Print unsupported walls last (#15411)

src/libslic3r/ExtrusionEntity.hpp

@@ -454,6 +454,10 @@ class ExtrusionLoop : public ExtrusionEntity
 {
 public:
     ExtrusionPaths paths;
+    // ORCA: Set on a loop extruded entirely in mid air and out of reach of the layer below: it has
+    // nothing to lean on until this layer is bridged, so the G-code writer holds it back until the
+    // infill is down. See defer_unsupported_loops() in PerimeterGenerator.cpp.
+    bool print_after_infill = false;
 
     ExtrusionLoop(ExtrusionLoopRole role = elrDefault) : m_loop_role(role) {}
     ExtrusionLoop(const ExtrusionPaths &paths, ExtrusionLoopRole role = elrDefault) : paths(paths), m_loop_role(role) {}

src/libslic3r/GCode.cpp

@@ -6603,6 +6603,8 @@ LayerResult GCode::process_layer(
                         }
                         // Then print infill
                         gcode += this->extrude_infill(print, by_region_specific, false);
+                        // Then the walls left hanging in mid air, now that the infill can anchor them
+                        gcode += this->extrude_perimeters(print, by_region_specific, first_layer, false, true);
                         // Then print perimeters of regions that has is_infill_first == true
                         gcode += this->extrude_perimeters(print, by_region_specific, first_layer, true);
                     }
@@ -6898,6 +6900,7 @@ LayerResult GCode::process_layer(
                             has_insert_timelapse_gcode = true;
                         }
                         gcode += this->extrude_infill(print, by_region_specific, false);
+                        gcode += this->extrude_perimeters(print, by_region_specific, first_layer, false, true);
                         gcode += this->extrude_perimeters(print, by_region_specific, first_layer, true);
                         // ironing
                         gcode += this->extrude_infill(print, by_region_specific, true);
@@ -7638,7 +7641,7 @@ std::string GCode::extrude_path(const ExtrusionPath& path, const std::string& de
 }
 
 // Extrude perimeters: Decide where to put seams (hide or align seams).
-std::string GCode::extrude_perimeters(const Print &print, const std::vector<ObjectByExtruder::Island::Region> &by_region, bool is_first_layer, bool is_infill_first)
+std::string GCode::extrude_perimeters(const Print &print, const std::vector<ObjectByExtruder::Island::Region> &by_region, bool is_first_layer, bool is_infill_first, bool unsupported_loops_only)
 {
     std::string gcode;
     for (const ObjectByExtruder::Island::Region &region : by_region)
@@ -7657,7 +7660,24 @@ std::string GCode::extrude_perimeters(const Print &print, const std::vector<Obje
                 m_config.wipe_inward_distance.value > 0. &&
                 scale_(FILAMENT_CONFIG(wipe_distance)) > SCALED_EPSILON)
                 wipe_support.emplace();
+
+            // ORCA: loops flagged as extruded in mid air, out of reach of the layer below, are held back
+            // for a second pass after the infill that anchors them. Infill already precedes infill first walls.
+            const bool defer_unsupported = !is_infill_first;
+            auto waits_for_infill = [](const ExtrusionEntity *ee) {
+                return ee->is_loop() && static_cast<const ExtrusionLoop *>(ee)->print_after_infill;
+            };
+
+            // The deferred pass runs after the infill, so the loops the first pass emitted are
+            // already down and belong in the prefix an inward wipe may land on.
+            if (wipe_support && defer_unsupported && unsupported_loops_only)
+                for (const ExtrusionEntity* ee : region.perimeters)
+                    if (!waits_for_infill(ee))
+                        wipe_support->append(*ee);
+
             for (const ExtrusionEntity* ee : region.perimeters) {
+                if (defer_unsupported && waits_for_infill(ee) != unsupported_loops_only)
+                    continue;
                 gcode += this->extrude_entity(*ee, "perimeter", -1., region.perimeters,
                                              wipe_support ? &*wipe_support : nullptr);
                 if (wipe_support)

src/libslic3r/GCode.hpp

@@ -534,7 +534,7 @@ private:
 		// For sequential print, the instance of the object to be printing has to be defined.
 		const size_t                     				 single_object_instance_idx);
 
-    std::string     extrude_perimeters(const Print& print, const std::vector<ObjectByExtruder::Island::Region>& by_region, bool is_first_layer, bool is_infill_first);
+    std::string     extrude_perimeters(const Print& print, const std::vector<ObjectByExtruder::Island::Region>& by_region, bool is_first_layer, bool is_infill_first, bool unsupported_loops_only = false);
     std::string     extrude_infill(const Print& print, const std::vector<ObjectByExtruder::Island::Region>& by_region, bool ironing);
     std::string     extrude_support(const ExtrusionEntityCollection& support_fills, const ExtrusionRole support_extrusion_role);
 

src/libslic3r/Layer.cpp

@@ -153,6 +153,7 @@ bool Layer::is_perimeter_compatible(const Print& print, const PrintRegion& a, co
         && config.gap_infill_speed.get_at(print.get_extruder_id(config.outer_wall_filament_id)) == other_config.gap_infill_speed.get_at(print.get_extruder_id(config.outer_wall_filament_id))
         && config.filter_out_gap_fill.value == other_config.filter_out_gap_fill.value
 		&& config.detect_overhang_wall                   == other_config.detect_overhang_wall
+		&& config.unsupported_wall_last                  == other_config.unsupported_wall_last
 		&& config.overhang_reverse                       == other_config.overhang_reverse
 		&& config.overhang_reverse_threshold             == other_config.overhang_reverse_threshold
 		&& config.wall_direction                         == other_config.wall_direction

src/libslic3r/PerimeterGenerator.cpp

@@ -550,6 +550,7 @@ static ExtrusionEntityCollection traverse_extrusions(const PerimeterGenerator& p
         if (!paths.empty()) {
             if (extrusion->is_closed) {
                 ExtrusionLoop extrusion_loop(std::move(paths), pg_extrusion.is_contour ? elrDefault : elrHole);
+                extrusion_loop.inset_idx = extrusion->inset_idx;
                 if ((perimeter_generator.config->wall_direction == WallDirection::CounterClockwise) ==
                     (pg_extrusion.is_contour || pg_extrusions.size() == 2))
                     extrusion_loop.make_counter_clockwise();
@@ -1318,6 +1319,73 @@ static void reorient_perimeters(ExtrusionEntityCollection &entities, bool steep_
     }
 }
 
+// A loop made of nothing but overhang paths lies entirely off the lower layer.
+static bool is_unsupported_loop(const ExtrusionEntity *entity)
+{
+    if (!entity->is_loop())
+        return false;
+    const ExtrusionPaths &paths = static_cast<const ExtrusionLoop *>(entity)->paths;
+    return !paths.empty() && std::all_of(paths.begin(), paths.end(),
+                                         [](const ExtrusionPath &path) { return path.role() == erOverhangPerimeter; });
+}
+
+// ORCA: A wall loop with nothing under it has nothing to lean on, so whatever the configured wall
+// sequence it is extruded after the loops that anchor it, innermost first. A loop that runs alongside
+// an anchored one belongs to the same wall stack and keeps its place ahead of the infill, which needs
+// it as an anchor; one that touches nothing has only that infill to rest on, so it is flagged for the
+// G-code writer to hold it back until the infill is down.
+static void defer_unsupported_loops(const PerimeterGenerator &perimeter_generator, ExtrusionEntityCollection &entities)
+{
+    if (!perimeter_generator.config->unsupported_wall_last)
+        return;
+
+    ExtrusionEntitiesPtr &src = entities.entities;
+    auto first_deferred = std::stable_partition(src.begin(), src.end(),
+                                                [](const ExtrusionEntity *entity) { return !is_unsupported_loop(entity); });
+    if (first_deferred == src.end())
+        return;
+
+    std::stable_sort(first_deferred, src.end(),
+                     [](const ExtrusionEntity *lhs, const ExtrusionEntity *rhs) { return lhs->inset_idx > rhs->inset_idx; });
+
+    auto collect_lines = [](const ExtrusionEntity *entity, Lines &out) {
+        Polylines polylines;
+        entity->collect_polylines(polylines);
+        append(out, to_lines(polylines));
+    };
+
+    Lines anchored;
+    for (auto it = src.begin(); it != first_deferred; ++it)
+        collect_lines(*it, anchored);
+
+    std::vector<ExtrusionLoop *> unattached;
+    for (auto it = first_deferred; it != src.end(); ++it)
+        unattached.emplace_back(static_cast<ExtrusionLoop *>(*it));
+
+    // A loop leaning on a loop that is itself anchored is anchored as well, so spread outwards from
+    // the anchored loops until no unsupported loop is left touching what was reached.
+    const double touch_distance = 1.5 * std::max(perimeter_generator.ext_perimeter_flow.scaled_spacing(),
+                                                 perimeter_generator.perimeter_flow.scaled_spacing());
+    while (!anchored.empty()) {
+        AABBTreeLines::LinesDistancer<Line> distancer{std::move(anchored)};
+        anchored.clear();
+        for (ExtrusionLoop *&loop : unattached) {
+            if (loop == nullptr)
+                continue;
+            const Points points = loop->as_polyline().points;
+            if (std::any_of(points.begin(), points.end(),
+                            [&distancer, touch_distance](const Point &point) { return distancer.distance_from_lines<false>(point) < touch_distance; })) {
+                collect_lines(loop, anchored);
+                loop = nullptr;
+            }
+        }
+    }
+
+    for (ExtrusionLoop *loop : unattached)
+        if (loop != nullptr)
+            loop->print_after_infill = true;
+}
+
 void PerimeterGenerator::process_classic()
 {
     group_region_by_fuzzify(*this);
@@ -1804,6 +1872,8 @@ void PerimeterGenerator::process_classic()
                 }
             }
             
+            defer_unsupported_loops(*this, entities);
+
             // append perimeters for this slice as a collection
             if (! entities.empty())
                 this->loops->append(entities);
@@ -2742,6 +2812,7 @@ void PerimeterGenerator::process_arachne()
                 reorient_perimeters(extrusion_coll, steep_overhang_contour, steep_overhang_hole,
                                     this->config->overhang_reverse_internal_only);
             }
+            defer_unsupported_loops(*this, extrusion_coll);
             this->loops->append(extrusion_coll);
         }
 

src/libslic3r/Preset.cpp

@@ -1058,6 +1058,7 @@ static std::vector<std::string> s_Preset_print_options{
     "reduce_crossing_wall",
     "detect_thin_wall",
     "detect_overhang_wall",
+    "unsupported_wall_last",
     "overhang_reverse",
     "overhang_reverse_threshold",
     "overhang_reverse_internal_only",

src/libslic3r/PrintConfig.cpp

@@ -5547,6 +5547,16 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionBool(true));
 
+    def = this->add("unsupported_wall_last", coBool);
+    def->label = L("Print unsupported walls last");
+    def->category = L("Quality");
+    def->tooltip = L("Wall loops that lie entirely in mid air are printed once something can hold them:\n"
+                     "they are extruded after the other walls of their island, innermost first, whatever the wall order is.\n"
+                     "A loop that only the bridges of this layer can anchor waits until those bridges are printed, while a loop running "
+                     "alongside a supported wall keeps its place before the infill, which needs it as an anchor.");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionBool(false));
+
     def = this->add("outer_wall_filament_id", coInt);
     def->gui_type = ConfigOptionDef::GUIType::i_enum_open;
     def->label = L("Outer walls");

src/libslic3r/PrintConfig.hpp

@@ -1353,6 +1353,7 @@ PRINT_CONFIG_CLASS_DEFINE(
     ((ConfigOptionFloatsNullable, filament_ironing_speed))
     // Detect bridging perimeters
     ((ConfigOptionBool, detect_overhang_wall))
+    ((ConfigOptionBool, unsupported_wall_last))
     ((ConfigOptionInt, outer_wall_filament_id))
     ((ConfigOptionInt, inner_wall_filament_id))
     ((ConfigOptionFloatOrPercent, inner_wall_line_width))

src/libslic3r/PrintObject.cpp

@@ -1501,6 +1501,7 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "fuzzy_skin_octaves"
             || opt_key == "fuzzy_skin_persistence"
             || opt_key == "detect_overhang_wall"
+            || opt_key == "unsupported_wall_last"
             || opt_key == "overhang_reverse"
             || opt_key == "overhang_reverse_internal_only"
             || opt_key == "overhang_reverse_threshold"

src/slic3r/GUI/ConfigManipulation.cpp

@@ -1134,6 +1134,7 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, in
     bool has_detect_overhang_wall = config->opt_bool("detect_overhang_wall");
     bool has_overhang_reverse     = config->opt_bool("overhang_reverse");
     bool allow_overhang_reverse   = !has_spiral_vase;
+    toggle_line("unsupported_wall_last", has_detect_overhang_wall);
     toggle_line("overhang_reverse", allow_overhang_reverse);
     toggle_line("overhang_reverse_internal_only", allow_overhang_reverse && has_overhang_reverse);
     bool has_overhang_reverse_internal_only = config->opt_bool("overhang_reverse_internal_only");

src/slic3r/GUI/Tab.cpp

@@ -2794,6 +2794,7 @@ void TabPrint::build()
 
         optgroup = page->new_optgroup(L("Overhangs"), L"param_overhang");
         optgroup->append_single_option_line("detect_overhang_wall", "quality_settings_overhangs#detect-overhang-wall");
+        optgroup->append_single_option_line("unsupported_wall_last", "quality_settings_overhangs#unsupported-wall-last");
         optgroup->append_single_option_line("make_overhang_printable", "quality_settings_overhangs#make-overhang-printable");
         optgroup->append_single_option_line("make_overhang_printable_angle", "quality_settings_overhangs#maximum-angle");
         optgroup->append_single_option_line("make_overhang_printable_hole_size", "quality_settings_overhangs#hole-area");

tests/fff_print/test_perimeters.cpp

@@ -4,9 +4,14 @@
 #include "libslic3r/ExtrusionEntityCollection.hpp"
 #include "libslic3r/Layer.hpp"
 #include "libslic3r/Print.hpp"
+#include "libslic3r/GCodeReader.hpp"
+#include "libslic3r/Model.hpp"
+#include "libslic3r/TriangleMesh.hpp"
 
 #include <algorithm>
 #include <cmath>
+#include <limits>
+#include <string>
 #include <vector>
 
 #include "test_helpers.hpp"
@@ -255,3 +260,238 @@ TEST_CASE("Only one wall on the first layer needs a bottom shell", "[Perimeters]
     // 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));
 }
+
+namespace {
+
+// The layer that closes the cavity of box_over_cavity(), the first one printed over air.
+const double cavity_ceiling_z = 6.2;
+
+// A cone standing on its tip, flaring by 5mm of radius per mm of height: at a layer height of 0.2 every
+// wall of a layer lands a full millimetre outside the one below, entirely off the layer below but right
+// alongside the walls printed with it.
+TriangleMesh flared_cone()
+{
+    TriangleMesh cone = make_cone(20., 4.);
+    cone.mirror(Z);
+    cone.translate(0., 0., 4.);
+    return cone;
+}
+
+// A 30mm box holding a 20mm cavity from z=2 to z=6, with a 4mm hole punched down through the ceiling
+// of that cavity. The layer at cavity_ceiling_z bridges the cavity, and the walls of the hole sit in
+// the middle of that bridge, 15mm clear of anything the layer below supports.
+Print &box_over_cavity(Print &print, Model &model, const DynamicPrintConfig &config)
+{
+    ModelObject *object = model.add_object();
+    object->name = "box_over_cavity.stl";
+    object->add_volume(make_cube(30., 30., 8.), ModelVolumeType::MODEL_PART, false);
+    TriangleMesh cavity = make_cube(20., 20., 4.);
+    cavity.translate(5.f, 5.f, 2.f);
+    object->add_volume(std::move(cavity), ModelVolumeType::NEGATIVE_VOLUME, false);
+    TriangleMesh hole = make_cube(4., 4., 6.);
+    hole.translate(13.f, 13.f, 5.f);
+    object->add_volume(std::move(hole), ModelVolumeType::NEGATIVE_VOLUME, false);
+    object->add_instance();
+    object->ensure_on_bed();
+
+    print.auto_assign_extruders(object);
+    print.apply(model, config);
+    print.validate();
+    print.set_status_silent();
+    return print;
+}
+
+// Every setting the assertions below depend on, so none of them rests on a default.
+DynamicPrintConfig unsupported_walls_config(const char *wall_generator, bool unsupported_wall_last)
+{
+    DynamicPrintConfig config = DynamicPrintConfig::full_print_config();
+    config.set_deserialize_strict({
+        { "wall_generator",             wall_generator },
+        { "layer_height",               0.2 },
+        { "initial_layer_print_height", 0.2 },
+        { "wall_loops",                 3 },
+        { "detect_overhang_wall",       true },
+        // Outer wall first, so an unsupported loop only ends up last if the feature puts it there.
+        { "wall_sequence",              "outer wall/inner wall" },
+        { "is_infill_first",            false },
+        { "sparse_infill_density",      "15%" },
+        { "unsupported_wall_last",      unsupported_wall_last },
+        { "gcode_comments",             true },
+    });
+    return config;
+}
+
+// A loop extruded entirely in mid air: every one of its paths is an overhang.
+bool unsupported_loop(const ExtrusionEntity *entity)
+{
+    if (! entity->is_loop())
+        return false;
+    const ExtrusionPaths &paths = static_cast<const ExtrusionLoop *>(entity)->paths;
+    return ! paths.empty() && std::all_of(paths.begin(), paths.end(),
+                                          [](const ExtrusionPath &path) { return path.role() == erOverhangPerimeter; });
+}
+
+// The loops of every wall island of the print, island by island, in extrusion order.
+std::vector<std::vector<const ExtrusionLoop*>> wall_islands(const Print &print)
+{
+    std::vector<std::vector<const ExtrusionLoop*>> islands;
+    for (const Layer *layer : print.objects().front()->layers())
+        for (const LayerRegion *region : layer->regions())
+            for (const ExtrusionEntity *island : region->perimeters.entities) {
+                std::vector<const ExtrusionLoop*> loops;
+                for (const ExtrusionEntity *entity : static_cast<const ExtrusionEntityCollection*>(island)->entities)
+                    if (entity->is_loop())
+                        loops.push_back(static_cast<const ExtrusionLoop*>(entity));
+                islands.push_back(std::move(loops));
+            }
+    return islands;
+}
+
+// Islands where a loop that is anchored is extruded after one that is not.
+int islands_with_a_supported_loop_last(const Print &print)
+{
+    int count = 0;
+    for (const std::vector<const ExtrusionLoop*> &loops : wall_islands(print)) {
+        bool seen_unsupported = false;
+        for (const ExtrusionLoop *loop : loops) {
+            if (unsupported_loop(loop))
+                seen_unsupported = true;
+            else if (seen_unsupported) {
+                ++ count;
+                break;
+            }
+        }
+    }
+    return count;
+}
+
+// The unsupported loops of the print, and those of them held back for the infill.
+std::vector<const ExtrusionLoop*> unsupported_loops(const Print &print, double print_z = -1.)
+{
+    std::vector<const ExtrusionLoop*> loops;
+    for (const Layer *layer : print.objects().front()->layers()) {
+        if (print_z >= 0. && std::abs(layer->print_z - print_z) > EPSILON)
+            continue;
+        for (const LayerRegion *region : layer->regions())
+            for (const ExtrusionEntity *island : region->perimeters.entities)
+                for (const ExtrusionEntity *entity : static_cast<const ExtrusionEntityCollection*>(island)->entities)
+                    if (unsupported_loop(entity))
+                        loops.push_back(static_cast<const ExtrusionLoop*>(entity));
+    }
+    return loops;
+}
+
+int loops_held_back_for_infill(const std::vector<const ExtrusionLoop*> &loops)
+{
+    return int(std::count_if(loops.begin(), loops.end(), [](const ExtrusionLoop *loop) { return loop->print_after_infill; }));
+}
+
+// The G-code emitted at `print_z`, so the order of one layer can be read on its own.
+std::string layer_gcode(const std::string &gcode, double print_z)
+{
+    std::string out;
+    GCodeReader reader;
+    reader.parse_buffer(gcode, [&out, print_z](GCodeReader &self, const GCodeReader::GCodeLine &line) {
+        if (std::abs(self.z() - print_z) < EPSILON)
+            out += line.raw() + "\n";
+    });
+    return out;
+}
+
+} // namespace
+
+// Whatever the wall order asks for, a loop with nothing under it cannot be extruded before the loops it
+// leans on. The flared cone gives every layer an outer wall that lands completely off the one below, and
+// the outer wall first sequence would otherwise put it down before any of them.
+TEST_CASE("Unsupported wall loops are extruded after the walls that anchor them", "[Perimeters]")
+{
+    const char *wall_generator = GENERATE("classic", "arachne");
+    CAPTURE(wall_generator);
+
+    auto slice_cone = [wall_generator](bool unsupported_wall_last, Print &print) {
+        init_and_process_print({ flared_cone() }, print, unsupported_walls_config(wall_generator, unsupported_wall_last));
+        REQUIRE_FALSE(print.objects().empty());
+    };
+
+    Print on;
+    slice_cone(true, on);
+    // Without unsupported loops to reorder the rest of the test would pass on an empty print.
+    REQUIRE(unsupported_loops(on).size() > 0);
+    CHECK(islands_with_a_supported_loop_last(on) == 0);
+
+    SECTION("the held back loops run innermost first") {
+        for (const std::vector<const ExtrusionLoop*> &loops : wall_islands(on)) {
+            int previous_inset = std::numeric_limits<int>::max();
+            for (const ExtrusionLoop *loop : loops)
+                if (unsupported_loop(loop)) {
+                    CHECK(loop->inset_idx <= previous_inset);
+                    previous_inset = loop->inset_idx;
+                }
+        }
+    }
+
+    SECTION("switched off, the configured wall order is left alone") {
+        Print off;
+        slice_cone(false, off);
+        REQUIRE(unsupported_loops(off).size() == unsupported_loops(on).size());
+        // Outer wall first puts the unsupported outer wall ahead of the walls behind it.
+        CHECK(islands_with_a_supported_loop_last(off) > 0);
+    }
+}
+
+// A loop the walls cannot reach is a different case: only the bridges of its own layer will ever hold it,
+// so it has to wait for them - while a loop that runs alongside a wall keeps its place, because the
+// bridges anchor on it instead.
+TEST_CASE("A wall loop out of reach of the layer below waits for the infill", "[Perimeters]")
+{
+    const char *wall_generator = GENERATE("classic", "arachne");
+    CAPTURE(wall_generator);
+
+    Print print;
+    Model model;
+    box_over_cavity(print, model, unsupported_walls_config(wall_generator, true));
+    print.process();
+
+    const std::vector<const ExtrusionLoop*> hole_loops = unsupported_loops(print, cavity_ceiling_z);
+    REQUIRE(hole_loops.size() > 0);
+    CHECK(loops_held_back_for_infill(hole_loops) == int(hole_loops.size()));
+
+    SECTION("a loop alongside a supported wall is not held back") {
+        Print cone;
+        init_and_process_print({ flared_cone() }, cone, unsupported_walls_config(wall_generator, true));
+        const std::vector<const ExtrusionLoop*> loops = unsupported_loops(cone);
+        REQUIRE(loops.size() > 0);
+        CHECK(loops_held_back_for_infill(loops) == 0);
+    }
+
+    SECTION("switched off, no loop is held back") {
+        Print off;
+        Model off_model;
+        box_over_cavity(off, off_model, unsupported_walls_config(wall_generator, false));
+        off.process();
+        const std::vector<const ExtrusionLoop*> loops = unsupported_loops(off, cavity_ceiling_z);
+        REQUIRE(loops.size() == hole_loops.size());
+        CHECK(loops_held_back_for_infill(loops) == 0);
+    }
+}
+
+// The held back loops reach the G-code in a second pass, after the infill of their layer: on the layer
+// that closes the cavity the walls of the hole are extruded once the bridge is down, so the layer emits
+// perimeters, then infill, then the perimeters that were waiting for it.
+TEST_CASE("Loops waiting for the infill are extruded after it", "[Perimeters]")
+{
+    const char *wall_generator = GENERATE("classic", "arachne");
+    CAPTURE(wall_generator);
+
+    auto ceiling_roles = [wall_generator](bool unsupported_wall_last) {
+        Print print;
+        Model model;
+        box_over_cavity(print, model, unsupported_walls_config(wall_generator, unsupported_wall_last));
+        const std::string layer = layer_gcode(gcode(print), cavity_ceiling_z);
+        REQUIRE_FALSE(layer.empty());
+        return role_sequence(layer, { "perimeter", "infill" });
+    };
+
+    CHECK(ceiling_roles(true)  == std::vector<std::string>{ "perimeter", "infill", "perimeter" });
+    CHECK(ceiling_roles(false) == std::vector<std::string>{ "perimeter", "infill" });
+}