Trigger extra perimeters also when a diagonal gap would be visible. #3732

lib/Slic3r/Test.pm

@@ -133,6 +133,13 @@ sub mesh {
         $facets = [
             [0,1,2],[1,0,3],[2,1,4],[2,5,0],[0,6,3],[1,3,7],[1,8,4],[4,9,2],[10,5,2],[5,6,0],[6,11,3],[3,12,7],[7,8,1],[4,8,11],[4,11,9],[9,10,2],[10,13,5],[14,6,5],[9,11,6],[11,12,3],[12,8,7],[11,8,15],[13,10,9],[5,13,14],[14,13,6],[6,13,9],[15,12,11],[15,8,12]
         ];
+    } elsif ($name eq 'step') {
+        $vertices = [
+            [0,20,5],[0,20,0],[0,0,5],[0,0,0],[20,0,0],[20,0,5],[1,19,5],[1,1,5],[19,1,5],[20,20,5],[19,19,5],[20,20,0],[19,19,10],[1,19,10],[1,1,10],[19,1,10]
+        ];
+        $facets = [
+            [0,1,2],[1,3,2],[3,4,5],[2,3,5],[6,0,2],[6,2,7],[5,8,7],[5,7,2],[9,10,8],[9,8,5],[9,0,6],[9,6,10],[9,11,1],[9,1,0],[3,1,11],[4,3,11],[5,11,9],[5,4,11],[12,10,6],[12,6,13],[6,7,14],[13,6,14],[7,8,15],[14,7,15],[15,8,10],[15,10,12],[12,13,14],[12,14,15]
+        ];
     } else {
         return undef;
     }

t/shells.t

@@ -1,4 +1,4 @@
-use Test::More tests => 21;
+use Test::More tests => 24;
 use strict;
 use warnings;
 
@@ -11,6 +11,7 @@ BEGIN {
 use List::Util qw(first sum);
 use Slic3r;
 use Slic3r::Geometry qw(epsilon);
+use Slic3r::Surface qw(S_TYPE_TOP);
 use Slic3r::Test;
 
 {
@@ -318,4 +319,23 @@ use Slic3r::Test;
     is $diagonal_moves, 0, 'no spiral moves on two-island object';
 }
 
+{
+    # GH: #3732
+    my $config = Slic3r::Config->new_from_defaults;
+    $config->set('perimeters', 2);
+    $config->set('extrusion_width', 0.55);
+    $config->set('first_layer_height', 0.25);
+    $config->set('infill_overlap', '50%');
+    $config->set('layer_height', 0.25);
+    $config->set('perimeters', 2);
+    $config->set('extra_perimeters', 1);
+    
+    my $tprint = Slic3r::Test::init_print('step', config => $config);
+    $tprint->print->process;
+    my $layerm19 = $tprint->print->get_object(0)->get_layer(19)->get_region(0);
+    is scalar(@{$layerm19->slices->filter_by_type(S_TYPE_TOP)}), 1, 'top slice detected';
+    is scalar(@{$layerm19->fill_surfaces->filter_by_type(S_TYPE_TOP)}), 0, 'no top fill_surface detected';
+    is $layerm19->perimeters->items_count, 3, 'extra perimeter detected';
+}
+
 __END__

xs/src/libslic3r/PerimeterGenerator.cpp

@@ -315,8 +315,7 @@ PerimeterGenerator::process()
             );
             
             // append infill areas to fill_surfaces
-            for (ExPolygons::const_iterator ex = expp.begin(); ex != expp.end(); ++ex)
-                this->fill_surfaces->surfaces.push_back(Surface(stInternal, *ex));  // use a bogus surface type
+            this->fill_surfaces->append(expp, stInternal);  // use a bogus surface type
         }
     }
 }

xs/src/libslic3r/PrintObject.cpp

@@ -384,7 +384,7 @@ PrintObject::detect_surfaces_type()
             const Layer* lower_layer = layer_idx > 0 ? this->get_layer(layer_idx-1) : NULL;
             
             // collapse very narrow parts (using the safety offset in the diff is not enough)
-            const float offset = layerm.flow(frExternalPerimeter).scaled_width() / 10.f;
+            const float offs = layerm.flow(frExternalPerimeter).scaled_width() / 10.f;
 
             const Polygons layerm_slices_surfaces = layerm.slices;
 
@@ -392,14 +392,14 @@ PrintObject::detect_surfaces_type()
             // of current layer and upper one)
             SurfaceCollection top;
             if (upper_layer != NULL) {
-                const Polygons upper_slices = this->config.interface_shells.value
+                Polygons upper_slices = this->config.interface_shells.value
                     ? (Polygons)upper_layer->get_region(region_id)->slices
                     : (Polygons)upper_layer->slices;
                 
                 top.append(
                     offset2_ex(
                         diff(layerm_slices_surfaces, upper_slices, true),
-                        -offset, offset
+                        -offs, offs
                     ),
                     stTop
                 );
@@ -426,7 +426,7 @@ PrintObject::detect_surfaces_type()
                 bottom.append(
                     offset2_ex(
                         diff(layerm_slices_surfaces, lower_layer->slices, true), 
-                        -offset, offset
+                        -offs, offs
                     ),
                     surface_type_bottom
                 );
@@ -443,7 +443,7 @@ PrintObject::detect_surfaces_type()
                                 lower_layer->get_region(region_id)->slices, 
                                 true
                             ), 
-                            -offset, offset
+                            -offs, offs
                         ),
                         stBottom
                     );
@@ -470,7 +470,7 @@ PrintObject::detect_surfaces_type()
                 const Polygons top_polygons = to_polygons(STDMOVE(top));
                 top.clear();
                 top.append(
-                    offset2_ex(diff(top_polygons, bottom, true), -offset, offset),
+                    offset2_ex(diff(top_polygons, bottom, true), -offs, offs),
                     stTop
                 );
             }
@@ -487,17 +487,18 @@ PrintObject::detect_surfaces_type()
                 layerm.slices.append(
                     offset2_ex(
                         diff(layerm_slices_surfaces, topbottom, true),
-                        -offset, offset
+                        -offs, offs
                     ),
                     stInternal
                 );
             }
             
-            /*
-            Slic3r::debugf "  layer %d has %d bottom, %d top and %d internal surfaces\n",
-                $layerm->layer->id, scalar(@bottom), scalar(@top), scalar(@internal) if $Slic3r::debug;
-            */
-
+            #ifdef SLIC3R_DEBUG
+            printf("  layer %zu has %zu bottom, %zu top and %zu internal surfaces\n",
+                layerm.layer()->id(), bottom.size(), top.size(),
+                layerm.slices.size()-bottom.size()-top.size());
+            #endif
+            
         } // for each layer of a region
         
         /*  Fill in layerm->fill_surfaces by trimming the layerm->slices by the cummulative layerm->fill_surfaces.
@@ -782,7 +783,6 @@ PrintObject::_make_perimeters()
         size_t region_id = region_it - this->_print->regions.begin();
         const PrintRegion &region = **region_it;
         
-        
         if (!region.config.extra_perimeters
             || region.config.perimeters == 0
             || region.config.fill_density == 0
@@ -791,7 +791,13 @@ PrintObject::_make_perimeters()
         for (size_t i = 0; i <= (this->layer_count()-2); ++i) {
             LayerRegion &layerm                     = *this->get_layer(i)->get_region(region_id);
             const LayerRegion &upper_layerm         = *this->get_layer(i+1)->get_region(region_id);
-            const Polygons upper_layerm_polygons    = upper_layerm.slices;
+            
+            // In order to avoid diagonal gaps (GH #3732) we ignore the external half of the upper
+            // perimeter, since it's not truly covering this layer.
+            const Polygons upper_layerm_polygons = offset(
+                upper_layerm.slices,
+                -upper_layerm.flow(frExternalPerimeter).scaled_width()/2
+            );
             
             // Filter upper layer polygons in intersection_ppl by their bounding boxes?
             // my $upper_layerm_poly_bboxes= [ map $_->bounding_box, @{$upper_layerm_polygons} ];

xs/src/libslic3r/SurfaceCollection.hpp

@@ -29,6 +29,7 @@ class SurfaceCollection
     void append(const ExPolygons &src, SurfaceType surfaceType);
     size_t polygons_count() const;
     bool empty() const { return this->surfaces.empty(); };
+    size_t size() const { return this->surfaces.size(); };
     void clear() { this->surfaces.clear(); };
 };