Some work to reduce recursive dependencies between classes

lib/Slic3r/GCode.pm

@@ -93,13 +93,8 @@ sub change_layer {
     $self->layer($layer);
     
     # avoid computing islands and overhangs if they're not needed
-    if ($self->config->only_retract_when_crossing_perimeters) {
-        $self->_layer_islands([ $layer->islands ]);
-        $self->_upper_layer_islands([ $layer->upper_layer_islands ]);
-    } else {
-        $self->_layer_islands([]);
-        $self->_upper_layer_islands([]);
-    }
+    $self->_layer_islands($layer->islands);
+    $self->_upper_layer_islands($layer->upper_layer ? $layer->upper_layer->islands : []);
     $self->_layer_overhangs_pp(
         # clone ExPolygons because they come from Surface objects but will be used outside here
         ($layer->id > 0 && ($layer->config->overhangs || $Slic3r::Config->start_perimeters_at_non_overhang))
@@ -437,7 +432,7 @@ sub _plan {
     my $need_retract = !$self->config->only_retract_when_crossing_perimeters;
     if (!$need_retract) {
         $need_retract = 1;
-        foreach my $island ($self->layer->upper_layer_islands) {
+        foreach my $island (@{$self->_upper_layer_islands}) {
             # discard the island if at any line is not enclosed in it
             next if first { !$island->encloses_line($_, scaled_epsilon) } @travel;
             # okay, this island encloses the full travel path

lib/Slic3r/Layer.pm

@@ -7,6 +7,7 @@ use Slic3r::Geometry::Clipper qw(union_ex);
 
 has 'id'                => (is => 'rw', required => 1, trigger => 1); # sequential number of layer, 0-based
 has 'object'            => (is => 'ro', weak_ref => 1, required => 1, handles => [qw(print config)]);
+has 'upper_layer'       => (is => 'rw', weak_ref => 1);
 has 'regions'           => (is => 'ro', default => sub { [] });
 has 'slicing_errors'    => (is => 'rw');
 
@@ -23,16 +24,10 @@ sub _trigger_id {
     $_->_trigger_layer for @{$self->regions || []};
 }
 
+# the purpose of this method is to be overridden for ::Support layers
 sub islands {
     my $self = shift;
-    return @{$self->slices};
-}
-
-sub upper_layer_islands {
-    my $self = shift;
-    
-    my $upper_layer = $self->object->layers->[ $self->id + 1 ] or return ();
-    return $upper_layer->islands;
+    return $self->slices;
 }
 
 sub region {
@@ -75,7 +70,7 @@ has 'support_interface_fills'   => (is => 'rw', default => sub { Slic3r::Extrusi
 
 sub islands {
     my $self = shift;
-    return @{$self->slices}, @{$self->support_islands};
+    return [ @{$self->slices}, @{$self->support_islands} ];
 }
 
 1;

lib/Slic3r/Layer/Region.pm

@@ -14,7 +14,7 @@ has 'layer' => (
     weak_ref    => 1,
     required    => 1,
     trigger     => 1,
-    handles     => [qw(id slice_z print_z height flow object print config)],
+    handles     => [qw(id slice_z print_z height flow config)],
 );
 has 'region'            => (is => 'ro', required => 1, handles => [qw(extruders)]);
 has 'perimeter_flow'    => (is => 'rw');
@@ -182,7 +182,7 @@ sub make_perimeters {
             
             # where offset2() collapses the expolygon, then there's no room for an inner loop
             # and we can extract the gap for later processing
-            if ($Slic3r::Config->gap_fill_speed > 0 && $self->object->config->fill_density > 0) {
+            if ($Slic3r::Config->gap_fill_speed > 0 && $self->config->fill_density > 0) {
                 my $diff = diff(
                     offset(\@last, -0.5*$spacing),
                     # +2 on the offset here makes sure that Clipper float truncation 
@@ -434,7 +434,7 @@ sub prepare_fill_surfaces {
 }
 
 sub process_external_surfaces {
-    my $self = shift;
+    my ($self, $lower_layer) = @_;
     
     my @surfaces = @{$self->fill_surfaces};
     my $margin = scale &Slic3r::EXTERNAL_INFILL_MARGIN;
@@ -447,8 +447,8 @@ sub process_external_surfaces {
         # would get merged into a single one while they need different directions
         # also, supply the original expolygon instead of the grown one, because in case
         # of very thin (but still working) anchors, the grown expolygon would go beyond them
-        my $angle = $self->id > 0
-            ? $self->_detect_bridge_direction($surface->expolygon)
+        my $angle = $lower_layer
+            ? $self->_detect_bridge_direction($surface->expolygon, $lower_layer)
             : undef;
         
         push @bottom, map $surface->clone(expolygon => $_, bridge_angle => $angle), @$grown;
@@ -466,7 +466,7 @@ sub process_external_surfaces {
     
     # if we're slicing with no infill, we can't extend external surfaces
     # over non-existent infill
-    my @fill_boundaries = $self->object->config->fill_density > 0
+    my @fill_boundaries = $self->config->fill_density > 0
         ? @surfaces
         : grep $_->surface_type != S_TYPE_INTERNAL, @surfaces;
     
@@ -495,11 +495,10 @@ sub process_external_surfaces {
 }
 
 sub _detect_bridge_direction {
-    my $self = shift;
-    my ($expolygon) = @_;
+    my ($self, $expolygon, $lower_layer) = @_;
     
     my $grown = $expolygon->offset_ex(+$self->perimeter_flow->scaled_width);
-    my @lower = @{$self->layer->object->layers->[ $self->id - 1 ]->slices};       # expolygons
+    my @lower = @{$lower_layer->slices};       # expolygons
     
     # detect what edges lie on lower slices
     my @edges = (); # polylines

lib/Slic3r/Print.pm

@@ -376,7 +376,7 @@ sub export_gcode {
     # this will detect bridges and reverse bridges
     # and rearrange top/bottom/internal surfaces
     $status_cb->(45, "Detect bridges");
-    $_->process_external_surfaces for map @{$_->regions}, map @{$_->layers}, @{$self->objects};
+    $_->process_external_surfaces for @{$self->objects};
     
     # detect which fill surfaces are near external layers
     # they will be split in internal and internal-solid surfaces

lib/Slic3r/Print/Object.pm

@@ -65,6 +65,9 @@ sub BUILD {
             print_z => $print_z,
             slice_z => scale $slice_z,
         );
+        if ($id > 0) {
+            $self->layers->[-2]->upper_layer($self->layers->[-1]);
+        }
         $id++;
         
         $slice_z += $height/2;   # add the other half layer
@@ -508,6 +511,17 @@ sub bridge_over_infill {
     }
 }
 
+sub process_external_surfaces {
+    my ($self) = @_;
+    
+    for my $region_id (0 .. ($self->print->regions_count-1)) {
+        $self->layers->[0]->regions->[$region_id]->process_external_surfaces(undef);
+        for my $layer_id (1 .. ($self->layer_count-1)) {
+            $self->layers->[$layer_id]->regions->[$region_id]->process_external_surfaces($self->layers->[$layer_id-1]);
+        }
+    }
+}
+
 sub discover_horizontal_shells {
     my $self = shift;