Made the sheath around the base support configurable. Without the sheath

it is easier to remove the support, but the support is more fragile.

lib/Slic3r/GUI/Tab.pm

@@ -480,7 +480,7 @@ sub build {
         brim_width
         support_material support_material_threshold support_material_enforce_layers
         raft_layers
-        support_material_pattern support_material_spacing support_material_angle
+        support_material_pattern support_material_with_sheath support_material_spacing support_material_angle
         support_material_interface_layers support_material_interface_spacing
         support_material_contact_distance support_material_buildplate_only dont_support_bridges
         notes
@@ -588,6 +588,7 @@ sub build {
             my $optgroup = $page->new_optgroup('Options for support material and raft');
             $optgroup->append_single_option_line('support_material_contact_distance');
             $optgroup->append_single_option_line('support_material_pattern');
+            $optgroup->append_single_option_line('support_material_with_sheath');
             $optgroup->append_single_option_line('support_material_spacing');
             $optgroup->append_single_option_line('support_material_angle');
             $optgroup->append_single_option_line('support_material_interface_layers');
@@ -826,7 +827,7 @@ sub _update {
     my $have_support_material = $config->support_material || $config->raft_layers > 0;
     my $have_support_interface = $config->support_material_interface_layers > 0;
     $self->get_field($_)->toggle($have_support_material)
-        for qw(support_material_threshold support_material_pattern
+        for qw(support_material_threshold support_material_pattern support_material_with_sheath
             support_material_spacing support_material_angle
             support_material_interface_layers dont_support_bridges
             support_material_extrusion_width support_material_contact_distance);

lib/Slic3r/Print/SupportMaterial.pm

@@ -592,6 +592,7 @@ sub generate_toolpaths {
     
     # prepare fillers
     my $pattern = $self->object_config->support_material_pattern;
+    my $with_sheath = $self->object_config->support_material_with_sheath;
     my @angles = ($self->object_config->support_material_angle);
     if ($pattern eq 'rectilinear-grid') {
         $pattern = 'rectilinear';
@@ -791,7 +792,7 @@ sub generate_toolpaths {
                 # use the proper spacing for first layer as we don't need to align
                 # its pattern to the other layers
                 $filler->spacing($base_flow->spacing);
-            } else {
+            } elsif ($with_sheath) {
                 # draw a perimeter all around support infill
                 # TODO: use brim ordering algorithm
                 my $mm3_per_mm = $_flow->mm3_per_mm;

slic3r.pl

@@ -418,6 +418,9 @@ $j
                         default: $config->{support_material_threshold})
     --support-material-pattern
                         Pattern to use for support material (default: $config->{support_material_pattern})
+    --support-material-with-sheath
+                        Add a sheath (a single perimeter line) around the base support.
+                        This makes the support more reliable, but also more difficult to remove. (default: yes)
     --support-material-spacing
                         Spacing between pattern lines (mm, default: $config->{support_material_spacing})
     --support-material-angle

xs/src/libslic3r/PrintConfig.cpp

@@ -1219,6 +1219,13 @@ PrintConfigDef::PrintConfigDef()
     def->max = 90;
     def->default_value = new ConfigOptionInt(0);
 
+    def = this->add("support_material_with_sheath", coBool);
+    def->label = "With sheath around the support";
+    def->category = "Support material";
+    def->tooltip = "Add a sheath (a single perimeter line) around the base support. This makes the support more reliable, but also more difficult to remove.";
+    def->cli = "support-material-with-sheath!";
+    def->default_value = new ConfigOptionBool(true);
+
     def = this->add("temperature", coInts);
     def->label = "Other layers";
     def->tooltip = "Extruder temperature for layers after the first one. Set this to zero to disable temperature control commands in the output.";

xs/src/libslic3r/PrintConfig.hpp

@@ -158,6 +158,7 @@ class PrintObjectConfig : public virtual StaticPrintConfig
     ConfigOptionFloat               support_material_spacing;
     ConfigOptionFloat               support_material_speed;
     ConfigOptionInt                 support_material_threshold;
+    ConfigOptionBool                support_material_with_sheath;
     ConfigOptionFloat               xy_size_compensation;
     
     PrintObjectConfig(bool initialize = true) : StaticPrintConfig() {
@@ -191,6 +192,7 @@ class PrintObjectConfig : public virtual StaticPrintConfig
         OPT_PTR(support_material_spacing);
         OPT_PTR(support_material_speed);
         OPT_PTR(support_material_threshold);
+        OPT_PTR(support_material_with_sheath);
         OPT_PTR(xy_size_compensation);
         
         return NULL;

xs/src/libslic3r/PrintObject.cpp

@@ -240,6 +240,7 @@ PrintObject::invalidate_state_by_config_options(const std::vector<t_config_optio
             || *opt_key == "support_material_pattern"
             || *opt_key == "support_material_spacing"
             || *opt_key == "support_material_threshold"
+            || *opt_key == "support_material_with_sheath"
             || *opt_key == "dont_support_bridges"
             || *opt_key == "first_layer_extrusion_width") {
             steps.insert(posSupportMaterial);