fix STEP progress message percent format (#14994)

src/libslic3r/Brim.cpp

@@ -32,15 +32,13 @@ static void append_and_translate(ExPolygons &dst, const ExPolygons &src, const P
     for (; dst_idx < dst.size(); ++dst_idx)
         dst[dst_idx].translate(instance_shift);
 }
-// BBS: generate brim area by objs
-static void append_and_translate(ExPolygons& dst, const ExPolygons& src,
-    const PrintInstance& instance, size_t instance_idx, std::map<ObjectInstanceID, ExPolygons>& brimAreaMap) {
+// Orca: Translate the brim area into print coordinates and store it per instance.
+static void append_and_translate(const ExPolygons& src, const PrintInstance& instance,
+    size_t instance_idx, std::map<ObjectInstanceID, ExPolygons>& brimAreaMap) {
     ExPolygons srcShifted = src;
     Point instance_shift = instance.shift_without_plate_offset();
-    for (size_t src_idx = 0; src_idx < srcShifted.size(); ++src_idx)
-        srcShifted[src_idx].translate(instance_shift);
-    srcShifted = diff_ex(srcShifted, dst);
-    //expolygons_append(dst, temp2);
+    for (ExPolygon& expoly : srcShifted)
+        expoly.translate(instance_shift);
     expolygons_append(brimAreaMap[{ instance.print_object->id(), instance_idx }], std::move(srcShifted));
 }
 
@@ -572,7 +570,7 @@ static ExPolygons outer_inner_brim_area(const Print& print,
                 for (size_t instance_idx = 0; instance_idx < object->instances().size(); ++instance_idx) {
                     const PrintInstance& instance = object->instances()[instance_idx];
                     if (!brim_area_object.empty())
-                        append_and_translate(brim_area, brim_area_object, instance, instance_idx, brimAreaMap);
+                        append_and_translate(brim_area_object, instance, instance_idx, brimAreaMap);
                     append_and_translate(no_brim_area, no_brim_area_object, instance);
                     append_and_translate(holes, holes_object, instance);
                     append_and_translate(objectIslands, objectIsland, instance);
@@ -875,6 +873,14 @@ void make_brim(const Print& print, PrintTryCancel try_cancel, Polygons& islands_
     ExPolygons           islands_area_ex = outer_inner_brim_area(print,
         float(flow.scaled_spacing()), brimAreaMap, objPrintVec, printExtruders);
 
+    if (!print.config().combine_brims) {
+        ExPolygons claimed_area;
+        for (auto& [_, areas] : brimAreaMap) {
+            areas = diff_ex(areas, claimed_area);
+            expolygons_append(claimed_area, areas);
+        }
+    }
+
     // BBS: Find boundingbox of the first layer
     for (const ObjectID printObjID : print.print_object_ids()) {
         BoundingBox bbx;

src/libslic3r/Format/STEP.hpp

@@ -78,7 +78,7 @@ public:
     Standard_Boolean UserBreak() override { return should_stop.load(); }
 
     void Show(const Message_ProgressScope&, const Standard_Boolean) override {
-        std::cout << "Progress: " << GetPosition() << "%" << std::endl;
+        std::cout << "Progress: " << std::fixed << std::setprecision(2) << 100.0 * GetPosition() << "%" << std::endl;
     }
 private:
     std::atomic<bool>& should_stop;

src/libslic3r/PerimeterGenerator.cpp

@@ -360,6 +360,14 @@ static ClipperLib_Z::Paths clip_extrusion(const ClipperLib_Z::Path& subject, con
     return clipped_paths;
 }
 
+static double clipper_z_path_length(const ClipperLib_Z::Path &path)
+{
+    double len = 0.;
+    for (size_t i = 1; i < path.size(); ++ i)
+        len += (Vec2d(double(path[i].x()), double(path[i].y())) - Vec2d(double(path[i - 1].x()), double(path[i - 1].y()))).norm();
+    return len;
+}
+
 struct PerimeterGeneratorArachneExtrusion
 {
     Arachne::ExtrusionLine* extrusion = nullptr;
@@ -571,17 +579,156 @@ static ExtrusionEntityCollection traverse_extrusions(const PerimeterGenerator& p
     return extrusion_coll;
 }
 
-// ORCA: only_one_wall_top detects the top as "slice − upper", so a feature rising from the middle of a
-// top surface becomes an enclosed hole that gets ringed with extra inner walls. Fill those holes back
-// into the top. Only holes that are both covered by the upper layer (excludes bridges) and backed by
-// solid material (excludes voids) are filled.
-static ExPolygons fill_enclosed_top_feature_holes(const ExPolygons &top, const Polygons &covered_by_upper, const ExPolygons &solid)
+// ORCA: only_one_wall_top acts on top surfaces, so without a top shell there is nothing for it to act on: zero top
+// shell layers retype the top surfaces as internal, see LayerRegion::prepare_fill_surfaces(). A 0% top surface
+// density does leave a top surface - just an unfilled one - so it does not disable the feature.
+// ConfigManipulation::toggle_print_fff_options() hides the option under the same condition, so a profile that left
+// it enabled does not act behind a hidden checkbox.
+static bool has_top_shell_layers(const PrintRegionConfig &config)
 {
-    ExPolygons filled = top;
-    for (ExPolygon &ex : filled)
-        ex.holes.clear();
-    const ExPolygons feature_holes = intersection_ex(intersection_ex(diff_ex(filled, top), covered_by_upper), solid);
-    return feature_holes.empty() ? top : union_ex(top, feature_holes);
+    return config.top_shell_layers.value > 0;
+}
+
+// ORCA: only_one_wall_first_layer thins the first layer to a single wall, the bottom counterpart of the above and
+// gated the same way: zero bottom shell layers retype the bottom surfaces as internal, so that wall would ring
+// sparse infill on the bed. The bottom surface density plays no part - an unfilled bottom surface is still a bottom
+// surface, exactly as for the top - and it cannot reach zero anyway, being capped at a 10% minimum.
+static bool has_bottom_shell_layers(const PrintRegionConfig &config)
+{
+    return config.bottom_shell_layers.value > 0;
+}
+
+// ORCA: the inner walls are only given up when a top fill takes their space, and it has to actually reach it -
+// a 0% top surface density leaves no fill at all, and without top_surface_expansion the fill never grows over
+// them. Either way the original generation is kept (re-onion the not-top region), which is what users of
+// only_one_wall_top alone have always got.
+static bool top_fill_replaces_inner_walls(const PrintRegionConfig &config)
+{
+    return has_top_shell_layers(config) && config.top_surface_density.value > 0 && config.top_surface_expansion.value > 0;
+}
+
+// ORCA: only_one_wall_top - cheap per-vertex classification of a wall against the top surface. Only Partial
+// needs the geometry clipped or measured; a segment crossing the top with no vertex inside is rare enough to ignore.
+enum class TopOverlap { None, Partial, Full };
+
+static bool point_over_top(const Point &p, const ExPolygons &top_region, const BoundingBox &top_region_bbox)
+{
+    if (! top_region_bbox.contains(p))
+        return false;
+    for (const ExPolygon &ex : top_region)
+        if (ex.contains(p, false))
+            return true;
+    return false;
+}
+
+static TopOverlap classify_over_top(const Points &pts, const ExPolygons &top_region, const BoundingBox &top_region_bbox)
+{
+    size_t inside = 0;
+    for (const Point &p : pts)
+        if (point_over_top(p, top_region, top_region_bbox))
+            ++ inside;
+    return inside == 0 ? TopOverlap::None : inside == pts.size() ? TopOverlap::Full : TopOverlap::Partial;
+}
+
+static TopOverlap classify_over_top(const Arachne::ExtrusionLine &el, const ExPolygons &top_region, const BoundingBox &top_region_bbox)
+{
+    size_t inside = 0;
+    for (const Arachne::ExtrusionJunction &j : el.junctions)
+        if (point_over_top(j.p, top_region, top_region_bbox))
+            ++ inside;
+    return inside == 0 ? TopOverlap::None : inside == el.junctions.size() ? TopOverlap::Full : TopOverlap::Partial;
+}
+
+// ORCA: only_one_wall_top for Arachne - cut out of the already generated inner walls the parts running over the top
+// surface, so geometry that continues upward keeps its walls. A wall too short over the top to be worth slitting open
+// is left whole, its footprint reported in kept_over_top for the caller to withhold from the top fill.
+static void clip_inner_walls_over_top(std::vector<Arachne::VariableWidthLines> &inner_perimeters, const ExPolygons &top_region, coord_t perimeter_width, Polygons &kept_over_top)
+{
+    const BoundingBox top_region_bbox = get_extents(top_region).inflated(SCALED_EPSILON);
+    auto covered_by = [](const Arachne::ExtrusionLine &el) {
+        Polyline centerline;
+        centerline.points.reserve(el.junctions.size());
+        coord_t width = 0;
+        for (const Arachne::ExtrusionJunction &j : el.junctions) {
+            centerline.points.emplace_back(j.p);
+            width = std::max(width, j.w);
+        }
+        return offset(centerline, float(width) / 2.f);
+    };
+    // Pull the cut back by half a wall width: the clip severs the centerline, but the bead's rounded end
+    // extends half a width past its endpoint and would otherwise overlap the top fill.
+    ClipperLib_Z::Paths top_paths_z;
+    for (const Polygon &poly : to_polygons(offset_ex(top_region, float(perimeter_width) / 2.f))) {
+        top_paths_z.emplace_back();
+        ClipperLib_Z::Path &out = top_paths_z.back();
+        out.reserve(poly.points.size());
+        for (const Point &pt : poly.points)
+            out.emplace_back(pt.x(), pt.y(), 0);
+    }
+    for (Arachne::VariableWidthLines &inner_perimeter : inner_perimeters) {
+        Arachne::VariableWidthLines kept;
+        kept.reserve(inner_perimeter.size());
+        for (Arachne::ExtrusionLine &el : inner_perimeter) {
+            if (el.empty())
+                continue;
+            const TopOverlap overlap = classify_over_top(el, top_region, top_region_bbox);
+            if (overlap == TopOverlap::None) {
+                kept.emplace_back(std::move(el));
+                continue;
+            }
+            if (overlap == TopOverlap::Full)
+                continue; // the clip below would return nothing anyway
+            ClipperLib_Z::Path subject;
+            subject.reserve(el.size());
+            for (const Arachne::ExtrusionJunction &j : el.junctions)
+                subject.emplace_back(j.p.x(), j.p.y(), j.w);
+            ClipperLib_Z::Paths pieces = clip_extrusion(subject, top_paths_z, ClipperLib_Z::ctDifference);
+
+            // Clipper treats the subject as an open polyline, so it also cuts a closed loop at its (arbitrary)
+            // start vertex and may reverse pieces. Stitch pieces sharing an endpoint back together.
+            auto same_pt = [](const ClipperLib_Z::IntPoint &p, const ClipperLib_Z::IntPoint &q) {
+                return std::abs(p.x() - q.x()) <= SCALED_EPSILON && std::abs(p.y() - q.y()) <= SCALED_EPSILON;
+            };
+            for (size_t i = 0; i < pieces.size(); ++ i) {
+                for (size_t j = i + 1; j < pieces.size();) {
+                    ClipperLib_Z::Path &a = pieces[i];
+                    ClipperLib_Z::Path &b = pieces[j];
+                    if (same_pt(a.front(), b.front()) || same_pt(a.front(), b.back()))
+                        std::reverse(a.begin(), a.end());
+                    if (same_pt(a.back(), b.back()))
+                        std::reverse(b.begin(), b.end());
+                    if (same_pt(a.back(), b.front())) {
+                        a.insert(a.end(), b.begin() + 1, b.end());
+                        pieces.erase(pieces.begin() + j);
+                        j = i + 1; // the merged path has new endpoints, restart the scan
+                    } else
+                        ++ j;
+                }
+            }
+
+            // If the clip removed next to nothing, keep the loop untouched instead of slitting it open. The
+            // half-width pull-back above already costs about one width per crossing, hence two widths.
+            double kept_length = 0.;
+            for (const ClipperLib_Z::Path &path : pieces)
+                kept_length += clipper_z_path_length(path);
+            if (clipper_z_path_length(subject) - kept_length < 2. * double(perimeter_width)) {
+                append(kept_over_top, covered_by(el));
+                kept.emplace_back(std::move(el));
+                continue;
+            }
+
+            for (const ClipperLib_Z::Path &path : pieces) {
+                Arachne::ExtrusionLine clipped(el.inset_idx, el.is_odd);
+                clipped.junctions.reserve(path.size());
+                for (const ClipperLib_Z::IntPoint &pt : path)
+                    clipped.junctions.emplace_back(Point(pt.x(), pt.y()), coord_t(pt.z()), el.inset_idx);
+                // Discard tiny leftovers that would print as zits.
+                if (clipped.size() >= 2 && clipped.getLength() >= perimeter_width)
+                    kept.emplace_back(std::move(clipped));
+            }
+        }
+        inner_perimeter = std::move(kept);
+    }
 }
 
 void PerimeterGenerator::split_top_surfaces(const ExPolygons &orig_polygons, ExPolygons &top_fills,
@@ -649,7 +796,6 @@ void PerimeterGenerator::split_top_surfaces(const ExPolygons &orig_polygons, ExP
     ExPolygons delete_bridge = diff_ex(orig_polygons, bridge_checker, ApplySafetyOffset::Yes);
 
     ExPolygons top_polygons = diff_ex(delete_bridge, upper_polygons_series_clipped, ApplySafetyOffset::Yes);
-    top_polygons = fill_enclosed_top_feature_holes(top_polygons, upper_polygons_series_clipped, orig_polygons);
 
     // get the not-top surface, from the "real top" but enlarged by external_infill_margin (and the
     // min_width_top_surface we removed a bit before)
@@ -1234,6 +1380,11 @@ void PerimeterGenerator::process_classic()
     for (const Surface &surface : all_surfaces)
         surface_exp.push_back(surface.expolygon);
     std::vector<size_t> surface_order = chain_expolygons(surface_exp);
+    // ORCA: neither one-wall option has a surface to act on without the shell behind it, see
+    // has_top_shell_layers() / has_bottom_shell_layers(). Gated here so every use below - including the
+    // topmost and first layers - sees the same answer.
+    const bool only_one_wall_top         = this->config->only_one_wall_top && has_top_shell_layers(*this->config);
+    const bool only_one_wall_first_layer = this->config->only_one_wall_first_layer && has_bottom_shell_layers(*this->config);
     for (size_t order_idx = 0; order_idx < surface_order.size(); order_idx++) {
         const Surface &surface = all_surfaces[surface_order[order_idx]];
         // detect how many perimeters must be generated for this island
@@ -1241,16 +1392,23 @@ void PerimeterGenerator::process_classic()
         int sparse_infill_density = this->config->sparse_infill_density.value;
         if (this->config->alternate_extra_wall && this->layer_id % 2 == 1 && !m_spiral_vase && sparse_infill_density > 0) // add alternating extra wall
             loop_number++;
-        if (this->layer_id == object_config->raft_layers && this->config->only_one_wall_first_layer)
+        if (this->layer_id == object_config->raft_layers && only_one_wall_first_layer)
             loop_number = 0;
         // Set the topmost layer to be one wall
-        if (loop_number > 0 && config->only_one_wall_top && this->upper_slices == nullptr)
+        if (loop_number > 0 && only_one_wall_top && this->upper_slices == nullptr)
             loop_number = 0;
 
         ExPolygons last        = union_ex(surface.expolygon.simplify_p(surface_simplify_resolution));
         ExPolygons gaps;
         ExPolygons top_fills;
         ExPolygons fill_clip;
+        // ORCA: only_one_wall_top, all empty unless this island has a top surface on this layer. See the
+        // post-onion reduction below: the region to keep clear of inner walls, the space freed by the dropped
+        // walls (goes to infill, not left as a void) and the space held by the kept ones (withheld from the fill).
+        ExPolygons one_wall_top_region;
+        ExPolygons one_wall_top_reclaimed;
+        Polygons   one_wall_top_kept_bands;
+        bool       apply_one_wall_top = false;
         if (loop_number >= 0) {
             // In case no perimeters are to be generated, loop_number will equal to -1.
             std::vector<PerimeterGeneratorLoops> contours(loop_number+1);    // depth => loops
@@ -1389,9 +1547,20 @@ void PerimeterGenerator::process_classic()
 
                 //BBS: refer to superslicer
                 //store surface for top infill if only_one_wall_top
-                if (i == 0 && i!=loop_number && config->only_one_wall_top && !surface.is_bridge() && this->upper_slices != NULL) {
+                if (i == 0 && i!=loop_number && only_one_wall_top && !surface.is_bridge() && this->upper_slices != NULL) {
+                    if (top_fill_replaces_inner_walls(*this->config)) {
+                        // ORCA: take the top fill and the keep-out region but leave `last` as the real geometry,
+                        // so the onion follows it and the walls over the top are reduced in one step below.
+                        ExPolygons non_top_polygons;
+                        this->split_top_surfaces(last, top_fills, non_top_polygons, fill_clip);
+                        apply_one_wall_top = !top_fills.empty();
+                        if (apply_one_wall_top)
+                            one_wall_top_region = diff_ex(last, non_top_polygons);
+                    } else {
+                        // Onion the not-top region only, so the remaining walls stop at the top boundary.
                         this->split_top_surfaces(last, top_fills, last, fill_clip);
                     }
+                }
 
                 if (i == loop_number && (! has_gap_fill || this->config->sparse_infill_density.value == 0)) {
                 	// The last run of this loop is executed to collect gaps for gap fill.
@@ -1400,6 +1569,46 @@ void PerimeterGenerator::process_classic()
                 }
             }
 
+            // ORCA: only_one_wall_top reduction - drop the inner walls (depth > 0) running over the top surface and
+            // take that space back from the gaps, leaving the top with the outer wall and the top infill. Classic
+            // perimeters are closed loops, so a wall can only be kept or dropped whole; one that merely grazes the
+            // top (same tolerance as the Arachne clip) is kept and withheld from the top fill instead.
+            if (apply_one_wall_top) {
+                const BoundingBox top_region_bbox   = get_extents(one_wall_top_region).inflated(SCALED_EPSILON);
+                const double      grazing_tolerance = 2. * double(perimeter_width);
+                // The band a wall covers, taken around its centerline so the orientation of holes does not matter.
+                auto wall_band = [perimeter_spacing](const Polygon &poly) {
+                    Polygon centerline = poly;
+                    centerline.make_counter_clockwise();
+                    return diff(offset(centerline, float(perimeter_spacing) / 2.f),
+                                offset(centerline, -float(perimeter_spacing) / 2.f));
+                };
+                Polygons dropped_wall_bands;
+                auto reduce_over_top = [&](PerimeterGeneratorLoops &loops) {
+                    loops.erase(std::remove_if(loops.begin(), loops.end(), [&](const PerimeterGeneratorLoop &loop) {
+                        const TopOverlap overlap = classify_over_top(loop.polygon.points, one_wall_top_region, top_region_bbox);
+                        if (overlap == TopOverlap::None)
+                            return false;
+                        // Only a wall straddling the boundary is worth measuring; a wall wholly over the top goes.
+                        if (overlap == TopOverlap::Partial &&
+                            total_length(intersection_pl(Polylines{ loop.polygon.split_at_first_point() }, one_wall_top_region)) < grazing_tolerance) {
+                            append(one_wall_top_kept_bands, wall_band(loop.polygon));
+                            return false;
+                        }
+                        append(dropped_wall_bands, wall_band(loop.polygon));
+                        return true;
+                    }), loops.end());
+                };
+                for (int d = 1; d <= loop_number; ++ d) {
+                    reduce_over_top(contours[d]);
+                    reduce_over_top(holes[d]);
+                }
+                if (! gaps.empty())
+                    gaps = diff_ex(gaps, one_wall_top_region);
+                if (! dropped_wall_bands.empty())
+                    one_wall_top_reclaimed = diff_ex(dropped_wall_bands, one_wall_top_region);
+            }
+
             // nest loops: holes first
             for (int d = 0; d <= loop_number; ++ d) {
                 PerimeterGeneratorLoops &holes_d = holes[d];
@@ -1634,7 +1843,10 @@ void PerimeterGenerator::process_classic()
                     and use zigzag).  */
                 //FIXME Vojtech: This grows by a rounded extrusion width, not by line spacing,
                 // therefore it may cover the area, but no the volume.
-                last = diff_ex(last, gap_fill.polygons_covered_by_width(10.f));
+                Polygons gap_fill_covered = gap_fill.polygons_covered_by_width(10.f);
+                last = diff_ex(last, gap_fill_covered);
+                if (! one_wall_top_reclaimed.empty())
+                    one_wall_top_reclaimed = diff_ex(one_wall_top_reclaimed, gap_fill_covered);
                 this->gap_fill->append(std::move(gap_fill.entities));
 
 			}
@@ -1679,9 +1891,15 @@ void PerimeterGenerator::process_classic()
         // append infill areas to fill_surfaces
         //if any top_fills, grow them by ext_perimeter_spacing/2 to have the real un-anchored fill
         ExPolygons top_infill_exp = intersection_ex(fill_clip, offset_ex(top_fills, double(ext_perimeter_spacing / 2)));
+        // ORCA: only_one_wall_top - route the top fill around the walls kept despite grazing the top.
+        if (!one_wall_top_kept_bands.empty())
+            top_infill_exp = diff_ex(top_infill_exp, one_wall_top_kept_bands);
         if (!top_fills.empty()) {
             infill_exp = union_ex(infill_exp, offset_ex(top_infill_exp, double(top_infill_peri_overlap)));
         }
+        // ORCA: only_one_wall_top - what the top fill does not cover of the dropped walls goes to infill.
+        if (!one_wall_top_reclaimed.empty())
+            infill_exp = union_ex(infill_exp, one_wall_top_reclaimed);
         this->fill_surfaces->append(infill_exp, stInternal);
 
         apply_extra_perimeters(infill_exp);
@@ -1700,6 +1918,8 @@ void PerimeterGenerator::process_classic()
                     double(-inset - infill_peri_overlap));
             if (!top_fills.empty())
                 polyWithoutOverlap = union_ex(polyWithoutOverlap, top_infill_exp);
+            if (!one_wall_top_reclaimed.empty())
+                polyWithoutOverlap = union_ex(polyWithoutOverlap, one_wall_top_reclaimed);
             this->fill_no_overlap->insert(this->fill_no_overlap->end(), polyWithoutOverlap.begin(), polyWithoutOverlap.end());
         }
 
@@ -2138,6 +2358,11 @@ void PerimeterGenerator::process_arachne()
     process_no_bridge(all_surfaces, perimeter_spacing, ext_perimeter_width);
     // BBS: don't simplify too much which influence arc fitting when export gcode if arc_fitting is enabled
     double surface_simplify_resolution = (print_config->enable_arc_fitting && !this->has_fuzzy_skin) ? 0.2 * m_scaled_resolution : m_scaled_resolution;
+    // ORCA: neither one-wall option has a surface to act on without the shell behind it, see
+    // has_top_shell_layers() / has_bottom_shell_layers(). Gated here so every use below - including the
+    // topmost and first layers - sees the same answer.
+    const bool only_one_wall_top         = this->config->only_one_wall_top && has_top_shell_layers(*this->config);
+    const bool only_one_wall_first_layer = this->config->only_one_wall_first_layer && has_bottom_shell_layers(*this->config);
     // we need to process each island separately because we might have different
     // extra perimeters for each one
     for (const Surface& surface : all_surfaces) {
@@ -2150,12 +2375,12 @@ void PerimeterGenerator::process_arachne()
 
         // Set the bottommost layer to be one wall
         const bool is_bottom_layer = (this->layer_id == object_config->raft_layers) ? true : false;
-        if (is_bottom_layer && this->config->only_one_wall_first_layer)
+        if (is_bottom_layer && only_one_wall_first_layer)
             loop_number = 0;
 
         // Orca: set the topmost layer to be one wall according to the config
         const bool is_topmost_layer = (this->upper_slices == nullptr) ? true : false;
-        if (is_topmost_layer && loop_number > 0 && config->only_one_wall_top)
+        if (is_topmost_layer && loop_number > 0 && only_one_wall_top)
             loop_number = 0;
         
         auto apply_precise_outer_wall = config->precise_outer_wall && config->wall_sequence == WallSequence::InnerOuter;
@@ -2175,10 +2400,10 @@ void PerimeterGenerator::process_arachne()
         //PS: One wall top surface for Arachne
         ExPolygons top_expolygons;
         // Calculate how many inner loops remain when TopSurfaces is selected.
-        const int inner_loop_number = (config->only_one_wall_top && upper_slices != nullptr) ? loop_number - 1 : -1;
+        const int inner_loop_number = (only_one_wall_top && upper_slices != nullptr) ? loop_number - 1 : -1;
 
         // Set one perimeter when TopSurfaces is selected.
-        if (config->only_one_wall_top && loop_number > 0)
+        if (only_one_wall_top && loop_number > 0)
             loop_number = 0;
 
         Arachne::WallToolPathsParams input_params_tmp = input_params;
@@ -2209,7 +2434,6 @@ void PerimeterGenerator::process_arachne()
                 upper_slices_clipped = ClipperUtils::clip_clipper_polygons_with_subject_bbox(*upper_slices, infill_contour_bbox);
 
             top_expolygons = diff_ex(infill_contour, upper_slices_clipped);
-            top_expolygons = fill_enclosed_top_feature_holes(top_expolygons, upper_slices_clipped, infill_contour);
 
             if (!top_expolygons.empty()) {
                 if (lower_slices != nullptr) {
@@ -2230,25 +2454,33 @@ void PerimeterGenerator::process_arachne()
                 // due to thin lines being generated
                 top_expolygons = offset2_ex(top_expolygons, -top_surface_min_width, top_surface_min_width + float(perimeter_width * 0.85));
 
-                // Get the not-top ExPolygons (including bridges) from current slices and expanded real top ExPolygons (without bridges).
-                const ExPolygons not_top_expolygons = diff_ex(infill_contour, top_expolygons);
-
-                // Get final top ExPolygons.
+                // Get final top ExPolygons (bridges were excluded above, so they stay walled).
                 top_expolygons = intersection_ex(top_expolygons, infill_contour);
 
-                const Polygons not_top_polygons = to_polygons(offset_ex(not_top_expolygons,wall_0_inset));
-                Arachne::WallToolPaths inner_wall_tool_paths(not_top_polygons, perimeter_spacing, perimeter_spacing, coord_t(inner_loop_number + 1), 0, layer_height, input_params_tmp);
+                // ORCA: onion the real region (inside the outer wall) so the remaining walls follow the actual
+                // geometry, then cut away the parts over the top surface. Re-onioning the non-top complement
+                // instead - the fallback when there is no top fill - walls the top/non-top interface and rings
+                // top-surface islands with inner walls that don't exist when the feature is disabled.
+                const bool     clip_walls_over_top = top_fill_replaces_inner_walls(*this->config);
+                const Polygons inner_region        = to_polygons(offset_ex(clip_walls_over_top ? infill_contour
+                                                                                               : diff_ex(infill_contour, top_expolygons),
+                                                                          wall_0_inset));
+                Arachne::WallToolPaths inner_wall_tool_paths(inner_region, perimeter_spacing, perimeter_spacing, coord_t(inner_loop_number + 1), 0, layer_height, input_params_tmp);
                 std::vector<Arachne::VariableWidthLines> inner_perimeters = inner_wall_tool_paths.getToolPaths();
 
-                // Recalculate indexes of inner perimeters before merging them.
-                if (!perimeters.empty()) {
-                    for (Arachne::VariableWidthLines &inner_perimeter : inner_perimeters) {
-                        if (inner_perimeter.empty())
-                            continue;
+                if (clip_walls_over_top) {
+                    Polygons kept_over_top;
+                    clip_inner_walls_over_top(inner_perimeters, top_expolygons, perimeter_width, kept_over_top);
+                    // Route the top fill around the walls kept despite grazing the top.
+                    if (! kept_over_top.empty())
+                        top_expolygons = diff_ex(top_expolygons, kept_over_top);
+                }
+
+                // Recalculate indexes of inner perimeters before merging them: they come after the single outer wall.
+                if (!perimeters.empty())
+                    for (Arachne::VariableWidthLines &inner_perimeter : inner_perimeters)
                         for (Arachne::ExtrusionLine &el : inner_perimeter)
                             ++el.inset_idx;
-                    }
-                }
 
                 perimeters.insert(perimeters.end(), inner_perimeters.begin(), inner_perimeters.end());
                 infill_contour = union_ex(top_expolygons, inner_wall_tool_paths.getInnerContour());

src/libslic3r/PrintObject.cpp

@@ -1364,7 +1364,6 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "infill_combination_max_layer_height"
             || opt_key == "bottom_shell_thickness"
             || opt_key == "top_shell_thickness"
-            || opt_key == "top_surface_expansion"
             || opt_key == "top_surface_expansion_margin"
             || opt_key == "top_surface_expansion_direction"
             || opt_key == "minimum_sparse_infill_area"
@@ -1400,7 +1399,6 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "infill_anchor"
             || opt_key == "infill_anchor_max"
             || opt_key == "top_surface_line_width"
-            || opt_key == "top_surface_density"
             || opt_key == "bottom_surface_density"
             || opt_key == "center_of_surface_pattern"
             || opt_key == "separated_infills" 
@@ -1434,6 +1432,24 @@ bool PrintObject::invalidate_state_by_config_options(
                 is_approx(new_density->value, 0.) || is_approx(new_density->value, 100.))
                 steps.emplace_back(posPerimeters);
             steps.emplace_back(posPrepareInfill);
+        } else if (opt_key == "top_surface_density") {
+            // ORCA: 0% means no top solid fill, which switches off both the top surface expansion and the wall
+            // removal over top surfaces. Only crossing zero matters; posPerimeters cascades to posPrepareInfill.
+            const auto *old_density = old_config.option<ConfigOptionPercent>(opt_key);
+            const auto *new_density = new_config.option<ConfigOptionPercent>(opt_key);
+            assert(old_density && new_density);
+            if (is_approx(old_density->value, 0.) || is_approx(new_density->value, 0.))
+                steps.emplace_back(posPerimeters);
+            steps.emplace_back(posInfill);
+        } else if (opt_key == "top_surface_expansion") {
+            // ORCA: without the expansion the top fill never reaches the space freed by only_one_wall_top, so the
+            // walls over top surfaces are kept. Only crossing zero matters; posPerimeters cascades to posPrepareInfill.
+            const auto *old_expansion = old_config.option<ConfigOptionFloat>(opt_key);
+            const auto *new_expansion = new_config.option<ConfigOptionFloat>(opt_key);
+            assert(old_expansion && new_expansion);
+            if (old_expansion->value <= 0. || new_expansion->value <= 0.)
+                steps.emplace_back(posPerimeters);
+            steps.emplace_back(posPrepareInfill);
         } else if (opt_key == "internal_solid_infill_line_width") {
             // This value is used for calculating perimeter - infill overlap, thus perimeters need to be recalculated.
             steps.emplace_back(posPerimeters);
@@ -1760,51 +1776,50 @@ void PrintObject::detect_surfaces_type()
                         }
                     }
 
-                    // ORCA: Expand the top surfaces outward by top_surface_expansion in every direction. This
-                    // enlarges the top solid infill and, in particular, grows it over the covered material left
-                    // by features rising from the middle of a top surface (filling holes and joining tops so the
-                    // features rest on it). The expansion stays inside the section it belongs to: each connected
-                    // solid island has its own outer wall, so the top is grown within each island separately and
-                    // clipped to it - growing one island's top across the gap into another island (which may have
-                    // no top surface, leaving a partially filled layer) is never allowed. The top infill sits
-                    // inside the perimeters, so the margin is measured from the walls: the island is inset by the
-                    // band the walls consume (outer wall + inner walls) plus the configured margin, making that
-                    // value the real clearance between the expanded top and the walls (avoiding a hull line). The
-                    // original top is unioned back in, so where it already sits within that band it is kept as-is.
-                    // Never claims a bottom surface.
-                    const double top_expansion = layerm->region().config().top_surface_expansion.value;
-                    if (top_expansion > 0. && ! top.empty()) {
+                    // ORCA: Grow the top surfaces by top_surface_expansion, so the top solid infill also covers the
+                    // material left by features rising from the middle of a top surface (filling the holes and
+                    // joining the tops, so the features rest on solid infill). Each connected island is grown and
+                    // clipped separately: growing one island's top across a gap into another - which may have no top
+                    // surface at all, leaving a partially filled layer - is never allowed. The original top is
+                    // unioned back in and bottom surfaces are never claimed, so this can only add area.
+                    const PrintRegionConfig &region_config  = layerm->region().config();
+                    const double             top_expansion  = region_config.top_surface_expansion.value;
+                    // Nothing to expand without a top fill: a 0% top surface density leaves the top layer with
+                    // walls only, and zero top shell layers retypes it as internal in prepare_fill_surfaces().
+                    if (top_expansion > 0. && region_config.top_shell_layers.value > 0 &&
+                        region_config.top_surface_density.value > 0. && ! top.empty()) {
                         const double     d = scale_(top_expansion);
-                        const auto       jt       = Clipper2Lib::JoinType::Miter;
                         const ExPolygons T = union_ex(to_expolygons(top));
-                        const int    wall_loops = layerm->region().config().wall_loops.value;
+                        // Walls are laid out on spacing, not width; and only_one_wall_top leaves a single wall over
+                        // a top surface, which is exactly the situation handled here.
+                        const int    wall_loops = region_config.only_one_wall_top.value ? std::min(region_config.wall_loops.value, 1)
+                                                                                        : region_config.wall_loops.value;
                         const double wall_band  = wall_loops <= 0 ? 0. :
                             double(layerm->flow(frExternalPerimeter).scaled_width()) +
-                            double(layerm->flow(frPerimeter).scaled_width()) * double(wall_loops - 1);
-                        const double margin     = scale_(layerm->region().config().top_surface_expansion_margin.value);
+                            double(layerm->flow(frPerimeter).scaled_spacing()) * double(wall_loops - 1);
+                        const double margin     = scale_(region_config.top_surface_expansion_margin.value);
                         // minimum real top to act on: ignore anything thinner than ~2 top-infill lines
                         const float  min_top    = float(layerm->flow(frTopSolidInfill).scaled_width());
-                        const auto   direction  = layerm->region().config().top_surface_expansion_direction.value;
+                        const auto   direction  = region_config.top_surface_expansion_direction.value;
 
                         ExPolygons grown;
                         for (const ExPolygon &island : union_ex(layerm_slices_surfaces)) {
                             // The top infill only exists inside the perimeters, so seed and measure from the infill
-                            // region (the island minus the wall band), not the raw slice. A section whose only
-                            // exposed top lies in the wall band - i.e. a layer where the top is just the walls
-                            // themselves - has no infill here and is skipped, instead of being flooded inward by
-                            // the expansion. Thin slivers inside the infill region are dropped by the opening too.
+                            // region (the island minus the wall band), not the raw slice: a section whose exposed top
+                            // is just the walls themselves is then skipped instead of being flooded inward. Clip the
+                            // layer's tops to the island first, to keep the boolean ops proportional to the island.
                             const ExPolygons infill_region = wall_band > 0. ? offset_ex(island, -float(wall_band)) : ExPolygons{ island };
-                            const ExPolygons island_top    = intersection_ex(T, infill_region);
+                            const ExPolygons island_top    = intersection_ex(
+                                ClipperUtils::clip_clipper_polygons_with_subject_bbox(T, get_extents(island).inflated(SCALED_EPSILON)),
+                                infill_region);
                             if (opening_ex(island_top, min_top).empty())
                                 continue; // no real top infill in this section - never expand into it
 
-                            // grow by d, then keep only the part allowed by the configured direction: inward fills
-                            // the holes/gaps left by features (clip the growth back to the top's own filled outline,
-                            // which leaves the outer edge fixed), outward grows the outer edge toward the walls (drop
-                            // the growth that fell into the original holes), and inward+outward keeps both.
-                            ExPolygons expanded = offset_ex_2(island_top, d, jt);
+                            // Grow, then keep only what the configured direction allows, using the top's own filled
+                            // outline (same outer edge, holes closed) to tell the two apart.
+                            ExPolygons expanded = offset_ex_2(island_top, d, Clipper2Lib::JoinType::Miter);
                             if (direction != TopSurfaceExpansionDirection::InwardAndOutward) {
-                                ExPolygons outline; // the top with its holes filled (same outer edge)
+                                ExPolygons outline;
                                 outline.reserve(island_top.size());
                                 for (const ExPolygon &ex : island_top)
                                     outline.emplace_back(ex.contour);

src/slic3r/GUI/ConfigManipulation.cpp

@@ -703,12 +703,13 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, in
     toggle_line("spiral_mode_max_xy_smoothing", has_spiral_vase && config->opt_bool("spiral_mode_smooth"));
     toggle_line("spiral_starting_flow_ratio", has_spiral_vase);
     toggle_line("spiral_finishing_flow_ratio", has_spiral_vase);
-    bool has_top_shell    = config->opt_int("top_shell_layers") > 0 || (has_spiral_vase && config->opt_int("bottom_shell_layers") > 1);
+    bool has_top_shell_layers = config->opt_int("top_shell_layers") > 0 || (has_spiral_vase && config->opt_int("bottom_shell_layers") > 1);
+    bool has_top_shell    = has_top_shell_layers && config->option<ConfigOptionPercent>("top_surface_density")->value > 0;
     bool has_bottom_shell = config->opt_int("bottom_shell_layers") > 0;
-    bool has_solid_infill = has_top_shell || has_bottom_shell;
+    bool has_solid_infill = has_top_shell_layers || has_bottom_shell;
     toggle_field("top_surface_pattern", has_top_shell);
     toggle_field("bottom_surface_pattern", has_bottom_shell);
-    toggle_field("top_surface_density", has_top_shell);
+    toggle_field("top_surface_density", has_top_shell_layers);
     toggle_field("bottom_surface_density", has_bottom_shell);
     toggle_field("top_layer_direction", has_top_shell);
     toggle_field("bottom_layer_direction", has_bottom_shell);
@@ -751,7 +752,7 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, in
     for (auto el : { "sparse_infill_speed", "bridge_speed", "internal_bridge_speed"})
         toggle_field(el, have_infill || has_solid_infill, variant_index);
 
-    toggle_field("top_shell_thickness", ! has_spiral_vase && has_top_shell);
+    toggle_field("top_shell_thickness", ! has_spiral_vase && has_top_shell_layers);
     toggle_field("bottom_shell_thickness", ! has_spiral_vase && has_bottom_shell);
 
     // Gap fill is newly allowed in between perimeter lines even for empty infill (see GH #1476).
@@ -1008,7 +1009,11 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, in
     toggle_line("make_overhang_printable_angle", have_make_overhang_printable);
     toggle_line("make_overhang_printable_hole_size", have_make_overhang_printable);
 
-    toggle_line("min_width_top_surface", config->opt_bool("only_one_wall_top") || ((config->opt_float("min_length_factor") > 0.5f) && have_arachne)); // 0.5 is default value
+    // Orca: the one-wall options act on top/bottom surfaces, which exist only with a shell. An unfilled surface
+    // (0% surface density) is still a surface, so these are gated on the layer counts alone.
+    toggle_line("only_one_wall_first_layer", has_bottom_shell);
+    toggle_line("only_one_wall_top", has_top_shell_layers);
+    toggle_line("min_width_top_surface", (has_top_shell_layers && config->opt_bool("only_one_wall_top")) || ((config->opt_float("min_length_factor") > 0.5f) && have_arachne)); // 0.5 is default value
 
     for (auto el : { "hole_to_polyhole_threshold", "hole_to_polyhole_twisted", "hole_to_polyhole_max_edges" })
         toggle_line(el, config->opt_bool("hole_to_polyhole"));

src/slic3r/GUI/Field.cpp

@@ -1334,27 +1334,7 @@ void SpinCtrl::BUILD() {
         if (!parsed || value < INT_MIN || value > INT_MAX)
             tmp_value = UNDEF_VALUE;
         else {
-            tmp_value = std::min(std::max((int)value, temp->GetMin()), temp->GetMax());
-#ifdef __WXOSX__
-#ifdef UNDEFINED__WXOSX__ // BBS
-            // Forcibly set the input value for SpinControl, since the value
-            // inserted from the keyboard or clipboard is not updated under OSX
-            SpinInput* spin = static_cast<SpinInput*>(window);
-            spin->SetValue(tmp_value);
-            // But in SetValue() is executed m_text_ctrl->SelectAll(), so
-            // discard this selection and set insertion point to the end of string
-            // temp->GetText()->SetInsertionPointEnd();
-#endif
-#else
-            // update value for the control only if it was changed in respect to the Min/max values
-            if (tmp_value != (int)value) {
-                temp->SetValue(tmp_value);
-                // But after SetValue() cursor ison the first position
-                // so put it to the end of string
-                // int pos = std::to_string(tmp_value).length();
-                // temp->SetSelection(pos, pos);
-            }
-#endif
+            tmp_value = (int)value;
         }
 	}), temp->GetTextCtrl()->GetId());
 
@@ -1375,6 +1355,10 @@ void SpinCtrl::propagate_value()
             on_kill_focus();
 	} else {
         auto ctrl = dynamic_cast<SpinInput *>(window);
+        tmp_value = std::min(std::max(tmp_value, ctrl->GetMin()), ctrl->GetMax());
+        if (ctrl->GetValue() != tmp_value)
+            ctrl->SetValue(tmp_value); // Clamp now when the user is done typing (kill focus / Enter / spin arrows)
+
         if (m_value.empty()
             ? !ctrl->GetTextCtrl()->GetLabel().IsEmpty()
             : ctrl->GetValue() != boost::any_cast<int>(m_value))

tests/fff_print/CMakeLists.txt

@@ -11,6 +11,7 @@ add_executable(${_TEST_NAME}_tests
 	test_gcodewriter.cpp
 	test_model.cpp
 	test_multifilament.cpp
+	test_perimeters.cpp
 	test_print.cpp
 	test_printobject.cpp
 	test_skirt_brim.cpp

tests/fff_print/test_perimeters.cpp

@@ -0,0 +1,257 @@
+#include <catch2/catch_all.hpp>
+
+#include "libslic3r/ExtrusionEntity.hpp"
+#include "libslic3r/ExtrusionEntityCollection.hpp"
+#include "libslic3r/Layer.hpp"
+#include "libslic3r/Print.hpp"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+#include "test_helpers.hpp"
+
+using namespace Slic3r;
+using namespace Slic3r::Test;
+
+namespace {
+
+// The layer at this Z is the last one of the base, so its top surface is the ledge.
+const double ledge_z = 5.0;
+
+// The first layer, at initial_layer_print_height.
+const double first_layer_z = 0.2;
+
+// TestMesh::step scaled 3x in X/Y: a 60x60x5 base carrying a 54x54 column up to z=10, leaving a 3mm
+// top ledge around a feature that keeps rising. That is the geometry both only_one_wall_top and the
+// top surface expansion act on. The ledge has to stay wider than the wall band plus two top-infill
+// lines, or the expansion discards it as a sliver and the tests below assert nothing.
+TriangleMesh step_with_ledge()
+{
+    TriangleMesh m = Slic3r::Test::mesh(TestMesh::step);
+    m.scale(Vec3f(3.f, 3.f, 1.f));
+    return m;
+}
+
+// Every setting the assertions depend on, so none of them rests on a default.
+DynamicPrintConfig base_config(const char *wall_generator)
+{
+    DynamicPrintConfig config = DynamicPrintConfig::full_print_config();
+    config.set_deserialize_strict({
+        { "wall_generator",             wall_generator },
+        { "layer_height",               0.2 },  // puts a layer boundary exactly on ledge_z
+        { "initial_layer_print_height", 0.2 },
+        { "wall_loops",                 3 },
+        { "sparse_infill_density",      "15%" },
+        { "top_shell_layers",           3 },
+        { "bottom_shell_layers",        3 },
+        { "top_surface_density",        "100%" },
+        { "top_surface_expansion",      0.0 },
+        { "only_one_wall_top",          false },
+        { "only_one_wall_first_layer",  false },
+        // Do not let the one-wall threshold discard the 3mm ledge before the feature sees it.
+        { "min_width_top_surface",      0.0 },
+    });
+    return config;
+}
+
+double collection_length(const ExtrusionEntityCollection &coll)
+{
+    double len = 0.;
+    for (const ExtrusionEntity *entity : coll.flatten().entities)
+        if (! entity->is_collection())
+            len += entity->length();
+    return len;
+}
+
+// Extruded length per layer. Two slices are compared through this rather than through their G-code,
+// because the G-code carries a config block that differs whenever any setting differs.
+struct SliceLengths {
+    std::vector<double> perimeters;
+    std::vector<double> fills;
+};
+
+SliceLengths slice_lengths(const Print &print)
+{
+    SliceLengths out;
+    for (const Layer *layer : print.objects().front()->layers()) {
+        double perimeters = 0., fills = 0.;
+        for (const LayerRegion *region : layer->regions()) {
+            perimeters += collection_length(region->perimeters);
+            fills      += collection_length(region->fills);
+        }
+        out.perimeters.push_back(perimeters);
+        out.fills.push_back(fills);
+    }
+    return out;
+}
+
+double perimeter_length_at(const Print &print, double print_z)
+{
+    for (const Layer *layer : print.objects().front()->layers())
+        if (std::abs(layer->print_z - print_z) < 1e-4) {
+            double len = 0.;
+            for (const LayerRegion *region : layer->regions())
+                len += collection_length(region->perimeters);
+            return len;
+        }
+    return 0.;
+}
+
+// Largest per-layer difference between two series; a negative result means they are not comparable.
+double max_difference(const std::vector<double> &a, const std::vector<double> &b)
+{
+    if (a.size() != b.size() || a.empty())
+        return -1.;
+    double worst = 0.;
+    for (size_t i = 0; i < a.size(); ++ i)
+        worst = std::max(worst, std::abs(a[i] - b[i]));
+    return worst;
+}
+
+} // namespace
+
+// The expansion only retypes area as top solid infill, so it can do nothing where there is no top
+// fill to begin with: zero top shell layers retypes the top surfaces as internal, and a top surface
+// density of 0% leaves the top layer with walls only. The last section is the control - the same
+// expansion on the same model does change the slice once a top fill exists - without which the two
+// equality checks above it would hold for an unrelated reason.
+TEST_CASE("Top surface expansion only acts where there is a top fill", "[Perimeters]")
+{
+    const char *wall_generator = GENERATE("classic", "arachne");
+    CAPTURE(wall_generator);
+
+    auto lengths_for = [wall_generator](int top_shell_layers, const char *top_surface_density, double expansion) {
+        DynamicPrintConfig config = base_config(wall_generator);
+        config.set_deserialize_strict({
+            { "top_shell_layers",      top_shell_layers },
+            { "top_surface_density",   top_surface_density },
+            { "top_surface_expansion", expansion },
+        });
+        Print print;
+        init_and_process_print({ step_with_ledge() }, print, config);
+        REQUIRE_FALSE(print.objects().empty());
+        return slice_lengths(print);
+    };
+
+    SECTION("no top shell layers") {
+        const SliceLengths off = lengths_for(0, "100%", 0.0);
+        const SliceLengths on  = lengths_for(0, "100%", 2.0);
+        REQUIRE(off.perimeters.size() == on.perimeters.size());
+        CHECK_THAT(max_difference(off.perimeters, on.perimeters), Catch::Matchers::WithinAbs(0., 1.0));
+        CHECK_THAT(max_difference(off.fills,      on.fills),      Catch::Matchers::WithinAbs(0., 1.0));
+    }
+
+    SECTION("zero top surface density") {
+        const SliceLengths off = lengths_for(3, "0%", 0.0);
+        const SliceLengths on  = lengths_for(3, "0%", 2.0);
+        REQUIRE(off.perimeters.size() == on.perimeters.size());
+        CHECK_THAT(max_difference(off.perimeters, on.perimeters), Catch::Matchers::WithinAbs(0., 1.0));
+        CHECK_THAT(max_difference(off.fills,      on.fills),      Catch::Matchers::WithinAbs(0., 1.0));
+    }
+
+    SECTION("with a top fill the same expansion does change the slice") {
+        const SliceLengths off = lengths_for(3, "100%", 0.0);
+        const SliceLengths on  = lengths_for(3, "100%", 2.0);
+        REQUIRE(off.fills.size() == on.fills.size());
+        CHECK(max_difference(off.fills, on.fills) > scale_(0.5));
+    }
+}
+
+// With no top shell the top surfaces are retyped as internal, so the top surface density has nothing
+// left to control: there is no top fill, and only_one_wall_top - the one route from the density to the
+// perimeters - is itself switched off for want of a top surface to act on.
+TEST_CASE("Top surface density does not affect a slice without a top shell", "[Perimeters]")
+{
+    const char *wall_generator = GENERATE("classic", "arachne");
+    CAPTURE(wall_generator);
+
+    auto lengths_for = [wall_generator](const char *top_surface_density) {
+        DynamicPrintConfig config = base_config(wall_generator);
+        config.set_deserialize_strict({
+            { "top_shell_layers",    0 },
+            { "only_one_wall_top",   true },
+            { "top_surface_density", top_surface_density },
+        });
+        Print print;
+        init_and_process_print({ step_with_ledge() }, print, config);
+        REQUIRE_FALSE(print.objects().empty());
+        return slice_lengths(print);
+    };
+
+    const SliceLengths solid = lengths_for("100%");
+    const SliceLengths none  = lengths_for("0%");
+    REQUIRE(solid.perimeters.size() == none.perimeters.size());
+    CHECK_THAT(max_difference(solid.perimeters, none.perimeters), Catch::Matchers::WithinAbs(0., 1.0));
+    CHECK_THAT(max_difference(solid.fills,      none.fills),      Catch::Matchers::WithinAbs(0., 1.0));
+}
+
+// On the ledge layer the inner walls are given up to the top fill, so that layer loses wall length.
+// The handover needs a top fill that reaches the freed space: at a top surface density of 0% there is
+// no top fill at all, and without top_surface_expansion the fill never grows over the walls. Either
+// way the feature still runs, through the original generation, which keeps the inner walls up to the
+// top boundary - putting that layer back between the plain and the one-wall slice.
+TEST_CASE("Only one wall on top surfaces drops inner walls only where a top fill replaces them", "[Perimeters]")
+{
+    const char *wall_generator = GENERATE("classic", "arachne");
+    CAPTURE(wall_generator);
+
+    auto ledge_perimeters_for = [wall_generator](bool only_one_wall_top, const char *top_surface_density, double expansion) {
+        DynamicPrintConfig config = base_config(wall_generator);
+        config.set_deserialize_strict({
+            { "only_one_wall_top",     only_one_wall_top },
+            { "top_surface_density",   top_surface_density },
+            { "top_surface_expansion", expansion },
+        });
+        Print print;
+        init_and_process_print({ step_with_ledge() }, print, config);
+        REQUIRE_FALSE(print.objects().empty());
+        return perimeter_length_at(print, ledge_z);
+    };
+
+    const double plain              = ledge_perimeters_for(false, "100%", 2.0);
+    const double one_wall           = ledge_perimeters_for(true,  "100%", 2.0);
+    const double one_wall_no_fill   = ledge_perimeters_for(true,  "0%",   2.0);
+    const double one_wall_no_expand = ledge_perimeters_for(true,  "100%", 0.0);
+
+    REQUIRE(plain > 0.);
+    CHECK(one_wall < plain);
+    // Both fall back to the original generation, which cuts the walls back to the top boundary but not past it.
+    CHECK(one_wall_no_fill > one_wall);
+    CHECK(one_wall_no_fill < plain);
+    CHECK(one_wall_no_expand > one_wall);
+    CHECK(one_wall_no_expand < plain);
+}
+
+// The bottom counterpart: the first layer is thinned to a single wall only where a bottom shell fills the
+// space behind it. With no bottom shell layers the bottom surfaces are retyped as internal, so that wall
+// would ring sparse infill on the bed - the option is switched off instead, and the GUI hides it in that
+// state so a profile that left it enabled cannot act behind a hidden checkbox.
+TEST_CASE("Only one wall on the first layer needs a bottom shell", "[Perimeters]")
+{
+    const char *wall_generator = GENERATE("classic", "arachne");
+    CAPTURE(wall_generator);
+
+    auto first_layer_perimeters_for = [wall_generator](bool only_one_wall_first_layer, int bottom_shell_layers) {
+        DynamicPrintConfig config = base_config(wall_generator);
+        config.set_deserialize_strict({
+            { "only_one_wall_first_layer", only_one_wall_first_layer },
+            { "bottom_shell_layers",       bottom_shell_layers },
+        });
+        Print print;
+        init_and_process_print({ step_with_ledge() }, print, config);
+        REQUIRE_FALSE(print.objects().empty());
+        return perimeter_length_at(print, first_layer_z);
+    };
+
+    const double plain             = first_layer_perimeters_for(false, 3);
+    const double one_wall          = first_layer_perimeters_for(true,  3);
+    // Both at zero bottom shell layers, so everything else that setting changes cancels out between them.
+    const double plain_no_shell    = first_layer_perimeters_for(false, 0);
+    const double one_wall_no_shell = first_layer_perimeters_for(true,  0);
+
+    REQUIRE(plain > 0.);
+    CHECK(one_wall < plain);
+    // No bottom shell: the option is inert, down to the same walls an unchecked box gives.
+    CHECK_THAT(one_wall_no_shell, Catch::Matchers::WithinAbs(plain_no_shell, 1.0));
+}

tests/fff_print/test_skirt_brim.cpp

@@ -153,6 +153,24 @@ TEST_CASE("Object brims are generated per instance", "[SkirtBrim]")
     }
 }
 
+TEST_CASE("Uncombined neighboring brims precede their respective objects", "[SkirtBrim]")
+{
+    Print print;
+    Model model;
+    place_two_cubes_apart(0, {
+        { "skirt_loops",   0 },
+        { "brim_type",     "outer_only" },
+        { "brim_width",    5 },
+        { "combine_brims", 0 },
+    }, print, model);
+    print.process();
+
+    REQUIRE(print.skirt_brim_groups().size() == 1);
+    REQUIRE(print.skirt_brim_groups().front().brims.size() == 2);
+    CHECK(role_sequence(gcode(print), { "brim", "perimeter" }) ==
+          std::vector<std::string>{ "brim", "perimeter", "brim", "perimeter" });
+}
+
 TEST_CASE("Combine brims merges neighboring object instances", "[SkirtBrim]")
 {
     Print print;