experimental feature: external perimeter overlap.

Have to test it, it may decrease printing quality (like printing external perimeter first)

resources/ui_layout/print.ui

@@ -228,6 +228,7 @@ group:Extrusion width
 group:Overlap
 	setting:infill_overlap
 	setting:bridge_overlap
+	setting:external_perimeter_overlap
 group:Flow
 	line:Flow ratio
 		setting:bridge_flow_ratio

src/libslic3r/PerimeterGenerator.cpp

@@ -39,13 +39,23 @@ void PerimeterGenerator::process()
     // other perimeters
     this->_mm3_per_mm               = this->perimeter_flow.mm3_per_mm();
     coord_t perimeter_width         = this->perimeter_flow.scaled_width();
+    //spacing between internal perimeters
     coord_t perimeter_spacing       = this->perimeter_flow.scaled_spacing();
     
     // external perimeters
     this->_ext_mm3_per_mm           = this->ext_perimeter_flow.mm3_per_mm();
     coord_t ext_perimeter_width     = this->ext_perimeter_flow.scaled_width();
+    //spacing between two external perimeter (where you don't have the space to add other loops)
     coord_t ext_perimeter_spacing   = this->ext_perimeter_flow.scaled_spacing();
+    //spacing between external perimeter and the second
     coord_t ext_perimeter_spacing2  = this->ext_perimeter_flow.scaled_spacing(this->perimeter_flow);
+    //external_perimeter_overlap effect: change distance between the extrenal periemter and the other ones.
+    if (this->config->external_perimeter_overlap.get_abs_value(1) != 1) {
+        //choose between the normal spacing and "don't touch it".
+        ext_perimeter_spacing2 =
+            ext_perimeter_spacing2 * this->config->external_perimeter_overlap.get_abs_value(1)
+            + (ext_perimeter_width + perimeter_width) * 0.5f * (1 - this->config->external_perimeter_overlap.get_abs_value(1));
+    }
     
     // overhang perimeters
     this->_mm3_per_mm_overhang      = this->overhang_flow.mm3_per_mm();
@@ -429,11 +439,11 @@ void PerimeterGenerator::process()
                                 if (!intersection_ex(thin[0], bound).empty()) {
                                     //be sure it's not too small to extrude reliably
                                     thin[0].remove_point_too_near((coord_t)SCALED_RESOLUTION);
-                                    if (thin[0].area() > min_width*(ext_perimeter_width + ext_perimeter_spacing2)) {
+                                    if (thin[0].area() > min_width*(ext_perimeter_width + ext_perimeter_spacing)) {
                                         thins.push_back(thin[0]);
                                         bound.remove_point_too_near((coord_t)SCALED_RESOLUTION);
                                         // the maximum thickness of our thin wall area is equal to the minimum thickness of a single loop (*1.2 because of circles approx. and enlrgment from 'div')
-                                        Slic3r::MedialAxis ma{ thin[0], (coord_t)((ext_perimeter_width + ext_perimeter_spacing2)*1.2),
+                                        Slic3r::MedialAxis ma{ thin[0], (coord_t)((ext_perimeter_width + ext_perimeter_spacing)*1.2),
                                             min_width, coord_t(this->layer_height) };
                                         ma.use_bounds(bound)
                                             .use_min_real_width((coord_t)scale_(this->ext_perimeter_flow.nozzle_diameter))

src/libslic3r/PrintConfig.cpp

@@ -706,11 +706,23 @@ void PrintConfigDef::init_fff_params()
     def->full_label = L("Ext. peri. cut corners");
     def->category = OptionCategory::width;
     def->tooltip = L("Activate this option to modify the flow to acknoledge that the nozzle is round and the corners will have a round shape, and so change the flow to realized that and avoid over-extrusion."
-        " 100% is activated, 0% is deactivated and 50% is half-activated");
+        " 100% is activated, 0% is deactivated and 50% is half-activated."
+        "\nNote: this change the flow by ~5% over a very small distance (~nozzle diameter), so it shouldn't be noticeable unless you have a very big nozzle and a very precise printer."
+        "\nIt's very experimental, please report about the usefulness. It may be removed if there is no use of it.");
     def->sidetext = L("%");
     def->mode = comExpert;
     def->set_default_value(new ConfigOptionPercent(0));
 
+    def = this->add("external_perimeter_overlap", coPercent);
+    def->label = L("external periemter overlap");
+    def->full_label = L("Ext. peri. overlap");
+    def->category = OptionCategory::width;
+    def->tooltip = L("This perimeter allow you to reduce the overlap between the perimeters and the external one, to reduce the impact of the perimeters artifacts."
+        "\nIt's very experimental, please report about the usefulness. It may be removed if there is no use of it.");
+    def->sidetext = L("%");
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionPercent(100));
+
     def = this->add("external_perimeter_speed", coFloatOrPercent);
     def->label = L("External");
     def->full_label = L("External perimeters speed");

src/libslic3r/PrintConfig.hpp

@@ -613,6 +613,7 @@ public:
     ConfigOptionBool                enforce_full_fill_volume;
     ConfigOptionFloatOrPercent      external_infill_margin;
     ConfigOptionFloatOrPercent      external_perimeter_extrusion_width;
+    ConfigOptionPercent             external_perimeter_overlap;
     ConfigOptionFloatOrPercent      external_perimeter_speed;
     ConfigOptionBool                external_perimeters_first;
     ConfigOptionBool                external_perimeters_vase;
@@ -695,6 +696,7 @@ protected:
         OPT_PTR(enforce_full_fill_volume);
         OPT_PTR(external_infill_margin);
         OPT_PTR(external_perimeter_extrusion_width);
+        OPT_PTR(external_perimeter_overlap);
         OPT_PTR(external_perimeter_speed);
         OPT_PTR(external_perimeters_first);
         OPT_PTR(external_perimeters_vase);

src/slic3r/GUI/Preset.cpp

@@ -529,7 +529,8 @@ const std::vector<std::string>& Preset::print_options()
         , "curve_smoothing_angle_convex"
         , "curve_smoothing_angle_concave",
         "print_extrusion_multiplier",
-        "external_perimeter_cut_corners"
+        "external_perimeter_cut_corners",
+        "external_perimeter_overlap"
     };
     return s_opts;
 }