diff --git a/lib/Slic3r/GUI.pm b/lib/Slic3r/GUI.pm
index 2e9bddd508..2af137d2bc 100644
--- a/lib/Slic3r/GUI.pm
+++ b/lib/Slic3r/GUI.pm
@@ -89,7 +89,7 @@ our $medium_font = Wx::SystemSettings::GetFont(wxSYS_DEFAULT_GUI_FONT);
 $medium_font->SetPointSize(12);
 our $grey = Wx::Colour->new(200,200,200);
 
-our $VERSION_CHECK_EVENT : shared = Wx::NewEventType;
+#our $VERSION_CHECK_EVENT : shared = Wx::NewEventType;
 
 our $DLP_projection_screen;
 
@@ -181,10 +181,10 @@ sub OnInit {
     }
     $self->{mainframe}->config_wizard if $run_wizard;
     
-    $self->check_version
-        if $self->have_version_check
-            && ($Settings->{_}{version_check} // 1)
-            && (!$Settings->{_}{last_version_check} || (time - $Settings->{_}{last_version_check}) >= 86400);
+#    $self->check_version
+#        if $self->have_version_check
+#            && ($Settings->{_}{version_check} // 1)
+#            && (!$Settings->{_}{last_version_check} || (time - $Settings->{_}{last_version_check}) >= 86400);
     
     EVT_IDLE($frame, sub {
         while (my $cb = shift @cb) {
@@ -192,24 +192,24 @@ sub OnInit {
         }
     });
     
-    EVT_COMMAND($self, -1, $VERSION_CHECK_EVENT, sub {
-        my ($self, $event) = @_;
-        my ($success, $response, $manual_check) = @{$event->GetData};
-        
-        if ($success) {
-            if ($response =~ /^obsolete ?= ?([a-z0-9.-]+,)*\Q$Slic3r::VERSION\E(?:,|$)/) {
-                my $res = Wx::MessageDialog->new(undef, "A new version is available. Do you want to open the Slic3r website now?",
-                    'Update', wxYES_NO | wxCANCEL | wxYES_DEFAULT | wxICON_INFORMATION | wxICON_ERROR)->ShowModal;
-                Wx::LaunchDefaultBrowser('http://slic3r.org/') if $res == wxID_YES;
-            } else {
-                Slic3r::GUI::show_info(undef, "You're using the latest version. No updates are available.") if $manual_check;
-            }
-            $Settings->{_}{last_version_check} = time();
-            $self->save_settings;
-        } else {
-            Slic3r::GUI::show_error(undef, "Failed to check for updates. Try later.") if $manual_check;
-        }
-    });
+#    EVT_COMMAND($self, -1, $VERSION_CHECK_EVENT, sub {
+#        my ($self, $event) = @_;
+#        my ($success, $response, $manual_check) = @{$event->GetData};
+#        
+#        if ($success) {
+#            if ($response =~ /^obsolete ?= ?([a-z0-9.-]+,)*\Q$Slic3r::VERSION\E(?:,|$)/) {
+#                my $res = Wx::MessageDialog->new(undef, "A new version is available. Do you want to open the Slic3r website now?",
+#                    'Update', wxYES_NO | wxCANCEL | wxYES_DEFAULT | wxICON_INFORMATION | wxICON_ERROR)->ShowModal;
+#                Wx::LaunchDefaultBrowser('http://slic3r.org/') if $res == wxID_YES;
+#            } else {
+#                Slic3r::GUI::show_info(undef, "You're using the latest version. No updates are available.") if $manual_check;
+#            }
+#            $Settings->{_}{last_version_check} = time();
+#            $self->save_settings;
+#        } else {
+#            Slic3r::GUI::show_error(undef, "Failed to check for updates. Try later.") if $manual_check;
+#        }
+#    });
     
     return 1;
 }
@@ -331,28 +331,28 @@ sub presets {
     return %presets;
 }
 
-sub have_version_check {
-    my ($self) = @_;
-    
-    # return an explicit 0
-    return ($Slic3r::have_threads && $Slic3r::build && $have_LWP) || 0;
-}
+#sub have_version_check {
+#    my ($self) = @_;
+#    
+#    # return an explicit 0
+#    return ($Slic3r::have_threads && $Slic3r::build && $have_LWP) || 0;
+#}
 
-sub check_version {
-    my ($self, $manual_check) = @_;
-    
-    Slic3r::debugf "Checking for updates...\n";
-    
-    @_ = ();
-    threads->create(sub {
-        my $ua = LWP::UserAgent->new;
-        $ua->timeout(10);
-        my $response = $ua->get('http://slic3r.org/updatecheck');
-        Wx::PostEvent($self, Wx::PlThreadEvent->new(-1, $VERSION_CHECK_EVENT,
-            threads::shared::shared_clone([ $response->is_success, $response->decoded_content, $manual_check ])));
-        Slic3r::thread_cleanup();
-    })->detach;
-}
+#sub check_version {
+#    my ($self, $manual_check) = @_;
+#    
+#    Slic3r::debugf "Checking for updates...\n";
+#    
+#    @_ = ();
+#    threads->create(sub {
+#        my $ua = LWP::UserAgent->new;
+#        $ua->timeout(10);
+#        my $response = $ua->get('http://slic3r.org/updatecheck');
+#        Wx::PostEvent($self, Wx::PlThreadEvent->new(-1, $VERSION_CHECK_EVENT,
+#            threads::shared::shared_clone([ $response->is_success, $response->decoded_content, $manual_check ])));
+#        Slic3r::thread_cleanup();
+#    })->detach;
+#}
 
 sub output_path {
     my ($self, $dir) = @_;
diff --git a/lib/Slic3r/GUI/Plater.pm b/lib/Slic3r/GUI/Plater.pm
index 5a215edebb..e4ac296380 100644
--- a/lib/Slic3r/GUI/Plater.pm
+++ b/lib/Slic3r/GUI/Plater.pm
@@ -34,7 +34,6 @@ use constant TB_SETTINGS => &Wx::NewId;
 use constant TB_LAYER_EDITING => &Wx::NewId;
 
 # package variables to avoid passing lexicals to threads
-our $THUMBNAIL_DONE_EVENT    : shared = Wx::NewEventType;
 our $PROGRESS_BAR_EVENT      : shared = Wx::NewEventType;
 our $ERROR_EVENT             : shared = Wx::NewEventType;
 # Emitted from the worker thread when the G-code export is finished.
@@ -307,14 +306,6 @@ sub new {
         for grep defined($_),
             $self, $self->{canvas}, $self->{canvas3D}, $self->{preview3D}, $self->{list};
     
-    EVT_COMMAND($self, -1, $THUMBNAIL_DONE_EVENT, sub {
-        my ($self, $event) = @_;
-        my ($obj_idx) = @{$event->GetData};
-        return if !$self->{objects}[$obj_idx];  # object was deleted before thumbnail generation completed
-        
-        $self->on_thumbnail_made($obj_idx);
-    });
-    
     EVT_COMMAND($self, -1, $PROGRESS_BAR_EVENT, sub {
         my ($self, $event) = @_;
         my ($percent, $message) = @{$event->GetData};
@@ -803,7 +794,7 @@ sub load_model_objects {
         $self->{list}->SetItem($obj_idx, 1, $model_object->instances_count);
         $self->{list}->SetItem($obj_idx, 2, ($model_object->instances->[0]->scaling_factor * 100) . "%");
     
-        $self->make_thumbnail($obj_idx);
+        $self->reset_thumbnail($obj_idx);
     }
     $self->arrange if $need_arrange;
     $self->update;
@@ -988,10 +979,7 @@ sub rotate {
     
     my $model_object = $self->{model}->objects->[$obj_idx];
     my $model_instance = $model_object->instances->[0];
-    
-    # we need thumbnail to be computed before allowing rotation
-    return if !$object->thumbnail;
-    
+        
     if (!defined $angle) {
         my $axis_name = $axis == X ? 'X' : $axis == Y ? 'Y' : 'Z';
         my $default = $axis == Z ? rad2deg($model_instance->rotation) : 0;
@@ -1016,7 +1004,7 @@ sub rotate {
         
         # realign object to Z = 0
         $model_object->center_around_origin;
-        $self->make_thumbnail($obj_idx);
+        $self->reset_thumbnail($obj_idx);
     }
     
     $model_object->update_bounding_box;
@@ -1048,7 +1036,7 @@ sub mirror {
     
     # realign object to Z = 0
     $model_object->center_around_origin;
-    $self->make_thumbnail($obj_idx);
+    $self->reset_thumbnail($obj_idx);
         
     # update print and start background processing
     $self->stop_background_process;
@@ -1068,9 +1056,6 @@ sub changescale {
     my $model_object = $self->{model}->objects->[$obj_idx];
     my $model_instance = $model_object->instances->[0];
     
-    # we need thumbnail to be computed before allowing scaling
-    return if !$object->thumbnail;
-    
     my $object_size = $model_object->bounding_box->size;
     my $bed_size = Slic3r::Polygon->new_scale(@{$self->{config}->bed_shape})->bounding_box->size;
     
@@ -1101,7 +1086,7 @@ sub changescale {
         #FIXME Scale the layer height profile when $axis == Z?
         #FIXME Scale the layer height ranges $axis == Z?
         # object was already aligned to Z = 0, so no need to realign it
-        $self->make_thumbnail($obj_idx);
+        $self->reset_thumbnail($obj_idx);
     } else {
         my $scale;
         if ($tosize) {
@@ -1621,12 +1606,6 @@ sub reload_from_disk {
     }
     
     $self->remove($obj_idx);
-    
-    # Trigger thumbnail generation again, because the remove() method altered
-    # object indexes before background thumbnail generation called its completion
-    # event, so the on_thumbnail_made callback is called with the wrong $obj_idx.
-    # When porting to C++ we'll probably have cleaner ways to do this.
-    $self->make_thumbnail($_-1) for @new_obj_idx;
 }
 
 sub export_object_stl {
@@ -1674,36 +1653,9 @@ sub _get_export_file {
     return $output_file;
 }
 
-sub make_thumbnail {
-    my $self = shift;
-    my ($obj_idx) = @_;
-    
-    my $plater_object = $self->{objects}[$obj_idx];
-    $plater_object->thumbnail(Slic3r::ExPolygon::Collection->new);
-    my $cb = sub {
-        $plater_object->make_thumbnail($self->{model}, $obj_idx);
-        
-        if ($Slic3r::have_threads) {
-            Wx::PostEvent($self, Wx::PlThreadEvent->new(-1, $THUMBNAIL_DONE_EVENT, shared_clone([ $obj_idx ])));
-            Slic3r::thread_cleanup();
-            threads->exit;
-        } else {
-            $self->on_thumbnail_made($obj_idx);
-        }
-    };
-    
-    @_ = ();
-    $Slic3r::have_threads
-        ? threads->create(sub { $cb->(); Slic3r::thread_cleanup(); })->detach
-        : $cb->();
-}
-
-sub on_thumbnail_made {
-    my $self = shift;
-    my ($obj_idx) = @_;
-    
-    $self->{objects}[$obj_idx]->transform_thumbnail($self->{model}, $obj_idx);
-    $self->{canvas}->Refresh;
+sub reset_thumbnail {
+    my ($self, $obj_idx) = @_;
+    $self->{objects}[$obj_idx]->thumbnail(undef);
 }
 
 # this method gets called whenever print center is changed or the objects' bounding box changes
@@ -1727,7 +1679,8 @@ sub update {
     } else {
         $self->resume_background_process;
     }
-    
+
+    $self->{canvas}->reload_scene if $self->{canvas};
     $self->{canvas3D}->reload_scene if $self->{canvas3D};
     $self->{preview3D}->reload_print if $self->{preview3D};
 }
@@ -1942,7 +1895,7 @@ sub object_settings_dialog {
     if ($dlg->PartsChanged) {
 	    # recenter and re-align to Z = 0
 	    $model_object->center_around_origin;
-        $self->make_thumbnail($obj_idx);
+        $self->reset_thumbnail($obj_idx);
     }
 	
 	# update print
@@ -1950,6 +1903,7 @@ sub object_settings_dialog {
 	    $self->stop_background_process;
         $self->{print}->reload_object($obj_idx);
         $self->schedule_background_process;
+        $self->{canvas}->reload_scene if $self->{canvas};
         $self->{canvas3D}->reload_scene if $self->{canvas3D};
     } else {
         $self->resume_background_process;
@@ -2245,18 +2199,19 @@ sub make_thumbnail {
     $self->thumbnail->clear;
     
     my $mesh = $model->objects->[$obj_idx]->raw_mesh;
-    if ($mesh->facets_count <= 5000) {
-        # remove polygons with area <= 1mm
-        my $area_threshold = Slic3r::Geometry::scale 1;
-        $self->thumbnail->append(
-            grep $_->area >= $area_threshold,
-            @{ $mesh->horizontal_projection },   # horizontal_projection returns scaled expolygons
-        );
-        $self->thumbnail->simplify(0.5);
-    } else {
+#FIXME The "correct" variant could be extremely slow.
+#    if ($mesh->facets_count <= 5000) {
+#        # remove polygons with area <= 1mm
+#        my $area_threshold = Slic3r::Geometry::scale 1;
+#        $self->thumbnail->append(
+#            grep $_->area >= $area_threshold,
+#            @{ $mesh->horizontal_projection },   # horizontal_projection returns scaled expolygons
+#        );
+#        $self->thumbnail->simplify(0.5);
+#    } else {
         my $convex_hull = Slic3r::ExPolygon->new($mesh->convex_hull);
         $self->thumbnail->append($convex_hull);
-    }
+#    }
     
     return $self->thumbnail;
 }
diff --git a/lib/Slic3r/GUI/Plater/2D.pm b/lib/Slic3r/GUI/Plater/2D.pm
index a24a5a6ff5..8d7b35ac78 100644
--- a/lib/Slic3r/GUI/Plater/2D.pm
+++ b/lib/Slic3r/GUI/Plater/2D.pm
@@ -13,10 +13,6 @@ use Wx qw(:misc :pen :brush :sizer :font :cursor wxTAB_TRAVERSAL);
 use Wx::Event qw(EVT_MOUSE_EVENTS EVT_PAINT EVT_ERASE_BACKGROUND EVT_SIZE);
 use base 'Wx::Panel';
 
-use constant CANVAS_TEXT => join('-', +(localtime)[3,4]) eq '13-8'
-    ? 'What do you want to print today? ™' # Sept. 13, 2006. The first part ever printed by a RepRap to make another RepRap.
-    : 'Drag your objects here';
-
 sub new {
     my $class = shift;
     my ($parent, $size, $objects, $model, $config) = @_;
@@ -128,7 +124,11 @@ sub repaint {
     if (!@{$self->{objects}}) {
         $dc->SetTextForeground(Wx::Colour->new(150,50,50));
         $dc->SetFont(Wx::Font->new(14, wxDEFAULT, wxNORMAL, wxNORMAL));
-        $dc->DrawLabel(CANVAS_TEXT, Wx::Rect->new(0, 0, $self->GetSize->GetWidth, $self->GetSize->GetHeight), wxALIGN_CENTER_HORIZONTAL | wxALIGN_CENTER_VERTICAL);
+        $dc->DrawLabel(
+            join('-', +(localtime)[3,4]) eq '13-8'
+                ? 'What do you want to print today? ™' # Sept. 13, 2006. The first part ever printed by a RepRap to make another RepRap.
+                : 'Drag your objects here',
+            Wx::Rect->new(0, 0, $self->GetSize->GetWidth, $self->GetSize->GetHeight), wxALIGN_CENTER_HORIZONTAL | wxALIGN_CENTER_VERTICAL);
     }
     
     # draw thumbnails
@@ -340,4 +340,32 @@ sub point_to_model_units {
     );
 }
 
+sub reload_scene {
+    my ($self, $force) = @_;
+
+    if (! $self->IsShown && ! $force) {
+        $self->{reload_delayed} = 1;
+        return;
+    }
+
+    $self->{reload_delayed} = 0;
+
+    foreach my $obj_idx (0..$#{$self->{model}->objects}) {
+        my $plater_object = $self->{objects}[$obj_idx];
+        next if $plater_object->thumbnail;
+        # The thumbnail is not valid, update it with a convex hull of an object.
+        $plater_object->thumbnail(Slic3r::ExPolygon::Collection->new);
+        $plater_object->make_thumbnail($self->{model}, $obj_idx);
+        $plater_object->transform_thumbnail($self->{model}, $obj_idx);
+    }
+
+    $self->Refresh;
+}
+
+# Called by the Platter wxNotebook when this page is activated.
+sub OnActivate {
+    my ($self) = @_;
+    $self->reload_scene(1) if ($self->{reload_delayed});
+}
+
 1;
diff --git a/lib/Slic3r/GUI/Preferences.pm b/lib/Slic3r/GUI/Preferences.pm
index 87aff6ef7a..836c8aec81 100644
--- a/lib/Slic3r/GUI/Preferences.pm
+++ b/lib/Slic3r/GUI/Preferences.pm
@@ -30,14 +30,14 @@ sub new {
         default     => $Slic3r::GUI::Settings->{_}{mode},
         width       => 100,
     ));
-    $optgroup->append_single_option_line(Slic3r::GUI::OptionsGroup::Option->new(
-        opt_id      => 'version_check',
-        type        => 'bool',
-        label       => 'Check for updates',
-        tooltip     => 'If this is enabled, Slic3r will check for updates daily and display a reminder if a newer version is available.',
-        default     => $Slic3r::GUI::Settings->{_}{version_check} // 1,
-        readonly    => !wxTheApp->have_version_check,
-    ));
+#    $optgroup->append_single_option_line(Slic3r::GUI::OptionsGroup::Option->new(
+#        opt_id      => 'version_check',
+#        type        => 'bool',
+#        label       => 'Check for updates',
+#        tooltip     => 'If this is enabled, Slic3r will check for updates daily and display a reminder if a newer version is available.',
+#        default     => $Slic3r::GUI::Settings->{_}{version_check} // 1,
+#        readonly    => !wxTheApp->have_version_check,
+#    ));
     $optgroup->append_single_option_line(Slic3r::GUI::OptionsGroup::Option->new(
         opt_id      => 'remember_output_path',
         type        => 'bool',
diff --git a/xs/src/libslic3r/TriangleMesh.cpp b/xs/src/libslic3r/TriangleMesh.cpp
index b7cdacfa47..7e16944d86 100644
--- a/xs/src/libslic3r/TriangleMesh.cpp
+++ b/xs/src/libslic3r/TriangleMesh.cpp
@@ -492,9 +492,9 @@ TriangleMesh::merge(const TriangleMesh &mesh)
     stl_get_size(&this->stl);
 }
 
-/* this will return scaled ExPolygons */
-ExPolygons
-TriangleMesh::horizontal_projection() const
+// Calculate projection of the mesh into the XY plane, in scaled coordinates.
+//FIXME This could be extremely slow! Use it for tiny meshes only!
+ExPolygons TriangleMesh::horizontal_projection() const
 {
     Polygons pp;
     pp.reserve(this->stl.stats.number_of_facets);
@@ -502,26 +502,25 @@ TriangleMesh::horizontal_projection() const
         stl_facet* facet = &this->stl.facet_start[i];
         Polygon p;
         p.points.resize(3);
-        p.points[0] = Point(facet->vertex[0].x / SCALING_FACTOR, facet->vertex[0].y / SCALING_FACTOR);
-        p.points[1] = Point(facet->vertex[1].x / SCALING_FACTOR, facet->vertex[1].y / SCALING_FACTOR);
-        p.points[2] = Point(facet->vertex[2].x / SCALING_FACTOR, facet->vertex[2].y / SCALING_FACTOR);
+        p.points[0] = Point::new_scale(facet->vertex[0].x, facet->vertex[0].y);
+        p.points[1] = Point::new_scale(facet->vertex[1].x, facet->vertex[1].y);
+        p.points[2] = Point::new_scale(facet->vertex[2].x, facet->vertex[2].y);
         p.make_counter_clockwise();  // do this after scaling, as winding order might change while doing that
         pp.push_back(p);
     }
     
     // the offset factor was tuned using groovemount.stl
-    return union_ex(offset(pp, 0.01 / SCALING_FACTOR), true);
+    return union_ex(offset(pp, scale_(0.01)), true);
 }
 
-Polygon
-TriangleMesh::convex_hull()
+Polygon TriangleMesh::convex_hull()
 {
     this->require_shared_vertices();
     Points pp;
     pp.reserve(this->stl.stats.shared_vertices);
-    for (int i = 0; i < this->stl.stats.shared_vertices; i++) {
+    for (int i = 0; i < this->stl.stats.shared_vertices; ++ i) {
         stl_vertex* v = &this->stl.v_shared[i];
-        pp.push_back(Point(v->x / SCALING_FACTOR, v->y / SCALING_FACTOR));
+        pp.emplace_back(Point::new_scale(v->x, v->y));
     }
     return Slic3r::Geometry::convex_hull(pp);
 }