Bugfix: when processing with fill_density = 0, top/bottom solid shells were missing regions thinner than 3 * extrusion width. Includes regression test. #1602

Conflicts:

	lib/Slic3r/Print/Object.pm
	t/fill.t

lib/Slic3r/Print/Object.pm

@@ -727,7 +727,8 @@ sub discover_horizontal_shells {
                     next if $n < 0 || $n > $#{$self->layers};
                     Slic3r::debugf "  looking for neighbors on layer %d...\n", $n;
                     
-                    my $neighbor_fill_surfaces = $self->layers->[$n]->regions->[$region_id]->fill_surfaces;
+                    my $neighbor_layerm = $self->layers->[$n]->regions->[$region_id];
+                    my $neighbor_fill_surfaces = $neighbor_layerm->fill_surfaces;
                     my @neighbor_fill_surfaces = map $_->clone, @$neighbor_fill_surfaces;  # clone because we will use these surfaces even after clearing the collection
                     
                     # find intersection between neighbor and current layer's surfaces
@@ -746,26 +747,41 @@ sub discover_horizontal_shells {
                     );
                     next EXTERNAL if !@$new_internal_solid;
                     
-                    # make sure the new internal solid is wide enough, as it might get collapsed when
+                    if ($layerm->config->fill_density == 0) {
-                    # spacing is added in Fill.pm
+                        # 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_PERIMETER)->scaled_width;
+                        my $too_narrow = diff(
+                            $new_internal_solid,
+                            offset2($new_internal_solid, -$margin, +$margin, CLIPPER_OFFSET_SCALE, JT_MITER, 5),
+                            1,
+                        );
+                        $new_internal_solid = $solid = diff(
+                            $new_internal_solid,
+                            $too_narrow,
+                        ) if @$too_narrow;
+                    }
+                    
+                    # make sure the new internal solid is wide enough, as it might get collapsed
+                    # when spacing is added in Fill.pm
                     {
+                        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 $margin = 3 * $layerm->flow(FLOW_ROLE_SOLID_INFILL)->scaled_width; # require at least this size
                         my $too_narrow = diff(
                             $new_internal_solid,
                             offset2($new_internal_solid, -$margin, +$margin, CLIPPER_OFFSET_SCALE, JT_MITER, 5),
                             1,
                         );
                         
-                        # if some parts are going to collapse, use a different strategy according to fill density
                         if (@$too_narrow) {
-                            if ($layerm->config->fill_density > 0) {
+                            # grow the collapsing parts and add the extra area to  the neighbor layer 
-                                # if we have internal infill, grow the collapsing parts and add the extra area to 
+                            # as well as to our original surfaces so that we support this 
-                                # 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
@@ -774,13 +790,6 @@ sub discover_horizontal_shells {
                                 [ map $_->p, @neighbor_fill_surfaces ],
                             )};
                             $new_internal_solid = $solid = [ @grown, @$new_internal_solid ];
-                            } else {
-                                # if we're printing a hollow object, we discard such small parts
-                                $new_internal_solid = $solid = diff(
-                                    $new_internal_solid,
-                                    $too_narrow,
-                                );
-                            }
                         }
                     }
                     

t/fill.t

@@ -2,7 +2,7 @@ use Test::More;
 use strict;
 use warnings;
 
-plan tests => 40;
+plan tests => 41;
 
 BEGIN {
     use FindBin;
@@ -12,7 +12,7 @@ BEGIN {
 use List::Util qw(first);
 use Slic3r;
 use Slic3r::Geometry qw(scale X Y convex_hull);
-use Slic3r::Geometry::Clipper qw(diff_ex);
+use Slic3r::Geometry::Clipper qw(union diff_ex);
 use Slic3r::Surface qw(:types);
 use Slic3r::Test;
 
@@ -218,4 +218,41 @@ for my $pattern (qw(rectilinear honeycomb hilbertcurve concentric)) {
         "solid_infill_below_area and solid_infill_every_layers are ignored when fill_density is 0";
 }
 
+{
+    my $config = Slic3r::Config->new_from_defaults;
+    $config->set('skirts', 0);
+    $config->set('perimeters', 3);
+    $config->set('fill_density', 0);
+    $config->set('layer_height', 0.2);
+    $config->set('first_layer_height', 0.2);
+    $config->set('nozzle_diameter', [0.35]);
+    $config->set('infill_extruder', 2);
+    $config->set('infill_extrusion_width', 0.52);
+    
+    my $print = Slic3r::Test::init_print('A', config => $config);
+    my %infill = ();  # Z => [ Line, Line ... ]
+    my $tool = undef;
+    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
+        my ($self, $cmd, $args, $info) = @_;
+        
+        if ($cmd =~ /^T(\d+)/) {
+            $tool = $1;
+        } elsif ($cmd eq 'G1' && $info->{extruding} && $info->{dist_XY} > 0) {
+            if ($tool == $config->infill_extruder-1) {
+                my $z = 1 * $self->Z;
+                $infill{$z} ||= [];
+                push @{$infill{$z}}, Slic3r::Line->new_scale(
+                    [ $self->X, $self->Y ],
+                    [ $info->{new_X}, $info->{new_Y} ],
+                );
+            }
+        }
+    });
+    my $grow_d = scale($config->infill_extrusion_width)/2;
+    my $layer0_infill = union([ map @{$_->grow($grow_d)}, @{ $infill{0.2} } ]);
+    my $layer1_infill = union([ map @{$_->grow($grow_d)}, @{ $infill{0.4} } ]);
+    my $diff = [ grep $_->area >= 2*$grow_d**2, @{diff_ex($layer0_infill, $layer1_infill)} ];
+    is scalar(@$diff), 0, 'no missing parts in solid shell when fill_density is 0';
+}
+
 __END__