diff --git a/CMakeLists.txt b/CMakeLists.txt
index 49717b68d..ba291e450 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -162,15 +162,15 @@ if (CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUXX)
     endif ()
 endif()
 
-if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
-    add_compile_options(-Wall)
+if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" OR "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall" )
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-reorder" )
 
     # On GCC and Clang, no return from a non-void function is a warning only. Here, we make it an error.
     add_compile_options(-Werror=return-type)
 
     #removes LOTS of extraneous Eigen warnings (GCC only supports it since 6.1)
-    #if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" OR CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 6.1)
+    #if("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" OR CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 6.1)
         # add_compile_options(-Wno-ignored-attributes) # Tamas: Eigen include dirs are marked as SYSTEM
     #endif()
 
@@ -317,10 +317,10 @@ endif()
 
 # Find eigen3 or use bundled version
 if (NOT SLIC3R_STATIC)
-    find_package(Eigen3 3)
+    find_package(Eigen3 3.3)
 endif ()
-if (NOT Eigen3_FOUND)
-    set(Eigen3_FOUND 1)
+if (NOT EIGEN3_FOUND)
+    set(EIGEN3_FOUND 1)
     set(EIGEN3_INCLUDE_DIR ${LIBDIR}/eigen/)
 endif ()
 include_directories(BEFORE SYSTEM ${EIGEN3_INCLUDE_DIR})
diff --git a/deps/deps-macos.cmake b/deps/deps-macos.cmake
index c7c6819e3..d22e4a2e2 100644
--- a/deps/deps-macos.cmake
+++ b/deps/deps-macos.cmake
@@ -111,6 +111,6 @@ ExternalProject_Add(dep_wxwidgets
         --with-expat=builtin
         --disable-debug
         --disable-debug_flag
-    BUILD_COMMAND make "-j${NPROC}" && make -C locale allmo
+    BUILD_COMMAND make "-j${NPROC}" && PATH=/usr/local/opt/gettext/bin/:$ENV{PATH} make -C locale allmo
     INSTALL_COMMAND make install
 )
diff --git a/doc/How to build - Mac OS.md b/doc/How to build - Mac OS.md
index b4196909d..082c560b7 100644
--- a/doc/How to build - Mac OS.md	
+++ b/doc/How to build - Mac OS.md	
@@ -1,7 +1,15 @@
 
 # Building PrusaSlicer on Mac OS
 
-To build PrusaSlicer on Mac OS, you will need to install XCode, [CMake](https://cmake.org/) (available on Brew) and possibly git.
+To build PrusaSlicer on Mac OS, you will need the following software:
+
+- XCode
+- CMake
+- git
+- gettext
+
+XCode is available through Apple's App Store, the other three tools are available on
+[brew](https://brew.sh/) (use `brew install cmake git gettext` to install them).
 
 ### Dependencies
 
diff --git a/src/libslic3r/GCode/WipeTower.cpp b/src/libslic3r/GCode/WipeTower.cpp
index 354ec6d9e..55a6c4437 100644
--- a/src/libslic3r/GCode/WipeTower.cpp
+++ b/src/libslic3r/GCode/WipeTower.cpp
@@ -157,7 +157,7 @@ public:
             change_analyzer_mm3_per_mm(len, e);
 			// Width of a squished extrusion, corrected for the roundings of the squished extrusions.
 			// This is left zero if it is a travel move.
-			float width = float(double(e) * /*Filament_Area*/2.40528 / (len * m_layer_height));
+			float width = float(double(e) * m_filpar[0].filament_area / (len * m_layer_height));
 			// Correct for the roundings of a squished extrusion.
 			width += m_layer_height * float(1. - M_PI / 4.);
 			if (m_extrusions.empty() || m_extrusions.back().pos != rotated_current_pos)
@@ -822,7 +822,7 @@ void WipeTower::toolchange_Unload(
     while (i < m_filpar[m_current_tool].ramming_speed.size())
     {
         const float x = volume_to_length(m_filpar[m_current_tool].ramming_speed[i] * 0.25f, line_width, m_layer_height);
-        const float e = m_filpar[m_current_tool].ramming_speed[i] * 0.25f / Filament_Area; // transform volume per sec to E move;
+        const float e = m_filpar[m_current_tool].ramming_speed[i] * 0.25f / filament_area(); // transform volume per sec to E move;
         const float dist = std::min(x - e_done, remaining);		  // distance to travel for either the next 0.25s, or to the next turnaround
         const float actual_time = dist/x * 0.25;
         writer.ram(writer.x(), writer.x() + (m_left_to_right ? 1.f : -1.f) * dist, 0, 0, e * (dist / x), dist / (actual_time / 60.));
diff --git a/src/libslic3r/GCode/WipeTower.hpp b/src/libslic3r/GCode/WipeTower.hpp
index badb3e8b2..6dfad1b8c 100644
--- a/src/libslic3r/GCode/WipeTower.hpp
+++ b/src/libslic3r/GCode/WipeTower.hpp
@@ -111,7 +111,8 @@ public:
 	// Set the extruder properties.
 	void set_extruder(size_t idx, std::string material, int temp, int first_layer_temp, float loading_speed, float loading_speed_start,
                       float unloading_speed, float unloading_speed_start, float delay, int cooling_moves,
-                      float cooling_initial_speed, float cooling_final_speed, std::string ramming_parameters, float max_volumetric_speed, float nozzle_diameter)
+                      float cooling_initial_speed, float cooling_final_speed, std::string ramming_parameters, float max_volumetric_speed,
+                      float nozzle_diameter, float filament_diameter)
 	{
         //while (m_filpar.size() < idx+1)   // makes sure the required element is in the vector
         m_filpar.push_back(FilamentParameters());
@@ -133,10 +134,12 @@ public:
             m_filpar[idx].cooling_final_speed     = cooling_final_speed;
         }
 
-        if (max_volumetric_speed != 0.f)
-            m_filpar[idx].max_e_speed = (max_volumetric_speed / Filament_Area);
+        m_filpar[idx].filament_area = (M_PI/4.f) * pow(filament_diameter, 2); // all extruders are assumed to have the same filament diameter at this point
         m_filpar[idx].nozzle_diameter = nozzle_diameter; // to be used in future with (non-single) multiextruder MM
 
+        if (max_volumetric_speed != 0.f)
+            m_filpar[idx].max_e_speed = (max_volumetric_speed / filament_area());
+
         m_perimeter_width = nozzle_diameter * Width_To_Nozzle_Ratio; // all extruders are now assumed to have the same diameter
 
         if (m_semm) {
@@ -248,6 +251,7 @@ public:
         float               max_e_speed = std::numeric_limits<float>::max();
         std::vector<float>  ramming_speed;
         float               nozzle_diameter;
+        float               filament_area;
     };
 
 private:
@@ -261,9 +265,11 @@ private:
 
 
     const bool  m_peters_wipe_tower   = false; // sparse wipe tower inspired by Peter's post processor - not finished yet
-    const float Filament_Area         = float(M_PI * 1.75f * 1.75f / 4.f); // filament area in mm^2
     const float Width_To_Nozzle_Ratio = 1.25f; // desired line width (oval) in multiples of nozzle diameter - may not be actually neccessary to adjust
     const float WT_EPSILON            = 1e-3f;
+    const float filament_area() const {
+        return m_filpar[0].filament_area; // all extruders are assumed to have the same filament diameter at this point
+    }
 
 
 	bool   m_semm               = true; // Are we using a single extruder multimaterial printer?
@@ -315,7 +321,7 @@ private:
 	{
 		if ( layer_height < 0 )
 			return m_extrusion_flow;
-		return layer_height * ( m_perimeter_width - layer_height * (1.f-float(M_PI)/4.f)) / Filament_Area;
+		return layer_height * ( m_perimeter_width - layer_height * (1.f-float(M_PI)/4.f)) / filament_area();
 	}
 
 	// Calculates length of extrusion line to extrude given volume
diff --git a/src/libslic3r/Print.cpp b/src/libslic3r/Print.cpp
index a9b8a827f..5702f49e3 100644
--- a/src/libslic3r/Print.cpp
+++ b/src/libslic3r/Print.cpp
@@ -1092,6 +1092,13 @@ std::string Print::validate() const
     }
 
     if (this->has_wipe_tower() && ! m_objects.empty()) {
+        // make sure all extruders use same diameter filament and have the same nozzle diameter
+        for (const auto& extruder_idx : extruders()) {
+            if (m_config.nozzle_diameter.get_at(extruder_idx) != m_config.nozzle_diameter.get_at(extruders().front())
+             || m_config.filament_diameter.get_at(extruder_idx) != m_config.filament_diameter.get_at(extruders().front()))
+                 return L("The wipe tower is only supported if all extruders have the same nozzle diameter and use filaments of the same diameter.");
+        }
+
         if (m_config.gcode_flavor != gcfRepRap && m_config.gcode_flavor != gcfRepetier && m_config.gcode_flavor != gcfMarlin)
             return L("The Wipe Tower is currently only supported for the Marlin, RepRap/Sprinter and Repetier G-code flavors.");
         if (! m_config.use_relative_e_distances)
@@ -1701,7 +1708,8 @@ void Print::_make_wipe_tower()
 			(float)m_config.filament_cooling_final_speed.get_at(i),
             m_config.filament_ramming_parameters.get_at(i),
             m_config.filament_max_volumetric_speed.get_at(i),
-            m_config.nozzle_diameter.get_at(i));
+            m_config.nozzle_diameter.get_at(i),
+            m_config.filament_diameter.get_at(i));
 
     m_wipe_tower_data.priming = Slic3r::make_unique<std::vector<WipeTower::ToolChangeResult>>(
         wipe_tower.prime((float)this->skirt_first_layer_height(), m_wipe_tower_data.tool_ordering.all_extruders(), false));
diff --git a/src/libslic3r/Utils.hpp b/src/libslic3r/Utils.hpp
index 09e24a475..8a4f1424b 100644
--- a/src/libslic3r/Utils.hpp
+++ b/src/libslic3r/Utils.hpp
@@ -172,7 +172,7 @@ extern std::string xml_escape(std::string text);
 #if defined __GNUC__ && __GNUC__ < 5 && !defined __clang__
 // Older GCCs don't have std::is_trivially_copyable
 // cf. https://gcc.gnu.org/onlinedocs/gcc-4.9.4/libstdc++/manual/manual/status.html#status.iso.2011
-#warning "GCC version < 5, faking std::is_trivially_copyable"
+// #warning "GCC version < 5, faking std::is_trivially_copyable"
 template<typename T> struct IsTriviallyCopyable { static constexpr bool value = true; };
 #else
 template<typename T> struct IsTriviallyCopyable : public std::is_trivially_copyable<T> {};
diff --git a/src/slic3r/GUI/GUI_ObjectList.cpp b/src/slic3r/GUI/GUI_ObjectList.cpp
index 429cc18ee..a2ddba376 100644
--- a/src/slic3r/GUI/GUI_ObjectList.cpp
+++ b/src/slic3r/GUI/GUI_ObjectList.cpp
@@ -487,13 +487,15 @@ void ObjectList::update_name_in_model(const wxDataViewItem& item) const
 {
     const int obj_idx = m_objects_model->GetObjectIdByItem(item);
     if (obj_idx < 0) return;
+    const int volume_id = m_objects_model->GetVolumeIdByItem(item);
 
-    if (m_objects_model->GetParent(item) == wxDataViewItem(0)) {
+    take_snapshot(wxString::Format(_(L("Rename %s")), volume_id < 0 ? _(L("Object")) : _(L("Sub-object"))));
+
+    if (m_objects_model->GetItemType(item) & itObject) {
         (*m_objects)[obj_idx]->name = m_objects_model->GetName(item).ToUTF8().data();
         return;
     }
 
-    const int volume_id = m_objects_model->GetVolumeIdByItem(item);
     if (volume_id < 0) return;
     (*m_objects)[obj_idx]->volumes[volume_id]->name = m_objects_model->GetName(item).ToUTF8().data();
 }
@@ -925,7 +927,7 @@ void ObjectList::OnDrop(wxDataViewEvent &event)
 
     if (m_dragged_data.type() == itInstance)
     {
-        take_snapshot(_(L("Instances to Separated Objects")));
+        Plater::TakeSnapshot snapshot(wxGetApp().plater(),_(L("Instances to Separated Objects")));
         instances_to_separated_object(m_dragged_data.obj_idx(), m_dragged_data.inst_idxs());
         m_dragged_data.clear();
         return;
@@ -943,7 +945,7 @@ void ObjectList::OnDrop(wxDataViewEvent &event)
 //     if (to_volume_id > from_volume_id) to_volume_id--;
 // #endif // __WXGTK__
 
-    take_snapshot(_(L("Remov Volume(s)")));
+    take_snapshot(_(L("Remove Volume(s)")));
 
     auto& volumes = (*m_objects)[m_dragged_data.obj_idx()]->volumes;
     auto delta = to_volume_id < from_volume_id ? -1 : 1;
@@ -3055,7 +3057,7 @@ void ObjectList::change_part_type()
 	if (new_type == type || new_type == ModelVolumeType::INVALID)
         return;
 
-    take_snapshot(_(L("Paste from Clipboard")));
+    take_snapshot(_(L("Change Part Type")));
 
     const auto item = GetSelection();
     volume->set_type(new_type);
@@ -3294,6 +3296,8 @@ void ObjectList::split_instances()
     if (obj_idx == -1)
         return;
 
+    Plater::TakeSnapshot snapshot(wxGetApp().plater(), _(L("Instances to Separated Objects")));
+
     if (selection.is_single_full_object())
     {
         instances_to_separated_objects(obj_idx);
diff --git a/src/slic3r/GUI/GUI_ObjectSettings.cpp b/src/slic3r/GUI/GUI_ObjectSettings.cpp
index 16c64360a..8728156ac 100644
--- a/src/slic3r/GUI/GUI_ObjectSettings.cpp
+++ b/src/slic3r/GUI/GUI_ObjectSettings.cpp
@@ -93,6 +93,7 @@ bool ObjectSettings::update_settings_list()
             btn->SetToolTip(_(L("Remove parameter")));
 
 			btn->Bind(wxEVT_BUTTON, [opt_key, config, this](wxEvent &event) {
+                wxGetApp().plater()->take_snapshot(wxString::Format(_(L("Delete Option %s")), opt_key));
 				config->erase(opt_key);
                 wxGetApp().obj_list()->changed_object();
                 wxTheApp->CallAfter([this]() {
@@ -137,6 +138,13 @@ bool ObjectSettings::update_settings_list()
                 if (is_extruders_cat)
                     option.opt.max = wxGetApp().extruders_edited_cnt();
                 optgroup->append_single_option_line(option);
+
+                optgroup->get_field(opt)->m_on_change = [optgroup](const std::string& opt_id, const boost::any& value) {
+                    // first of all take a snapshot and then change value in configuration
+                    wxGetApp().plater()->take_snapshot(wxString::Format(_(L("Change Option %s")), opt_id));
+                    optgroup->on_change_OG(opt_id, value);
+                };
+
             }
             optgroup->reload_config();
 
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp b/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp
index 4b975e87e..a65074646 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp
@@ -166,7 +166,7 @@ void GLGizmoBase::set_highlight_color(const float* color)
 
 void GLGizmoBase::enable_grabber(unsigned int id)
 {
-    if ((0 <= id) && (id < (unsigned int)m_grabbers.size()))
+    if (id < m_grabbers.size())
         m_grabbers[id].enabled = true;
 
     on_enable_grabber(id);
@@ -174,7 +174,7 @@ void GLGizmoBase::enable_grabber(unsigned int id)
 
 void GLGizmoBase::disable_grabber(unsigned int id)
 {
-    if ((0 <= id) && (id < (unsigned int)m_grabbers.size()))
+    if (id < m_grabbers.size())
         m_grabbers[id].enabled = false;
 
     on_disable_grabber(id);
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp b/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp
index 7846edb22..8733c9a11 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp
@@ -93,19 +93,19 @@ protected:
     }
     virtual void on_set_hover_id()
     {
-        for (unsigned int i = 0; i < 3; ++i)
+        for (int i = 0; i < 3; ++i)
         {
             m_gizmos[i].set_hover_id((m_hover_id == i) ? 0 : -1);
         }
     }
     virtual void on_enable_grabber(unsigned int id)
     {
-        if ((0 <= id) && (id < 3))
+        if (id < 3)
             m_gizmos[id].enable_grabber(0);
     }
     virtual void on_disable_grabber(unsigned int id)
     {
-        if ((0 <= id) && (id < 3))
+        if (id < 3)
             m_gizmos[id].disable_grabber(0);
     }
     virtual void on_start_dragging();
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
index 8027906a9..6875a5b88 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
@@ -82,7 +82,9 @@ void GLGizmoSlaSupports::set_sla_support_data(ModelObject* model_object, const S
             editing_mode_reload_cache();
         }
 
-        if (m_editing_mode_cache.empty() && m_model_object->sla_points_status != sla::PointsStatus::UserModified)
+        if (m_editing_mode_cache.empty()
+         && m_model_object->sla_points_status != sla::PointsStatus::UserModified
+         && m_model_object->sla_points_status != sla::PointsStatus::None)
             get_data_from_backend();
 
         if (m_state == On) {
@@ -1122,9 +1124,13 @@ void GLGizmoSlaSupports::on_start_dragging()
 
 void GLGizmoSlaSupports::on_load(cereal::BinaryInputArchive& ar)
 {
+    if (m_editing_mode)
+        editing_mode_discard_changes();
+
     ar(m_clipping_plane_distance,
        m_clipping_plane_normal,
-       m_current_mesh_object_id
+       m_current_mesh_object_id,
+       m_editing_mode_cache
     );
 }
 
@@ -1134,7 +1140,8 @@ void GLGizmoSlaSupports::on_save(cereal::BinaryOutputArchive& ar) const
 {
     ar(m_clipping_plane_distance,
        m_clipping_plane_normal,
-       m_current_mesh_object_id
+       m_current_mesh_object_id,
+       m_editing_mode_cache
     );
 }
 
@@ -1177,16 +1184,16 @@ void GLGizmoSlaSupports::editing_mode_discard_changes()
     // If the points were autogenerated, they may not be on the ModelObject yet.
     // Because the user probably messed with the cache, we will get the data
     // from the backend again.
-
-    if (m_model_object->sla_points_status == sla::PointsStatus::AutoGenerated)
+    /*if (m_model_object->sla_points_status == sla::PointsStatus::AutoGenerated) {
         get_data_from_backend();
-    else {
-        m_editing_mode_cache.clear();
-        for (const sla::SupportPoint& point : m_model_object->sla_support_points)
-            m_editing_mode_cache.emplace_back(point, false);
-    }
-        m_editing_mode = false;
-        m_unsaved_changes = false;
+        }
+    else
+        editing_mode_reload_cache();*/
+
+    m_editing_mode_cache = m_old_cache;
+
+    m_editing_mode = false;
+    m_unsaved_changes = false;
 }
 
 
@@ -1196,7 +1203,13 @@ void GLGizmoSlaSupports::editing_mode_apply_changes()
     // If there are no changes, don't touch the front-end. The data in the cache could have been
     // taken from the backend and copying them to ModelObject would needlessly invalidate them.
     if (m_unsaved_changes) {
+        // In order to make the undo/redo snapshot, we must first temporarily restore
+        // the editing cache to the state before the edits were made.
+        std::vector<CacheEntry> backup = m_editing_mode_cache;
+        m_editing_mode_cache = m_old_cache;
         wxGetApp().plater()->take_snapshot(_(L("Support points edit")));
+        m_editing_mode_cache = std::move(backup);
+
         m_model_object->sla_points_status = sla::PointsStatus::UserModified;
         m_model_object->sla_support_points.clear();
         for (const CacheEntry& cache_entry : m_editing_mode_cache)
@@ -1216,6 +1229,7 @@ void GLGizmoSlaSupports::editing_mode_apply_changes()
 void GLGizmoSlaSupports::editing_mode_reload_cache()
 {
     m_editing_mode_cache.clear();
+
     for (const sla::SupportPoint& point : m_model_object->sla_support_points)
         m_editing_mode_cache.emplace_back(point, false);
 
@@ -1271,6 +1285,8 @@ void GLGizmoSlaSupports::switch_to_editing_mode()
         editing_mode_reload_cache();
     m_unsaved_changes = false;
     m_editing_mode = true;
+    m_old_cache = m_editing_mode_cache;
+    select_point(NoPoints);
 }
 
 
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
index fbc438f1d..5ef1e6aea 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
@@ -98,6 +98,8 @@ private:
     float m_new_point_head_diameter;        // Size of a new point.
     float m_minimal_point_distance = 20.f;
     mutable std::vector<CacheEntry> m_editing_mode_cache; // a support point and whether it is currently selected
+    std::vector<CacheEntry> m_old_cache; // to restore after discarding changes or undo/redo
+
     float m_clipping_plane_distance = 0.f;
     mutable float m_old_clipping_plane_distance = 0.f;
     mutable Vec3d m_old_clipping_plane_normal;
diff --git a/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp b/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
index dc819961f..6c2de1c35 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
@@ -223,7 +223,7 @@ void GLGizmosManager::update_data()
     enable_grabber(Rotate, 1, !is_wipe_tower);
 
     bool enable_scale_xyz = selection.is_single_full_instance() || selection.is_single_volume() || selection.is_single_modifier();
-    for (int i = 0; i < 6; ++i)
+    for (unsigned int i = 0; i < 6; ++i)
     {
         enable_grabber(Scale, i, enable_scale_xyz);
     }
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index bf27b0512..2c9f41c56 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -3733,9 +3733,10 @@ void Plater::priv::take_snapshot(const std::string& snapshot_name)
     if (this->m_prevent_snapshots > 0) 
         return;
     assert(this->m_prevent_snapshots >= 0);
-    unsigned int flags = 0;
+    UndoRedo::SnapshotData snapshot_data;
+    snapshot_data.printer_technology = this->printer_technology;
     if (this->view3D->is_layers_editing_enabled())
-    	flags |= UndoRedo::Snapshot::VARIABLE_LAYER_EDITING_ACTIVE;
+    	snapshot_data.flags |= UndoRedo::SnapshotData::VARIABLE_LAYER_EDITING_ACTIVE;
     //FIXME updating the Wipe tower config values at the ModelWipeTower from the Print config.
     // This is a workaround until we refactor the Wipe Tower position / orientation to live solely inside the Model, not in the Print config.
     if (this->printer_technology == ptFFF) {
@@ -3743,7 +3744,7 @@ void Plater::priv::take_snapshot(const std::string& snapshot_name)
         model.wipe_tower.position = Vec2d(config.opt_float("wipe_tower_x"), config.opt_float("wipe_tower_y"));
         model.wipe_tower.rotation = config.opt_float("wipe_tower_rotation_angle");
     }
-    this->undo_redo_stack.take_snapshot(snapshot_name, model, view3D->get_canvas3d()->get_selection(), view3D->get_canvas3d()->get_gizmos_manager(), this->printer_technology, flags);
+    this->undo_redo_stack.take_snapshot(snapshot_name, model, view3D->get_canvas3d()->get_selection(), view3D->get_canvas3d()->get_gizmos_manager(), snapshot_data);
     this->undo_redo_stack.release_least_recently_used();
     // Save the last active preset name of a particular printer technology.
     ((this->printer_technology == ptFFF) ? m_last_fff_printer_profile_name : m_last_sla_printer_profile_name) = wxGetApp().preset_bundle->printers.get_selected_preset_name();
@@ -3777,11 +3778,11 @@ void Plater::priv::undo_redo_to(size_t time_to_load)
 void Plater::priv::undo_redo_to(std::vector<UndoRedo::Snapshot>::const_iterator it_snapshot)
 {
 	bool 				temp_snapshot_was_taken 	= this->undo_redo_stack.temp_snapshot_active();
-	PrinterTechnology 	new_printer_technology 		= it_snapshot->printer_technology;
+	PrinterTechnology 	new_printer_technology 		= it_snapshot->snapshot_data.printer_technology;
 	bool 				printer_technology_changed 	= this->printer_technology != new_printer_technology;
 	if (printer_technology_changed) {
 		// Switching the printer technology when jumping forwards / backwards in time. Switch to the last active printer profile of the other type.
-		std::string s_pt = (it_snapshot->printer_technology == ptFFF) ? "FFF" : "SLA";
+		std::string s_pt = (it_snapshot->snapshot_data.printer_technology == ptFFF) ? "FFF" : "SLA";
 		if (! wxGetApp().check_unsaved_changes(from_u8((boost::format(_utf8(
 			L("%1% printer was active at the time the target Undo / Redo snapshot was taken. Switching to %1% printer requires reloading of %1% presets."))) % s_pt).str())))
 			// Don't switch the profiles.
@@ -3797,17 +3798,18 @@ void Plater::priv::undo_redo_to(std::vector<UndoRedo::Snapshot>::const_iterator
                 model.wipe_tower.rotation = config.opt_float("wipe_tower_rotation_angle");
     }
     // Flags made of Snapshot::Flags enum values.
-    unsigned int new_flags = it_snapshot->flags;
-	unsigned int top_snapshot_flags = 0;
+    unsigned int new_flags = it_snapshot->snapshot_data.flags;
+	UndoRedo::SnapshotData top_snapshot_data;
+    top_snapshot_data.printer_technology = this->printer_technology;
     if (this->view3D->is_layers_editing_enabled())
-    	top_snapshot_flags |= UndoRedo::Snapshot::VARIABLE_LAYER_EDITING_ACTIVE;
-	bool   		 new_variable_layer_editing_active = (new_flags & UndoRedo::Snapshot::VARIABLE_LAYER_EDITING_ACTIVE) != 0;
+    	top_snapshot_data.flags |= UndoRedo::SnapshotData::VARIABLE_LAYER_EDITING_ACTIVE;
+	bool   		 new_variable_layer_editing_active = (new_flags & UndoRedo::SnapshotData::VARIABLE_LAYER_EDITING_ACTIVE) != 0;
 	// Disable layer editing before the Undo / Redo jump.
     if (!new_variable_layer_editing_active && view3D->is_layers_editing_enabled())
         view3D->get_canvas3d()->force_main_toolbar_left_action(view3D->get_canvas3d()->get_main_toolbar_item_id("layersediting"));
     // Do the jump in time.
     if (it_snapshot->timestamp < this->undo_redo_stack.active_snapshot_time() ?
-		this->undo_redo_stack.undo(model, this->view3D->get_canvas3d()->get_selection(), this->view3D->get_canvas3d()->get_gizmos_manager(), this->printer_technology, top_snapshot_flags, it_snapshot->timestamp) :
+		this->undo_redo_stack.undo(model, this->view3D->get_canvas3d()->get_selection(), this->view3D->get_canvas3d()->get_gizmos_manager(), top_snapshot_data, it_snapshot->timestamp) :
 		this->undo_redo_stack.redo(model, this->view3D->get_canvas3d()->get_gizmos_manager(), it_snapshot->timestamp)) {
 		if (printer_technology_changed) {
 			// Switch to the other printer technology. Switch to the last printer active for that particular technology.
@@ -3910,8 +3912,6 @@ void Plater::load_project()
     // Ask user for a project file name.
     wxString input_file;
     wxGetApp().load_project(this, input_file);
-    // Take the Undo / Redo snapshot.
-	Plater::TakeSnapshot snapshot(this, _(L("Load Project")) + ": " + wxString::FromUTF8(into_path(input_file).stem().string().c_str()));
     // And finally load the new project.
     load_project(input_file);
 }
@@ -3921,6 +3921,9 @@ void Plater::load_project(const wxString& filename)
     if (filename.empty())
         return;
 
+    // Take the Undo / Redo snapshot.
+    Plater::TakeSnapshot snapshot(this, _(L("Load Project")) + ": " + wxString::FromUTF8(into_path(filename).stem().string().c_str()));
+
     p->reset();
     p->set_project_filename(filename);
 
diff --git a/src/slic3r/GUI/wxExtensions.hpp b/src/slic3r/GUI/wxExtensions.hpp
index 9a6460dcb..a704f79d7 100644
--- a/src/slic3r/GUI/wxExtensions.hpp
+++ b/src/slic3r/GUI/wxExtensions.hpp
@@ -323,9 +323,9 @@ public:
 	}
 
 	bool SwapChildrens(int frst_id, int scnd_id) {
-		if (GetChildCount() < 2 || 
-			frst_id < 0 || frst_id >= GetChildCount() || 
-			scnd_id < 0 || scnd_id >= GetChildCount())
+		if (GetChildCount() < 2 ||
+			frst_id < 0 || (size_t)frst_id >= GetChildCount() ||
+			scnd_id < 0 || (size_t)scnd_id >= GetChildCount())
 			return false;
 
 		ObjectDataViewModelNode new_scnd = *GetNthChild(frst_id);
diff --git a/src/slic3r/Utils/UndoRedo.cpp b/src/slic3r/Utils/UndoRedo.cpp
index a8f9cc134..eba839ffb 100644
--- a/src/slic3r/Utils/UndoRedo.cpp
+++ b/src/slic3r/Utils/UndoRedo.cpp
@@ -17,6 +17,7 @@
 #define CEREAL_FUTURE_EXPERIMENTAL
 #include <cereal/archives/adapters.hpp>
 
+#include <libslic3r/Config.hpp>
 #include <libslic3r/ObjectID.hpp>
 #include <libslic3r/Utils.hpp>
 
@@ -35,6 +36,10 @@
 namespace Slic3r {
 namespace UndoRedo {
 
+SnapshotData::SnapshotData() : printer_technology(ptUnknown), flags(0)
+{
+}
+
 static std::string topmost_snapshot_name = "@@@ Topmost @@@";
 
 bool Snapshot::is_topmost() const
@@ -496,12 +501,12 @@ public:
 	}
 
     // Store the current application state onto the Undo / Redo stack, remove all snapshots after m_active_snapshot_time.
-    void take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, Slic3r::PrinterTechnology printer_technology, unsigned int flags);
+    void take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, const SnapshotData &snapshot_data);
     void load_snapshot(size_t timestamp, Slic3r::Model& model, Slic3r::GUI::GLGizmosManager& gizmos);
 
 	bool has_undo_snapshot() const;
 	bool has_redo_snapshot() const;
-    bool undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, Slic3r::GUI::GLGizmosManager &gizmos, PrinterTechnology printer_technology, unsigned int flags, size_t jump_to_time);
+    bool undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, Slic3r::GUI::GLGizmosManager &gizmos, const SnapshotData &snapshot_data, size_t jump_to_time);
     bool redo(Slic3r::Model &model, Slic3r::GUI::GLGizmosManager &gizmos, size_t jump_to_time);
 	void release_least_recently_used();
 
@@ -786,7 +791,7 @@ template<typename T> void StackImpl::load_mutable_object(const Slic3r::ObjectID
 }
 
 // Store the current application state onto the Undo / Redo stack, remove all snapshots after m_active_snapshot_time.
-void StackImpl::take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, Slic3r::PrinterTechnology printer_technology, unsigned int flags)
+void StackImpl::take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, const SnapshotData &snapshot_data)
 {
 	// Release old snapshot data.
 	assert(m_active_snapshot_time <= m_current_time);
@@ -806,11 +811,11 @@ void StackImpl::take_snapshot(const std::string& snapshot_name, const Slic3r::Mo
 	this->save_mutable_object<Selection>(m_selection);
     this->save_mutable_object<Slic3r::GUI::GLGizmosManager>(gizmos);
     // Save the snapshot info.
-	m_snapshots.emplace_back(snapshot_name, m_current_time ++, model.id().id, printer_technology, flags);
+	m_snapshots.emplace_back(snapshot_name, m_current_time ++, model.id().id, snapshot_data);
 	m_active_snapshot_time = m_current_time;
 	// Save snapshot info of the last "current" aka "top most" state, that is only being serialized
 	// if undoing an action. Such a snapshot has an invalid Model ID assigned if it was not taken yet.
-	m_snapshots.emplace_back(topmost_snapshot_name, m_active_snapshot_time, 0, printer_technology, flags);
+	m_snapshots.emplace_back(topmost_snapshot_name, m_active_snapshot_time, 0, snapshot_data);
 	// Release empty objects from the history.
 	this->collect_garbage();
 	assert(this->valid());
@@ -856,7 +861,7 @@ bool StackImpl::has_redo_snapshot() const
 	return ++ it != m_snapshots.end();
 }
 
-bool StackImpl::undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, Slic3r::GUI::GLGizmosManager &gizmos, PrinterTechnology printer_technology, unsigned int flags, size_t time_to_load)
+bool StackImpl::undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selection, Slic3r::GUI::GLGizmosManager &gizmos, const SnapshotData &snapshot_data, size_t time_to_load)
 {
 	assert(this->valid());
 	if (time_to_load == SIZE_MAX) {
@@ -870,7 +875,7 @@ bool StackImpl::undo(Slic3r::Model &model, const Slic3r::GUI::Selection &selecti
 	bool new_snapshot_taken = false;
 	if (m_active_snapshot_time == m_snapshots.back().timestamp && ! m_snapshots.back().is_topmost_captured()) {
 		// The current state is temporary. The current state needs to be captured to be redoable.
-        this->take_snapshot(topmost_snapshot_name, model, selection, gizmos, printer_technology, flags);
+        this->take_snapshot(topmost_snapshot_name, model, selection, gizmos, snapshot_data);
         // The line above entered another topmost_snapshot_name.
 		assert(m_snapshots.back().is_topmost());
 		assert(! m_snapshots.back().is_topmost_captured());
@@ -1019,12 +1024,12 @@ void Stack::set_memory_limit(size_t memsize) { pimpl->set_memory_limit(memsize);
 size_t Stack::get_memory_limit() const { return pimpl->get_memory_limit(); }
 size_t Stack::memsize() const { return pimpl->memsize(); }
 void Stack::release_least_recently_used() { pimpl->release_least_recently_used(); }
-void Stack::take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, Slic3r::PrinterTechnology printer_technology, unsigned int flags)
-	{ pimpl->take_snapshot(snapshot_name, model, selection, gizmos, printer_technology, flags); }
+void Stack::take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, const SnapshotData &snapshot_data)
+	{ pimpl->take_snapshot(snapshot_name, model, selection, gizmos, snapshot_data); }
 bool Stack::has_undo_snapshot() const { return pimpl->has_undo_snapshot(); }
 bool Stack::has_redo_snapshot() const { return pimpl->has_redo_snapshot(); }
-bool Stack::undo(Slic3r::Model& model, const Slic3r::GUI::Selection& selection, Slic3r::GUI::GLGizmosManager& gizmos, PrinterTechnology printer_technology, unsigned int flags, size_t time_to_load)
-	{ return pimpl->undo(model, selection, gizmos, printer_technology, flags, time_to_load); }
+bool Stack::undo(Slic3r::Model& model, const Slic3r::GUI::Selection& selection, Slic3r::GUI::GLGizmosManager& gizmos, const SnapshotData &snapshot_data, size_t time_to_load)
+	{ return pimpl->undo(model, selection, gizmos, snapshot_data, time_to_load); }
 bool Stack::redo(Slic3r::Model& model, Slic3r::GUI::GLGizmosManager& gizmos, size_t time_to_load) { return pimpl->redo(model, gizmos, time_to_load); }
 const Selection& Stack::selection_deserialized() const { return pimpl->selection_deserialized(); }
 
diff --git a/src/slic3r/Utils/UndoRedo.hpp b/src/slic3r/Utils/UndoRedo.hpp
index 916e44aa2..c17802560 100644
--- a/src/slic3r/Utils/UndoRedo.hpp
+++ b/src/slic3r/Utils/UndoRedo.hpp
@@ -21,23 +21,36 @@ namespace GUI {
 
 namespace UndoRedo {
 
-struct Snapshot
+// Data structure to be stored with each snapshot.
+// Storing short data (bit masks, ints) with each snapshot instead of being serialized into the Undo / Redo stack
+// is likely cheaper in term of both the runtime and memory allocation.
+// Also the SnapshotData is available without having to deserialize the snapshot from the Undo / Redo stack,
+// which may be handy sometimes.
+struct SnapshotData
 {
-	Snapshot(size_t timestamp) : timestamp(timestamp) {}
-	Snapshot(const std::string &name, size_t timestamp, size_t model_id, Slic3r::PrinterTechnology printer_technology, unsigned int flags) :
-		name(name), timestamp(timestamp), model_id(model_id), printer_technology(printer_technology), flags(flags) {}
+	// Constructor is defined in .cpp due to the forward declaration of enum PrinterTechnology.
+	SnapshotData();
+
+	PrinterTechnology 	printer_technology;
+	// Bitmap of Flags (see the Flags enum).
+	unsigned int        flags;
 
 	// Bitmask of various binary flags to be stored with the snapshot.
 	enum Flags {
 		VARIABLE_LAYER_EDITING_ACTIVE = 1,
 	};
+};
+
+struct Snapshot
+{
+	Snapshot(size_t timestamp) : timestamp(timestamp) {}
+	Snapshot(const std::string &name, size_t timestamp, size_t model_id, const SnapshotData &snapshot_data) :
+		name(name), timestamp(timestamp), model_id(model_id), snapshot_data(snapshot_data) {}
 	
 	std::string 		name;
 	size_t 				timestamp;
 	size_t 				model_id;
-	PrinterTechnology 	printer_technology;
-	// Bitmap of Flags (see the Flags enum).
-	unsigned int        flags;
+	SnapshotData  		snapshot_data;
 
 	bool		operator< (const Snapshot &rhs) const { return this->timestamp < rhs.timestamp; }
 	bool		operator==(const Snapshot &rhs) const { return this->timestamp == rhs.timestamp; }
@@ -77,7 +90,7 @@ public:
 	void release_least_recently_used();
 
 	// Store the current application state onto the Undo / Redo stack, remove all snapshots after m_active_snapshot_time.
-    void take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, Slic3r::PrinterTechnology printer_technology, unsigned int flags);
+    void take_snapshot(const std::string& snapshot_name, const Slic3r::Model& model, const Slic3r::GUI::Selection& selection, const Slic3r::GUI::GLGizmosManager& gizmos, const SnapshotData &snapshot_data);
 
 	// To be queried to enable / disable the Undo / Redo buttons at the UI.
 	bool has_undo_snapshot() const;
@@ -85,7 +98,7 @@ public:
 
 	// Roll back the time. If time_to_load is SIZE_MAX, the previous snapshot is activated.
 	// Undoing an action may need to take a snapshot of the current application state, so that redo to the current state is possible.
-    bool undo(Slic3r::Model& model, const Slic3r::GUI::Selection& selection, Slic3r::GUI::GLGizmosManager& gizmos, PrinterTechnology printer_technology, unsigned int flags, size_t time_to_load = SIZE_MAX);
+    bool undo(Slic3r::Model& model, const Slic3r::GUI::Selection& selection, Slic3r::GUI::GLGizmosManager& gizmos, const SnapshotData &snapshot_data, size_t time_to_load = SIZE_MAX);
 
 	// Jump forward in time. If time_to_load is SIZE_MAX, the next snapshot is activated.
     bool redo(Slic3r::Model& model, Slic3r::GUI::GLGizmosManager& gizmos, size_t time_to_load = SIZE_MAX);