bugfix: dense_infill too small region make export gcode crash

xs/src/libslic3r/Fill/FillRectilinear2.cpp

@@ -1481,10 +1481,10 @@ void FillRectilinear2Peri::fill_surface_extrusion(const Surface *surface, const
     //you don't want to sort the extrusions: big infill first, small second
     eecroot->no_sort = true;
 
+    // === extrude perimeter ===
     Polylines polylines_1;
     //generate perimeter:
-    //TODO: better optimize start/end point?
-    ExPolygons path_perimeter = offset_ex(surface->expolygon, scale_(-this->spacing/2));
+    ExPolygons path_perimeter = offset2_ex(surface->expolygon, scale_(-this->spacing), scale_(this->spacing / 2));
     for (ExPolygon &expolygon : path_perimeter) {
         expolygon.contour.make_counter_clockwise();
         polylines_1.push_back(expolygon.contour.split_at_index(0));
@@ -1494,48 +1494,61 @@ void FillRectilinear2Peri::fill_surface_extrusion(const Surface *surface, const
         }
     }
 
-    // Save into layer.
-    auto *eec = new ExtrusionEntityCollection();
-    /// pass the no_sort attribute to the extrusion path
-    eec->no_sort = this->no_sort();
-    /// add it into the collection
-    eecroot->entities.push_back(eec);
-    /// push the path
-    extrusion_entities_append_paths(
-        eec->entities, STDMOVE(polylines_1),
-        flow.bridge ?
-    erBridgeInfill :
-                   (surface->is_solid() ?
-                   ((surface->is_top()) ? erTopSolidInfill : erSolidInfill) :
-                   erInternalInfill),
-                   flow.mm3_per_mm() * params.flow_mult, flow.width * params.flow_mult, flow.height);
+    if (!polylines_1.empty()) {
+        // Save into layer.
+        ExtrusionEntityCollection *eec = new ExtrusionEntityCollection();
+        /// pass the no_sort attribute to the extrusion path
+        eec->no_sort = this->no_sort();
+        /// add it into the collection
+        eecroot->entities.push_back(eec);
+        /// push the path
+        extrusion_entities_append_paths(
+            eec->entities, (polylines_1),
+            flow.bridge ?
+        erBridgeInfill :
+                       (surface->is_solid() ?
+                       ((surface->is_top()) ? erTopSolidInfill : erSolidInfill) :
+                       erInternalInfill),
+                       flow.mm3_per_mm() * params.flow_mult, flow.width * params.flow_mult, flow.height);
+    }
 
+    // === extrude dense infill ===
     Polylines polylines_2;
+    bool canFill = true;
     //50% overlap with the new perimeter
     ExPolygons path_inner = offset2_ex(surface->expolygon, scale_(-this->spacing * 1.5), scale_(this->spacing));
     for (ExPolygon &expolygon : path_inner) {
         Surface surfInner(*surface, expolygon);
         if (!fill_surface_by_lines(&surfInner, params, 0.f, 0.f, polylines_2)) {
             printf("FillRectilinear2::fill_surface() failed to fill a region.\n");
+            canFill = false;
         }
     }
-    // Save into layer.
-    eec = new ExtrusionEntityCollection();
-    /// pass the no_sort attribute to the extrusion path
-    eec->no_sort = this->no_sort();
-    /// add it into the collection
-    eecroot->entities.push_back(eec);
-    /// push the path
-    extrusion_entities_append_paths(
-        eec->entities, STDMOVE(polylines_2),
-        flow.bridge ?
-    erBridgeInfill :
-                   (surface->is_solid() ?
-                   ((surface->is_top()) ? erTopSolidInfill : erSolidInfill) :
-                   erInternalInfill),
-                   flow.mm3_per_mm() * params.flow_mult, flow.width * params.flow_mult, flow.height);
-
-    out.entities.push_back(eecroot);
+    if (canFill && !polylines_2.empty()) {
+        // Save into layer.
+        ExtrusionEntityCollection *eec = new ExtrusionEntityCollection();
+        /// pass the no_sort attribute to the extrusion path
+        eec->no_sort = this->no_sort();
+        /// add it into the collection
+        eecroot->entities.push_back(eec);
+        /// push the path
+        extrusion_entities_append_paths(
+            eec->entities, (polylines_2),
+            flow.bridge ?
+        erBridgeInfill :
+                       (surface->is_solid() ?
+                       ((surface->is_top()) ? erTopSolidInfill : erSolidInfill) :
+                       erInternalInfill),
+                       flow.mm3_per_mm() * params.flow_mult, flow.width * params.flow_mult, flow.height);
+    }
+
+    // === end ===
+    if (!eecroot->empty()) {
+        out.entities.push_back(eecroot);
+    } else {
+        delete eecroot;
+    }
+
 }
 
 } // namespace Slic3r