optimize the brdige over infill by extractng only the sparse infill lines from previous layer

src/libslic3r/Fill/Fill.cpp

@@ -643,6 +643,94 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
 #endif
 }
 
+Polylines Layer::generate_sparse_infill_polylines_for_anchoring() const
+{
+    std::vector<SurfaceFill>  surface_fills = group_fills(*this);
+    const Slic3r::BoundingBox bbox          = this->object()->bounding_box();
+    const auto                resolution    = this->object()->print()->config().gcode_resolution.value;
+
+    Polylines sparse_infill_polylines{};
+
+    for (SurfaceFill &surface_fill : surface_fills) {
+        // skip patterns for which additional input is nullptr
+        switch (surface_fill.params.pattern) {
+        case ipLightning: continue; break;
+        case ipAdaptiveCubic: continue; break;
+        case ipSupportCubic: continue; break;
+        case ipCount: continue; break;
+        case ipSupportBase: continue; break;
+        case ipEnsuring: continue; break;
+        case ipRectilinear:
+        case ipMonotonic:
+        case ipMonotonicLines:
+        case ipAlignedRectilinear:
+        case ipGrid:
+        case ipTriangles:
+        case ipStars:
+        case ipCubic:
+        case ipLine:
+        case ipConcentric:
+        case ipHoneycomb:
+        case ip3DHoneycomb:
+        case ipGyroid:
+        case ipHilbertCurve:
+        case ipArchimedeanChords:
+        case ipOctagramSpiral: break;
+        }
+
+        // Create the filler object.
+        std::unique_ptr<Fill> f = std::unique_ptr<Fill>(Fill::new_from_type(surface_fill.params.pattern));
+        f->set_bounding_box(bbox);
+        f->layer_id = this->id();
+        f->z        = this->print_z;
+        f->angle    = surface_fill.params.angle;
+        // f->adapt_fill_octree   = (surface_fill.params.pattern == ipSupportCubic) ? support_fill_octree : adaptive_fill_octree;
+        f->print_config        = &this->object()->print()->config();
+        f->print_object_config = &this->object()->config();
+
+        // calculate flow spacing for infill pattern generation
+        double link_max_length = 0.;
+        if (!surface_fill.params.bridge) {
+#if 0
+            link_max_length = layerm.region()->config().get_abs_value(surface.is_external() ? "external_fill_link_max_length" : "fill_link_max_length", flow.spacing());
+//            printf("flow spacing: %f,  is_external: %d, link_max_length: %lf\n", flow.spacing(), int(surface.is_external()), link_max_length);
+#else
+            if (surface_fill.params.density > 80.) // 80%
+                link_max_length = 3. * f->spacing;
+#endif
+        }
+
+        // Maximum length of the perimeter segment linking two infill lines.
+        f->link_max_length = (coord_t) scale_(link_max_length);
+        // Used by the concentric infill pattern to clip the loops to create extrusion paths.
+        f->loop_clipping = coord_t(scale_(surface_fill.params.flow.nozzle_diameter()) * LOOP_CLIPPING_LENGTH_OVER_NOZZLE_DIAMETER);
+
+        LayerRegion &layerm = *m_regions[surface_fill.region_id];
+
+        // apply half spacing using this flow's own spacing and generate infill
+        FillParams params;
+        params.density           = float(0.01 * surface_fill.params.density);
+        params.dont_adjust       = false; //  surface_fill.params.dont_adjust;
+        params.anchor_length     = surface_fill.params.anchor_length;
+        params.anchor_length_max = surface_fill.params.anchor_length_max;
+        params.resolution        = resolution;
+        params.use_arachne       = false;
+        params.layer_height      = layerm.layer()->height;
+
+        for (ExPolygon &expoly : surface_fill.expolygons) {
+            // Spacing is modified by the filler to indicate adjustments. Reset it for each expolygon.
+            f->spacing                     = surface_fill.params.spacing;
+            surface_fill.surface.expolygon = std::move(expoly);
+            try {
+                Polylines polylines = f->fill_surface(&surface_fill.surface, params);
+                sparse_infill_polylines.insert(sparse_infill_polylines.end(), polylines.begin(), polylines.end());
+            } catch (InfillFailedException &) {}
+        }
+    }
+
+    return sparse_infill_polylines;
+}
+
 // Create ironing extrusions over top surfaces.
 void Layer::make_ironing()
 {

src/libslic3r/Layer.hpp

@@ -369,6 +369,7 @@ public:
     // Phony version of make_fills() without parameters for Perl integration only.
     void                    make_fills() { this->make_fills(nullptr, nullptr, nullptr); }
     void                    make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive::Octree* support_fill_octree, FillLightning::Generator* lightning_generator);
+    Polylines               generate_sparse_infill_polylines_for_anchoring() const;
     void 					make_ironing();
 
     void                    export_region_slices_to_svg(const char *path) const;

src/libslic3r/PrintObject.cpp

@@ -397,6 +397,7 @@ void PrintObject::infill()
     this->prepare_infill();
 
     if (this->set_started(posInfill)) {
+        m_print->set_status(45, L("making infill"));
         auto [adaptive_fill_octree, support_fill_octree] = this->prepare_adaptive_infill_data();
         auto lightning_generator                         = this->prepare_lightning_infill_data();
 
@@ -1658,18 +1659,8 @@ void PrintObject::bridge_over_infill()
                 continue;
             }
 
-            // Now, temporarily fill the previous layer and extract the extrusions.
+            // generate sparse infill polylines from lower layers to get anchorable polylines
-            // TODO - the make_fills function does a lot of work, some of it is not needed (e.g. sorting the paths)
+            Polylines lower_layer_polylines = po->get_layer(lidx)->lower_layer->generate_sparse_infill_polylines_for_anchoring();
-            // It would be nice to have a function that only creates the fill polylines, ideally without modifying the global state
-            po->get_layer(lidx)->lower_layer->make_fills(nullptr, nullptr, nullptr);
-            Polylines lower_layer_polylines;
-            for (const LayerRegion *region : layer->lower_layer->m_regions) {
-                for (const ExtrusionEntity *ee : region->fills().entities) {
-                    assert(ee->is_collection());
-                    auto region_polylines = dynamic_cast<const ExtrusionEntityCollection *>(ee)->as_polylines();
-                    lower_layer_polylines.insert(lower_layer_polylines.end(), region_polylines.begin(), region_polylines.end());
-                }
-            }
 
             for (std::pair<const LayerSlice *, SurfacesPtr> candidates : bridging_surface_candidates) {
                 if (candidates.second.empty()) {
@@ -1786,7 +1777,7 @@ void PrintObject::bridge_over_infill()
                     assert(candidate->surface_type == stInternalSolid);
                     Polygons bridged_area               = expand(to_polygons(candidate->expolygon), flow.scaled_spacing());
                     Polygons infill_region              = to_polygons(surface_to_region[candidate]->fill_expolygons());
-                    bool touches_perimeter = !diff(bridged_area, infill_region).empty();
+                    bool     touches_perimeter          = !diff(bridged_area, infill_region).empty();
                     bool     touches_solid_region_under = !intersection(bridged_area, not_sparse_infill).empty();
 
                     bridged_area =