diff --git a/lib/Slic3r/GUI.pm b/lib/Slic3r/GUI.pm
index 7f4a028a5..58c4964d9 100644
--- a/lib/Slic3r/GUI.pm
+++ b/lib/Slic3r/GUI.pm
@@ -269,6 +269,13 @@ sub save_settings {
     Slic3r::Config->write_ini("$datadir/slic3r.ini", $Settings);
 }
 
+# Called after the Preferences dialog is closed and the program settings are saved.
+# Update the UI based on the current preferences.
+sub update_ui_from_settings {
+    my ($self) = @_;
+    $self->{mainframe}->update_ui_from_settings;
+}
+
 sub presets {
     my ($self, $section) = @_;
     
diff --git a/lib/Slic3r/GUI/MainFrame.pm b/lib/Slic3r/GUI/MainFrame.pm
index 9aefb7b6c..ac81c48e0 100644
--- a/lib/Slic3r/GUI/MainFrame.pm
+++ b/lib/Slic3r/GUI/MainFrame.pm
@@ -83,6 +83,8 @@ sub new {
         # propagate event
         $event->Skip;
     });
+
+    $self->update_ui_from_settings;
     
     return $self;
 }
@@ -212,9 +214,9 @@ sub _init_menubar {
         $self->_append_menu_item($fileMenu, "Slice to SV&G…\tCtrl+G", 'Slice file to SVG', sub {
             $self->quick_slice(save_as => 1, export_svg => 1);
         }, undef, 'shape_handles.png');
-        $self->_append_menu_item($fileMenu, "(&Re)Slice Now\tCtrl+S", 'Start new slicing process', sub {
-            $self->reslice_now;
-        }, undef, 'shape_handles.png');
+        $self->{menu_item_reslice_now} = $self->_append_menu_item(
+            $fileMenu, "(&Re)Slice Now\tCtrl+S", 'Start new slicing process', 
+            sub { $self->reslice_now; }, undef, 'shape_handles.png');
         $fileMenu->AppendSeparator();
         $self->_append_menu_item($fileMenu, "Repair STL file…", 'Automatically repair an STL file', sub {
             $self->repair_stl;
@@ -448,6 +450,13 @@ sub quick_slice {
     Slic3r::GUI::catch_error($self, sub { $progress_dialog->Destroy if $progress_dialog });
 }
 
+sub reslice_now {
+    my ($self) = @_;
+    if ($self->{plater}) {
+        $self->{plater}->reslice;
+    }
+}
+
 sub repair_stl {
     my $self = shift;
     
@@ -803,4 +812,12 @@ sub _set_menu_item_icon {
     }
 }
 
+# Called after the Preferences dialog is closed and the program settings are saved.
+# Update the UI based on the current preferences.
+sub update_ui_from_settings {
+    my ($self) = @_;
+    $self->{menu_item_reslice_now}->Enable(! $Slic3r::GUI::Settings->{_}{background_processing});
+    $self->{plater}->update_ui_from_settings if ($self->{plater});
+}
+
 1;
diff --git a/lib/Slic3r/GUI/Plater.pm b/lib/Slic3r/GUI/Plater.pm
index 648fd3b1e..a8c117ccd 100644
--- a/lib/Slic3r/GUI/Plater.pm
+++ b/lib/Slic3r/GUI/Plater.pm
@@ -33,6 +33,7 @@ use constant TB_SETTINGS => &Wx::NewId;
 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.
 our $EXPORT_COMPLETED_EVENT  : shared = Wx::NewEventType;
 our $PROCESS_COMPLETED_EVENT : shared = Wx::NewEventType;
 
@@ -191,8 +192,7 @@ sub new {
     
     # right pane buttons
     $self->{btn_export_gcode} = Wx::Button->new($self, -1, "Export G-code…", wxDefaultPosition, [-1, 30], wxBU_LEFT);
-    $self->{btn_reslice} = Wx::Button->new($self, -1, "Slice now…", wxDefaultPosition, [-1, 30], wxBU_LEFT);
-    $self->{btn_print} = Wx::Button->new($self, -1, "Print…", wxDefaultPosition, [-1, 30], wxBU_LEFT);
+    $self->{btn_reslice} = Wx::Button->new($self, -1, "Slice now", wxDefaultPosition, [-1, 30], wxBU_LEFT);
     $self->{btn_print} = Wx::Button->new($self, -1, "Print…", wxDefaultPosition, [-1, 30], wxBU_LEFT);
     $self->{btn_send_gcode} = Wx::Button->new($self, -1, "Send to printer", wxDefaultPosition, [-1, 30], wxBU_LEFT);
     $self->{btn_export_stl} = Wx::Button->new($self, -1, "Export STL…", wxDefaultPosition, [-1, 30], wxBU_LEFT);
@@ -210,6 +210,7 @@ sub new {
             export_gcode    cog_go.png
             print           arrow_up.png
             send_gcode      arrow_up.png
+            reslice         reslice.png
             export_stl      brick_go.png
             
             increase        add.png
@@ -239,6 +240,7 @@ sub new {
     EVT_BUTTON($self, $self->{btn_send_gcode}, sub {
         $self->{send_gcode_file} = $self->export_gcode(Wx::StandardPaths::Get->GetTempDir());
     });
+    EVT_BUTTON($self, $self->{btn_reslice}, \&reslice);
     EVT_BUTTON($self, $self->{btn_export_stl}, \&export_stl);
     
     if ($self->{htoolbar}) {
@@ -391,8 +393,10 @@ sub new {
         }
         
         my $buttons_sizer = Wx::BoxSizer->new(wxHORIZONTAL);
+        $self->{buttons_sizer} = $buttons_sizer;
         $buttons_sizer->AddStretchSpacer(1);
         $buttons_sizer->Add($self->{btn_export_stl}, 0, wxALIGN_RIGHT, 0);
+        $buttons_sizer->Add($self->{btn_reslice}, 0, wxALIGN_RIGHT, 0);
         $buttons_sizer->Add($self->{btn_print}, 0, wxALIGN_RIGHT, 0);
         $buttons_sizer->Add($self->{btn_send_gcode}, 0, wxALIGN_RIGHT, 0);
         $buttons_sizer->Add($self->{btn_export_gcode}, 0, wxALIGN_RIGHT, 0);
@@ -416,6 +420,8 @@ sub new {
         $sizer->SetSizeHints($self);
         $self->SetSizer($sizer);
     }
+
+    $self->update_ui_from_settings();
     
     return $self;
 }
@@ -453,6 +459,25 @@ sub GetFrame {
     return &Wx::GetTopLevelParent($self);
 }
 
+# Called after the Preferences dialog is closed and the program settings are saved.
+# Update the UI based on the current preferences.
+sub update_ui_from_settings
+{
+    my ($self) = @_;
+    if (defined($self->{btn_reslice}) && $self->{buttons_sizer}->IsShown($self->{btn_reslice}) != (! $Slic3r::GUI::Settings->{_}{background_processing})) {
+        $self->{buttons_sizer}->Show($self->{btn_reslice}, ! $Slic3r::GUI::Settings->{_}{background_processing});
+        $self->{buttons_sizer}->Layout;
+    }
+}
+
+# Update presets (Print settings, Filament, Printer) from their respective tabs.
+# Called by 
+#       Slic3r::GUI::Tab::Print::_on_presets_changed
+#       Slic3r::GUI::Tab::Filament::_on_presets_changed
+#       Slic3r::GUI::Tab::Printer::_on_presets_changed
+# when the presets are loaded or the user selects another preset.
+# For Print settings and Printer, synchronize the selection index with their tabs.
+# For Filament, synchronize the selection index for a single extruder printer only, otherwise keep the selection.
 sub update_presets {
     my $self = shift;
     my ($group, $presets, $selected, $is_dirty) = @_;
@@ -1109,6 +1134,22 @@ sub resume_background_process {
     }
 }
 
+sub reslice {
+    # explicitly cancel a previous thread and start a new one.
+    my ($self) = @_;
+    # Don't reslice if export of G-code or sending to OctoPrint is running.
+    if ($Slic3r::have_threads && ! defined($self->{export_gcode_output_file}) && ! defined($self->{send_gcode_file})) {
+        $self->stop_background_process;
+        $self->statusbar->SetCancelCallback(sub {
+            $self->stop_background_process;
+            $self->statusbar->SetStatusText("Slicing cancelled");
+            # this updates buttons status
+            $self->object_list_changed;
+        });
+        $self->start_background_process;
+    }
+}
+
 sub export_gcode {
     my ($self, $output_file) = @_;
     
@@ -1243,6 +1284,7 @@ sub on_progress_event {
     $self->statusbar->SetStatusText("$message…");
 }
 
+# Called when the G-code export finishes, either successfully or with an error.
 # This gets called also if we don't have threads.
 sub on_export_completed {
     my ($self, $result) = @_;
@@ -1259,6 +1301,7 @@ sub on_export_completed {
     my $send_gcode = 0;
     my $do_print = 0;
     if ($result) {
+        # G-code file exported successfully.
         if ($self->{print_file}) {
             $message = "File added to print queue";
             $do_print = 1;
@@ -1276,6 +1319,7 @@ sub on_export_completed {
     wxTheApp->notify($message);
     
     $self->do_print if $do_print;
+    # Send $self->{send_gcode_file} to OctoPrint.
     $self->send_gcode if $send_gcode;
     $self->{print_file} = undef;
     $self->{send_gcode_file} = undef;
@@ -1301,6 +1345,8 @@ sub do_print {
     $self->GetFrame->select_tab(1);
 }
 
+# Send $self->{send_gcode_file} to OctoPrint.
+#FIXME Currently this call blocks the UI. Make it asynchronous.
 sub send_gcode {
     my ($self) = @_;
     
@@ -1611,15 +1657,19 @@ sub object_settings_dialog {
     }
 }
 
+# Called to update various buttons depending on whether there are any objects or
+# whether background processing (export of a G-code, sending to Octoprint, forced background re-slicing) is active.
 sub object_list_changed {
     my $self = shift;
     
+    # Enable/disable buttons depending on whether there are any objects on the platter.
     my $have_objects = @{$self->{objects}} ? 1 : 0;
     my $method = $have_objects ? 'Enable' : 'Disable';
     $self->{"btn_$_"}->$method
-        for grep $self->{"btn_$_"}, qw(reslice reset arrange export_gcode export_stl print send_gcode);
+        for grep $self->{"btn_$_"}, qw(reset arrange reslice export_gcode export_stl print send_gcode);
     
     if ($self->{export_gcode_output_file} || $self->{send_gcode_file}) {
+        $self->{btn_reslice}->Disable;
         $self->{btn_export_gcode}->Disable;
         $self->{btn_print}->Disable;
         $self->{btn_send_gcode}->Disable;
diff --git a/lib/Slic3r/GUI/Preferences.pm b/lib/Slic3r/GUI/Preferences.pm
index ed210d229..8455304e9 100644
--- a/lib/Slic3r/GUI/Preferences.pm
+++ b/lib/Slic3r/GUI/Preferences.pm
@@ -91,6 +91,9 @@ sub _accept {
     
     $self->EndModal(wxID_OK);
     $self->Close;  # needed on Linux
+
+    # Nothify the UI to update itself from the ini file.
+    wxTheApp->update_ui_from_settings;
 }
 
 1;
diff --git a/var/reslice.png b/var/reslice.png
new file mode 100644
index 000000000..167c0eccd
Binary files /dev/null and b/var/reslice.png differ