diff --git a/lib/Slic3r/GUI/Plater/3DPreview.pm b/lib/Slic3r/GUI/Plater/3DPreview.pm
index fa71fcb1d..af31ae61f 100644
--- a/lib/Slic3r/GUI/Plater/3DPreview.pm
+++ b/lib/Slic3r/GUI/Plater/3DPreview.pm
@@ -123,6 +123,7 @@ sub load_print {
         foreach my $object (@{$self->print->objects}) {
             $self->canvas->load_print_object_toolpaths($object);
             
+            # Show the objects in very transparent color.
             #my @volume_ids = $self->canvas->load_object($object->model_object);
             #$self->canvas->volumes->[$_]->color->[3] = 0.2 for @volume_ids;
         }
diff --git a/lib/Slic3r/GUI/Tab.pm b/lib/Slic3r/GUI/Tab.pm
index 72e798b5e..d1ea0e432 100644
--- a/lib/Slic3r/GUI/Tab.pm
+++ b/lib/Slic3r/GUI/Tab.pm
@@ -775,7 +775,8 @@ sub _update {
         
         my $new_conf = Slic3r::Config->new;
         if ($dialog->ShowModal() == wxID_YES) {
-            $new_conf->set("fill_pattern", 1);
+            $new_conf->set("fill_pattern", 'rectilinear');
+            $new_conf->set("fill_density", 100);
         } else {
             $new_conf->set("fill_density", 40);
         }
diff --git a/lib/Slic3r/Print/GCode.pm b/lib/Slic3r/Print/GCode.pm
index 27cca3221..e862a59e1 100644
--- a/lib/Slic3r/Print/GCode.pm
+++ b/lib/Slic3r/Print/GCode.pm
@@ -40,6 +40,8 @@ sub BUILD {
         my $gcodegen = Slic3r::GCode->new;
         $self->_gcodegen($gcodegen);
         $gcodegen->set_placeholder_parser($self->placeholder_parser);
+        # Tell the G-code generator, how many times the $gcodegen->change_layer() will be called.
+        # $gcodegen->change_layer() in turn increments the progress bar status. 
         $gcodegen->set_layer_count($layer_count);
         $gcodegen->set_enable_cooling_markers(1);
         $gcodegen->apply_print_config($self->config);
@@ -353,6 +355,8 @@ sub _print_first_layer_temperature {
 # Called per object's layer.
 # First a $gcode string is collected,
 # then filtered and finally written to a file $fh.
+#FIXME If printing multiple objects at once, this incorrectly applies cooling logic to a single object's layer instead
+# of all the objects printed.
 sub process_layer {
     my $self = shift;
     my ($layer, $object_copies) = @_;
@@ -610,7 +614,8 @@ sub process_layer {
         $layer->print_z,
     ) if defined $self->_cooling_buffer;
     
-    print {$self->fh} $self->filter($gcode);
+    $gcode = $self->filter($gcode);
+    print {$self->fh} $gcode if defined($gcode);
 }
 
 # Extrude perimeters: Decide where to put seams (hide or align seams).
@@ -655,6 +660,7 @@ sub flush_filters {
 
 sub filter {
     my ($self, $gcode, $flush) = @_;
+    $flush //= 0;
     
     # apply vibration limit if enabled;
     # this injects pauses according to time (thus depends on actual speeds)
diff --git a/xs/xsp/Surface.xsp b/xs/xsp/Surface.xsp
index ebacd1795..597ed1b5d 100644
--- a/xs/xsp/Surface.xsp
+++ b/xs/xsp/Surface.xsp
@@ -109,6 +109,7 @@ _constant()
     S_TYPE_INTERNALSOLID    = stInternalSolid
     S_TYPE_INTERNALBRIDGE   = stInternalBridge
     S_TYPE_INTERNALVOID     = stInternalVoid
+    S_TYPW_PERIMETER        = stPerimeter
   PROTOTYPE:
   CODE:
     RETVAL = ix;