Ported PrintObject::prepare_infill & combine_infill from Perl to C++.version_1.37.0

10 files changed, 526 insertions, 591 deletions

diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 40db9ad3f..793654300 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -52,7 +52,6 @@ sub slice {
     die "No layers were detected. You might want to repair your STL file(s) or check their size or thickness and retry.\n"
         if !@{$self->layers};
     
-    $self->set_typed_slices(0);
     $self->set_step_done(STEP_SLICE);
 }
 
@@ -81,105 +80,7 @@ sub prepare_infill {
     $self->set_step_started(STEP_PREPARE_INFILL);
     $self->print->status_cb->(30, "Preparing infill");
     
-    # This will assign a type (top/bottom/internal) to $layerm->slices.
-    # Then the classifcation of $layerm->slices is transfered onto 
-    # the $layerm->fill_surfaces by clipping $layerm->fill_surfaces
-    # by the cummulative area of the previous $layerm->fill_surfaces.
-    $self->detect_surfaces_type;
-    # Mark the object to have the region slices classified (typed, which also means they are split based on whether they are supported, bridging, top layers etc.)
-    $self->set_typed_slices(1);
-    
-    # Decide what surfaces are to be filled.
-    # Here the S_TYPE_TOP / S_TYPE_BOTTOMBRIDGE / S_TYPE_BOTTOM infill is turned to just S_TYPE_INTERNAL if zero top / bottom infill layers are configured.
-    # Also tiny S_TYPE_INTERNAL surfaces are turned to S_TYPE_INTERNAL_SOLID.
-#    BOOST_LOG_TRIVIAL(info) << "Preparing fill surfaces...";
-    $_->prepare_fill_surfaces for map @{$_->regions}, @{$self->layers};
-
-    # this will detect bridges and reverse bridges
-    # and rearrange top/bottom/internal surfaces
-    # It produces enlarged overlapping bridging areas.
-    #
-    # 1) S_TYPE_BOTTOMBRIDGE / S_TYPE_BOTTOM infill is grown by 3mm and clipped by the total infill area. Bridges are detected. The areas may overlap.
-    # 2) S_TYPE_TOP is grown by 3mm and clipped by the grown bottom areas. The areas may overlap.
-    # 3) Clip the internal surfaces by the grown top/bottom surfaces.
-    # 4) Merge surfaces with the same style. This will mostly get rid of the overlaps.
-    #FIXME This does not likely merge surfaces, which are supported by a material with different colors, but same properties.
-    $self->process_external_surfaces;
-
-    # Add solid fills to ensure the shell vertical thickness.
-    $self->discover_vertical_shells;
-
-    # Debugging output.
-    if ($SLIC3R_DEBUG_SLICE_PROCESSING) {
-        for my $region_id (0 .. ($self->print->region_count-1)) {
-            for (my $i = 0; $i < $self->layer_count; $i++) {
-                my $layerm = $self->get_layer($i)->regions->[$region_id];
-                $layerm->export_region_slices_to_svg_debug("6_discover_vertical_shells-final");
-                $layerm->export_region_fill_surfaces_to_svg_debug("6_discover_vertical_shells-final");
-            } # for each layer
-        } # for each region
-    }
-
-    # Detect, which fill surfaces are near external layers.
-    # They will be split in internal and internal-solid surfaces.
-    # The purpose is to add a configurable number of solid layers to support the TOP surfaces
-    # and to add a configurable number of solid layers above the BOTTOM / BOTTOMBRIDGE surfaces
-    # to close these surfaces reliably.
-    #FIXME Vojtech: Is this a good place to add supporting infills below sloping perimeters?
-    $self->discover_horizontal_shells;
-
-    if ($SLIC3R_DEBUG_SLICE_PROCESSING) {
-        # Debugging output.
-        for my $region_id (0 .. ($self->print->region_count-1)) {
-            for (my $i = 0; $i < $self->layer_count; $i++) {
-                my $layerm = $self->get_layer($i)->regions->[$region_id];
-                $layerm->export_region_slices_to_svg_debug("7_discover_horizontal_shells-final");
-                $layerm->export_region_fill_surfaces_to_svg_debug("7_discover_horizontal_shells-final");
-            } # for each layer
-        } # for each region
-    }
-
-    # Only active if config->infill_only_where_needed. This step trims the sparse infill,
-    # so it acts as an internal support. It maintains all other infill types intact.
-    # Here the internal surfaces and perimeters have to be supported by the sparse infill.
-    #FIXME The surfaces are supported by a sparse infill, but the sparse infill is only as large as the area to support.
-    # Likely the sparse infill will not be anchored correctly, so it will not work as intended.
-    # Also one wishes the perimeters to be supported by a full infill.
-    $self->clip_fill_surfaces;
-
-    if ($SLIC3R_DEBUG_SLICE_PROCESSING) {
-        # Debugging output.
-        for my $region_id (0 .. ($self->print->region_count-1)) {
-            for (my $i = 0; $i < $self->layer_count; $i++) {
-                my $layerm = $self->get_layer($i)->regions->[$region_id];
-                $layerm->export_region_slices_to_svg_debug("8_clip_surfaces-final");
-                $layerm->export_region_fill_surfaces_to_svg_debug("8_clip_surfaces-final");
-            } # for each layer
-        } # for each region
-    }
-    
-    # the following step needs to be done before combination because it may need
-    # to remove only half of the combined infill
-    $self->bridge_over_infill;
-
-    # combine fill surfaces to honor the "infill every N layers" option
-    $self->combine_infill;
-    
-    # Debugging output.
-    if ($SLIC3R_DEBUG_SLICE_PROCESSING) {
-        for my $region_id (0 .. ($self->print->region_count-1)) {
-            for (my $i = 0; $i < $self->layer_count; $i++) {
-                my $layerm = $self->get_layer($i)->regions->[$region_id];
-                $layerm->export_region_slices_to_svg_debug("9_prepare_infill-final");
-                $layerm->export_region_fill_surfaces_to_svg_debug("9_prepare_infill-final");
-            } # for each layer
-        } # for each region
-        for (my $i = 0; $i < $self->layer_count; $i++) {
-            my $layer = $self->get_layer($i);
-            $layer->export_region_slices_to_svg_debug("9_prepare_infill-final");
-            $layer->export_region_fill_surfaces_to_svg_debug("9_prepare_infill-final");
-        } # for each layer
-    }
+    $self->_prepare_infill;
 
     $self->set_step_done(STEP_PREPARE_INFILL);
 }
@@ -214,430 +115,4 @@ sub generate_support_material {
     $self->print->status_cb->(85, $stats);
 }
 
-# Idempotence of this method is guaranteed by the fact that we don't remove things from
-# fill_surfaces but we only turn them into VOID surfaces, thus preserving the boundaries.
-sub clip_fill_surfaces {
-    my $self = shift;
-    return unless $self->config->infill_only_where_needed;
-    
-    # We only want infill under ceilings; this is almost like an
-    # internal support material.
-    
-    # proceed top-down skipping bottom layer
-    my $upper_internal = [];
-    for my $layer_id (reverse 1..($self->layer_count - 1)) {
-        my $layer       = $self->get_layer($layer_id);
-        my $lower_layer = $self->get_layer($layer_id-1);
-        
-        # detect things that we need to support
-        my $overhangs = [];  # Polygons
-        
-        # we need to support any solid surface
-        push @$overhangs, map $_->p,
-            grep $_->is_solid, map @{$_->fill_surfaces}, @{$layer->regions};
-        
-        # we also need to support perimeters when there's at least one full
-        # unsupported loop
-        {
-            # get perimeters area as the difference between slices and fill_surfaces
-            my $perimeters = diff(
-                [ map @$_, @{$layer->slices} ],
-                [ map $_->p, map @{$_->fill_surfaces}, @{$layer->regions} ],
-            );
-            
-            # only consider the area that is not supported by lower perimeters
-            $perimeters = intersection(
-                $perimeters,
-                [ map $_->p, map @{$_->fill_surfaces}, @{$lower_layer->regions} ],
-                1,
-            );
-            
-            # only consider perimeter areas that are at least one extrusion width thick
-            #FIXME Offset2 eats out from both sides, while the perimeters are create outside in.
-            #Should the $pw not be half of the current value?
-            my $pw = min(map $_->flow(FLOW_ROLE_PERIMETER)->scaled_width, @{$layer->regions});
-            $perimeters = offset2($perimeters, -$pw, +$pw);
-            
-            # append such thick perimeters to the areas that need support
-            push @$overhangs, @$perimeters;
-        }
-        
-        # find new internal infill
-        $upper_internal = my $new_internal = intersection(
-            [
-                @$overhangs,
-                @$upper_internal,
-            ],
-            [
-                # our current internal fill boundaries
-                map $_->p,
-                    grep $_->surface_type == S_TYPE_INTERNAL || $_->surface_type == S_TYPE_INTERNALVOID,
-                        map @{$_->fill_surfaces}, @{$lower_layer->regions}
-            ],
-        );
-        
-        # apply new internal infill to regions
-        foreach my $layerm (@{$lower_layer->regions}) {
-            my (@internal, @other) = ();
-            foreach my $surface (map $_->clone, @{$layerm->fill_surfaces}) {
-                if ($surface->surface_type == S_TYPE_INTERNAL || $surface->surface_type == S_TYPE_INTERNALVOID) {
-                    push @internal, $surface;
-                } else {
-                    push @other, $surface;
-                }
-            }
-            
-            my @new = map Slic3r::Surface->new(
-                expolygon       => $_,
-                surface_type    => S_TYPE_INTERNAL,
-            ),
-                @{intersection_ex(
-                    [ map $_->p, @internal ],
-                    $new_internal,
-                    1,
-                )};
-            
-            push @other, map Slic3r::Surface->new(
-                expolygon       => $_,
-                surface_type    => S_TYPE_INTERNALVOID,
-            ),
-                @{diff_ex(
-                    [ map $_->p, @internal ],
-                    $new_internal,
-                    1,
-                )};
-            
-            # If there are voids it means that our internal infill is not adjacent to
-            # perimeters. In this case it would be nice to add a loop around infill to
-            # make it more robust and nicer. TODO.
-            
-            $layerm->fill_surfaces->clear;
-            $layerm->fill_surfaces->append($_) for (@new, @other);
-
-            if ($SLIC3R_DEBUG_SLICE_PROCESSING) {
-                $layerm->export_region_fill_surfaces_to_svg_debug("6_clip_fill_surfaces");
-            }
-        }
-    }
-}
-
-sub discover_horizontal_shells {
-    my $self = shift;
-    
-    Slic3r::debugf "==> DISCOVERING HORIZONTAL SHELLS\n";
-    
-    for my $region_id (0 .. ($self->print->region_count-1)) {
-        for (my $i = 0; $i < $self->layer_count; $i++) {
-            my $layerm = $self->get_layer($i)->regions->[$region_id];
-            
-            if ($layerm->region->config->solid_infill_every_layers && $layerm->region->config->fill_density > 0
-                && ($i % $layerm->region->config->solid_infill_every_layers) == 0) {
-                # This is the layer to put the sparse infill in. Mark S_TYPE_INTERNAL surfaces as S_TYPE_INTERNALSOLID or S_TYPE_INTERNALBRIDGE.
-                # If the sparse infill is not active, the internal surfaces are of type S_TYPE_INTERNAL.
-                my $type = $layerm->region->config->fill_density == 100 ? S_TYPE_INTERNALSOLID : S_TYPE_INTERNALBRIDGE;
-                $_->surface_type($type) for @{$layerm->fill_surfaces->filter_by_type(S_TYPE_INTERNAL)};
-            }
-
-            # If ensure_vertical_shell_thickness, then the rest has already been performed by discover_vertical_shells().
-            next if ($layerm->region->config->ensure_vertical_shell_thickness);
-            
-            EXTERNAL: foreach my $type (S_TYPE_TOP, S_TYPE_BOTTOM, S_TYPE_BOTTOMBRIDGE) {
-                # find slices of current type for current layer
-                # use slices instead of fill_surfaces because they also include the perimeter area
-                # which needs to be propagated in shells; we need to grow slices like we did for
-                # fill_surfaces though.  Using both ungrown slices and grown fill_surfaces will
-                # not work in some situations, as there won't be any grown region in the perimeter 
-                # area (this was seen in a model where the top layer had one extra perimeter, thus
-                # its fill_surfaces were thinner than the lower layer's infill), however it's the best
-                # solution so far. Growing the external slices by EXTERNAL_INFILL_MARGIN will put
-                # too much solid infill inside nearly-vertical slopes.
-                my $solid = [
-                    # Surfaces including the area of perimeters. Everything, that is visible from the top / bottom
-                    # (not covered by a layer above / below).
-                    # This does not contain the areas covered by perimeters!
-                    (map $_->p, @{$layerm->slices->filter_by_type($type)}),
-                    # Infill areas (slices without the perimeters).
-                    (map $_->p, @{$layerm->fill_surfaces->filter_by_type($type)}),
-                ];
-                next if !@$solid;
-                Slic3r::debugf "Layer %d has %s surfaces\n", $i, ($type == S_TYPE_TOP) ? 'top' : 'bottom';
-                
-                my $solid_layers = ($type == S_TYPE_TOP)
-                    ? $layerm->region->config->top_solid_layers
-                    : $layerm->region->config->bottom_solid_layers;
-                NEIGHBOR: for (my $n = ($type == S_TYPE_TOP) ? $i-1 : $i+1; 
-                                abs($n - $i) < $solid_layers;
-                                ($type == S_TYPE_TOP) ? $n-- : $n++) {
-                    
-                    next if $n < 0 || $n >= $self->layer_count;
-                    Slic3r::debugf "  looking for neighbors on layer %d...\n", $n;
-                    
-                    # Reference to the lower layer of a TOP surface, or an upper layer of a BOTTOM surface.
-                    my $neighbor_layerm = $self->get_layer($n)->regions->[$region_id];
-                    # Reference to the neighbour fill surfaces.
-                    my $neighbor_fill_surfaces = $neighbor_layerm->fill_surfaces;
-                    # Clone because we will use these surfaces even after clearing the collection.
-                    my @neighbor_fill_surfaces = map $_->clone, @$neighbor_fill_surfaces;
-                    
-                    # find intersection between neighbor and current layer's surfaces
-                    # intersections have contours and holes
-                    # we update $solid so that we limit the next neighbor layer to the areas that were
-                    # found on this one - in other words, solid shells on one layer (for a given external surface)
-                    # are always a subset of the shells found on the previous shell layer
-                    # this approach allows for DWIM in hollow sloping vases, where we want bottom
-                    # shells to be generated in the base but not in the walls (where there are many
-                    # narrow bottom surfaces): reassigning $solid will consider the 'shadow' of the 
-                    # upper perimeter as an obstacle and shell will not be propagated to more upper layers
-                    #FIXME How does it work for S_TYPE_INTERNALBRIDGE? This is set for sparse infill. Likely this does not work.
-                    my $new_internal_solid = $solid = intersection(
-                        $solid,
-                        [ map $_->p, grep { ($_->surface_type == S_TYPE_INTERNAL) || ($_->surface_type == S_TYPE_INTERNALSOLID) } @neighbor_fill_surfaces ],
-                        1,
-                    );
-                    next EXTERNAL if !@$new_internal_solid;
-                    
-                    if ($layerm->region->config->fill_density == 0) {
-                        # if we're printing a hollow object we discard any solid shell thinner
-                        # than a perimeter width, since it's probably just crossing a sloping wall
-                        # and it's not wanted in a hollow print even if it would make sense when
-                        # obeying the solid shell count option strictly (DWIM!)
-                        my $margin = $neighbor_layerm->flow(FLOW_ROLE_EXTERNAL_PERIMETER)->scaled_width;
-                        my $regularized = offset2($new_internal_solid, -$margin, +$margin, JT_MITER, 5);
-                        my $too_narrow = diff(
-                            $new_internal_solid,
-                            $regularized,
-                            1,
-                        );
-                        # Trim the regularized region by the original region.
-                        $new_internal_solid = $solid = intersection(
-                            $new_internal_solid,
-                            $regularized,
-                        ) if @$too_narrow;
-                    }
-                    
-                    # make sure the new internal solid is wide enough, as it might get collapsed
-                    # when spacing is added in Fill.pm
-                    if ($layerm->region->config->ensure_vertical_shell_thickness) {
-                        # The possible thin sickles of top / bottom surfaces on steeply sloping surfaces touch
-                        # the projections of top / bottom perimeters, therefore they will be sufficiently inflated by
-                        # merging them with the projections of the top / bottom perimeters.
-                    } else {
-                        #FIXME Vojtech: Disable this and you will be sorry.
-                        # https://github.com/prusa3d/Slic3r/issues/26 bottom
-                        my $margin = 3 * $layerm->flow(FLOW_ROLE_SOLID_INFILL)->scaled_width; # require at least this size
-                        # we use a higher miterLimit here to handle areas with acute angles
-                        # in those cases, the default miterLimit would cut the corner and we'd
-                        # get a triangle in $too_narrow; if we grow it below then the shell
-                        # would have a different shape from the external surface and we'd still
-                        # have the same angle, so the next shell would be grown even more and so on.
-                        my $too_narrow = diff(
-                            $new_internal_solid,
-                            offset2($new_internal_solid, -$margin, +$margin, JT_MITER, 5),
-                            1,
-                        );
-                        
-                        if (@$too_narrow) {
-                            # grow the collapsing parts and add the extra area to  the neighbor layer 
-                            # as well as to our original surfaces so that we support this 
-                            # additional area in the next shell too
-                        
-                            # make sure our grown surfaces don't exceed the fill area
-                            my @grown = @{intersection(
-                                offset($too_narrow, +$margin),
-                                # Discard bridges as they are grown for anchoring and we can't
-                                # remove such anchors. (This may happen when a bridge is being 
-                                # anchored onto a wall where little space remains after the bridge
-                                # is grown, and that little space is an internal solid shell so 
-                                # it triggers this too_narrow logic.)
-                                [ map $_->p, grep { $_->is_internal && !$_->is_bridge } @neighbor_fill_surfaces ],
-                            )};
-                            $new_internal_solid = $solid = [ @grown, @$new_internal_solid ];
-                        }
-                    }
-                    
-                    # internal-solid are the union of the existing internal-solid surfaces
-                    # and new ones
-                    my $internal_solid = union_ex([
-                        ( map $_->p, grep $_->surface_type == S_TYPE_INTERNALSOLID, @neighbor_fill_surfaces ),
-                        @$new_internal_solid,
-                    ]);
-                    
-                    # subtract intersections from layer surfaces to get resulting internal surfaces
-                    my $internal = diff_ex(
-                        [ map $_->p, grep $_->surface_type == S_TYPE_INTERNAL, @neighbor_fill_surfaces ],
-                        [ map @$_, @$internal_solid ],
-                        1,
-                    );
-                    Slic3r::debugf "    %d internal-solid and %d internal surfaces found\n",
-                        scalar(@$internal_solid), scalar(@$internal);
-                    
-                    # assign resulting internal surfaces to layer
-                    $neighbor_fill_surfaces->clear;
-                    $neighbor_fill_surfaces->append($_)
-                        for map Slic3r::Surface->new(expolygon => $_, surface_type => S_TYPE_INTERNAL),
-                            @$internal;
-                    
-                    # assign new internal-solid surfaces to layer
-                    $neighbor_fill_surfaces->append($_)
-                        for map Slic3r::Surface->new(expolygon => $_, surface_type => S_TYPE_INTERNALSOLID),
-                        @$internal_solid;
-                    
-                    # assign top and bottom surfaces to layer
-                    foreach my $s (@{Slic3r::Surface::Collection->new(grep { ($_->surface_type == S_TYPE_TOP) || $_->is_bottom } @neighbor_fill_surfaces)->group}) {
-                        my $solid_surfaces = diff_ex(
-                            [ map $_->p, @$s ],
-                            [ map @$_, @$internal_solid, @$internal ],
-                            1,
-                        );
-                        $neighbor_fill_surfaces->append($_)
-                            for map $s->[0]->clone(expolygon => $_), @$solid_surfaces;
-                    }
-                }
-            } # foreach my $type (S_TYPE_TOP, S_TYPE_BOTTOM, S_TYPE_BOTTOMBRIDGE)
-        } # for each layer
-    } # for each region
-
-    # Debugging output.
-    if ($SLIC3R_DEBUG_SLICE_PROCESSING) {
-        for my $region_id (0 .. ($self->print->region_count-1)) {
-            for (my $i = 0; $i < $self->layer_count; $i++) {
-                my $layerm = $self->get_layer($i)->regions->[$region_id];
-                $layerm->export_region_slices_to_svg_debug("5_discover_horizontal_shells");
-                $layerm->export_region_fill_surfaces_to_svg_debug("5_discover_horizontal_shells");
-            } # for each layer
-        } # for each region
-    }
-}
-
-# combine fill surfaces across layers to honor the "infill every N layers" option
-# Idempotence of this method is guaranteed by the fact that we don't remove things from
-# fill_surfaces but we only turn them into VOID surfaces, thus preserving the boundaries.
-sub combine_infill {
-    my $self = shift;
-    
-    # define the type used for voids
-    my %voidtype = (
-        &S_TYPE_INTERNAL() => S_TYPE_INTERNALVOID,
-    );
-    
-    # work on each region separately
-    for my $region_id (0 .. ($self->print->region_count-1)) {
-        my $region = $self->print->get_region($region_id);
-        my $every = $region->config->infill_every_layers;
-        next unless $every > 1 && $region->config->fill_density > 0;
-        
-        # limit the number of combined layers to the maximum height allowed by this regions' nozzle
-        my $nozzle_diameter = min(
-            $self->print->config->get_at('nozzle_diameter', $region->config->infill_extruder-1),
-            $self->print->config->get_at('nozzle_diameter', $region->config->solid_infill_extruder-1),
-        );
-        
-        # define the combinations
-        my %combine = ();   # layer_idx => number of additional combined lower layers
-        {
-            my $current_height = my $layers = 0;
-            for my $layer_idx (0 .. ($self->layer_count-1)) {
-                my $layer = $self->get_layer($layer_idx);
-                next if $layer->id == 0;  # skip first print layer (which may not be first layer in array because of raft)
-                my $height = $layer->height;
-                
-                # check whether the combination of this layer with the lower layers' buffer
-                # would exceed max layer height or max combined layer count
-                if ($current_height + $height >= $nozzle_diameter + epsilon || $layers >= $every) {
-                    # append combination to lower layer
-                    $combine{$layer_idx-1} = $layers;
-                    $current_height = $layers = 0;
-                }
-                
-                $current_height += $height;
-                $layers++;
-            }
-            
-            # append lower layers (if any) to uppermost layer
-            $combine{$self->layer_count-1} = $layers;
-        }
-        
-        # loop through layers to which we have assigned layers to combine
-        for my $layer_idx (sort keys %combine) {
-            next unless $combine{$layer_idx} > 1;
-            
-            # get all the LayerRegion objects to be combined
-            my @layerms = map $self->get_layer($_)->get_region($region_id),
-                ($layer_idx - ($combine{$layer_idx}-1) .. $layer_idx);
-            
-            # only combine internal infill
-            for my $type (S_TYPE_INTERNAL) {
-                # we need to perform a multi-layer intersection, so let's split it in pairs
-                
-                # initialize the intersection with the candidates of the lowest layer
-                my $intersection = [ map $_->expolygon, @{$layerms[0]->fill_surfaces->filter_by_type($type)} ];
-                
-                # start looping from the second layer and intersect the current intersection with it
-                for my $layerm (@layerms[1 .. $#layerms]) {
-                    $intersection = intersection_ex(
-                        [ map @$_, @$intersection ],
-                        [ map @{$_->expolygon}, @{$layerm->fill_surfaces->filter_by_type($type)} ],
-                    );
-                }
-                
-                my $area_threshold = $layerms[0]->infill_area_threshold;
-                @$intersection = grep $_->area > $area_threshold, @$intersection;
-                next if !@$intersection;
-                Slic3r::debugf "  combining %d %s regions from layers %d-%d\n",
-                    scalar(@$intersection),
-                    ($type == S_TYPE_INTERNAL ? 'internal' : 'internal-solid'),
-                    $layer_idx-($every-1), $layer_idx;
-                
-                # $intersection now contains the regions that can be combined across the full amount of layers
-                # so let's remove those areas from all layers
-                
-                 my @intersection_with_clearance = map @{$_->offset(
-                       $layerms[-1]->flow(FLOW_ROLE_SOLID_INFILL)->scaled_width    / 2
-                     + $layerms[-1]->flow(FLOW_ROLE_PERIMETER)->scaled_width / 2
-                     # Because fill areas for rectilinear and honeycomb are grown 
-                     # later to overlap perimeters, we need to counteract that too.
-                     + (($type == S_TYPE_INTERNALSOLID || $region->config->fill_pattern =~ /(rectilinear|grid|line|honeycomb)/)
-                       ? $layerms[-1]->flow(FLOW_ROLE_SOLID_INFILL)->scaled_width
-                       : 0)
-                     )}, @$intersection;
-
-                
-                foreach my $layerm (@layerms) {
-                    my @this_type   = @{$layerm->fill_surfaces->filter_by_type($type)};
-                    my @other_types = map $_->clone, grep $_->surface_type != $type, @{$layerm->fill_surfaces};
-                    
-                    my @new_this_type = map Slic3r::Surface->new(expolygon => $_, surface_type => $type),
-                        @{diff_ex(
-                            [ map $_->p, @this_type ],
-                            [ @intersection_with_clearance ],
-                        )};
-                    
-                    # apply surfaces back with adjusted depth to the uppermost layer
-                    if ($layerm->layer->id == $self->get_layer($layer_idx)->id) {
-                        push @new_this_type,
-                            map Slic3r::Surface->new(
-                                expolygon        => $_,
-                                surface_type     => $type,
-                                thickness        => sum(map $_->layer->height, @layerms),
-                                thickness_layers => scalar(@layerms),
-                            ),
-                            @$intersection;
-                    } else {
-                        # save void surfaces
-                        push @new_this_type,
-                            map Slic3r::Surface->new(expolygon => $_, surface_type => $voidtype{$type}),
-                            @{intersection_ex(
-                                [ map @{$_->expolygon}, @this_type ],
-                                [ @intersection_with_clearance ],
-                            )};
-                    }
-                    
-                    $layerm->fill_surfaces->clear;
-                    $layerm->fill_surfaces->append($_) for (@new_this_type, @other_types);
-                }
-            }
-        }
-    }
-}
-
 1;
diff --git a/xs/src/libslic3r/ClipperUtils.cpp b/xs/src/libslic3r/ClipperUtils.cpp
index 1a4550248..86123b23c 100644
--- a/xs/src/libslic3r/ClipperUtils.cpp
+++ b/xs/src/libslic3r/ClipperUtils.cpp
@@ -505,13 +505,8 @@ inline ClipperLib::PolyTree _clipper_do_polytree2(const ClipperLib::ClipType cli
     ClipperLib::Paths input_clip    = Slic3rMultiPoints_to_ClipperPaths(clip);
     
     // perform safety offset
-    if (safety_offset_) {
-        if (clipType == ClipperLib::ctUnion) {
-            safety_offset(&input_subject);
-        } else {
-            safety_offset(&input_clip);
-        }
-    }
+    if (safety_offset_)
+        safety_offset((clipType == ClipperLib::ctUnion) ? &input_subject : &input_clip);
     
     ClipperLib::Clipper clipper;
     clipper.AddPaths(input_subject, ClipperLib::ptSubject, true);
@@ -528,8 +523,7 @@ inline ClipperLib::PolyTree _clipper_do_polytree2(const ClipperLib::ClipType cli
     return retval;
 }
 
-ClipperLib::PolyTree
-_clipper_do_pl(const ClipperLib::ClipType clipType, const Polylines &subject, 
+ClipperLib::PolyTree _clipper_do_pl(const ClipperLib::ClipType clipType, const Polylines &subject, 
     const Polygons &clip, const ClipperLib::PolyFillType fillType,
     const bool safety_offset_)
 {
@@ -554,33 +548,25 @@ _clipper_do_pl(const ClipperLib::ClipType clipType, const Polylines &subject,
     return retval;
 }
 
-Polygons
-_clipper(ClipperLib::ClipType clipType, const Polygons &subject, 
-    const Polygons &clip, bool safety_offset_)
+Polygons _clipper(ClipperLib::ClipType clipType, const Polygons &subject, const Polygons &clip, bool safety_offset_)
 {
     return ClipperPaths_to_Slic3rPolygons(_clipper_do<ClipperLib::Paths>(clipType, subject, clip, ClipperLib::pftNonZero, safety_offset_));
 }
 
-ExPolygons
-_clipper_ex(ClipperLib::ClipType clipType, const Polygons &subject, 
-    const Polygons &clip, bool safety_offset_)
+ExPolygons _clipper_ex(ClipperLib::ClipType clipType, const Polygons &subject, const Polygons &clip, bool safety_offset_)
 {
     ClipperLib::PolyTree polytree = _clipper_do_polytree2(clipType, subject, clip, ClipperLib::pftNonZero, safety_offset_);
     return PolyTreeToExPolygons(polytree);
 }
 
-Polylines
-_clipper_pl(ClipperLib::ClipType clipType, const Polylines &subject, 
-    const Polygons &clip, bool safety_offset_)
+Polylines _clipper_pl(ClipperLib::ClipType clipType, const Polylines &subject, const Polygons &clip, bool safety_offset_)
 {
     ClipperLib::Paths output;
     ClipperLib::PolyTreeToPaths(_clipper_do_pl(clipType, subject, clip, ClipperLib::pftNonZero, safety_offset_), output);
     return ClipperPaths_to_Slic3rPolylines(output);
 }
 
-Polylines
-_clipper_pl(ClipperLib::ClipType clipType, const Polygons &subject, 
-    const Polygons &clip, bool safety_offset_)
+Polylines _clipper_pl(ClipperLib::ClipType clipType, const Polygons &subject, const Polygons &clip, bool safety_offset_)
 {
     // transform input polygons into polylines
     Polylines polylines;
diff --git a/xs/src/libslic3r/ClipperUtils.hpp b/xs/src/libslic3r/ClipperUtils.hpp
index 247a53d8f..eb83c31a3 100644
--- a/xs/src/libslic3r/ClipperUtils.hpp
+++ b/xs/src/libslic3r/ClipperUtils.hpp
@@ -185,32 +185,27 @@ inline Slic3r::Lines intersection_ln(const Slic3r::Line &subject, const Slic3r::
 }
 
 // union
-inline Slic3r::Polygons
-union_(const Slic3r::Polygons &subject, bool safety_offset_ = false)
+inline Slic3r::Polygons union_(const Slic3r::Polygons &subject, bool safety_offset_ = false)
 {
     return _clipper(ClipperLib::ctUnion, subject, Slic3r::Polygons(), safety_offset_);
 }
 
-inline Slic3r::Polygons
-union_(const Slic3r::Polygons &subject, const Slic3r::Polygons &subject2, bool safety_offset_ = false)
+inline Slic3r::Polygons union_(const Slic3r::Polygons &subject, const Slic3r::Polygons &subject2, bool safety_offset_ = false)
 {
     return _clipper(ClipperLib::ctUnion, subject, subject2, safety_offset_);
 }
 
-inline Slic3r::ExPolygons
-union_ex(const Slic3r::Polygons &subject, bool safety_offset_ = false)
+inline Slic3r::ExPolygons union_ex(const Slic3r::Polygons &subject, bool safety_offset_ = false)
 {
     return _clipper_ex(ClipperLib::ctUnion, subject, Slic3r::Polygons(), safety_offset_);
 }
 
-inline Slic3r::ExPolygons
-union_ex(const Slic3r::ExPolygons &subject, bool safety_offset_ = false)
+inline Slic3r::ExPolygons union_ex(const Slic3r::ExPolygons &subject, bool safety_offset_ = false)
 {
     return _clipper_ex(ClipperLib::ctUnion, to_polygons(subject), Slic3r::Polygons(), safety_offset_);
 }
 
-inline Slic3r::ExPolygons
-union_ex(const Slic3r::Surfaces &subject, bool safety_offset_ = false)
+inline Slic3r::ExPolygons union_ex(const Slic3r::Surfaces &subject, bool safety_offset_ = false)
 {
     return _clipper_ex(ClipperLib::ctUnion, to_polygons(subject), Slic3r::Polygons(), safety_offset_);
 }
diff --git a/xs/src/libslic3r/Fill/FillBase.cpp b/xs/src/libslic3r/Fill/FillBase.cpp
index d2f874436..8ed6408d1 100644
--- a/xs/src/libslic3r/Fill/FillBase.cpp
+++ b/xs/src/libslic3r/Fill/FillBase.cpp
@@ -11,6 +11,7 @@
 #include "FillPlanePath.hpp"
 #include "FillRectilinear.hpp"
 #include "FillRectilinear2.hpp"
+#include "FillRectilinear3.hpp"
 
 namespace Slic3r {
 
@@ -31,7 +32,7 @@ Fill* Fill::new_from_type(const InfillPattern type)
     case ipArchimedeanChords:   return new FillArchimedeanChords();
     case ipHilbertCurve:        return new FillHilbertCurve();
     case ipOctagramSpiral:      return new FillOctagramSpiral();
-    default: CONFESS("unknown type"); return NULL;
+    default: CONFESS("unknown type"); return nullptr;
     }
 }
 
@@ -39,7 +40,7 @@ Fill* Fill::new_from_type(const std::string &type)
 {
     static t_config_enum_values enum_keys_map = ConfigOptionEnum<InfillPattern>::get_enum_values();
     t_config_enum_values::const_iterator it = enum_keys_map.find(type);
-    return (it == enum_keys_map.end()) ? NULL : new_from_type(InfillPattern(it->second));
+    return (it == enum_keys_map.end()) ? nullptr : new_from_type(InfillPattern(it->second));
 }
 
 Polylines Fill::fill_surface(const Surface *surface, const FillParams &params)
diff --git a/xs/src/libslic3r/Point.hpp b/xs/src/libslic3r/Point.hpp
index f2d3a6e65..a56e642aa 100644
--- a/xs/src/libslic3r/Point.hpp
+++ b/xs/src/libslic3r/Point.hpp
@@ -35,9 +35,7 @@ public:
     Point(int _x, int _y): x(_x), y(_y) {};
     Point(long long _x, long long _y): x(coord_t(_x)), y(coord_t(_y)) {};  // for Clipper
     Point(double x, double y);
-    static Point new_scale(coordf_t x, coordf_t y) {
-        return Point(scale_(x), scale_(y));
-    };
+    static Point new_scale(coordf_t x, coordf_t y) { return Point(coord_t(scale_(x)), coord_t(scale_(y))); }
 
     bool operator==(const Point& rhs) const { return this->x == rhs.x && this->y == rhs.y; }
     bool operator!=(const Point& rhs) const { return ! (*this == rhs); }
@@ -182,9 +180,10 @@ private:
 
 class Point3 : public Point
 {
-    public:
+public:
     coord_t z;
     explicit Point3(coord_t _x = 0, coord_t _y = 0, coord_t _z = 0): Point(_x, _y), z(_z) {};
+    static Point3 new_scale(coordf_t x, coordf_t y, coordf_t z) { return Point3(coord_t(scale_(x)), coord_t(scale_(y)), coord_t(scale_(z))); }
 };
 
 std::ostream& operator<<(std::ostream &stm, const Pointf &pointf);
diff --git a/xs/src/libslic3r/Print.hpp b/xs/src/libslic3r/Print.hpp
index a5cab89ee..3b9b77982 100644
--- a/xs/src/libslic3r/Print.hpp
+++ b/xs/src/libslic3r/Print.hpp
@@ -191,6 +191,7 @@ public:
     void _slice();
     std::string _fix_slicing_errors();
     void _simplify_slices(double distance);
+    void _prepare_infill();
     bool has_support_material() const;
     void detect_surfaces_type();
     void process_external_surfaces();
@@ -198,6 +199,9 @@ public:
     void bridge_over_infill();
     void _make_perimeters();
     void _infill();
+    void clip_fill_surfaces();
+    void discover_horizontal_shells();
+    void combine_infill();
     void _generate_support_material();
 
 private:
diff --git a/xs/src/libslic3r/PrintConfig.cpp b/xs/src/libslic3r/PrintConfig.cpp
index f54be8e22..8688c1525 100644
--- a/xs/src/libslic3r/PrintConfig.cpp
+++ b/xs/src/libslic3r/PrintConfig.cpp
@@ -68,7 +68,7 @@ PrintConfigDef::PrintConfigDef()
     def = this->add("bridge_angle", coFloat);
     def->label = "Bridging angle";
     def->category = "Infill";
-    def->tooltip = "Bridging angle override. If left to zero, the bridging angle will be calculated automatically. Otherwise the provided angle will be used for all bridges, use 180° for zero angle.";
+    def->tooltip = "Bridging angle override. If left to zero, the bridging angle will be calculated automatically. Otherwise the provided angle will be used for all bridges. Use 180° for zero angle.";
     def->sidetext = "°";
     def->cli = "bridge-angle=f";
     def->min = 0;
diff --git a/xs/src/libslic3r/PrintObject.cpp b/xs/src/libslic3r/PrintObject.cpp
index 26f6c50a0..9bf74bee7 100644
--- a/xs/src/libslic3r/PrintObject.cpp
+++ b/xs/src/libslic3r/PrintObject.cpp
@@ -3,6 +3,7 @@
 #include "ClipperUtils.hpp"
 #include "Geometry.hpp"
 #include "SupportMaterial.hpp"
+#include "Surface.hpp"
 
 #include <utility>
 #include <boost/log/trivial.hpp>
@@ -32,8 +33,8 @@
 
 namespace Slic3r {
 
-PrintObject::PrintObject(Print* print, ModelObject* model_object, const BoundingBoxf3 &modobj_bbox)
-:   typed_slices(false),
+PrintObject::PrintObject(Print* print, ModelObject* model_object, const BoundingBoxf3 &modobj_bbox) :  
+    typed_slices(false),
     _print(print),
     _model_object(model_object),
     layer_height_profile_valid(false)
@@ -46,12 +47,10 @@ PrintObject::PrintObject(Print* print, ModelObject* model_object, const Bounding
         // don't assume it's already aligned and we don't alter the original position in model.
         // We store the XY translation so that we can place copies correctly in the output G-code
         // (copies are expressed in G-code coordinates and this translation is not publicly exposed).
-        this->_copies_shift = Point(
-            scale_(modobj_bbox.min.x), scale_(modobj_bbox.min.y));
-
+        this->_copies_shift = Point::new_scale(modobj_bbox.min.x, modobj_bbox.min.y);
         // Scale the object size and store it
         Pointf3 size = modobj_bbox.size();
-        this->size = Point3(scale_(size.x), scale_(size.y), scale_(size.z));
+        this->size = Point3::new_scale(size.x, size.y, size.z);
     }
     
     this->reload_model_instances();
@@ -283,6 +282,105 @@ bool PrintObject::has_support_material() const
         || this->config.support_material_enforce_layers > 0;
 }
 
+void PrintObject::_prepare_infill()
+{
+    // This will assign a type (top/bottom/internal) to $layerm->slices.
+    // Then the classifcation of $layerm->slices is transfered onto 
+    // the $layerm->fill_surfaces by clipping $layerm->fill_surfaces
+    // by the cummulative area of the previous $layerm->fill_surfaces.
+    this->detect_surfaces_type();
+    
+    // Decide what surfaces are to be filled.
+    // Here the S_TYPE_TOP / S_TYPE_BOTTOMBRIDGE / S_TYPE_BOTTOM infill is turned to just S_TYPE_INTERNAL if zero top / bottom infill layers are configured.
+    // Also tiny S_TYPE_INTERNAL surfaces are turned to S_TYPE_INTERNAL_SOLID.
+    BOOST_LOG_TRIVIAL(info) << "Preparing fill surfaces...";
+    for (auto *layer : this->layers)
+        for (auto *region : layer->regions)
+            region->prepare_fill_surfaces();
+
+    // this will detect bridges and reverse bridges
+    // and rearrange top/bottom/internal surfaces
+    // It produces enlarged overlapping bridging areas.
+    //
+    // 1) S_TYPE_BOTTOMBRIDGE / S_TYPE_BOTTOM infill is grown by 3mm and clipped by the total infill area. Bridges are detected. The areas may overlap.
+    // 2) S_TYPE_TOP is grown by 3mm and clipped by the grown bottom areas. The areas may overlap.
+    // 3) Clip the internal surfaces by the grown top/bottom surfaces.
+    // 4) Merge surfaces with the same style. This will mostly get rid of the overlaps.
+    //FIXME This does not likely merge surfaces, which are supported by a material with different colors, but same properties.
+    this->process_external_surfaces();
+
+    // Add solid fills to ensure the shell vertical thickness.
+    this->discover_vertical_shells();
+
+    // Debugging output.
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    for (size_t region_id = 0; region_id < this->print()->regions.size(); ++ region_id)
+        for (const Layer *layer : this->layers) {
+            LayerRegion *layerm = layer->regions[region_id];
+            layerm->export_region_slices_to_svg_debug("6_discover_vertical_shells-final");
+            layerm->export_region_fill_surfaces_to_svg_debug("6_discover_vertical_shells-final");
+        } // for each layer
+    } // for each region
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+
+    // Detect, which fill surfaces are near external layers.
+    // They will be split in internal and internal-solid surfaces.
+    // The purpose is to add a configurable number of solid layers to support the TOP surfaces
+    // and to add a configurable number of solid layers above the BOTTOM / BOTTOMBRIDGE surfaces
+    // to close these surfaces reliably.
+    //FIXME Vojtech: Is this a good place to add supporting infills below sloping perimeters?
+    this->discover_horizontal_shells();
+
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    for (size_t region_id = 0; region_id < this->print()->regions.size(); ++ region_id)
+        for (const Layer *layer : this->layers) {
+            LayerRegion *layerm = layer->regions[region_id];
+            layerm->export_region_slices_to_svg_debug("7_discover_horizontal_shells-final");
+            layerm->export_region_fill_surfaces_to_svg_debug("7_discover_horizontal_shells-final");
+        } // for each layer
+    } // for each region
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+
+    // Only active if config->infill_only_where_needed. This step trims the sparse infill,
+    // so it acts as an internal support. It maintains all other infill types intact.
+    // Here the internal surfaces and perimeters have to be supported by the sparse infill.
+    //FIXME The surfaces are supported by a sparse infill, but the sparse infill is only as large as the area to support.
+    // Likely the sparse infill will not be anchored correctly, so it will not work as intended.
+    // Also one wishes the perimeters to be supported by a full infill.
+    this->clip_fill_surfaces();
+
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    for (size_t region_id = 0; region_id < this->print()->regions.size(); ++ region_id)
+        for (const Layer *layer : this->layers) {
+            LayerRegion *layerm = layer->regions[region_id];
+            layerm->export_region_slices_to_svg_debug("8_clip_surfaces-final");
+            layerm->export_region_fill_surfaces_to_svg_debug("8_clip_surfaces-final");
+        } // for each layer
+    } // for each region
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+    
+    // the following step needs to be done before combination because it may need
+    // to remove only half of the combined infill
+    this->bridge_over_infill();
+
+    // combine fill surfaces to honor the "infill every N layers" option
+    this->combine_infill();
+
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    for (size_t region_id = 0; region_id < this->print()->regions.size(); ++ region_id)
+        for (const Layer *layer : this->layers) {
+            LayerRegion *layerm = layer->regions[region_id];
+            layerm->export_region_slices_to_svg_debug("9_prepare_infill-final");
+            layerm->export_region_fill_surfaces_to_svg_debug("9_prepare_infill-final");
+        } // for each layer
+    } // for each region
+    for (const Layer *layer : this->layers) {
+        layer->export_region_slices_to_svg_debug("9_prepare_infill-final");
+        layer->export_region_fill_surfaces_to_svg_debug("9_prepare_infill-final");
+    } // for each layer
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+}
+
 // This function analyzes slices of a region (SurfaceCollection slices).
 // Each region slice (instance of Surface) is analyzed, whether it is supported or whether it is the top surface.
 // Initially all slices are of type stInternal.
@@ -334,8 +432,8 @@ void PrintObject::detect_surfaces_type()
                     LayerRegion *layerm = layer->get_region(idx_region);
                     // comparison happens against the *full* slices (considering all regions)
                     // unless internal shells are requested
-                    Layer       *upper_layer = idx_layer + 1 < this->layer_count() ? this->get_layer(idx_layer + 1) : nullptr;
-                    Layer       *lower_layer = idx_layer > 0 ? this->get_layer(idx_layer - 1) : nullptr;
+                    Layer       *upper_layer = (idx_layer + 1 < this->layer_count()) ? this->layers[idx_layer + 1] : nullptr;
+                    Layer       *lower_layer = (idx_layer > 0) ? this->layers[idx_layer - 1] : nullptr;
                     // collapse very narrow parts (using the safety offset in the diff is not enough)
                     float        offset = layerm->flow(frExternalPerimeter).scaled_width() / 10.f;
 
@@ -473,7 +571,10 @@ void PrintObject::detect_surfaces_type()
                 } // for each layer of a region
             });
         BOOST_LOG_TRIVIAL(debug) << "Detecting solid surfaces for region " << idx_region << " - clipping in parallel - end";
-    } // for each $self->print->region_count
+    } // for each this->print->region_count
+
+    // Mark the object to have the region slices classified (typed, which also means they are split based on whether they are supported, bridging, top layers etc.)
+    this->typed_slices = true;
 }
 
 void PrintObject::process_external_surfaces()
@@ -669,7 +770,6 @@ void PrintObject::discover_vertical_shells()
                     ExPolygons shell_ex;
 #endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
                     float min_perimeter_infill_spacing = float(infill_line_spacing) * 1.05f;
-                    if (1)
                     {
                         PROFILE_BLOCK(discover_vertical_shells_region_layer_collect);
 #if 0
@@ -698,8 +798,7 @@ void PrintObject::discover_vertical_shells()
                         bool hole_first = true;
                         for (int n = (int)idx_layer - n_extra_bottom_layers; n <= (int)idx_layer + n_extra_top_layers; ++ n)
                             if (n >= 0 && n < (int)this->layers.size()) {
-                                Layer       &neighbor_layer = *this->layers[n];
-                                LayerRegion &neighbor_region = *neighbor_layer.get_region(int(idx_region));
+                                Layer &neighbor_layer = *this->layers[n];
                                 const DiscoverVerticalShellsCacheEntry &cache = cache_top_botom_regions[n];
                                 if (hole_first) {
                                     hole_first = false;
@@ -880,8 +979,7 @@ void PrintObject::discover_vertical_shells()
 
 /* This method applies bridge flow to the first internal solid layer above
    sparse infill */
-void
-PrintObject::bridge_over_infill()
+void PrintObject::bridge_over_infill()
 {
     BOOST_LOG_TRIVIAL(info) << "Bridge over infill...";
 
@@ -906,7 +1004,7 @@ PrintObject::bridge_over_infill()
             if (layer_it == this->layers.begin()) continue;
             
             Layer* layer        = *layer_it;
-            LayerRegion* layerm = layer->get_region(region_id);
+            LayerRegion* layerm = layer->regions[region_id];
             
             // extract the stInternalSolid surfaces that might be transformed into bridges
             Polygons internal_solid;
@@ -921,7 +1019,7 @@ PrintObject::bridge_over_infill()
                 
                 // iterate through lower layers spanned by bridge_flow
                 double bottom_z = layer->print_z - bridge_flow.height;
-                for (int i = (layer_it - this->layers.begin()) - 1; i >= 0; --i) {
+                for (int i = int(layer_it - this->layers.begin()) - 1; i >= 0; --i) {
                     const Layer* lower_layer = this->layers[i];
                     
                     // stop iterating if layer is lower than bottom_z
@@ -941,7 +1039,7 @@ PrintObject::bridge_over_infill()
                 // therefore it may create 1) gaps, and 2) sharp corners, which are outside the original contour.
                 // The gaps will be filled by a separate region, which makes the infill less stable and it takes longer.
                 {
-                    double min_width = bridge_flow.scaled_width() * 3;
+                    float min_width = float(bridge_flow.scaled_width()) * 3.f;
                     to_bridge_pp = offset2(to_bridge_pp, -min_width, +min_width);
                 }
                 
@@ -1069,6 +1167,8 @@ void PrintObject::_slice()
 {
     BOOST_LOG_TRIVIAL(info) << "Slicing objects...";
 
+    this->typed_slices = false;
+
 #if 0
     // Disable parallelization for debugging purposes.
     static tbb::task_scheduler_init *tbb_init = nullptr;
@@ -1221,7 +1321,7 @@ std::vector<ExPolygons> PrintObject::_slice_region(size_t region_id, const std::
                 // consider the first one
                 this->model_object()->instances.front()->transform_mesh(&mesh, true);
                 // align mesh to Z = 0 (it should be already aligned actually) and apply XY shift
-                mesh.translate(- unscale(this->_copies_shift.x), - unscale(this->_copies_shift.y), -this->model_object()->bounding_box().min.z);
+                mesh.translate(- float(unscale(this->_copies_shift.x)), - float(unscale(this->_copies_shift.y)), -float(this->model_object()->bounding_box().min.z));
                 // perform actual slicing
                 TriangleMeshSlicer mslicer(&mesh);
                 mslicer.slice(z, &layers);
@@ -1462,6 +1562,387 @@ void PrintObject::_infill()
     this->state.set_done(posInfill);
 }
 
+// Only active if config->infill_only_where_needed. This step trims the sparse infill,
+// so it acts as an internal support. It maintains all other infill types intact.
+// Here the internal surfaces and perimeters have to be supported by the sparse infill.
+//FIXME The surfaces are supported by a sparse infill, but the sparse infill is only as large as the area to support.
+// Likely the sparse infill will not be anchored correctly, so it will not work as intended.
+// Also one wishes the perimeters to be supported by a full infill.
+// Idempotence of this method is guaranteed by the fact that we don't remove things from
+// fill_surfaces but we only turn them into VOID surfaces, thus preserving the boundaries.
+void PrintObject::clip_fill_surfaces()
+{
+    if (! this->config.infill_only_where_needed.value ||
+        ! std::any_of(this->print()->regions.begin(), this->print()->regions.end(), 
+            [](const PrintRegion *region) { return region->config.fill_density > 0; }))
+        return;
+
+    // We only want infill under ceilings; this is almost like an
+    // internal support material.
+    // Proceed top-down, skipping the bottom layer.
+    Polygons upper_internal;
+    for (int layer_id = int(this->layers.size()) - 1; layer_id > 0; -- layer_id) {
+        Layer *layer       = this->layers[layer_id];
+        Layer *lower_layer = this->layers[layer_id - 1];
+        // Detect things that we need to support.
+        // Cummulative slices.
+        Polygons slices;
+        for (const ExPolygon &expoly : layer->slices.expolygons)
+            polygons_append(slices, to_polygons(expoly));
+        // Cummulative fill surfaces.
+        Polygons fill_surfaces;
+        // Solid surfaces to be supported.
+        Polygons overhangs;
+        for (const LayerRegion *layerm : layer->regions)
+            for (const Surface &surface : layerm->fill_surfaces.surfaces) {
+                Polygons polygons = to_polygons(surface.expolygon);
+                if (surface.is_solid())
+                    polygons_append(overhangs, polygons);
+                polygons_append(fill_surfaces, std::move(polygons));
+            }
+        Polygons lower_layer_fill_surfaces;
+        Polygons lower_layer_internal_surfaces;
+        for (const LayerRegion *layerm : lower_layer->regions)
+            for (const Surface &surface : layerm->fill_surfaces.surfaces) {
+                Polygons polygons = to_polygons(surface.expolygon);
+                if (surface.surface_type == stInternal || surface.surface_type == stInternalVoid)
+                    polygons_append(lower_layer_internal_surfaces, polygons);
+                polygons_append(lower_layer_fill_surfaces, std::move(polygons));
+            }
+        // We also need to support perimeters when there's at least one full unsupported loop
+        {
+            // Get perimeters area as the difference between slices and fill_surfaces
+            // Only consider the area that is not supported by lower perimeters
+            Polygons perimeters = intersection(diff(slices, fill_surfaces), lower_layer_fill_surfaces);
+            // Only consider perimeter areas that are at least one extrusion width thick.
+            //FIXME Offset2 eats out from both sides, while the perimeters are create outside in.
+            //Should the pw not be half of the current value?
+            float pw = FLT_MAX;
+            for (const LayerRegion *layerm : layer->regions)
+                pw = std::min<float>(pw, layerm->flow(frPerimeter).scaled_width());
+            // Append such thick perimeters to the areas that need support
+            polygons_append(overhangs, offset2(perimeters, -pw, +pw));
+        }
+        // Find new internal infill.
+        polygons_append(overhangs, std::move(upper_internal));
+        upper_internal = intersection(overhangs, lower_layer_internal_surfaces);
+        // Apply new internal infill to regions.
+        for (LayerRegion *layerm : lower_layer->regions) {
+            if (layerm->region()->config.fill_density.value == 0)
+                continue;
+            SurfaceType internal_surface_types[] = { stInternal, stInternalVoid };
+            Polygons internal;
+            for (Surface &surface : layerm->fill_surfaces.surfaces)
+                if (surface.surface_type == stInternal || surface.surface_type == stInternalVoid)
+                    polygons_append(internal, std::move(surface.expolygon));
+            layerm->fill_surfaces.remove_types(internal_surface_types, 2);
+            layerm->fill_surfaces.append(intersection_ex(internal, upper_internal, true), stInternal);
+            layerm->fill_surfaces.append(diff_ex        (internal, upper_internal, true), stInternalVoid);
+            // If there are voids it means that our internal infill is not adjacent to
+            // perimeters. In this case it would be nice to add a loop around infill to
+            // make it more robust and nicer. TODO.
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+            layerm->export_region_fill_surfaces_to_svg_debug("6_clip_fill_surfaces");
+#endif
+        }
+    }
+}
+
+void PrintObject::discover_horizontal_shells()
+{
+    BOOST_LOG_TRIVIAL(trace) << "discover_horizontal_shells()";
+    
+    for (size_t region_id = 0; region_id < this->print()->regions.size(); ++ region_id) {
+        for (int i = 0; i < int(this->layers.size()); ++ i) {
+            LayerRegion       *layerm = this->layers[i]->regions[region_id];
+            PrintRegionConfig &region_config = layerm->region()->config;
+            if (region_config.solid_infill_every_layers.value > 0 && region_config.fill_density.value > 0 &&
+                (i % region_config.solid_infill_every_layers) == 0) {
+                // Insert a solid internal layer. Mark stInternal surfaces as stInternalSolid or stInternalBridge.
+                SurfaceType type = (region_config.fill_density == 100) ? stInternalSolid : stInternalBridge;
+                for (Surface &surface : layerm->fill_surfaces.surfaces)
+                    if (surface.surface_type == stInternal)
+                        surface.surface_type = type;
+            }
+
+            // If ensure_vertical_shell_thickness, then the rest has already been performed by discover_vertical_shells().
+            if (region_config.ensure_vertical_shell_thickness.value)
+                continue;
+            
+            for (int idx_surface_type = 0; idx_surface_type < 3; ++ idx_surface_type) {
+                SurfaceType type = (idx_surface_type == 0) ? stTop : (idx_surface_type == 1) ? stBottom : stBottomBridge;
+                // Find slices of current type for current layer.
+                // Use slices instead of fill_surfaces, because they also include the perimeter area,
+                // which needs to be propagated in shells; we need to grow slices like we did for
+                // fill_surfaces though. Using both ungrown slices and grown fill_surfaces will
+                // not work in some situations, as there won't be any grown region in the perimeter 
+                // area (this was seen in a model where the top layer had one extra perimeter, thus
+                // its fill_surfaces were thinner than the lower layer's infill), however it's the best
+                // solution so far. Growing the external slices by EXTERNAL_INFILL_MARGIN will put
+                // too much solid infill inside nearly-vertical slopes.
+
+                // Surfaces including the area of perimeters. Everything, that is visible from the top / bottom
+                // (not covered by a layer above / below).
+                // This does not contain the areas covered by perimeters!
+                Polygons solid;
+                for (const Surface &surface : layerm->slices.surfaces)
+                    if (surface.surface_type == type)
+                        polygons_append(solid, to_polygons(surface.expolygon));
+                // Infill areas (slices without the perimeters).
+                for (const Surface &surface : layerm->fill_surfaces.surfaces)
+                    if (surface.surface_type == type)
+                        polygons_append(solid, to_polygons(surface.expolygon));
+                if (solid.empty())
+                    continue;
+//                Slic3r::debugf "Layer %d has %s surfaces\n", $i, ($type == S_TYPE_TOP) ? 'top' : 'bottom';
+                
+                size_t solid_layers = (type == stTop) ? region_config.top_solid_layers.value : region_config.bottom_solid_layers.value;                
+                for (int n = (type == stTop) ? i-1 : i+1; std::abs(n - i) < solid_layers; (type == stTop) ? -- n : ++ n) {
+                    if (n < 0 || n >= int(this->layers.size()))
+                        continue;
+//                    Slic3r::debugf "  looking for neighbors on layer %d...\n", $n;                  
+                    // Reference to the lower layer of a TOP surface, or an upper layer of a BOTTOM surface.
+                    LayerRegion *neighbor_layerm = this->layers[n]->regions[region_id];
+                    
+                    // find intersection between neighbor and current layer's surfaces
+                    // intersections have contours and holes
+                    // we update $solid so that we limit the next neighbor layer to the areas that were
+                    // found on this one - in other words, solid shells on one layer (for a given external surface)
+                    // are always a subset of the shells found on the previous shell layer
+                    // this approach allows for DWIM in hollow sloping vases, where we want bottom
+                    // shells to be generated in the base but not in the walls (where there are many
+                    // narrow bottom surfaces): reassigning $solid will consider the 'shadow' of the 
+                    // upper perimeter as an obstacle and shell will not be propagated to more upper layers
+                    //FIXME How does it work for S_TYPE_INTERNALBRIDGE? This is set for sparse infill. Likely this does not work.
+                    Polygons new_internal_solid;
+                    {
+                        Polygons internal;
+                        for (const Surface &surface : neighbor_layerm->fill_surfaces.surfaces)
+                            if (surface.surface_type == stInternal || surface.surface_type == stInternalSolid)
+                                polygons_append(internal, to_polygons(surface.expolygon));
+                        new_internal_solid = intersection(solid, internal, true);
+                    }
+                    if (new_internal_solid.empty()) {
+                        // No internal solid needed on this layer. In order to decide whether to continue
+                        // searching on the next neighbor (thus enforcing the configured number of solid
+                        // layers, use different strategies according to configured infill density:
+                        if (region_config.fill_density.value == 0) {
+                            // If user expects the object to be void (for example a hollow sloping vase),
+                            // don't continue the search. In this case, we only generate the external solid
+                            // shell if the object would otherwise show a hole (gap between perimeters of 
+                            // the two layers), and internal solid shells are a subset of the shells found 
+                            // on each previous layer.
+                            goto EXTERNAL;
+                        } else {
+                            // If we have internal infill, we can generate internal solid shells freely.
+                            continue;
+                        }
+                    }
+                    
+                    if (region_config.fill_density.value == 0) {
+                        // if we're printing a hollow object we discard any solid shell thinner
+                        // than a perimeter width, since it's probably just crossing a sloping wall
+                        // and it's not wanted in a hollow print even if it would make sense when
+                        // obeying the solid shell count option strictly (DWIM!)
+                        float margin = float(neighbor_layerm->flow(frExternalPerimeter).scaled_width());
+                        Polygons too_narrow = diff(
+                            new_internal_solid, 
+                            offset2(new_internal_solid, -margin, +margin, jtMiter, 5), 
+                            true);
+                        // Trim the regularized region by the original region.
+                        if (! too_narrow.empty())
+                            new_internal_solid = solid = diff(new_internal_solid, too_narrow);
+                    }
+
+                    // make sure the new internal solid is wide enough, as it might get collapsed
+                    // when spacing is added in Fill.pm
+                    {
+                        //FIXME Vojtech: Disable this and you will be sorry.
+                        // https://github.com/prusa3d/Slic3r/issues/26 bottom
+                        float margin = 3.f * layerm->flow(frSolidInfill).scaled_width(); // require at least this size
+                        // we use a higher miterLimit here to handle areas with acute angles
+                        // in those cases, the default miterLimit would cut the corner and we'd
+                        // get a triangle in $too_narrow; if we grow it below then the shell
+                        // would have a different shape from the external surface and we'd still
+                        // have the same angle, so the next shell would be grown even more and so on.
+                        Polygons too_narrow = diff(
+                            new_internal_solid,
+                            offset2(new_internal_solid, -margin, +margin, ClipperLib::jtMiter, 5),
+                            true);
+                        if (! too_narrow.empty()) {
+                            // grow the collapsing parts and add the extra area to  the neighbor layer 
+                            // as well as to our original surfaces so that we support this 
+                            // additional area in the next shell too
+                            // make sure our grown surfaces don't exceed the fill area
+                            Polygons internal;
+                            for (const Surface &surface : neighbor_layerm->fill_surfaces.surfaces)
+                                if (surface.is_internal() && !surface.is_bridge())
+                                    polygons_append(internal, to_polygons(surface.expolygon));
+                            polygons_append(new_internal_solid, 
+                                intersection(
+                                    offset(too_narrow, +margin),
+                                    // Discard bridges as they are grown for anchoring and we can't
+                                    // remove such anchors. (This may happen when a bridge is being 
+                                    // anchored onto a wall where little space remains after the bridge
+                                    // is grown, and that little space is an internal solid shell so 
+                                    // it triggers this too_narrow logic.)
+                                    internal));
+                            solid = new_internal_solid;
+                        }
+                    }
+                    
+                    // internal-solid are the union of the existing internal-solid surfaces
+                    // and new ones
+                    SurfaceCollection backup = std::move(neighbor_layerm->fill_surfaces);
+                    polygons_append(new_internal_solid, to_polygons(backup.filter_by_type(stInternalSolid)));
+                    ExPolygons internal_solid = union_ex(new_internal_solid, false);
+                    // assign new internal-solid surfaces to layer
+                    neighbor_layerm->fill_surfaces.set(internal_solid, stInternalSolid);
+                    // subtract intersections from layer surfaces to get resulting internal surfaces
+                    Polygons polygons_internal = to_polygons(std::move(internal_solid));
+                    ExPolygons internal = diff_ex(
+                        to_polygons(backup.filter_by_type(stInternal)),
+                        polygons_internal,
+                        true);
+                    // assign resulting internal surfaces to layer
+                    neighbor_layerm->fill_surfaces.append(internal, stInternal);
+                    polygons_append(polygons_internal, to_polygons(std::move(internal)));
+                    // assign top and bottom surfaces to layer
+                    SurfaceType surface_types_solid[] = { stTop, stBottom, stBottomBridge };
+                    backup.keep_types(surface_types_solid, 3);
+                    std::vector<SurfacesPtr> top_bottom_groups;
+                    backup.group(&top_bottom_groups);
+                    for (SurfacesPtr &group : top_bottom_groups)
+                        neighbor_layerm->fill_surfaces.append(
+                            diff_ex(to_polygons(group), polygons_internal),
+                            group.front()->surface_type);
+                }
+		EXTERNAL:;
+            } // foreach type (stTop, stBottom, stBottomBridge)
+        } // for each layer
+    } // for each region
+
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    for (size_t region_id = 0; region_id < this->print()->regions.size(); ++ region_id)
+        for (const Layer *layer : this->layers) {
+            const LayerRegion *layerm = layer->regions[region_id];
+            layerm->export_region_slices_to_svg_debug("5_discover_horizontal_shells");
+            layerm->export_region_fill_surfaces_to_svg_debug("5_discover_horizontal_shells");
+        } // for each layer
+    } // for each region
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+}
+
+// combine fill surfaces across layers to honor the "infill every N layers" option
+// Idempotence of this method is guaranteed by the fact that we don't remove things from
+// fill_surfaces but we only turn them into VOID surfaces, thus preserving the boundaries.
+void PrintObject::combine_infill()
+{
+    // Work on each region separately.
+    for (size_t region_id = 0; region_id < this->print()->regions.size(); ++ region_id) {
+        const PrintRegion *region = this->print()->regions[region_id];
+        const int every = region->config.infill_every_layers.value;
+        if (every < 2 || region->config.fill_density == 0.)
+            continue;
+        // Limit the number of combined layers to the maximum height allowed by this regions' nozzle.
+        //FIXME limit the layer height to max_layer_height
+        double nozzle_diameter = std::min(
+            this->print()->config.nozzle_diameter.get_at(region->config.infill_extruder.value - 1),
+            this->print()->config.nozzle_diameter.get_at(region->config.solid_infill_extruder.value - 1));
+        // define the combinations
+        std::vector<size_t> combine(this->layers.size(), 0);
+        {
+            double current_height = 0.;
+            size_t num_layers = 0;
+            for (size_t layer_idx = 0; layer_idx < this->layers.size(); ++ layer_idx) {
+                const Layer *layer = this->layers[layer_idx];
+                if (layer->id() == 0)
+                    // Skip first print layer (which may not be first layer in array because of raft).
+                    continue;
+                // Check whether the combination of this layer with the lower layers' buffer
+                // would exceed max layer height or max combined layer count.
+                if (current_height + layer->height >= nozzle_diameter + EPSILON || num_layers >= every) {
+                    // Append combination to lower layer.
+                    combine[layer_idx - 1] = num_layers;
+                    current_height = 0.;
+                    num_layers = 0;
+                }
+                current_height += layer->height;
+                ++ num_layers;
+            }
+            
+            // Append lower layers (if any) to uppermost layer.
+            combine[this->layers.size() - 1] = num_layers;
+        }
+        
+        // loop through layers to which we have assigned layers to combine
+        for (size_t layer_idx = 0; layer_idx < this->layers.size(); ++ layer_idx) {
+            size_t num_layers = combine[layer_idx];
+			if (num_layers <= 1)
+                continue;
+            // Get all the LayerRegion objects to be combined.
+            std::vector<LayerRegion*> layerms;
+            layerms.reserve(num_layers);
+			for (size_t i = layer_idx + 1 - num_layers; i <= layer_idx; ++ i)
+                layerms.emplace_back(this->layers[i]->regions[region_id]);
+            // We need to perform a multi-layer intersection, so let's split it in pairs.
+            // Initialize the intersection with the candidates of the lowest layer.
+            ExPolygons intersection = to_expolygons(layerms.front()->fill_surfaces.filter_by_type(stInternal));
+            // Start looping from the second layer and intersect the current intersection with it.
+            for (size_t i = 1; i < layerms.size(); ++ i)
+                intersection = intersection_ex(
+                    to_polygons(intersection),
+                    to_polygons(layerms[i]->fill_surfaces.filter_by_type(stInternal)),
+                    false);
+            double area_threshold = layerms.front()->infill_area_threshold();
+            if (! intersection.empty() && area_threshold > 0.)
+                intersection.erase(std::remove_if(intersection.begin(), intersection.end(), 
+                    [area_threshold](const ExPolygon &expoly) { return expoly.area() <= area_threshold; }), 
+                    intersection.end());
+            if (intersection.empty())
+                continue;
+//            Slic3r::debugf "  combining %d %s regions from layers %d-%d\n",
+//                scalar(@$intersection),
+//                ($type == S_TYPE_INTERNAL ? 'internal' : 'internal-solid'),
+//                $layer_idx-($every-1), $layer_idx;
+            // intersection now contains the regions that can be combined across the full amount of layers,
+            // so let's remove those areas from all layers.
+            Polygons intersection_with_clearance;
+            intersection_with_clearance.reserve(intersection.size());
+            float clearance_offset = 
+                0.5f * layerms.back()->flow(frPerimeter).scaled_width() +
+             // Because fill areas for rectilinear and honeycomb are grown 
+             // later to overlap perimeters, we need to counteract that too.
+                ((region->config.fill_pattern == ipRectilinear   ||
+                  region->config.fill_pattern == ipGrid          ||
+                  region->config.fill_pattern == ipLine          ||
+                  region->config.fill_pattern == ipHoneycomb) ? 1.5f : 0.5f) * 
+                    layerms.back()->flow(frSolidInfill).scaled_width();
+            for (ExPolygon &expoly : intersection)
+                polygons_append(intersection_with_clearance, offset(expoly, clearance_offset));
+            for (LayerRegion *layerm : layerms) {
+                Polygons internal = to_polygons(layerm->fill_surfaces.filter_by_type(stInternal));
+                layerm->fill_surfaces.remove_type(stInternal);
+                layerm->fill_surfaces.append(diff_ex(internal, intersection_with_clearance, false), stInternal);
+                if (layerm == layerms.back()) {
+                    // Apply surfaces back with adjusted depth to the uppermost layer.
+                    Surface templ(stInternal, ExPolygon());
+                    templ.thickness = 0.;
+                    for (LayerRegion *layerm2 : layerms)
+                        templ.thickness += layerm2->layer()->height;
+                    templ.thickness_layers = (unsigned short)layerms.size();
+                    layerm->fill_surfaces.append(intersection, templ);
+                } else {
+                    // Save void surfaces.
+                    layerm->fill_surfaces.append(
+                        intersection_ex(internal, intersection_with_clearance, false),
+                        stInternalVoid);
+                }
+            }
+        }
+    }
+}
+
 void PrintObject::_generate_support_material()
 {
     PrintObjectSupportMaterial support_material(this, PrintObject::slicing_parameters());
diff --git a/xs/src/libslic3r/SurfaceCollection.hpp b/xs/src/libslic3r/SurfaceCollection.hpp
index 0edca6a5a..29cfeb1db 100644
--- a/xs/src/libslic3r/SurfaceCollection.hpp
+++ b/xs/src/libslic3r/SurfaceCollection.hpp
@@ -13,8 +13,8 @@ public:
     Surfaces surfaces;
     
     SurfaceCollection() {};
-    SurfaceCollection(const Surfaces &_surfaces)
-        : surfaces(_surfaces) {};
+    SurfaceCollection(const Surfaces &surfaces) : surfaces(surfaces) {};
+    SurfaceCollection(Surfaces &&surfaces) : surfaces(std::move(surfaces)) {};
     operator Polygons() const;
     operator ExPolygons() const;
     void simplify(double tolerance);
diff --git a/xs/xsp/Print.xsp b/xs/xsp/Print.xsp
index 9c5bf1e2f..b937fe6e8 100644
--- a/xs/xsp/Print.xsp
+++ b/xs/xsp/Print.xsp
@@ -65,11 +65,6 @@ _constant()
         %code%{ RETVAL = &THIS->size; %};
     Clone<BoundingBox> bounding_box();
     
-    bool typed_slices()
-        %code%{ RETVAL = THIS->typed_slices; %};
-    void set_typed_slices(bool value)
-        %code%{ THIS->typed_slices = value; %};
-    
     Points _shifted_copies()
         %code%{ RETVAL = THIS->_shifted_copies; %};
     void set_shifted_copies(Points value)
@@ -108,10 +103,9 @@ _constant()
     void _slice();
     std::string _fix_slicing_errors();
     void _simplify_slices(double distance);
+    void _prepare_infill();
     void detect_surfaces_type();
     void process_external_surfaces();
-    void discover_vertical_shells();
-    void bridge_over_infill();
     void _make_perimeters();
     void _infill();
     void _generate_support_material();