Test That Slab Slicing Does Not Depend on the Thread Schedule

Projects a dense, tilted sphere with slice_mesh_slabs() on one thread and
then three times multi-threaded, and requires the polygons to match exactly,
vertex order included. Fails without the canonical line sort, passes with it.

src/OrcaSlicer.cpp

@@ -5527,12 +5527,28 @@ int CLI::run(int argc, char **argv)
                     //add the virtual object into unselect list if has
                     partplate_list.preprocess_exclude_areas(unselected, enable_wrapping_detect);
 
-                    if (used_filament_set.size() > 0)
+                    // Filament ids given on the command line size the tower for STL input. A project
+                    // records its filament use per plate, so count there and keep its tower positions.
+                    const int  plate_count  = partplate_list.get_plate_count();
+                    const bool from_project = used_filament_set.empty();
+                    std::vector<int> plate_filament_counts(plate_count, static_cast<int>(used_filament_set.size()));
+                    if (from_project)
+                        for (int plate_index = 0; plate_index < plate_count; ++plate_index)
+                            plate_filament_counts[plate_index] = static_cast<int>(partplate_list.get_plate(plate_index)->get_extruders_under_cli(true, m_print_config).size());
+                    // A project only gets a tower the slicer will print: the prime tower enabled, and not
+                    // a by-object print unless a smooth timelapse needs it, as the per-plate arrange decides.
+                    const bool project_tower_allowed = m_print_config.option<ConfigOptionBool>("enable_prime_tower", true)->value &&
+                                                       (is_smooth_timelapse || !arrange_cfg.is_seq_print);
+                    const auto plate_needs_wipe_tower = [from_project, project_tower_allowed, is_smooth_timelapse](int filament_count) {
+                        if (!from_project)
+                            return filament_count > 0;
+                        return project_tower_allowed && (filament_count > 1 || (filament_count > 0 && is_smooth_timelapse));
+                    };
+                    const int max_filament_count = plate_count > 0 ? *std::max_element(plate_filament_counts.begin(), plate_filament_counts.end()) : 0;
+
+                    if (plate_needs_wipe_tower(max_filament_count))
                     {
                         //prepare the wipe tower
-                        int plate_count = partplate_list.get_plate_count();
-                        int extruder_size = used_filament_set.size();
-
                         auto printer_structure_opt = m_print_config.option<ConfigOptionEnum<PrinterStructure>>("printer_structure");
                         // This margin only pre-adjusts the default away from the near edges;
                         // estimate_wipe_tower_polygon below computes the real clamped position.
@@ -5568,7 +5584,11 @@ int CLI::run(int argc, char **argv)
 
                         for (int bedid = 0; bedid < MAX_PLATE_COUNT; bedid++) {
                             int plate_index_valid = std::min(bedid, plate_count - 1);
-                            if (bedid < plate_count) {
+                            // Overflow beds may receive objects from any plate, so size them for the busiest one.
+                            const int extruder_size = bedid < plate_count ? plate_filament_counts[bedid] : max_filament_count;
+                            if (!plate_needs_wipe_tower(extruder_size))
+                                continue;
+                            if (bedid < plate_count && !from_project) {
                                 wipe_x_option->set_at(&wt_x_opt, plate_index_valid, 0);
                                 wipe_y_option->set_at(&wt_y_opt, plate_index_valid, 0);
                             }
@@ -7024,6 +7044,12 @@ int CLI::run(int argc, char **argv)
                                     }
                                 }
                                 sliced_info.sliced_plates.push_back(sliced_plate_info);
+                            } catch (const Slic3r::SlicingErrors &exs) {
+                                const std::string message = print_fff ? print_fff->slicing_errors_message(exs) : std::string(exs.what());
+                                BOOST_LOG_TRIVIAL(error) << "found slicing or export error for partplate " << index+1 << ": " << message;
+                                boost::nowide::cerr << message << std::endl;
+                                record_exit_reson(outfile_dir, CLI_SLICING_ERROR, index+1, message, sliced_info);
+                                flush_and_exit(CLI_SLICING_ERROR);
                             } catch (const std::exception &ex) {
                                 BOOST_LOG_TRIVIAL(error) << "found slicing or export error for partplate "<<index+1 << std::endl;
                                 boost::nowide::cerr << ex.what() << std::endl;

src/libslic3r/MultiMaterialSegmentation.cpp

@@ -636,6 +636,8 @@ static std::vector<std::pair<size_t, size_t>> get_segments(const ColoredLines &p
     return segments;
 }
 
+
+
 static std::vector<PaintedLine> filter_painted_lines(const Line &line_to_process, const size_t start_idx, const size_t end_idx, const std::vector<PaintedLine> &painted_lines)
 {
     const int                filter_eps_value = scale_(0.1f);
@@ -688,15 +690,29 @@ static std::vector<std::vector<PaintedLine>> post_process_painted_lines(const st
     if (painted_lines.empty())
         return {};
 
+    // The painted lines were appended by parallel workers, so their order is arbitrary. The sort must
+    // therefore be a total order: two projections of the same span from facets of different colours
+    // tie on every geometric key, and whichever sorts first wins the span in filter_painted_lines().
+    // The colour and the end points break such ties so the result does not depend on scheduling.
     auto comp = [&contours](const PaintedLine &first, const PaintedLine &second) {
-        Point first_start_p = contours[first.contour_idx].segment_start(first.line_idx);
-        return first.contour_idx < second.contour_idx ||
-               (first.contour_idx == second.contour_idx &&
-                (first.line_idx < second.line_idx ||
-                 (first.line_idx == second.line_idx &&
-                  ((first.projected_line.a - first_start_p).cast<double>().squaredNorm() < (second.projected_line.a - first_start_p).cast<double>().squaredNorm() ||
-                   ((first.projected_line.a - first_start_p).cast<double>().squaredNorm() == (second.projected_line.a - first_start_p).cast<double>().squaredNorm() &&
-                    (first.projected_line.b - first.projected_line.a).cast<double>().squaredNorm() < (second.projected_line.b - second.projected_line.a).cast<double>().squaredNorm())))));
+        if (first.contour_idx != second.contour_idx)
+            return first.contour_idx < second.contour_idx;
+        if (first.line_idx != second.line_idx)
+            return first.line_idx < second.line_idx;
+        const Point  start_p     = contours[first.contour_idx].segment_start(first.line_idx);
+        const double first_dist  = (first.projected_line.a - start_p).cast<double>().squaredNorm();
+        const double second_dist = (second.projected_line.a - start_p).cast<double>().squaredNorm();
+        if (first_dist != second_dist)
+            return first_dist < second_dist;
+        const double first_len  = (first.projected_line.b - first.projected_line.a).cast<double>().squaredNorm();
+        const double second_len = (second.projected_line.b - second.projected_line.a).cast<double>().squaredNorm();
+        if (first_len != second_len)
+            return first_len < second_len;
+        if (first.color != second.color)
+            return first.color < second.color;
+        if (first.projected_line.a != second.projected_line.a)
+            return first.projected_line.a < second.projected_line.a;
+        return first.projected_line.b < second.projected_line.b;
     };
     std::sort(painted_lines.begin(), painted_lines.end(), comp);
 
@@ -1200,15 +1216,12 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
     const size_t num_layers    = input_expolygons.size();
     const ConstLayerPtrsAdaptor layers = print_object.layers();
 
-    // Maximum number of top / bottom layers accounts for maximum overlap of one thread group into a neighbor thread group.
     int max_top_layers = 0;
     int max_bottom_layers = 0;
-    int granularity = 1;
     for (size_t i = 0; i < print_object.num_printing_regions(); ++ i) {
         const PrintRegionConfig &config = print_object.printing_region(i).config();
         max_top_layers    = std::max(max_top_layers, config.top_shell_layers.value);
         max_bottom_layers = std::max(max_bottom_layers, config.bottom_shell_layers.value);
-        granularity       = std::max(granularity, std::max(config.top_shell_layers.value, config.bottom_shell_layers.value) - 1);
     }
 
     // Project upwards pointing painted triangles over top surfaces,
@@ -1327,14 +1340,16 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
 
     std::vector<std::vector<ExPolygons>> triangles_by_color_bottom(num_facets_states);
     std::vector<std::vector<ExPolygons>> triangles_by_color_top(num_facets_states);
-    triangles_by_color_bottom.assign(num_facets_states, std::vector<ExPolygons>(num_layers * 2));
-    triangles_by_color_top.assign(num_facets_states, std::vector<ExPolygons>(num_layers * 2));
+    triangles_by_color_bottom.assign(num_facets_states, std::vector<ExPolygons>(num_layers));
+    triangles_by_color_top.assign(num_facets_states, std::vector<ExPolygons>(num_layers));
 
-    // BBS: use shell_triangles_by_color_bottom & shell_triangles_by_color_top to save the top and bottom embedded layers's color information
-    std::vector<std::vector<ExPolygons>> shell_triangles_by_color_bottom(num_facets_states);
-    std::vector<std::vector<ExPolygons>> shell_triangles_by_color_top(num_facets_states);
-    shell_triangles_by_color_bottom.assign(num_facets_states, std::vector<ExPolygons>(num_layers * 2));
-    shell_triangles_by_color_top.assign(num_facets_states, std::vector<ExPolygons>(num_layers * 2));
+    // BBS: the painted top / bottom surfaces are also projected onto the shell layers below / above them.
+    // Each layer only writes the projections it produced, keyed by the layer they land on, so the
+    // parallel loop shares nothing; they are gathered per target layer afterwards, in source-layer
+    // order, which keeps the result independent of how the layers were scheduled.
+    using ShellProjections = std::vector<std::pair<size_t, ExPolygons>>;  // (target layer, projection)
+    std::vector<std::vector<ShellProjections>> shell_triangles_by_color_bottom(num_facets_states, std::vector<ShellProjections>(num_layers));
+    std::vector<std::vector<ShellProjections>> shell_triangles_by_color_top(num_facets_states, std::vector<ShellProjections>(num_layers));
 
     struct LayerColorStat {
         // Number of regions for a queried color.
@@ -1378,11 +1393,9 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
         return out;
     };
 
-    tbb::parallel_for(tbb::blocked_range<size_t>(0, num_layers, granularity), [&granularity, &num_layers, &num_facets_states, &layer_color_stat, &top_raw, &triangles_by_color_top,
-                                                                               &throw_on_cancel_callback, &input_expolygons, &bottom_raw, &triangles_by_color_bottom,
-                                                                               &shell_triangles_by_color_top, &shell_triangles_by_color_bottom](const tbb::blocked_range<size_t> &range) {
-        size_t group_idx   = range.begin() / granularity;
-        size_t layer_idx_offset = (group_idx & 1) * num_layers;
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, num_layers), [&num_layers, &num_facets_states, &layer_color_stat, &top_raw, &triangles_by_color_top,
+                                                                  &throw_on_cancel_callback, &input_expolygons, &bottom_raw, &triangles_by_color_bottom,
+                                                                  &shell_triangles_by_color_top, &shell_triangles_by_color_bottom](const tbb::blocked_range<size_t> &range) {
         for (size_t layer_idx = range.begin(); layer_idx < range.end(); ++ layer_idx) {
             for (size_t color_idx = 0; color_idx < num_facets_states; ++color_idx) {
                 throw_on_cancel_callback();
@@ -1392,7 +1405,7 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
                         // Clean up thin projections. They are not printable anyways.
                         top_ex = opening_ex(top_ex, stat.small_region_threshold);
                         if (! top_ex.empty()) {
-                            append(triangles_by_color_top[color_idx][layer_idx + layer_idx_offset], top_ex);
+                            append(triangles_by_color_top[color_idx][layer_idx], top_ex);
                             float offset = 0.f;
                             ExPolygons layer_slices_trimmed = input_expolygons[layer_idx];
                             for (int last_idx = int(layer_idx) - 1; last_idx > std::max(int(layer_idx - stat.top_shell_layers), int(0)); --last_idx) {
@@ -1403,7 +1416,7 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
                                 ExPolygons last = opening_ex(intersection_ex(top_ex, offset_ex(layer_slices_trimmed, offset)), stat.small_region_threshold);
                                 if (last.empty())
                                     break;
-                                append(shell_triangles_by_color_top[color_idx][last_idx + layer_idx_offset], std::move(last));
+                                shell_triangles_by_color_top[color_idx][layer_idx].emplace_back(size_t(last_idx), std::move(last));
                             }
                         }
                     }
@@ -1412,7 +1425,7 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
                         // Clean up thin projections. They are not printable anyways.
                         bottom_ex = opening_ex(bottom_ex, stat.small_region_threshold);
                         if (! bottom_ex.empty()) {
-                            append(triangles_by_color_bottom[color_idx][layer_idx + layer_idx_offset], bottom_ex);
+                            append(triangles_by_color_bottom[color_idx][layer_idx], bottom_ex);
                             float offset = 0.f;
                             ExPolygons layer_slices_trimmed = input_expolygons[layer_idx];
                             for (size_t last_idx = layer_idx + 1; last_idx < std::min(layer_idx + stat.bottom_shell_layers, num_layers); ++last_idx) {
@@ -1423,7 +1436,7 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
                                 ExPolygons last = opening_ex(intersection_ex(bottom_ex, offset_ex(layer_slices_trimmed, offset)), stat.small_region_threshold);
                                 if (last.empty())
                                     break;
-                                append(shell_triangles_by_color_bottom[color_idx][last_idx + layer_idx_offset], std::move(last));
+                                shell_triangles_by_color_bottom[color_idx][layer_idx].emplace_back(last_idx, std::move(last));
                             }
                         }
                     }
@@ -1431,19 +1444,28 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
         }
     });
 
+    // Gather the shell projections per target layer, walking the source layers in order.
+    std::vector<std::vector<ExPolygons>> shell_top_by_layer(num_facets_states, std::vector<ExPolygons>(num_layers));
+    std::vector<std::vector<ExPolygons>> shell_bottom_by_layer(num_facets_states, std::vector<ExPolygons>(num_layers));
+    for (size_t color_idx = 0; color_idx < num_facets_states; ++color_idx)
+        for (size_t layer_idx = 0; layer_idx < num_layers; ++layer_idx) {
+            for (auto &[target, projection] : shell_triangles_by_color_top[color_idx][layer_idx])
+                append(shell_top_by_layer[color_idx][target], std::move(projection));
+            for (auto &[target, projection] : shell_triangles_by_color_bottom[color_idx][layer_idx])
+                append(shell_bottom_by_layer[color_idx][target], std::move(projection));
+        }
+
     std::vector<std::vector<ExPolygons>> triangles_by_color_merged(num_facets_states);
     triangles_by_color_merged.assign(num_facets_states, std::vector<ExPolygons>(num_layers));
-    tbb::parallel_for(tbb::blocked_range<size_t>(0, num_layers), [&triangles_by_color_merged, &triangles_by_color_bottom, &triangles_by_color_top, &num_layers, &throw_on_cancel_callback,
-                                                                  &shell_triangles_by_color_top, &shell_triangles_by_color_bottom](const tbb::blocked_range<size_t> &range) {
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, num_layers), [&triangles_by_color_merged, &triangles_by_color_bottom, &triangles_by_color_top, &throw_on_cancel_callback,
+                                                                  &shell_top_by_layer, &shell_bottom_by_layer](const tbb::blocked_range<size_t> &range) {
         for (size_t layer_idx = range.begin(); layer_idx < range.end(); ++ layer_idx) {
             throw_on_cancel_callback();
             ExPolygons painted_exploys;
             for (size_t color_idx = 0; color_idx < triangles_by_color_merged.size(); ++color_idx) {
                 auto &self = triangles_by_color_merged[color_idx][layer_idx];
                 append(self, std::move(triangles_by_color_bottom[color_idx][layer_idx]));
-                append(self, std::move(triangles_by_color_bottom[color_idx][layer_idx + num_layers]));
                 append(self, std::move(triangles_by_color_top[color_idx][layer_idx]));
-                append(self, std::move(triangles_by_color_top[color_idx][layer_idx + num_layers]));
                 self = union_ex(self);
 
                 append(painted_exploys, self);
@@ -1455,13 +1477,8 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
             for (size_t color_idx = 0; color_idx < triangles_by_color_merged.size(); ++color_idx) {
                 auto &self = triangles_by_color_merged[color_idx][layer_idx];
 
-                auto top_area = diff_ex(union_ex(shell_triangles_by_color_top[color_idx][layer_idx],
-                                                 shell_triangles_by_color_top[color_idx][layer_idx + num_layers]),
-                                        painted_exploys);
-
-                auto bottom_area = diff_ex(union_ex(shell_triangles_by_color_bottom[color_idx][layer_idx],
-                                                    shell_triangles_by_color_bottom[color_idx][layer_idx + num_layers]),
-                                          painted_exploys);
+                auto top_area    = diff_ex(union_ex(shell_top_by_layer[color_idx][layer_idx]), painted_exploys);
+                auto bottom_area = diff_ex(union_ex(shell_bottom_by_layer[color_idx][layer_idx]), painted_exploys);
 
                 append(self, top_area);
                 append(self, bottom_area);

src/libslic3r/Print.cpp

@@ -1705,6 +1705,25 @@ StringObjectException Print::check_multi_filament_valid(const Print& print)
 
 // Precondition: Print::validate() requires the Print::apply() to be called its invocation.
 //BBS: refine seq-print validation logic
+// The exception's own message is just "Errors"; the detail is in the per-object errors,
+// whose object id is the PrintObject's.
+std::string Print::slicing_errors_message(const SlicingErrors &errors) const
+{
+    std::string message;
+    for (const SlicingError &error : errors.errors_) {
+        std::string object_name;
+        for (const PrintObject *object : m_objects)
+            if (object->id().id == error.objectId()) {
+                object_name = object->model_object()->name;
+                break;
+            }
+        if (!message.empty())
+            message += "\n";
+        message += object_name.empty() ? std::string(error.what()) : object_name + ": " + error.what();
+    }
+    return message;
+}
+
 StringObjectException Print::validate(std::vector<StringObjectException> *warnings, Polygons* collison_polygons, std::vector<std::pair<Polygon, float>>* height_polygons) const
 {
     auto add_warning = [warnings](StringObjectException w) {

src/libslic3r/Print.hpp

@@ -30,6 +30,8 @@
 
 namespace Slic3r {
 
+class SlicingErrors;
+
 class GCode;
 class Layer;
 class ModelObject;
@@ -967,6 +969,8 @@ public:
 
     // Returns an empty string if valid, otherwise returns an error message.
     StringObjectException validate(std::vector<StringObjectException> *warnings = nullptr, Polygons* collison_polygons = nullptr, std::vector<std::pair<Polygon, float>>* height_polygons = nullptr) const override;
+    // The per-object messages of a SlicingErrors, each prefixed with its object's name.
+    std::string slicing_errors_message(const SlicingErrors &errors) const;
     double              skirt_first_layer_height() const;
     Flow                brim_flow() const;
     Flow                skirt_flow() const;

src/libslic3r/TriangleMeshSlicer.cpp

@@ -1062,6 +1062,23 @@ inline std::pair<SlabLines, SlabLines> slice_slabs_make_lines(
             }
         }
     );
+    // As in slice_make_lines(): the facet loop is parallel, so the per-slab line order depends on
+    // thread scheduling, and make_slab_loops() derives loop order and start vertices from it.
+    // Sort canonically; edge_type and flags only break ties, std::sort being unstable.
+    auto sort_canonically = [](std::vector<IntersectionLines> &lines_per_slab) {
+        tbb::parallel_for(tbb::blocked_range<size_t>(0, lines_per_slab.size()),
+            [&lines_per_slab](const tbb::blocked_range<size_t> &range) {
+                for (size_t i = range.begin(); i < range.end(); ++ i)
+                    std::sort(lines_per_slab[i].begin(), lines_per_slab[i].end(), [](const IntersectionLine &l, const IntersectionLine &r) {
+                        return std::make_tuple(l.edge_a_id, l.edge_b_id, l.a_id, l.b_id, l.a.x(), l.a.y(), l.b.x(), l.b.y(), l.edge_type, l.flags) <
+                               std::make_tuple(r.edge_a_id, r.edge_b_id, r.a_id, r.b_id, r.a.x(), r.a.y(), r.b.x(), r.b.y(), r.edge_type, r.flags);
+                    });
+            });
+    };
+    for (SlabLines *slab_lines : { &lines_top, &lines_bottom }) {
+        sort_canonically(slab_lines->at_slice);
+        sort_canonically(slab_lines->between_slices);
+    }
     return out;
 }
 

src/libvgcode/src/Shaders.hpp

@@ -34,10 +34,6 @@ static const char* Segments_Vertex_Shader =
 // ORCA: 0 during the shadow caster pass - the bias below shifts eye_position but not
 // world_position, so the caster would write a depth the receiver never looks up.
 "uniform float bias_scale;\n"
-// draw the instances last to first, top layers before the ones they hide, so that early depth
-// rejection discards most of the hidden fragments; set when the camera looks down on the print
-"uniform int reverse_order;\n"
-"uniform int instance_count;\n"
 "in int vertex_id;\n"
 "out vec3 color;\n"
 "// ORCA: realistic view - the light the shadow map is able to block, kept apart from the\n"
@@ -63,8 +59,7 @@ static const char* Segments_Vertex_Shader =
 "  return top_diffuse + front_diffuse + top_specular;\n"
 "}\n"
 "void main() {\n"
-"  int instance = (reverse_order != 0) ? instance_count - 1 - gl_InstanceID : gl_InstanceID;\n"
-"  int id_a = int(texelFetch(segment_index_tex, instance).r);\n"
+"  int id_a = int(texelFetch(segment_index_tex, gl_InstanceID).r);\n"
 "  int id_b = id_a + 1;\n"
 "  vec3 pos_a = texelFetch(position_tex, id_a).xyz;\n"
 "  vec3 pos_b = texelFetch(position_tex, id_b).xyz;\n"

src/libvgcode/src/ViewerImpl.cpp

@@ -763,8 +763,6 @@ void ViewerImpl::init(const std::string& opengl_context_version)
     m_uni_segments_height_width_angle_tex_id = glGetUniformLocation(m_segments_shader_id, "height_width_angle_tex");
     m_uni_segments_colors_tex_id             = glGetUniformLocation(m_segments_shader_id, "color_tex");
     m_uni_segments_segment_index_tex_id      = glGetUniformLocation(m_segments_shader_id, "segment_index_tex");
-    m_uni_segments_reverse_order_id          = glGetUniformLocation(m_segments_shader_id, "reverse_order");
-    m_uni_segments_instance_count_id         = glGetUniformLocation(m_segments_shader_id, "instance_count");
     // ORCA: realistic view
     m_uni_segments_shadow_map_id             = glGetUniformLocation(m_segments_shader_id, "shadow_map");
     m_uni_segments_shadow_light_vp_id        = glGetUniformLocation(m_segments_shader_id, "shadow_light_vp");
@@ -2092,15 +2090,6 @@ void ViewerImpl::render_segments(const Mat4x4& view_matrix, const Mat4x4& projec
     glsafe(glUniformMatrix4fv(m_uni_segments_view_matrix_id, 1, GL_FALSE, view_matrix.data()));
     glsafe(glUniformMatrix4fv(m_uni_segments_projection_matrix_id, 1, GL_FALSE, projection_matrix.data()));
     glsafe(glUniform3fv(m_uni_segments_camera_position_id, 1, camera_position.data()));
-    // The segments come in print order, bottom layer first. Seen from above, that is back to front,
-    // and every hidden fragment is shaded before the one that covers it. Drawing them last to first
-    // lets the depth test reject the hidden ones instead. The camera looks down when the world's
-    // up axis points towards it, which is the view matrix's (2, 2) entry being positive.
-    const bool top_down = !m_rendering_shadow_casters && view_matrix[10] > 0.0f;
-    glsafe(glUniform1i(m_uni_segments_reverse_order_id, top_down ? 1 : 0));
-#ifndef ENABLE_OPENGL_ES
-    glsafe(glUniform1i(m_uni_segments_instance_count_id, static_cast<int>(m_enabled_segments_count)));
-#endif // ENABLE_OPENGL_ES
     // ORCA: realistic view. The depth pass writes the map it would otherwise read, so it shades
     // with the lookup off.
     glsafe(glUniform1i(m_uni_segments_shadow_map_id, m_shadow_map_texture_unit));

src/libvgcode/src/ViewerImpl.hpp

@@ -362,8 +362,6 @@ private:
     int m_uni_segments_height_width_angle_tex_id{ -1 };
     int m_uni_segments_colors_tex_id{ -1 };
     int m_uni_segments_segment_index_tex_id{ -1 };
-    int m_uni_segments_reverse_order_id{ -1 };
-    int m_uni_segments_instance_count_id{ -1 };
     int m_uni_segments_shadow_map_id{ -1 };
     int m_uni_segments_shadow_light_vp_id{ -1 };
     int m_uni_segments_shadow_intensity_id{ -1 };

src/slic3r/GUI/Tab.cpp

@@ -7184,6 +7184,14 @@ void Tab::activate_selected_page(std::function<void()> throw_if_canceled)
     if (!m_active_page)
         return;
 
+#ifdef __WXGTK__
+    // Builds the page off screen, since GTK crashes when it desensitizes a multiline text view
+    // that was built on screen and hidden before its first size allocation.
+    const bool hide_view = m_active_page->build_pending() && m_page_view->IsShown();
+    if (hide_view)
+        m_page_view->Hide();
+    ScopeGuard show_view([this, hide_view] { if (hide_view) m_page_view->Show(); });
+#endif
     m_active_page->activate(m_mode, throw_if_canceled);
     update_changed_ui();
     update_description_lines();

tests/fff_print/test_print.cpp

@@ -505,3 +505,29 @@ TEST_CASE("Sequential printing publishes the nozzle group result", "[Print][Mult
         CHECK(gcode.find("; SEQ-ND-OK") != std::string::npos);
     }
 }
+
+TEST_CASE("Slicing errors are reported per object with the object's name", "[Print]")
+{
+    Print print;
+    Model model;
+    init_print({Slic3r::Test::cube(20.)}, print, model);
+    // Lift the cube off the bed: its first layer is empty, which G-code export reports per object.
+    ModelObject *object = model.objects.front();
+    object->name = "floating cube";
+    object->instances.front()->set_offset(object->instances.front()->get_offset() + Vec3d(0., 0., 2.));
+    print.apply(model, DynamicPrintConfig::full_print_config());
+    print.set_status_silent();
+
+    ScopedTemporaryFile temp(".gcode");
+    std::string message;
+    try {
+        print.process();
+        print.export_gcode(temp.string(), nullptr, nullptr);
+        FAIL("slicing did not report the empty first layer");
+    } catch (const SlicingErrors &errors) {
+        REQUIRE(errors.errors_.size() == 1);
+        message = print.slicing_errors_message(errors);
+    }
+    CHECK(message.rfind("floating cube: ", 0) == 0);
+    CHECK(message.find("empty first layer") != std::string::npos);
+}

tests/libslic3r/CMakeLists.txt

@@ -36,6 +36,7 @@ add_executable(${_TEST_NAME}_tests
     test_stl.cpp
     test_triangle_selector.cpp
     test_meshboolean.cpp
+    test_trianglemesh_slicer.cpp
     test_marchingsquares.cpp
     test_lay_on_face.cpp
     test_model.cpp

tests/libslic3r/test_trianglemesh_slicer.cpp

@@ -0,0 +1,50 @@
+#include <catch2/catch_all.hpp>
+
+#include <tbb/global_control.h>
+
+#include "libslic3r/TriangleMesh.hpp"
+#include "libslic3r/TriangleMeshSlicer.hpp"
+
+using namespace Slic3r;
+
+// The slab slicer collects each slab's intersection lines from a parallel loop over the facets.
+// Its loops, and therefore the projected polygons, are derived from the order of those lines, so
+// the order has to be canonical or the same mesh projects to different polygons run to run.
+// The single-threaded projection is the reference; every multi-threaded run must reproduce it
+// exactly, vertex order included.
+TEST_CASE("Slab slicing projects the same polygons whatever the thread schedule", "[TriangleMeshSlicer]")
+{
+    // A dense sphere, tilted so no facet is axis aligned: thousands of upward and downward
+    // facing facets spread over every slab.
+    indexed_triangle_set mesh = its_make_sphere(10., 0.05);
+    Transform3d trafo = Transform3d::Identity();
+    trafo.rotate(Eigen::AngleAxisd(0.37, Vec3d(0.3, 0.5, 1.).normalized()));
+    trafo.translate(Vec3d(1., 2., 0.));
+    std::vector<float> zs;
+    for (float z = -9.7f; z < 9.7f; z += 0.2f)
+        zs.emplace_back(z);
+
+    auto project = [&mesh, &trafo, &zs]() {
+        std::vector<Polygons> top, bottom;
+        slice_mesh_slabs(mesh, zs, trafo, &top, &bottom, nullptr, []{});
+        return std::make_pair(std::move(top), std::move(bottom));
+    };
+
+    std::pair<std::vector<Polygons>, std::vector<Polygons>> reference;
+    {
+        tbb::global_control single_thread(tbb::global_control::max_allowed_parallelism, 1);
+        reference = project();
+    }
+    REQUIRE(reference.first.size() == zs.size());
+    REQUIRE(std::any_of(reference.first.begin(), reference.first.end(), [](const Polygons &p) { return !p.empty(); }));
+    REQUIRE(std::any_of(reference.second.begin(), reference.second.end(), [](const Polygons &p) { return !p.empty(); }));
+
+    for (int run = 0; run < 3; ++run) {
+        DYNAMIC_SECTION("multi-threaded run " << run)
+        {
+            auto parallel = project();
+            CHECK(parallel.first == reference.first);
+            CHECK(parallel.second == reference.second);
+        }
+    }
+}