Export negative parts.

src/libslic3r/CSGMesh/CSGMesh.hpp

@@ -82,6 +82,40 @@ struct CSGPart {
     {}
 };
 
+//Prusa
+// Check if there are only positive parts (Union) within the collection.
+template<class Cont> bool is_all_positive(const Cont &csgmesh)
+{
+    bool is_all_pos =
+        std::all_of(csgmesh.begin(),
+                    csgmesh.end(),
+                    [](auto &part) {
+                        return csg::get_operation(part) == csg::CSGType::Union;
+                    });
+
+    return is_all_pos;
+}
+
+//Prusa
+// Merge all the positive parts of the collection into a single triangle mesh without performing
+// any booleans.
+template<class Cont>
+indexed_triangle_set csgmesh_merge_positive_parts(const Cont &csgmesh)
+{
+    indexed_triangle_set m;
+    for (auto &csgpart : csgmesh) {
+        auto op = csg::get_operation(csgpart);
+        const indexed_triangle_set * pmesh = csg::get_mesh(csgpart);
+        if (pmesh && op == csg::CSGType::Union) {
+            indexed_triangle_set mcpy = *pmesh;
+            its_transform(mcpy, csg::get_transform(csgpart), true);
+            its_merge(m, mcpy);
+        }
+    }
+
+    return m;
+}
+
 }} // namespace Slic3r::csg
 
 #endif // CSGMESH_HPP

src/libslic3r/CSGMesh/PerformCSGMeshBooleans.hpp

@@ -257,7 +257,7 @@ void perform_csgmesh_booleans_mcut(MeshBoolean::mcut::McutMeshPtr& mcutm,
 
 
 template<class It, class Visitor>
-std::tuple<BooleanFailReason,std::string> check_csgmesh_booleans(const Range<It> &csgrange, Visitor &&vfn)
+std::tuple<BooleanFailReason,std::string, It> check_csgmesh_booleans(const Range<It> &csgrange, Visitor &&vfn)
 {
     using namespace detail_cgal;
     BooleanFailReason fail_reason = BooleanFailReason::OK;
@@ -304,23 +304,23 @@ std::tuple<BooleanFailReason,std::string> check_csgmesh_booleans(const Range<It>
     };
     execution::for_each(ex_tbb, size_t(0), csgrange.size(), check_part);
 
-    //It ret = csgrange.end();
-    //for (size_t i = 0; i < csgrange.size(); ++i) {
-    //    if (!cgalmeshes[i]) {
-    //        auto it = csgrange.begin();
-    //        std::advance(it, i);
-    //        vfn(it);
+    It ret = csgrange.end();
+    for (size_t i = 0; i < csgrange.size(); ++i) {
+        if (!cgalmeshes[i]) {
+            auto it = csgrange.begin();
+            std::advance(it, i);
+            vfn(it);
 
-    //        if (ret == csgrange.end())
-    //            ret = it;
-    //    }
-    //}
+            if (ret == csgrange.end())
+                ret = it;
+        }
+    }
 
-    return { fail_reason,fail_part_name };
+    return { fail_reason,fail_part_name, ret};
 }
 
 template<class It>
-std::tuple<BooleanFailReason, std::string> check_csgmesh_booleans(const Range<It> &csgrange, bool use_mcut=false)
+std::tuple<BooleanFailReason, std::string, It> check_csgmesh_booleans(const Range<It> &csgrange, bool use_mcut=false)
 {
     if(!use_mcut)
         return check_csgmesh_booleans(csgrange, [](auto &) {});
@@ -354,7 +354,7 @@ std::tuple<BooleanFailReason, std::string> check_csgmesh_booleans(const Range<It
             McutMeshes[i] = std::move(m);
         };
         execution::for_each(ex_tbb, size_t(0), csgrange.size(), check_part);
-        return { fail_reason,fail_part_name };
+        return { fail_reason,fail_part_name, csgrange.end() };
     }
 }
 

src/slic3r/GUI/Plater.cpp

@@ -11686,14 +11686,37 @@ void Plater::export_stl(bool extended, bool selection_only, bool multi_stls)
     }
 
     // Following lambda generates a combined mesh for export with normals pointing outwards.
-    auto mesh_to_export_fff_no_boolean = [](const ModelObject &mo, int instance_id) {
+    auto mesh_to_export_fff_no_boolean = [this](const ModelObject &mo, int instance_id) {
         TriangleMesh mesh;
-        for (const ModelVolume *v : mo.volumes)
+
+        //Prusa export negative parts
+        std::vector<csg::CSGPart> csgmesh;
+        csgmesh.reserve(2 * mo.volumes.size());
+        csg::model_to_csgmesh(mo, Transform3d::Identity(), std::back_inserter(csgmesh),
+                              csg::mpartsPositive | csg::mpartsNegative | csg::mpartsDoSplits);
+
+        auto csgrange = range(csgmesh);
+        if (csg::is_all_positive(csgrange)) {
+            mesh = TriangleMesh{csg::csgmesh_merge_positive_parts(csgrange)};
+        } else if (std::get<2>(csg::check_csgmesh_booleans(csgrange)) == csgrange.end()) {
+            try {
+                auto cgalm = csg::perform_csgmesh_booleans(csgrange);
+                mesh = MeshBoolean::cgal::cgal_to_triangle_mesh(*cgalm);
+            } catch (...) {}
+        }
+
+        if (mesh.empty()) {
+            get_notification_manager()->push_plater_error_notification(
+                _u8L("Unable to perform boolean operation on model meshes. "
+                     "Only positive parts will be exported."));
+
+            for (const ModelVolume* v : mo.volumes)
                 if (v->is_model_part()) {
                     TriangleMesh vol_mesh(v->mesh());
                     vol_mesh.transform(v->get_matrix(), true);
                     mesh.merge(vol_mesh);
                 }
+        }
         if (instance_id == -1) {
             TriangleMesh vols_mesh(mesh);
             mesh = TriangleMesh();