Fixed inconsistency between 1st layer islands and ordering vector

leading to crashes.
Fixes SPE-1495

src/libslic3r/Layer.cpp

@@ -53,22 +53,7 @@ void Layer::make_slices()
         this->lslices = slices;
     }
 
-    // prepare lslices ordered by print order
-    this->lslice_indices_sorted_by_print_order.clear();
-    this->lslice_indices_sorted_by_print_order.reserve(lslices.size());
-    // prepare ordering points
-    Points ordering_points;
-    ordering_points.reserve( this->lslices.size());
-    for (const ExPolygon &ex :  this->lslices)
-        ordering_points.push_back(ex.contour.first_point());
-    
-    // sort slices
-    std::vector<Points::size_type> order = chain_points(ordering_points);
-
-    // populate slices vector
-    for (size_t i : order) {
-        this->lslice_indices_sorted_by_print_order.emplace_back(i);
-    }
+    this->lslice_indices_sorted_by_print_order = chain_expolygons(this->lslices);
 }
 
 // used by Layer::build_up_down_graph()

src/libslic3r/Layer.hpp

@@ -318,7 +318,7 @@ public:
 
     Layer              *upper_layer;
     Layer              *lower_layer;
-    bool                slicing_errors;
+//    bool                slicing_errors;
     coordf_t            slice_z;       // Z used for slicing in unscaled coordinates
     coordf_t            print_z;       // Z used for printing in unscaled coordinates
     coordf_t            height;        // layer height in unscaled coordinates
@@ -387,7 +387,8 @@ protected:
     friend std::string fix_slicing_errors(LayerPtrs&, const std::function<void()>&);
 
     Layer(size_t id, PrintObject *object, coordf_t height, coordf_t print_z, coordf_t slice_z) :
-        upper_layer(nullptr), lower_layer(nullptr), slicing_errors(false),
+        upper_layer(nullptr), lower_layer(nullptr), 
+        //slicing_errors(false),
         slice_z(slice_z), print_z(print_z), height(height),
         m_id(id), m_object(object) {}
     virtual ~Layer();

src/libslic3r/PrintObjectSlice.cpp

@@ -1,9 +1,10 @@
+#include "ClipperUtils.hpp"
 #include "ElephantFootCompensation.hpp"
 #include "I18N.hpp"
 #include "Layer.hpp"
 #include "MultiMaterialSegmentation.hpp"
 #include "Print.hpp"
-#include "ClipperUtils.hpp"
+#include "ShortestPath.hpp"
 
 #include <boost/log/trivial.hpp>
 
@@ -398,6 +399,10 @@ static std::vector<std::vector<ExPolygons>> slices_to_regions(
     return slices_by_region;
 }
 
+// Layer::slicing_errors is no more set since 1.41.1 or possibly earlier, thus this code
+// was not really functional for a long day and nobody missed it.
+// Could we reuse this fixing code one day?
+/*
 std::string fix_slicing_errors(LayerPtrs &layers, const std::function<void()> &throw_if_canceled)
 {
     // Collect layers with slicing errors.
@@ -480,6 +485,7 @@ std::string fix_slicing_errors(LayerPtrs &layers, const std::function<void()> &t
         "The model has overlapping or self-intersecting facets. I tried to repair it, "
         "however you might want to check the results or repair the input file and retry.\n";
 }
+*/
 
 // Called by make_perimeters()
 // 1) Decides Z positions of the layers,
@@ -502,12 +508,18 @@ void PrintObject::slice()
     m_layers = new_layers(this, generate_object_layers(m_slicing_params, layer_height_profile));
     this->slice_volumes();
     m_print->throw_if_canceled();
+#if 0
+    // Layer::slicing_errors is no more set since 1.41.1 or possibly earlier, thus this code
+    // was not really functional for a long day and nobody missed it.
+    // Could we reuse this fixing code one day?
+
     // Fix the model.
     //FIXME is this the right place to do? It is done repeateadly at the UI and now here at the backend.
     std::string warning = fix_slicing_errors(m_layers, [this](){ m_print->throw_if_canceled(); });
     m_print->throw_if_canceled();
     if (! warning.empty())
         BOOST_LOG_TRIVIAL(info) << warning;
+#endif
     // Update bounding boxes, back up raw slices of complex models.
     tbb::parallel_for(
         tbb::blocked_range<size_t>(0, m_layers.size()),
@@ -799,8 +811,12 @@ void PrintObject::slice_volumes()
 	    if (elephant_foot_compensation_scaled > 0.f && ! m_layers.empty()) {
 	    	// The Elephant foot has been compensated, therefore the 1st layer's lslices are shrank with the Elephant foot compensation value.
 	    	// Store the uncompensated value there.
-	    	assert(m_layers.front()->id() == 0);
-			m_layers.front()->lslices = std::move(lslices_1st_layer);
+            //FIXME is this operation needed? MMU painting and brim now have to do work arounds to work with compensated layer, not with the uncompensated layer.
+            // There may be subtle issues removing this block such as support raft sticking too well with the first object layer.
+            Layer &layer = *m_layers.front();
+	    	assert(layer.id() == 0);
+			layer.lslices = std::move(lslices_1st_layer);
+            layer.lslice_indices_sorted_by_print_order = chain_expolygons(layer.lslices);
 		}
 	}
 

src/libslic3r/ShortestPath.cpp

@@ -1076,6 +1076,15 @@ std::vector<size_t> chain_points(const Points &points, Point *start_near)
 	return out;
 }
 
+std::vector<size_t> chain_expolygons(const ExPolygons &expolygons, Point *start_near)
+{
+    Points ordering_points;
+    ordering_points.reserve(expolygons.size());
+    for (const ExPolygon &ex : expolygons)
+        ordering_points.push_back(ex.contour.first_point());
+    return chain_points(ordering_points);
+}
+
 #ifndef NDEBUG
 	// #define DEBUG_SVG_OUTPUT
 #endif /* NDEBUG */

src/libslic3r/ShortestPath.hpp

@@ -12,7 +12,11 @@ namespace ClipperLib { class PolyNode; }
 
 namespace Slic3r {
 
+class ExPolygon;
+using ExPolygons = std::vector<ExPolygon>;
+
 std::vector<size_t> 				 chain_points(const Points &points, Point *start_near = nullptr);
+std::vector<size_t> 				 chain_expolygons(const ExPolygons &expolygons, Point *start_near = nullptr);
 
 std::vector<std::pair<size_t, bool>> chain_extrusion_entities(std::vector<ExtrusionEntity*> &entities, const Point *start_near = nullptr);
 void                                 reorder_extrusion_entities(std::vector<ExtrusionEntity*> &entities, const std::vector<std::pair<size_t, bool>> &chain);