic3r/ExPolygon.pm
index ed572d694a..26f0d471b9 100644
--- a/lib/Slic3r/ExPolygon.pm
+++ b/lib/Slic3r/ExPolygon.pm
@@ -61,13 +61,12 @@ sub boost_polygon {
 
 sub offset {
     my $self = shift;
-    my ($distance, $scale, $joinType, $miterLimit) = @_;
-    $scale      ||= &Slic3r::SCALING_FACTOR * 1000000;
-    $joinType   = JT_MITER if !defined $joinType;
-    $miterLimit ||= 2;
-    
-    my $offsets = Math::Clipper::offset($self, $distance, $scale, $joinType, $miterLimit);
-    return @$offsets;
+    return Slic3r::Geometry::Clipper::offset($self, @_);
+}
+
+sub offset_ex {
+    my $self = shift;
+    return Slic3r::Geometry::Clipper::offset_ex($self, @_);
 }
 
 sub safety_offset {
diff --git a/lib/Slic3r/Fill.pm b/lib/Slic3r/Fill.pm
index 8068bb87e8..5c694d95e5 100644
--- a/lib/Slic3r/Fill.pm
+++ b/lib/Slic3r/Fill.pm
@@ -170,7 +170,7 @@ sub make_fill {
                             ? ($surface->surface_type == S_TYPE_TOP ? EXTR_ROLE_TOPSOLIDFILL : EXTR_ROLE_SOLIDFILL)
                             : EXTR_ROLE_FILL),
                     depth_layers => $surface->depth_layers,
-                    flow_spacing => $params->{flow_spacing} || $flow_spacing,
+                    flow_spacing => $params->{flow_spacing} || (warn "Warning: no flow_spacing was returned by the infill engine, please report this to the developer\n"),
                 ), @paths,
             ],
         );
diff --git a/lib/Slic3r/Fill/Concentric.pm b/lib/Slic3r/Fill/Concentric.pm
index 94866e2aea..c0d172cfe3 100644
--- a/lib/Slic3r/Fill/Concentric.pm
+++ b/lib/Slic3r/Fill/Concentric.pm
@@ -18,7 +18,7 @@ sub fill_surface {
     my $min_spacing = scale $params{flow_spacing};
     my $distance = $min_spacing / $params{density};
     
-    my $flow_spacing;
+    my $flow_spacing = $params{flow_spacing};
     if ($params{density} == 1) {
         $distance = $self->adjust_solid_spacing(
             width       => $bounding_box->[X2] - $bounding_box->[X1],
diff --git a/lib/Slic3r/Fill/Honeycomb.pm b/lib/Slic3r/Fill/Honeycomb.pm
index 229c725686..1e407e2e6e 100644
--- a/lib/Slic3r/Fill/Honeycomb.pm
+++ b/lib/Slic3r/Fill/Honeycomb.pm
@@ -94,7 +94,8 @@ sub fill_surface {
         paths => [ map Slic3r::ExtrusionPath->pack(polyline => $_, role => -1), @paths ],
     );
     
-    return {}, map $_->polyline, $collection->shortest_path;
+    return { flow_spacing => $params{flow_spacing} },
+        map $_->polyline, $collection->shortest_path;
 }
 
 1;
diff --git a/lib/Slic3r/Fill/PlanePath.pm b/lib/Slic3r/Fill/PlanePath.pm
index daeb13deae..d33b6e6fc3 100644
--- a/lib/Slic3r/Fill/PlanePath.pm
+++ b/lib/Slic3r/Fill/PlanePath.pm
@@ -60,7 +60,7 @@ sub fill_surface {
     # paths must be rotated back
     $self->rotate_points_back(\@paths, $rotate_vector);
     
-    return {}, @paths;
+    return { flow_spacing => $params{flow_spacing} }, @paths;
 }
 
 1;
diff --git a/lib/Slic3r/Fill/Rectilinear.pm b/lib/Slic3r/Fill/Rectilinear.pm
index 2de7872a6d..121249eaa8 100644
--- a/lib/Slic3r/Fill/Rectilinear.pm
+++ b/lib/Slic3r/Fill/Rectilinear.pm
@@ -3,7 +3,7 @@ use Moo;
 
 extends 'Slic3r::Fill::Base';
 
-use Slic3r::Geometry qw(X1 Y1 X2 Y2 A B X Y scale unscale epsilon);
+use Slic3r::Geometry qw(X1 Y1 X2 Y2 A B X Y scale unscale scaled_epsilon);
 
 sub fill_surface {
     my $self = shift;
@@ -22,7 +22,7 @@ sub fill_surface {
     my $distance_between_lines = $min_spacing / $params{density};
     my $line_oscillation = $distance_between_lines - $min_spacing;
     
-    my $flow_spacing;
+    my $flow_spacing = $params{flow_spacing};
     if ($params{density} == 1) {
         $distance_between_lines = $self->adjust_solid_spacing(
             width       => $bounding_box->[X2] - $bounding_box->[X1],
@@ -36,7 +36,7 @@ sub fill_surface {
     my $x = $bounding_box->[X1];
     my $is_line_pattern = $self->isa('Slic3r::Fill::Line');
     my @vertical_lines = ();
-    for (my $i = 0; $x <= $bounding_box->[X2] + scale epsilon; $i++) {
+    for (my $i = 0; $x <= $bounding_box->[X2] + scaled_epsilon; $i++) {
         my $vertical_line = Slic3r::Line->new([$x, $bounding_box->[Y2]], [$x, $bounding_box->[Y1]]);
         if ($is_line_pattern && $i % 2) {
             $vertical_line->[A][X] += $line_oscillation;
@@ -49,7 +49,7 @@ sub fill_surface {
     # clip paths against a slightly offsetted expolygon, so that the first and last paths
     # are kept even if the expolygon has vertical sides
     my @paths = @{ Boost::Geometry::Utils::polygon_linestring_intersection(
-        +($expolygon->offset_ex(scale epsilon))[0]->boost_polygon,  # TODO: we should use all the resulting expolygons and clip the linestrings to a multipolygon object
+        +($expolygon->offset_ex(scaled_epsilon))[0]->boost_polygon,  # TODO: we should use all the resulting expolygons and clip the linestrings to a multipolygon object
         Boost::Geometry::Utils::linestring(@vertical_lines),
     ) };
     for (@paths) {
@@ -64,7 +64,7 @@ sub fill_surface {
         );
         @paths = ();
         
-        my $tolerance = 10 * scale epsilon;
+        my $tolerance = 10 * scaled_epsilon;
         my $diagonal_distance = $distance_between_lines * 5;
         my $can_connect = $is_line_pattern
             ? sub {
diff --git a/lib/Slic3r/Format/AMF.pm b/lib/Slic3r/Format/AMF.pm
index ce388ec2ec..552f1fdbd9 100644
--- a/lib/Slic3r/Format/AMF.pm
+++ b/lib/Slic3r/Format/AMF.pm
@@ -12,28 +12,18 @@ sub read_file {
     
     open my $fh, '<', $file or die "Failed to open $file\n";
     
-    my $vertices = [];
-    my $materials = {};
-    my $meshes_by_material = {};
+    my $model = Slic3r::Model->new;
     XML::SAX::PurePerl
-        ->new(Handler => Slic3r::Format::AMF::Parser->new(
-            _vertices           => $vertices,
-            _materials          => $materials,
-            _meshes_by_material => $meshes_by_material,
-         ))
+        ->new(Handler => Slic3r::Format::AMF::Parser->new(_model => $model))
         ->parse_file($fh);
-    
     close $fh;
     
-    $_ = Slic3r::TriangleMesh->new(vertices => $vertices, facets => $_)
-        for values %$meshes_by_material;
-    
-    return $materials, $meshes_by_material;
+    return $model;
 }
 
 sub write_file {
     my $self = shift;
-    my ($file, $materials, $meshes_by_material) = @_;
+    my ($file, $model, %params) = @_;
     
     my %vertices_offset = ();
     
@@ -42,20 +32,21 @@ sub write_file {
     printf $fh qq{<?xml version="1.0" encoding="UTF-8"?>\n};
     printf $fh qq{<amf unit="millimeter">\n};
     printf $fh qq{  <metadata type="cad">Slic3r %s</metadata>\n}, $Slic3r::VERSION;
-    foreach my $material_id (keys %$materials) {
-        printf $fh qq{  <material id="%s">\n}, $material_id;
-        for (keys %{$materials->{$material_id}}) {
-             printf $fh qq{    <metadata type=\"%s\">%s</metadata>\n}, $_, $materials->{$material_id}{$_};
+    for my $material_id (sort keys %{ $model->materials }) {
+        my $material = $model->materials->{$material_id};
+        printf $fh qq{  <material id="%d">\n}, $material_id;
+        for (keys %$material) {
+             printf $fh qq{    <metadata type=\"%s\">%s</metadata>\n}, $_, $material->{$_};
         }
         printf $fh qq{  </material>\n};
     }
-    printf $fh qq{  <object id="0">\n};
-    printf $fh qq{    <mesh>\n};
-    printf $fh qq{      <vertices>\n};
-    my $vertices_count = 0;
-    foreach my $mesh (values %$meshes_by_material) {
-        $vertices_offset{$mesh} = $vertices_count;
-        foreach my $vertex (@{$mesh->vertices}, ) {
+    my $instances = '';
+    for my $object_id (0 .. $#{ $model->objects }) {
+        my $object = $model->objects->[$object_id];
+        printf $fh qq{  <object id="%d">\n}, $object_id;
+        printf $fh qq{    <mesh>\n};
+        printf $fh qq{      <vertices>\n};
+        foreach my $vertex (@{$object->vertices}, ) {
             printf $fh qq{        <vertex>\n};
             printf $fh qq{          <coordinates>\n};
             printf $fh qq{            <x>%s</x>\n}, $vertex->[X];
@@ -63,24 +54,35 @@ sub write_file {
             printf $fh qq{            <z>%s</z>\n}, $vertex->[Z];
             printf $fh qq{          </coordinates>\n};
             printf $fh qq{        </vertex>\n};
-            $vertices_count++;
+        }
+        printf $fh qq{      </vertices>\n};
+        foreach my $volume (@{ $object->volumes }) {
+            printf $fh qq{      <volume%s>\n},
+                (!defined $volume->material_id) ? '' : (sprintf ' materialid="%s"', $volume->material_id);
+            foreach my $facet (@{$volume->facets}) {
+                printf $fh qq{        <triangle>\n};
+                printf $fh qq{          <v%d>%d</v%d>\n}, (4+$_), $facet->[$_], (4+$_) for -3..-1;
+                printf $fh qq{        </triangle>\n};
+            }
+            printf $fh qq{      </volume>\n};
+        }
+        printf $fh qq{    </mesh>\n};
+        printf $fh qq{  </object>\n};
+        if ($object->instances) {
+            foreach my $instance (@{$object->instances}) {
+                $instances .= sprintf qq{    <instance objectid="%d">\n}, $object_id;
+                $instances .= sprintf qq{      <deltax>%s</deltax>\n}, $instance->offset->[X];
+                $instances .= sprintf qq{      <deltax>%s</deltax>\n}, $instance->offset->[Y];
+                $instances .= sprintf qq{      <rz>%s</rz>\n}, $instance->rotation;
+                $instances .= sprintf qq{    </instance>\n};
+            }
         }
     }
-    printf $fh qq{      </vertices>\n};
-    foreach my $material_id (sort keys %$meshes_by_material) {
-        my $mesh = $meshes_by_material->{$material_id};
-        printf $fh qq{      <volume%s>\n},
-            ($material_id eq '_') ? '' : " materialid=\"$material_id\"";
-        foreach my $facet (@{$mesh->facets}) {
-            printf $fh qq{        <triangle>\n};
-            printf $fh qq{          <v%d>%d</v%d>\n}, $_, $facet->[$_] + $vertices_offset{$mesh}, $_
-                for -3..-1;
-            printf $fh qq{        </triangle>\n};
-        }
-        printf $fh qq{      </volume>\n};
+    if ($instances) {
+        printf $fh qq{  <constellation id="1">\n};
+        printf $fh $instances;
+        printf $fh qq{  </constellation>\n};
     }
-    printf $fh qq{    </mesh>\n};
-    printf $fh qq{  </object>\n};
     printf $fh qq{</amf>\n};
     close $fh;
 }
diff --git a/lib/Slic3r/Format/AMF/Parser.pm b/lib/Slic3r/Format/AMF/Parser.pm
index 1d8d4dc396..93b35765eb 100644
--- a/lib/Slic3r/Format/AMF/Parser.pm
+++ b/lib/Slic3r/Format/AMF/Parser.pm
@@ -11,6 +11,8 @@ my %xyz_index = (x => 0, y => 1, z => 2); #=
 sub new {
     my $self = shift->SUPER::new(@_);
     $self->{_tree} = [];
+    $self->{_objects_map} = {};  # this hash maps AMF object IDs to object indexes in $model->objects
+    $self->{_instances} = {};   # apply these lazily to make sure all objects have been parsed
     $self;
 }
 
@@ -18,23 +20,35 @@ sub start_element {
     my $self = shift;
     my $data = shift;
     
-    if ($data->{LocalName} eq 'vertex') {
+    if ($data->{LocalName} eq 'object') {
+        $self->{_object} = $self->{_model}->add_object;
+        $self->{_objects_map}{ $self->_get_attribute($data, 'id') } = $#{ $self->{_model}->objects };
+    } elsif ($data->{LocalName} eq 'vertex') {
         $self->{_vertex} = ["", "", ""];
     } elsif ($self->{_vertex} && $data->{LocalName} =~ /^[xyz]$/ && $self->{_tree}[-1] eq 'coordinates') {
         $self->{_coordinate} = $data->{LocalName};
     } elsif ($data->{LocalName} eq 'volume') {
-        $self->{_volume_materialid} = $self->_get_attribute($data, 'materialid') || '_';
-        $self->{_volume} = [];
+        $self->{_volume} = $self->{_object}->add_volume(
+            material_id => $self->_get_attribute($data, 'materialid') || undef,
+        );
     } elsif ($data->{LocalName} eq 'triangle') {
         $self->{_triangle} = ["", "", ""];
     } elsif ($self->{_triangle} && $data->{LocalName} =~ /^v([123])$/ && $self->{_tree}[-1] eq 'triangle') {
         $self->{_vertex_idx} = $1-1;
     } elsif ($data->{LocalName} eq 'material') {
-        $self->{_material_id} = $self->_get_attribute($data, 'id') || '_';
-        $self->{_material} = {};
+        my $material_id = $self->_get_attribute($data, 'id') || '_';
+        $self->{_material} = $self->{_model}->materials->{ $material_id } = {};
     } elsif ($data->{LocalName} eq 'metadata' && $self->{_tree}[-1] eq 'material') {
         $self->{_material_metadata_type} = $self->_get_attribute($data, 'type');
         $self->{_material}{ $self->{_material_metadata_type} } = "";
+    } elsif ($data->{LocalName} eq 'constellation') {
+        $self->{_constellation} = 1; # we merge all constellations as we don't support more than one
+    } elsif ($data->{LocalName} eq 'instance' && $self->{_constellation}) {
+        my $object_id = $self->_get_attribute($data, 'objectid');
+        $self->{_instances}{$object_id} ||= [];
+        push @{ $self->{_instances}{$object_id} }, $self->{_instance} = {};
+    } elsif ($data->{LocalName} =~ /^(?:deltax|deltay|rz)$/ && $self->{_instance}) {
+        $self->{_instance_property} = $data->{LocalName};
     }
     
     push @{$self->{_tree}}, $data->{LocalName};
@@ -50,6 +64,8 @@ sub characters {
         $self->{_triangle}[ $self->{_vertex_idx} ] .= $data->{Data};
     } elsif ($self->{_material_metadata_type}) {
         $self->{_material}{ $self->{_material_metadata_type} } .= $data->{Data};
+    } elsif ($self->{_instance_property}) {
+        $self->{_instance}{ $self->{_instance_property} } .= $data->{Data};
     }
 }
 
@@ -59,26 +75,49 @@ sub end_element {
     
     pop @{$self->{_tree}};
     
-    if ($data->{LocalName} eq 'vertex') {
-        push @{$self->{_vertices}}, $self->{_vertex};
+    if ($data->{LocalName} eq 'object') {
+        $self->{_object} = undef;
+    } elsif ($data->{LocalName} eq 'vertex') {
+        push @{$self->{_object}->vertices}, $self->{_vertex};
         $self->{_vertex} = undef;
     } elsif ($self->{_coordinate} && $data->{LocalName} =~ /^[xyz]$/) {
         $self->{_coordinate} = undef;
     } elsif ($data->{LocalName} eq 'volume') {
-        $self->{_meshes_by_material}{ $self->{_volume_materialid} } ||= [];
-        push @{ $self->{_meshes_by_material}{ $self->{_volume_materialid} } }, @{$self->{_volume}};
         $self->{_volume} = undef;
     } elsif ($data->{LocalName} eq 'triangle') {
-        push @{$self->{_volume}}, $self->{_triangle};
+        push @{$self->{_volume}->facets}, $self->{_triangle};
         $self->{_triangle} = undef;
-    } elsif ($self->{_vertex_idx} && $data->{LocalName} =~ /^v[123]$/) {
+    } elsif (defined $self->{_vertex_idx} && $data->{LocalName} =~ /^v[123]$/) {
         $self->{_vertex_idx} = undef;
     } elsif ($data->{LocalName} eq 'material') {
-        $self->{_materials}{ $self->{_material_id} } = $self->{_material};
-        $self->{_material_id} = undef;
         $self->{_material} = undef;
     } elsif ($data->{LocalName} eq 'metadata' && $self->{_material}) {
         $self->{_material_metadata_type} = undef;
+    } elsif ($data->{LocalName} eq 'constellation') {
+        $self->{_constellation} = undef;
+    } elsif ($data->{LocalName} eq 'instance') {
+        $self->{_instance} = undef;
+    } elsif ($data->{LocalName} =~ /^(?:deltax|deltay|rz)$/ && $self->{_instance}) {
+        $self->{_instance_property} = undef;
+    }
+}
+
+sub end_document {
+    my $self = shift;
+    
+    foreach my $object_id (keys %{ $self->{_instances} }) {
+        my $new_object_id = $self->{_objects_map}{$object_id};
+        if (!$new_object_id) {
+            warn "Undefined object $object_id referenced in constellation\n";
+            next;
+        }
+        
+        foreach my $instance (@{ $self->{_instances}{$object_id} }) {
+            $self->{_model}->objects->[$new_object_id]->add_instance(
+                rotation => $instance->{rz} || 0,
+                offset   => [ $instance->{deltax} || 0, $instance->{deltay} ],
+            );
+        }
     }
 }
 
diff --git a/lib/Slic3r/Format/OBJ.pm b/lib/Slic3r/Format/OBJ.pm
index 210853025c..d663cfb5a7 100644
--- a/lib/Slic3r/Format/OBJ.pm
+++ b/lib/Slic3r/Format/OBJ.pm
@@ -17,7 +17,10 @@ sub read_file {
     }
     close $fh;
     
-    return Slic3r::TriangleMesh->new(vertices => $vertices, facets => $facets);
+    my $model = Slic3r::Model->new;
+    my $object = $model->add_object(vertices => $vertices);
+    my $volume = $object->add_volume(facets => $facets);
+    return $model;
 }
 
 1;
diff --git a/lib/Slic3r/Format/STL.pm b/lib/Slic3r/Format/STL.pm
index 9706fd00dc..5325a4ea6f 100644
--- a/lib/Slic3r/Format/STL.pm
+++ b/lib/Slic3r/Format/STL.pm
@@ -117,7 +117,10 @@ sub read_file {
         }
     }
     
-    return Slic3r::TriangleMesh->new(vertices => $vertices, facets => $facets);
+    my $model = Slic3r::Model->new;
+    my $object = $model->add_object(vertices => $vertices);
+    my $volume = $object->add_volume(facets => $facets);
+    return $model;
 }
 
 sub _read_ascii {
@@ -161,13 +164,13 @@ sub _read_binary {
 
 sub write_file {
     my $self = shift;
-    my ($file, $mesh, $binary) = @_;
+    my ($file, $model, %params) = @_;
     
     open my $fh, '>', $file;
     
-    $binary
-        ? _write_binary($fh, $mesh)
-        : _write_ascii($fh, $mesh);
+    $params{binary}
+        ? _write_binary($fh, $model->mesh)
+        : _write_ascii($fh, $model->mesh);
     
     close $fh;
 }
diff --git a/lib/Slic3r/GCode.pm b/lib/Slic3r/GCode.pm
index b5e020ace0..4f29fa0b95 100644
--- a/lib/Slic3r/GCode.pm
+++ b/lib/Slic3r/GCode.pm
@@ -1,8 +1,9 @@
 package Slic3r::GCode;
 use Moo;
 
+use List::Util qw(first);
 use Slic3r::ExtrusionPath ':roles';
-use Slic3r::Geometry qw(scale unscale);
+use Slic3r::Geometry qw(scale unscale scaled_epsilon points_coincide PI X Y);
 
 has 'layer'              => (is => 'rw');
 has 'shift_x'            => (is => 'rw', default => sub {0} );
@@ -48,8 +49,6 @@ my %role_speeds = (
     &EXTR_ROLE_SUPPORTMATERIAL              => 'perimeter',
 );
 
-use Slic3r::Geometry qw(points_coincide PI X Y);
-
 sub extruder {
     my $self = shift;
     return $Slic3r::extruders->[$self->extruder_idx];
@@ -132,15 +131,13 @@ sub extrude_path {
     my $gcode = "";
     
     # retract if distance from previous position is greater or equal to the one
-    # specified by the user *and* to the maximum distance between infill lines
+    # specified by the user
     {
-        my $distance_from_last_pos = $self->last_pos->distance_to($path->points->[0]) * &Slic3r::SCALING_FACTOR;
-        my $distance_threshold = $self->extruder->retract_before_travel;
-        $distance_threshold = 2 * ($self->layer ? $self->layer->flow->width : $Slic3r::flow->width) / $Slic3r::Config->fill_density * sqrt(2)
-            if 0 && $Slic3r::Config->fill_density > 0 && $description =~ /fill/;
-    
-        if ($distance_from_last_pos >= $distance_threshold) {
-            $gcode .= $self->retract(travel_to => $path->points->[0]);
+        my $travel = Slic3r::Line->new($self->last_pos, $path->points->[0]);
+        if ($travel->length >= scale $self->extruder->retract_before_travel) {
+            if (!$Slic3r::Config->only_retract_when_crossing_perimeters || $path->role != EXTR_ROLE_FILL || !first { $_->expolygon->encloses_line($travel, scaled_epsilon) } @{$self->layer->slices}) {
+                $gcode .= $self->retract(travel_to => $path->points->[0]);
+            }
         }
     }
     
@@ -424,25 +421,34 @@ sub set_temperature {
     
     return "" if $wait && $Slic3r::Config->gcode_flavor eq 'makerbot';
     
-    my ($code, $comment) = $wait
+    my ($code, $comment) = ($wait && $Slic3r::Config->gcode_flavor ne 'teacup')
         ? ('M109', 'wait for temperature to be reached')
         : ('M104', 'set temperature');
-    return sprintf "$code %s%d %s; $comment\n",
+    my $gcode = sprintf "$code %s%d %s; $comment\n",
         ($Slic3r::Config->gcode_flavor eq 'mach3' ? 'P' : 'S'), $temperature,
         (defined $tool && $tool != $self->extruder_idx) ? "T$tool " : "";
+    
+    $gcode .= "M116 ; wait for temperature to be reached\n"
+        if $Slic3r::Config->gcode_flavor eq 'teacup' && $wait;
+    
+    return $gcode;
 }
 
 sub set_bed_temperature {
     my $self = shift;
     my ($temperature, $wait) = @_;
     
-    my ($code, $comment) = $wait
+    my ($code, $comment) = ($wait && $Slic3r::Config->gcode_flavor ne 'teacup')
         ? (($Slic3r::Config->gcode_flavor eq 'makerbot' ? 'M109'
-            : $Slic3r::Config->gcode_flavor eq 'teacup' ? 'M109 P1'
             : 'M190'), 'wait for bed temperature to be reached')
         : ('M140', 'set bed temperature');
-    return sprintf "$code %s%d ; $comment\n",
+    my $gcode = sprintf "$code %s%d ; $comment\n",
         ($Slic3r::Config->gcode_flavor eq 'mach3' ? 'P' : 'S'), $temperature;
+    
+    $gcode .= "M116 ; wait for bed temperature to be reached\n"
+        if $Slic3r::Config->gcode_flavor eq 'teacup' && $wait;
+    
+    return $gcode;
 }
 
 1;
diff --git a/lib/Slic3r/GUI.pm b/lib/Slic3r/GUI.pm
index 8bd7fa684e..887d353202 100644
--- a/lib/Slic3r/GUI.pm
+++ b/lib/Slic3r/GUI.pm
@@ -22,6 +22,10 @@ use constant MI_REPEAT_QUICK  => &Wx::NewId;
 use constant MI_QUICK_SAVE_AS => &Wx::NewId;
 use constant MI_SLICE_SVG     => &Wx::NewId;
 
+use constant MI_PLATER_EXPORT_GCODE => &Wx::NewId;
+use constant MI_PLATER_EXPORT_STL   => &Wx::NewId;
+use constant MI_PLATER_EXPORT_AMF   => &Wx::NewId;
+
 use constant MI_TAB_PLATER    => &Wx::NewId;
 use constant MI_TAB_PRINT     => &Wx::NewId;
 use constant MI_TAB_FILAMENT  => &Wx::NewId;
@@ -47,7 +51,7 @@ sub OnInit {
     $self->{notifier} = Slic3r::GUI::Notifier->new;
     
     # locate or create data directory
-    $datadir = Wx::StandardPaths::Get->GetUserDataDir;
+    $datadir ||= Wx::StandardPaths::Get->GetUserDataDir;
     Slic3r::debugf "Data directory: %s\n", $datadir;
     my $run_wizard = (-d $datadir) ? 0 : 1;
     for ($datadir, "$datadir/print", "$datadir/filament", "$datadir/printer") {
@@ -98,6 +102,17 @@ sub OnInit {
         EVT_MENU($frame, wxID_EXIT, sub {$_[0]->Close(0)});
     }
     
+    # Plater menu
+    my $platerMenu = Wx::Menu->new;
+    {
+        $platerMenu->Append(MI_PLATER_EXPORT_GCODE, "Export G-code...", 'Export current plate as G-code');
+        $platerMenu->Append(MI_PLATER_EXPORT_STL, "Export STL...", 'Export current plate as STL');
+        $platerMenu->Append(MI_PLATER_EXPORT_AMF, "Export AMF...", 'Export current plate as AMF');
+        EVT_MENU($frame, MI_PLATER_EXPORT_GCODE, sub { $self->{skeinpanel}{plater}->export_gcode });
+        EVT_MENU($frame, MI_PLATER_EXPORT_STL, sub { $self->{skeinpanel}{plater}->export_stl });
+        EVT_MENU($frame, MI_PLATER_EXPORT_AMF, sub { $self->{skeinpanel}{plater}->export_amf });
+    }
+    
     # Window menu
     my $windowMenu = Wx::Menu->new;
     {
@@ -128,6 +143,7 @@ sub OnInit {
     {
         my $menubar = Wx::MenuBar->new;
         $menubar->Append($fileMenu, "&File");
+        $menubar->Append($platerMenu, "&Plater");
         $menubar->Append($windowMenu, "&Window");
         $menubar->Append($helpMenu, "&Help");
         $frame->SetMenuBar($menubar);
diff --git a/lib/Slic3r/GUI/Plater.pm b/lib/Slic3r/GUI/Plater.pm
index 7155f21eec..ff98c74588 100644
--- a/lib/Slic3r/GUI/Plater.pm
+++ b/lib/Slic3r/GUI/Plater.pm
@@ -296,7 +296,7 @@ sub load_file {
     my $process_dialog = Wx::ProgressDialog->new('Loading…', "Processing input file…", 100, $self, 0);
     $process_dialog->Pulse;
     local $SIG{__WARN__} = Slic3r::GUI::warning_catcher($self);
-    $self->{print}->add_object_from_file($input_file);
+    $self->{print}->add_objects_from_file($input_file);
     my $obj_idx = $#{$self->{print}->objects};
     $process_dialog->Destroy;
     
@@ -419,9 +419,7 @@ sub rotate {
     # rotate, realign to 0,0 and update size
     $object->mesh->rotate($angle);
     $object->mesh->align_to_origin;
-    my @size = $object->mesh->size;
-    $object->x_length($size[X]);
-    $object->y_length($size[Y]);
+    $object->size([ $object->mesh->size ]);
     
     $self->make_thumbnail($obj_idx);
     $self->recenter;
@@ -458,9 +456,7 @@ sub changescale {
     my $mesh = $object->mesh;
     $mesh->scale($scale/100 / $self->{scale}[$obj_idx]);
     $object->mesh->align_to_origin;
-    my @size = $object->mesh->size;
-    $object->x_length($size[X]);
-    $object->y_length($size[Y]);
+    $object->size([ $object->mesh->size ]);
     
     $self->{scale}[$obj_idx] = $scale/100;
     $self->{list}->SetItem($obj_idx, 2, "$scale%");
@@ -512,6 +508,8 @@ sub export_gcode {
     
     # set this before spawning the thread because ->config needs GetParent and it's not available there
     $self->{print}->config($self->skeinpanel->config);
+    $self->{print}->extra_variables->{"${_}_preset"} = $self->skeinpanel->{options_tabs}{$_}->current_preset->{name}
+        for qw(print filament printer);
     
     # select output file
     $self->{output_file} = $main::opt{output};
@@ -634,39 +632,58 @@ sub on_export_failed {
 
 sub export_stl {
     my $self = shift;
-    
-    my $print = $self->{print};
         
-    # select output file
+    my $output_file = $self->_get_export_file('STL') or return;
+    Slic3r::Format::STL->write_file($output_file, $self->make_model, binary => 1);
+    $self->statusbar->SetStatusText("STL file exported to $output_file");
+}
+
+sub export_amf {
+    my $self = shift;
+        
+    my $output_file = $self->_get_export_file('AMF') or return;
+    Slic3r::Format::AMF->write_file($output_file, $self->make_model);
+    $self->statusbar->SetStatusText("AMF file exported to $output_file");
+}
+
+sub _get_export_file {
+    my $self = shift;
+    my ($format) = @_;
+    
+    my $suffix = $format eq 'STL' ? '.stl' : '.amf.xml';
+    
     my $output_file = $main::opt{output};
     {
-        $output_file = $print->expanded_output_filepath($output_file);
-        $output_file =~ s/\.gcode$/.stl/i;
-        my $dlg = Wx::FileDialog->new($self, 'Save STL file as:', dirname($output_file),
+        $output_file = $self->{print}->expanded_output_filepath($output_file);
+        $output_file =~ s/\.gcode$/$suffix/i;
+        my $dlg = Wx::FileDialog->new($self, "Save $format file as:", dirname($output_file),
             basename($output_file), $Slic3r::GUI::SkeinPanel::model_wildcard, wxFD_SAVE | wxFD_OVERWRITE_PROMPT);
         if ($dlg->ShowModal != wxID_OK) {
             $dlg->Destroy;
-            return;
+            return undef;
         }
         $output_file = $Slic3r::GUI::SkeinPanel::last_output_file = $dlg->GetPath;
         $dlg->Destroy;
     }
+    return $output_file;
+}
+
+sub make_model {
+    my $self = shift;
     
-    my $mesh = Slic3r::TriangleMesh->new(facets => [], vertices => []);
-    for my $obj_idx (0 .. $#{$print->objects}) {
-        for my $copy (@{$print->copies->[$obj_idx]}) {
-            my $cloned_mesh = $print->objects->[$obj_idx]->mesh->clone;
-            $cloned_mesh->move(@$copy);
-            my $vertices_offset = scalar @{$mesh->vertices};
-            push @{$mesh->vertices}, @{$cloned_mesh->vertices};
-            push @{$mesh->facets}, map [ $_->[0], map $vertices_offset + $_, @$_[-3..-1] ], @{$cloned_mesh->facets};
+    my $model = Slic3r::Model->new;
+    for my $obj_idx (0 .. $#{$self->{print}->objects}) {
+        my $mesh = $self->{print}->objects->[$obj_idx]->mesh->clone;
+        $mesh->scale(&Slic3r::SCALING_FACTOR);
+        my $object = $model->add_object(vertices => $mesh->vertices);
+        $object->add_volume(facets => $mesh->facets);
+        for my $copy (@{$self->{print}->copies->[$obj_idx]}) {
+            $object->add_instance(rotation => 0, offset => [ map unscale $_, @$copy ]);
         }
     }
-    $mesh->scale(&Slic3r::SCALING_FACTOR);
-    $mesh->align_to_origin;
+    # TODO: $model->align_to_origin;
     
-    Slic3r::Format::STL->write_file($output_file, $mesh, 1);
-    $self->statusbar->SetStatusText("STL file exported to $output_file");
+    return $model;
 }
 
 sub make_thumbnail {
diff --git a/lib/Slic3r/GUI/SkeinPanel.pm b/lib/Slic3r/GUI/SkeinPanel.pm
index 764f60a81f..babd1cfbc6 100644
--- a/lib/Slic3r/GUI/SkeinPanel.pm
+++ b/lib/Slic3r/GUI/SkeinPanel.pm
@@ -96,7 +96,7 @@ sub do_slice {
         Slic3r::GUI->save_settings;
         
         my $print = Slic3r::Print->new(config => $config);
-        $print->add_object_from_file($input_file);
+        $print->add_objects_from_file($input_file);
         $print->validate;
 
         # select output file
diff --git a/lib/Slic3r/GUI/Tab.pm b/lib/Slic3r/GUI/Tab.pm
index cd68593aee..16107b5481 100644
--- a/lib/Slic3r/GUI/Tab.pm
+++ b/lib/Slic3r/GUI/Tab.pm
@@ -401,7 +401,7 @@ sub build {
         },
         {
             title => 'Advanced',
-            options => [qw(infill_every_layers fill_angle solid_infill_below_area)],
+            options => [qw(infill_every_layers fill_angle solid_infill_below_area only_retract_when_crossing_perimeters)],
         },
     ]);
     
diff --git a/lib/Slic3r/Geometry.pm b/lib/Slic3r/Geometry.pm
index 979a2eb0ef..dfad17ad05 100644
--- a/lib/Slic3r/Geometry.pm
+++ b/lib/Slic3r/Geometry.pm
@@ -20,6 +20,7 @@ our @EXPORT_OK = qw(
     shortest_path collinear scale unscale merge_collinear_lines
     rad2deg_dir bounding_box_center line_intersects_any douglas_peucker
     polyline_remove_short_segments normal triangle_normal polygon_is_convex
+    scaled_epsilon
 );
 
 
@@ -38,6 +39,7 @@ use constant MAX => 1;
 our $parallel_degrees_limit = abs(deg2rad(3));
 
 sub epsilon () { 1E-4 }
+sub scaled_epsilon () { epsilon / &Slic3r::SCALING_FACTOR }
 
 sub scale   ($) { $_[0] / &Slic3r::SCALING_FACTOR }
 sub unscale ($) { $_[0] * &Slic3r::SCALING_FACTOR }
diff --git a/lib/Slic3r/Geometry/Clipper.pm b/lib/Slic3r/Geometry/Clipper.pm
index a76048fc4e..5a1dfdd916 100644
--- a/lib/Slic3r/Geometry/Clipper.pm
+++ b/lib/Slic3r/Geometry/Clipper.pm
@@ -4,29 +4,34 @@ use warnings;
 
 require Exporter;
 our @ISA = qw(Exporter);
-our @EXPORT_OK = qw(explode_expolygon explode_expolygons safety_offset offset
+our @EXPORT_OK = qw(safety_offset offset offset_ex
     diff_ex diff union_ex intersection_ex xor_ex PFT_EVENODD JT_MITER JT_ROUND
     JT_SQUARE is_counter_clockwise);
 
-use Math::Clipper 1.09 ':all';
+use Math::Clipper 1.09 qw(:cliptypes :polyfilltypes :jointypes is_counter_clockwise area);
 use Slic3r::Geometry qw(scale);
 our $clipper = Math::Clipper->new;
 
-sub explode_expolygon {
-    my ($expolygon) = @_;
-    return ($expolygon->{outer}, @{ $expolygon->{holes} });
-}
-
-sub explode_expolygons {
-    my ($expolygons) = @_;
-    return map explode_expolygon($_), @$expolygons;
-}
-
 sub safety_offset {
     my ($polygons, $factor) = @_;
     return Math::Clipper::offset($polygons, $factor || (scale 1e-05), 100, JT_MITER, 2);
 }
 
+sub offset {
+    my ($polygons, $distance, $scale, $joinType, $miterLimit) = @_;
+    $scale      ||= &Slic3r::SCALING_FACTOR * 1000000;
+    $joinType   = JT_MITER if !defined $joinType;
+    $miterLimit ||= 2;
+    
+    my $offsets = Math::Clipper::offset($polygons, $distance, $scale, $joinType, $miterLimit);
+    return @$offsets;
+}
+
+sub offset_ex {
+    # offset polygons and then apply holes to the right contours
+    return @{ union_ex([ offset(@_) ]) };
+}
+
 sub diff_ex {
     my ($subject, $clip, $safety_offset) = @_;
     
diff --git a/lib/Slic3r/Layer.pm b/lib/Slic3r/Layer.pm
index 9794e0ed9e..2c1bc52ba8 100644
--- a/lib/Slic3r/Layer.pm
+++ b/lib/Slic3r/Layer.pm
@@ -346,7 +346,7 @@ sub make_perimeters {
     {
         my @thin_paths = ();
         my %properties = (
-            role            => EXTR_ROLE_PERIMETER,
+            role            => EXTR_ROLE_EXTERNAL_PERIMETER,
             flow_spacing    => $self->perimeter_flow->spacing,
         );
         for (@{ $self->thin_walls }) {
@@ -386,13 +386,30 @@ sub prepare_fill_surfaces {
     if ($Slic3r::Config->fill_density == 0) {
         @surfaces = grep $_->surface_type != S_TYPE_INTERNAL, @surfaces;
     }
+    
+    # remove unprintable regions (they would slow down the infill process and also cause
+    # some weird failures during bridge neighbor detection)
+    {
+        my $distance = scale $self->infill_flow->spacing / 2;
+        @surfaces = map {
+            my $surface = $_;
+            
+            # offset inwards
+            my @offsets = $surface->expolygon->offset_ex(-$distance);
+            @offsets = @{union_ex(Math::Clipper::offset([ map @$_, @offsets ], $distance, 100, JT_MITER))};
+            map Slic3r::Surface->new(
+                expolygon => $_,
+                surface_type => $surface->surface_type,
+            ), @offsets;
+        } @surfaces;
+    }
         
     # turn too small internal regions into solid regions
     {
         my $min_area = scale scale $Slic3r::Config->solid_infill_below_area; # scaling an area requires two calls!
         my @small = grep $_->surface_type == S_TYPE_INTERNAL && $_->expolygon->contour->area <= $min_area, @surfaces;
         $_->surface_type(S_TYPE_INTERNALSOLID) for @small;
-        Slic3r::debugf "identified %d small surfaces at layer %d\n", scalar(@small), $self->id if @small > 0;
+        Slic3r::debugf "identified %d small solid surfaces at layer %d\n", scalar(@small), $self->id if @small > 0;
     }
     
     $self->fill_surfaces([@surfaces]);
diff --git a/lib/Slic3r/Model.pm b/lib/Slic3r/Model.pm
new file mode 100644
index 0000000000..b648d4b34f
--- /dev/null
+++ b/lib/Slic3r/Model.pm
@@ -0,0 +1,112 @@
+package Slic3r::Model;
+use Moo;
+
+use Slic3r::Geometry qw(X Y Z);
+
+has 'materials' => (is => 'ro', default => sub { {} });
+has 'objects'   => (is => 'ro', default => sub { [] });
+
+sub add_object {
+    my $self = shift;
+    
+    my $object = Slic3r::Model::Object->new(model => $self, @_);
+    push @{$self->objects}, $object;
+    return $object;
+}
+
+# flattens everything to a single mesh
+sub mesh {
+    my $self = shift;
+    
+    my $vertices = [];
+    my $facets = [];
+    foreach my $object (@{$self->objects}) {
+        my @instances = $object->instances ? @{$object->instances} : (undef);
+        foreach my $instance (@instances) {
+            my @vertices = @{$object->vertices};
+            if ($instance) {
+                # save Z coordinates, as rotation and translation discard them
+                my @z = map $_->[Z], @vertices;
+                
+                if ($instance->rotation) {
+                    # transform vertex coordinates
+                    my $rad = Slic3r::Geometry::deg2rad($instance->rotation);
+                    @vertices = Slic3r::Geometry::rotate_points($rad, undef, @vertices);
+                }
+                @vertices = Slic3r::Geometry::move_points($instance->offset, @vertices);
+                
+                # reapply Z coordinates
+                $vertices[$_][Z] = $z[$_] for 0 .. $#z;
+            }
+            
+            my $v_offset = @$vertices;
+            push @$vertices, @vertices;
+            foreach my $volume (@{$object->volumes}) {
+                push @$facets, map {
+                    my $f = [@$_];
+                    $f->[$_] += $v_offset for -3..-1;
+                    $f;
+                } @{$volume->facets};
+            }
+        }
+    }
+    
+    return Slic3r::TriangleMesh->new(
+        vertices => $vertices,
+        facets   => $facets,
+    );
+}
+
+package Slic3r::Model::Material;
+use Moo;
+
+has 'model'         => (is => 'ro', weak_ref => 1, required => 1);
+has 'attributes'    => (is => 'rw', default => sub { {} });
+
+package Slic3r::Model::Object;
+use Moo;
+
+has 'model'     => (is => 'ro', weak_ref => 1, required => 1);
+has 'vertices'  => (is => 'ro', default => sub { [] });
+has 'volumes'   => (is => 'ro', default => sub { [] });
+has 'instances' => (is => 'rw');
+
+sub add_volume {
+    my $self = shift;
+    
+    my $volume = Slic3r::Model::Volume->new(object => $self, @_);
+    push @{$self->volumes}, $volume;
+    return $volume;
+}
+
+sub add_instance {
+    my $self = shift;
+    
+    $self->instances([]) if !defined $self->instances;
+    push @{$self->instances}, Slic3r::Model::Instance->new(object => $self, @_);
+    return $self->instances->[-1];
+}
+
+package Slic3r::Model::Volume;
+use Moo;
+
+has 'object'        => (is => 'ro', weak_ref => 1, required => 1);
+has 'material_id'   => (is => 'rw');
+has 'facets'        => (is => 'rw', default => sub { [] });
+
+sub mesh {
+    my $self = shift;
+    return Slic3r::TriangleMesh->new(
+        vertices => $self->object->vertices,
+        facets   => $self->facets,
+    );
+}
+
+package Slic3r::Model::Instance;
+use Moo;
+
+has 'object'    => (is => 'ro', weak_ref => 1, required => 1);
+has 'rotation'  => (is => 'rw', default => sub { 0 });
+has 'offset'    => (is => 'rw');
+
+1;
diff --git a/lib/Slic3r/Polygon.pm b/lib/Slic3r/Polygon.pm
index fa7ee712d8..ba09dcc2d5 100644
--- a/lib/Slic3r/Polygon.pm
+++ b/lib/Slic3r/Polygon.pm
@@ -71,13 +71,7 @@ sub safety_offset {
 
 sub offset {
     my $self = shift;
-    my ($distance, $scale, $joinType, $miterLimit) = @_;
-    $scale      ||= &Slic3r::SCALING_FACTOR * 1000000;
-    $joinType   = JT_MITER if !defined $joinType;
-    $miterLimit ||= 2;
-    
-    my $offsets = Math::Clipper::offset([$self], $distance, $scale, $joinType, $miterLimit);
-    return map Slic3r::Polygon->new($_), @$offsets;
+    return map Slic3r::Polygon->new($_), Slic3r::Geometry::Clipper::offset([$self], @_);
 }
 
 # this method subdivides the polygon segments to that no one of them
diff --git a/lib/Slic3r/Polyline.pm b/lib/Slic3r/Polyline.pm
index 786957dab1..da9cc04795 100644
--- a/lib/Slic3r/Polyline.pm
+++ b/lib/Slic3r/Polyline.pm
@@ -144,6 +144,7 @@ sub rotate {
     my $self = shift;
     my ($angle, $center) = @_;
     @$self = Slic3r::Geometry::rotate_points($angle, $center, @$self);
+    bless $_, 'Slic3r::Point' for @$self;
     return $self;
 }
 
@@ -151,6 +152,7 @@ sub translate {
     my $self = shift;
     my ($x, $y) = @_;
     @$self = Slic3r::Geometry::move_points([$x, $y], @$self);
+    bless $_, 'Slic3r::Point' for @$self;
     return $self;
 }
 
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index c5aec01a70..479cdc752a 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -5,11 +5,12 @@ use File::Basename qw(basename fileparse);
 use File::Spec;
 use Math::ConvexHull 1.0.4 qw(convex_hull);
 use Slic3r::ExtrusionPath ':roles';
-use Slic3r::Geometry qw(X Y Z X1 Y1 X2 Y2 PI scale unscale move_points);
+use Slic3r::Geometry qw(X Y Z X1 Y1 X2 Y2 PI scale unscale move_points nearest_point);
 use Slic3r::Geometry::Clipper qw(diff_ex union_ex intersection_ex offset JT_ROUND JT_SQUARE);
 use Time::HiRes qw(gettimeofday tv_interval);
 
 has 'config'                 => (is => 'rw', default => sub { Slic3r::Config->new_from_defaults }, trigger => 1);
+has 'extra_variables'        => (is => 'rw', default => sub {{}});
 has 'objects'                => (is => 'rw', default => sub {[]});
 has 'copies'                 => (is => 'rw', default => sub {[]});  # obj_idx => [copies...]
 has 'total_extrusion_length' => (is => 'rw');
@@ -42,6 +43,14 @@ sub _trigger_config {
     # store config in a handy place
     $Slic3r::Config = $self->config;
     
+    # legacy with existing config files
+    $self->config->set('first_layer_height', $self->config->layer_height)
+        if !$self->config->first_layer_height;
+    $self->config->set_ifndef('small_perimeter_speed',  $self->config->perimeter_speed);
+    $self->config->set_ifndef('bridge_speed',           $self->config->infill_speed);
+    $self->config->set_ifndef('solid_infill_speed',     $self->config->infill_speed);
+    $self->config->set_ifndef('top_solid_infill_speed', $self->config->solid_infill_speed);
+    
     # initialize extruder(s)
     $Slic3r::extruders = [];
     for my $t (0, map $_-1, map $self->config->get($_), qw(perimeter_extruder infill_extruder support_material_extruder)) {
@@ -71,36 +80,45 @@ sub _trigger_config {
     # G-code flavors
     $self->config->set('extrusion_axis', 'A') if $self->config->gcode_flavor eq 'mach3';
     $self->config->set('extrusion_axis', '')  if $self->config->gcode_flavor eq 'no-extrusion';
-    
-    # legacy with existing config files
-    $self->config->set_ifndef('small_perimeter_speed',  $self->config->perimeter_speed);
-    $self->config->set_ifndef('bridge_speed',           $self->config->infill_speed);
-    $self->config->set_ifndef('solid_infill_speed',     $self->config->infill_speed);
-    $self->config->set_ifndef('top_solid_infill_speed', $self->config->solid_infill_speed);
 }
 
-sub add_object_from_file {
+sub add_objects_from_file {
     my $self = shift;
     my ($input_file) = @_;
     
-    my $object;
-    if ($input_file =~ /\.stl$/i) {
-        my $mesh = Slic3r::Format::STL->read_file($input_file);
+    my $model = $input_file =~ /\.stl$/i            ? Slic3r::Format::STL->read_file($input_file)
+              : $input_file =~ /\.obj$/i            ? Slic3r::Format::OBJ->read_file($input_file)
+              : $input_file =~ /\.amf(\.xml)?$/i    ? Slic3r::Format::AMF->read_file($input_file)
+              : die "Input file must have .stl, .obj or .amf(.xml) extension\n";
+    
+    my @print_objects = $self->add_model($model);
+    $_->input_file($input_file) for @print_objects;
+}
+
+sub add_model {
+    my $self = shift;
+    my ($model) = @_;
+    
+    my @print_objects = ();
+    foreach my $object (@{ $model->objects }) {
+        my $mesh = $object->volumes->[0]->mesh;
         $mesh->check_manifoldness;
-        $object = $self->add_object_from_mesh($mesh);
-    } elsif ($input_file =~ /\.obj$/i) {
-        my $mesh = Slic3r::Format::OBJ->read_file($input_file);
-        $mesh->check_manifoldness;
-        $object = $self->add_object_from_mesh($mesh);
-    } elsif ( $input_file =~ /\.amf(\.xml)?$/i) {
-        my ($materials, $meshes_by_material) = Slic3r::Format::AMF->read_file($input_file);
-        $_->check_manifoldness for values %$meshes_by_material;
-        $object = $self->add_object_from_mesh($meshes_by_material->{_} || +(values %$meshes_by_material)[0]);
-    } else {
-        die "Input file must have .stl, .obj or .amf(.xml) extension\n";
+        
+        if ($object->instances) {
+            # we ignore the per-instance rotation currently and only 
+            # consider the first one
+            $mesh->rotate($object->instances->[0]->rotation);
+        }
+        
+        push @print_objects, $self->add_object_from_mesh($mesh);
+        
+        if ($object->instances) {
+            # replace the default [0,0] instance with the custom ones
+            @{$self->copies->[-1]} = map [ scale $_->offset->[X], scale $_->offset->[X] ], @{$object->instances};
+        }
     }
-    $object->input_file($input_file);
-    return $object;
+    
+    return @print_objects;
 }
 
 sub add_object_from_mesh {
@@ -112,11 +130,9 @@ sub add_object_from_mesh {
     $mesh->align_to_origin;
     
     # initialize print object
-    my @size = $mesh->size;
     my $object = Slic3r::Print::Object->new(
-        mesh     => $mesh,
-        x_length => $size[X],
-        y_length => $size[Y],
+        mesh => $mesh,
+        size => [ $mesh->size ],
     );
     
     push @{$self->objects}, $object;
@@ -201,8 +217,8 @@ sub duplicate {
         for my $x_copy (1..$Slic3r::Config->duplicate_grid->[X]) {
             for my $y_copy (1..$Slic3r::Config->duplicate_grid->[Y]) {
                 push @{$self->copies->[0]}, [
-                    ($object->x_length + $dist) * ($x_copy-1),
-                    ($object->y_length + $dist) * ($y_copy-1),
+                    ($object->size->[X] + $dist) * ($x_copy-1),
+                    ($object->size->[Y] + $dist) * ($y_copy-1),
                 ];
             }
         }
@@ -220,8 +236,8 @@ sub arrange_objects {
     my $total_parts = scalar map @$_, @{$self->copies};
     my $partx = my $party = 0;
     foreach my $object (@{$self->objects}) {
-        $partx = $object->x_length if $object->x_length > $partx;
-        $party = $object->y_length if $object->y_length > $party;
+        $partx = $object->size->[X] if $object->size->[X] > $partx;
+        $party = $object->size->[Y] if $object->size->[Y] > $party;
     }
     
     # object distance is max(duplicate_distance, clearance_radius)
@@ -246,9 +262,9 @@ sub bounding_box {
         foreach my $copy (@{$self->copies->[$obj_idx]}) {
             push @points,
                 [ $copy->[X], $copy->[Y] ],
-                [ $copy->[X] + $object->x_length, $copy->[Y] ],
-                [ $copy->[X] + $object->x_length, $copy->[Y] + $object->y_length ],
-                [ $copy->[X], $copy->[Y] + $object->y_length ];
+                [ $copy->[X] + $object->size->[X], $copy->[Y] ],
+                [ $copy->[X] + $object->size->[X], $copy->[Y] + $object->size->[Y] ],
+                [ $copy->[X], $copy->[Y] + $object->size->[Y] ];
         }
     }
     return Slic3r::Geometry::bounding_box(\@points);
@@ -497,7 +513,7 @@ sub make_skirt {
     my @skirt = ();
     for (my $i = $Slic3r::Config->skirts; $i > 0; $i--) {
         my $distance = scale ($Slic3r::Config->skirt_distance + ($flow->spacing * $i));
-        my $outline = offset([$convex_hull], $distance, &Slic3r::SCALING_FACTOR * 100, JT_ROUND);
+        my $outline = Math::Clipper::offset([$convex_hull], $distance, &Slic3r::SCALING_FACTOR * 100, JT_ROUND);
         push @skirt, Slic3r::ExtrusionLoop->pack(
             polygon => Slic3r::Polygon->new(@{$outline->[0]}),
             role => EXTR_ROLE_SKIRT,
@@ -569,15 +585,6 @@ sub write_gcode {
     print $fh $gcodegen->set_tool(0);
     print $fh $gcodegen->set_fan(0, 1) if $Slic3r::Config->cooling && $Slic3r::Config->disable_fan_first_layers;
     
-    # this spits out some platic at start from each extruder when they are first used;
-    # the primary extruder will compensate by the normal retraction length, while 
-    # the others will compensate for their toolchange length + restart extra.
-    # this is a temporary solution as all extruders should use some kind of skirt 
-    # to be put into a consistent state.
-    $_->retracted($_->retract_length_toolchange + $_->retract_restart_extra_toolchange)
-        for @{$Slic3r::extruders}[1 .. $#{$Slic3r::extruders}];
-    $gcodegen->retract;
-    
     # write start commands to file
     printf $fh $gcodegen->set_bed_temperature($Slic3r::Config->first_layer_bed_temperature, 1),
         if $Slic3r::Config->first_layer_bed_temperature && $Slic3r::Config->start_gcode !~ /M190/i;
@@ -647,6 +654,7 @@ sub write_gcode {
         
         # extrude brim
         if ($layer_id == 0 && !$brim_done) {
+            $gcode .= $gcodegen->set_tool($Slic3r::Config->support_material_extruder-1);
             $gcodegen->shift_x($shift[X]);
             $gcodegen->shift_y($shift[Y]);
             $gcode .= $gcodegen->extrude_loop($_, 'brim') for @{$self->brim};
@@ -811,6 +819,7 @@ sub expanded_output_filepath {
     return $Slic3r::Config->replace_options($path, {
         input_filename      => $input_filename,
         input_filename_base => $input_filename_base,
+        %{ $self->extra_variables },
     });
 }
 
diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index c06358b835..696d72ca3c 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -8,8 +8,7 @@ use Slic3r::Surface ':types';
 
 has 'input_file'        => (is => 'rw', required => 0);
 has 'mesh'              => (is => 'rw', required => 0);
-has 'x_length'          => (is => 'rw', required => 1);
-has 'y_length'          => (is => 'rw', required => 1);
+has 'size'              => (is => 'rw', required => 1);
 
 has 'layers' => (
     traits  => ['Array'],
diff --git a/slic3r.pl b/slic3r.pl
index 0f9baa58c6..e5c63b99e1 100755
--- a/slic3r.pl
+++ b/slic3r.pl
@@ -27,6 +27,7 @@ my %cli_options = ();
         'save=s'                => \$opt{save},
         'load=s@'               => \$opt{load},
         'ignore-nonexistent-config' => \$opt{ignore_nonexistent_config},
+        'datadir=s'             => \$opt{datadir},
         'export-svg'            => \$opt{export_svg},
         'merge|m'               => \$opt{merge},
     );
@@ -70,6 +71,10 @@ if ($opt{save}) {
 # launch GUI
 my $gui;
 if (!@ARGV && !$opt{save} && eval "require Slic3r::GUI; 1") {
+    {
+        no warnings 'once';
+        $Slic3r::GUI::datadir = $opt{datadir} if $opt{datadir};
+    }
     $gui = Slic3r::GUI->new;
     $gui->{skeinpanel}->load_config_file($_) for @{$opt{load}};
     $gui->{skeinpanel}->load_config($cli_config);
@@ -83,9 +88,9 @@ if (@ARGV) {  # slicing from command line
     
     while (my $input_file = shift @ARGV) {
         my $print = Slic3r::Print->new(config => $config);
-        $print->add_object_from_file($input_file);
+        $print->add_objects_from_file($input_file);
         if ($opt{merge}) {
-            $print->add_object_from_file($_) for splice @ARGV, 0;
+            $print->add_objects_from_file($_) for splice @ARGV, 0;
         }
         $print->duplicate;
         $print->arrange_objects if @{$print->objects} > 1;
@@ -213,6 +218,9 @@ $j
     --layer-gcode       Load layer-change G-code from the supplied file (default: nothing).
     --extra-perimeters  Add more perimeters when needed (default: yes)
     --randomize-start   Randomize starting point across layers (default: yes)
+    --only-retract-when-crossing-perimeters
+                        Disable retraction when travelling between infill paths inside the same island.
+                        (default: no)
     --solid-infill-below-area
                         Force solid infill when a region has a smaller area than this threshold
                         (mm^2, default: $config->{solid_infill_below_area})
diff --git a/t/arcs.t b/t/arcs.t
index 1ffcd87b09..972620402b 100644
--- a/t/arcs.t
+++ b/t/arcs.t
@@ -11,7 +11,7 @@ BEGIN {
 
 use Slic3r;
 use Slic3r::ExtrusionPath ':roles';
-use Slic3r::Geometry qw(epsilon scale X Y);
+use Slic3r::Geometry qw(scaled_epsilon scale X Y);
 
 {
     my $path = Slic3r::ExtrusionPath->new(polyline => Slic3r::Polyline->new(
@@ -61,17 +61,17 @@ use Slic3r::Geometry qw(epsilon scale X Y);
     isa_ok $collection2->paths->[0], 'Slic3r::ExtrusionPath::Arc', 'path';
     
     my $expected_length = scale 7.06858347057701;
-    ok abs($collection1->paths->[0]->length - $expected_length) < scale epsilon, 'cw oriented arc has correct length';
-    ok abs($collection2->paths->[0]->length - $expected_length) < scale epsilon, 'ccw oriented arc has correct length';
+    ok abs($collection1->paths->[0]->length - $expected_length) < scaled_epsilon, 'cw oriented arc has correct length';
+    ok abs($collection2->paths->[0]->length - $expected_length) < scaled_epsilon, 'ccw oriented arc has correct length';
 
     is $collection1->paths->[0]->orientation, 'cw', 'cw orientation was correctly detected';
     is $collection2->paths->[0]->orientation, 'ccw', 'ccw orientation was correctly detected';
     
     my $center1 = [ map sprintf('%.0f', $_), @{ $collection1->paths->[0]->center } ];
-    ok abs($center1->[X] - scale 10) < scale epsilon && abs($center1->[Y] - scale 10) < scale epsilon, 'center was correctly detected';
+    ok abs($center1->[X] - scale 10) < scaled_epsilon && abs($center1->[Y] - scale 10) < scaled_epsilon, 'center was correctly detected';
     
     my $center2 = [ map sprintf('%.0f', $_), @{ $collection2->paths->[0]->center } ];
-    ok abs($center2->[X] - scale 10) < scale epsilon && abs($center1->[Y] - scale 10) < scale epsilon, 'center was correctly detected';
+    ok abs($center2->[X] - scale 10) < scaled_epsilon && abs($center1->[Y] - scale 10) < scaled_epsilon, 'center was correctly detected';
 }
 
 #==========================================================
diff --git a/t/fill.t b/t/fill.t
index f45aab2dae..2a7ef1f933 100644
--- a/t/fill.t
+++ b/t/fill.t
@@ -2,7 +2,7 @@ use Test::More;
 use strict;
 use warnings;
 
-plan tests => 2;
+plan tests => 4;
 
 BEGIN {
     use FindBin;
@@ -10,14 +10,13 @@ BEGIN {
 }
 
 use Slic3r;
+use Slic3r::Geometry qw(scale X Y);
+use Slic3r::Surface qw(:types);
 
-my $print = Slic3r::Print->new(
-    x_length => 50,
-    y_length => 50,
-);
+sub scale_points (@) { map [scale $_->[X], scale $_->[Y]], @_ }
 
 {
-    my $filler = Slic3r::Fill::Rectilinear->new(print => $print);
+    my $filler = Slic3r::Fill::Rectilinear->new(print => Slic3r::Print->new);
     my $surface_width = 250;
     my $distance = $filler->adjust_solid_spacing(
         width       => $surface_width,
@@ -27,4 +26,20 @@ my $print = Slic3r::Print->new(
     is $surface_width % $distance, 0, 'adjusted solid distance';
 }
 
+{
+    my $filler = Slic3r::Fill::Rectilinear->new(
+        print               => Slic3r::Print->new,
+        max_print_dimension => scale 100,
+    );
+    my $surface = Slic3r::Surface->new(
+        surface_type    => S_TYPE_TOP,
+        expolygon       => Slic3r::ExPolygon->new([ scale_points [0,0], [50,0], [50,50], [0,50] ]),
+    );
+    foreach my $angle (0, 45) {
+        $surface->expolygon->rotate($angle, [0,0]);
+        my ($params, @paths) = $filler->fill_surface($surface, flow_spacing => 0.69, density => 0.4);
+        is scalar @paths, 1, 'one continuous path';
+    }
+}
+
 __END__
diff --git a/utils/amf-to-stl.pl b/utils/amf-to-stl.pl
index 847e5e7498..b421dd33a0 100755
--- a/utils/amf-to-stl.pl
+++ b/utils/amf-to-stl.pl
@@ -25,12 +25,12 @@ my %opt = ();
 }
 
 {
-    my $mesh = Slic3r::Format::AMF->read_file($ARGV[0]);
+    my $model = Slic3r::Format::AMF->read_file($ARGV[0]);
     my $output_file = $ARGV[0];
     $output_file =~ s/\.amf(?:\.xml)?$/\.stl/i;
     
     printf "Writing to %s\n", basename($output_file);
-    Slic3r::Format::STL->write_file($output_file, $mesh, !$opt{ascii});
+    Slic3r::Format::STL->write_file($output_file, $model, binary => !$opt{ascii});
 }
 
 
diff --git a/utils/post-processing/filament-weight.pl b/utils/post-processing/filament-weight.pl
index c564b4d805..5ed8364612 100755
--- a/utils/post-processing/filament-weight.pl
+++ b/utils/post-processing/filament-weight.pl
@@ -1,20 +1,30 @@
 #!/usr/bin/perl -i
 #
-# Post-processing script for adding weight of required filament to
-# G-code output.
+# Post-processing script for adding weight and cost of required
+# filament to G-code output.
 
 use strict;
 use warnings;
 
 # example densities, adjust according to filament specifications
-use constant PLA => 1.25; # g/cm3
-use constant ABS => 1.05; # g/cm3
+use constant PLA_P => 1.25; # g/cm3
+use constant ABS_P => 1.05; # g/cm3
+
+# example costs, adjust according to filament prices
+use constant PLA_PRICE => 0.05; # EUR/g
+use constant ABS_PRICE => 0.02; # EUR/g
+use constant CURRENCY => "EUR";
 
 while (<>) {
     if (/^(;\s+filament\s+used\s+=\s.*\((\d+(?:\.\d+)?)cm3)\)/) {
-        my $pla = $2 * PLA;
-        my $abs = $2 * ABS;
-        printf "%s or %.2fg PLA/%.2fg ABS)\n", $1, $pla, $abs;
+        my $pla_weight = $2 * PLA_P;
+        my $abs_weight = $2 * ABS_P;
+
+        my $pla_costs = $pla_weight * PLA_PRICE;
+        my $abs_costs = $abs_weight * ABS_PRICE;
+
+        printf "%s or %.2fg PLA/%.2fg ABS)\n", $1, $pla_weight, $abs_weight;
+        printf "; costs = %s %.2f (PLA), %s %.2f (ABS)\n", CURRENCY, $pla_costs, CURRENCY, $abs_costs;
     } else {
         print;
     }
diff --git a/utils/split_stl.pl b/utils/split_stl.pl
index af98901163..42d2926bd0 100755
--- a/utils/split_stl.pl
+++ b/utils/split_stl.pl
@@ -25,15 +25,20 @@ my %opt = ();
 }
 
 {
-    my $mesh = Slic3r::Format::STL->read_file($ARGV[0]);
+    my $model = Slic3r::Format::STL->read_file($ARGV[0]);
     my $basename = $ARGV[0];
     $basename =~ s/\.stl$//i;
     
     my $part_count = 0;
-    foreach my $new_mesh ($mesh->split_mesh) {
+    foreach my $new_mesh ($model->mesh->split_mesh) {
+        my $new_model = Slic3r::Model->new;
+        $new_model
+            ->add_object(vertices   => $new_mesh->vertices)
+            ->add_volume(facets     => $new_mesh->facets);
+        
         my $output_file = sprintf '%s_%02d.stl', $basename, ++$part_count;
         printf "Writing to %s\n", basename($output_file);
-        Slic3r::Format::STL->write_file($output_file, $new_mesh, !$opt{ascii});
+        Slic3r::Format::STL->write_file($output_file, $new_model, binary => !$opt{ascii});
     }
 }
 
diff --git a/utils/stl-to-amf.pl b/utils/stl-to-amf.pl
index f4805369b8..78e5989b4d 100755
--- a/utils/stl-to-amf.pl
+++ b/utils/stl-to-amf.pl
@@ -18,29 +18,50 @@ my %opt = ();
 {
     my %options = (
         'help'                  => sub { usage() },
+        'distinct-materials'    => \$opt{distinct_materials},
     );
     GetOptions(%options) or usage(1);
     $ARGV[0] or usage(1);
 }
 
 {
-    my @meshes = map Slic3r::Format::STL->read_file($_), @ARGV;
+    my @models = map Slic3r::Format::STL->read_file($_), @ARGV;
     my $output_file = $ARGV[0];
     $output_file =~ s/\.stl$/.amf.xml/i;
     
-    my $materials = {};
-    my $meshes_by_material = {};
-    if (@meshes == 1) {
-        $meshes_by_material->{_} = $meshes[0];
+    my $new_model = Slic3r::Model->new;
+    
+    if ($opt{distinct_materials} && @models > 1) {
+        my $new_object = $new_model->add_object;
+        for my $m (0 .. $#models) {
+            my $model = $models[$m];
+            my $v_offset = @{$new_object->vertices};
+            push @{$new_object->vertices}, @{$model->objects->[0]->vertices};
+            my @new_facets = map {
+                my $f = [@$_];
+                $f->[$_] += $v_offset for -3..-1;
+                $f;
+            } @{ $model->objects->[0]->volumes->[0]->facets };
+            
+            my $material_id = scalar keys %{$new_model->materials};
+            $new_model->materials->{$material_id} = { Name => basename($ARGV[$m]) };
+            $new_object->add_volume(
+                material_id => $material_id,
+                facets      => [@new_facets],
+            );
+        }
     } else {
-        for (0..$#meshes) {
-            $materials->{$_+1} = { Name => basename($ARGV[$_]) };
-            $meshes_by_material->{$_+1} = $meshes[$_];
+        foreach my $model (@models) {
+            $new_model->add_object(
+                vertices => $model->objects->[0]->vertices,
+            )->add_volume(
+                facets => $model->objects->[0]->volumes->[0]->facets,
+            );
         }
     }
     
     printf "Writing to %s\n", basename($output_file);
-    Slic3r::Format::AMF->write_file($output_file, $materials, $meshes_by_material);
+    Slic3r::Format::AMF->write_file($output_file, $new_model);
 }
 
 
@@ -51,6 +72,7 @@ sub usage {
 Usage: amf-to-stl.pl [ OPTIONS ] file.stl [ file2.stl [ file3.stl ] ]
 
     --help              Output this usage screen and exit
+    --distinct-materials Assign each STL file to a different material
     
 EOF
     exit ($exit_code || 0);