Bugfix: is_printable() wasn't discarding narrow ring-shaped top/bottom surfaces because it was only considering the contour. This caused extra shell material even in hollow prints. #1049

lib/Slic3r/ExPolygon.pm

@@ -62,6 +62,17 @@ sub is_valid {
         && (!first { $_->is_counter_clockwise } $self->holes);
 }
 
+# returns false if the expolygon is too tight to be printed
+sub is_printable {
+    my $self = shift;
+    my ($width) = @_;
+    
+    # try to get an inwards offset
+    # for a distance equal to half of the extrusion width;
+    # if no offset is possible, then expolygon is not printable.
+    return Slic3r::Geometry::Clipper::offset($self, -$width / 2) ? 1 : 0;
+}
+
 sub boost_polygon {
     my $self = shift;
     return Boost::Geometry::Utils::polygon(@$self);

lib/Slic3r/ExtrusionPath.pm

@@ -97,8 +97,6 @@ sub first_point {
     return $self->polyline->[0];
 }
 
-sub is_printable { 1 }
-
 sub is_perimeter {
     my $self = shift;
     return $self->role == EXTR_ROLE_PERIMETER

lib/Slic3r/Polygon.pm

@@ -128,7 +128,7 @@ sub subdivide {
     }
 }
 
-# returns false if the polyline is too tight to be printed
+# returns false if the polygon is too tight to be printed
 sub is_printable {
     my $self = shift;
     my ($width) = @_;

lib/Slic3r/Print/Object.pm

@@ -360,8 +360,8 @@ sub detect_surfaces_type {
             [ map @$_, @$clip_surfaces ],
             1,
         );
-        return grep $_->contour->is_printable($layerm->perimeter_flow->scaled_width),
-            map Slic3r::Surface->new(expolygon => $_, surface_type => $result_type), 
+        return map Slic3r::Surface->new(expolygon => $_, surface_type => $result_type),
+            grep $_->is_printable($layerm->perimeter_flow->scaled_width),
             @$expolygons;
     };