Free a sharing object's own layers only when it takes over the shared ones

src/libslic3r/Print.cpp

@@ -2971,11 +2971,6 @@ void Print::auto_assign_extruders(ModelObject* model_object) const
 
 void  PrintObject::set_shared_object(PrintObject *object)
 {
-    // Orca: from now on m_layers / m_support_layers only alias the shared object's layers, so release the
-    // ones this object still owns (it may have sliced itself before it became shareable again).
-    // Both are no-ops once m_shared_object is set, so this cannot free layers owned by another object.
-    clear_support_layers();
-    clear_layers();
     m_shared_object = object;
     BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << boost::format(": this=%1%, found shared object from %2%")%this%m_shared_object;
 }
@@ -2996,6 +2991,15 @@ void  PrintObject::clear_shared_object()
 void  PrintObject::copy_layers_from_shared_object()
 {
     if (m_shared_object) {
+        // Orca: Print::process() calls this once per slice for each sharing object, after clear_shared_object() has
+        // emptied any earlier alias, so the vectors hold only layers this object sliced itself before it started sharing
+        // (or nothing). Free them here, as clear_support_layers() / clear_layers() would; those skip deletion while
+        // m_shared_object is set. The belt-only data they also free is always empty here, because belt printers never
+        // share layers.
+        for (SupportLayer *layer : m_support_layers)
+            delete layer;
+        for (Layer *layer : m_layers)
+            delete layer;
         m_layers.clear();
         m_support_layers.clear();
 

src/libslic3r/Support/TreeSupport.cpp

@@ -1976,8 +1976,8 @@ coordf_t TreeSupport::get_radius(const SupportNode* node)
     return node->radius;
 }
 
-// Orca: these are hit up to several times per node per layer in drop_nodes(), so hand out a
-// reference into the TreeSupportData cache instead of copying the ExPolygons out of it.
+// Orca: drop_nodes() calls these several times per node per layer, so they return a reference into the
+// TreeSupportData cache. The cache only ever inserts, so its entries never move while nodes drop in parallel.
 const ExPolygons& TreeSupport::get_avoidance(coordf_t radius, size_t obj_layer_nr)
 {
     return m_ts_data->get_avoidance(radius, obj_layer_nr);
@@ -2805,9 +2805,10 @@ void TreeSupport::draw_circles()
 #endif  // SUPPORT_TREE_DEBUG_TO_SVG
 
     SupportLayerPtrs& ts_layers = m_object->support_layers();
-    // Orca: the vector owns its layers, so the dropped ones have to be deleted, not just unlinked.
+    // Orca: the vector owns its layers, so the dropped ones are deleted before they are erased.
     // std::stable_partition (unlike std::remove_if) leaves exactly the dropped layers in the tail.
-    auto iter = std::stable_partition(ts_layers.begin(), ts_layers.end(), [](SupportLayer* ts_layer) { return ts_layer->height >= EPSILON; });
+    // Only heights below EPSILON are dropped; written as !(height < EPSILON), a NaN height is kept.
+    auto iter = std::stable_partition(ts_layers.begin(), ts_layers.end(), [](SupportLayer* ts_layer) { return !(ts_layer->height < EPSILON); });
     for (auto it = iter; it != ts_layers.end(); ++it)
         delete *it;
     ts_layers.erase(iter, ts_layers.end());

tests/fff_print/test_print.cpp

@@ -43,6 +43,7 @@
 #include "libslic3r/GCode/GCodeProcessor.hpp"
 #include "libslic3r/Exception.hpp"
 #include "libslic3r/LifecycleEvents.hpp"
+#include "libslic3r/Utils.hpp"
 
 #include "test_helpers.hpp"
 #include "test_utils.hpp"
@@ -156,6 +157,81 @@ SCENARIO("Changing the number of solid shell layers does not make all surfaces i
     }
 }
 
+// Two copies of one object share a single slice. When a copy that has sliced itself becomes identical to an
+// earlier object, it keeps its own layers while that object slices and only then takes the shared layers over.
+TEST_CASE("An object that starts sharing another object's slices keeps its own layers until it takes them over", "[Print][Regression]")
+{
+    DynamicPrintConfig config = DynamicPrintConfig::full_print_config();
+    config.set_deserialize_strict({
+        { "layer_height",               0.2 },
+        { "initial_layer_print_height", 0.2 },
+        { "raft_layers",                1 }, // each object gets support layers of its own
+        { "sparse_infill_density",      "20%" }, // object_a's override below differs from this
+    });
+    // Activates the slicing-pipeline hook installed for the second slice below.
+    config.set_key_value("slicing_pipeline_plugin", new ConfigOptionStrings({"probe"}));
+
+    Print print;
+    Model model;
+    init_print({cube(20)}, print, model, config);
+    ModelObject *object_a = model.objects.front();
+    // add_object() gives the copy extruder 1, and objects only share slices when their configs match.
+    object_a->config.set_key_value("extruder", new ConfigOptionInt(1));
+    ModelObject *object_b = model.add_object(*object_a); // shares object_a's mesh
+    for (ModelInstance *instance : object_b->instances)
+        instance->set_offset(instance->get_offset() + Vec3d(40., 0., 0.));
+    // A per-object override makes the objects differ, so each slices itself.
+    object_a->config.set_key_value("sparse_infill_density", new ConfigOptionPercent(40));
+
+    print.apply(model, config);
+    print.process();
+    REQUIRE(print.objects().size() == 2);
+    // The non-const accessors hand out the layer vectors themselves, which the checks below compare.
+    PrintObject *print_b = print.get_object(1);
+    REQUIRE(print_b->model_object()->id() == object_b->id()); // Print slices its own copy of the model
+    REQUIRE(print_b->get_shared_object() == nullptr);
+    const LayerPtrs        own_layers         = print_b->layers();
+    const SupportLayerPtrs own_support_layers = print_b->support_layers();
+    REQUIRE(!own_layers.empty());
+    REQUIRE(!own_support_layers.empty());
+
+    // Without the override the objects are identical again: print_a redoes the steps the setting invalidated,
+    // and print_b shares it.
+    object_a->config.erase("sparse_infill_density");
+    print.apply(model, config);
+    REQUIRE(print.objects().size() == 2);
+    PrintObject *print_a = print.get_object(0);
+
+    // Erasing the override invalidates print_a's posPrepareInfill and the steps after it. Its hook is the first one
+    // print_a fires, and it runs after print_b starts sharing but before print_b takes the shared layers over.
+    bool hook_fired          = false;
+    bool shared_while_a_runs = false;
+    bool kept_layers         = false;
+    bool kept_support_layers = false;
+    {
+        Print::set_slicing_pipeline_hook_fn([&](Print &, const PrintObject *object, SlicingPipelineStepPlugin) {
+            if (object != print_a || hook_fired)
+                return;
+            hook_fired          = true;
+            shared_while_a_runs = print_b->get_shared_object() == print_a;
+            kept_layers         = print_b->layers() == own_layers;
+            kept_support_layers = print_b->support_layers() == own_support_layers;
+        });
+        const ScopeGuard reset_hook([] { Print::set_slicing_pipeline_hook_fn(nullptr); });
+        print.process();
+    }
+
+    REQUIRE(hook_fired);
+    CHECK(print.objects()[1] == print_b);
+    CHECK(shared_while_a_runs);
+    CHECK(kept_layers);
+    CHECK(kept_support_layers);
+    CHECK(print_b->get_shared_object() == print_a);
+    REQUIRE(!print_a->layers().empty());
+    CHECK(print_b->layers() == print_a->layers());
+    CHECK(print_b->support_layers() == print_a->support_layers());
+}
+
 // ---------------------------------------------------------------------------
 // Print::validate() warning collection
 //