NEW: Open "Bottom Z distance" setting for users

Users can set distance between support bottom contacts and object
once enable normal/tree support.

Jira: STUDIO-1383

TODO：Func seems good though, some details (e.g., bottom_interface
detection) need to be optimized furthur. Will keep follow-up.

Change-Id: I85815e7aa6cf1a5d0249633cd8ab995873461e8a
(cherry picked from commit eab39e89c94d749ebe6266ab745cbb70a068277d)

src/libslic3r/Preset.cpp

@@ -714,7 +714,7 @@ static std::vector<std::string> s_Preset_print_options {
     "support_angle", "support_interface_top_layers", "support_interface_bottom_layers",
     "support_interface_pattern", "support_interface_spacing", "support_interface_loop_pattern",
     "support_top_z_distance", "support_on_build_plate_only","support_critical_regions_only", "bridge_no_support", "thick_bridges", "max_bridge_length", "print_sequence",
-    "filename_format", "wall_filament",
+    "filename_format", "wall_filament", "support_bottom_z_distance",
     "sparse_infill_filament", "solid_infill_filament", "support_filament", "support_interface_filament",
     "ooze_prevention", "standby_temperature_delta", "interface_shells", "line_width", "initial_layer_line_width",
     "inner_wall_line_width", "outer_wall_line_width", "sparse_infill_line_width", "internal_solid_infill_line_width",

src/libslic3r/PrintConfig.cpp

@@ -2430,6 +2430,15 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionFloat(0.2));
 
+    // BBS:MusangKing
+    def = this->add("support_bottom_z_distance", coFloat);
+    def->label = L("Bottom Z distance");
+    def->category = L("Support");
+    def->tooltip = L("The z gap between the bottom support interface and object");
+    def->sidetext = L("mm");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(0.2));
+
     def = this->add("enforce_support_layers", coInt);
     //def->label = L("Enforce support for the first");
     def->category = L("Support");
@@ -3733,7 +3742,7 @@ void PrintConfigDef::handle_legacy(t_config_option_key &opt_key, std::string &va
         , "support_sharp_tails","remove_small_overhangs", "support_with_sheath",
         "tree_support_branch_diameter_angle", "tree_support_collision_resolution",
         "small_perimeter_speed", "max_volumetric_speed", "max_print_speed",
-        "support_bottom_z_distance", "support_closing_radius",
+        "support_closing_radius",
         "remove_freq_sweep", "remove_bed_leveling", "remove_extrusion_calibration",
         "support_transition_line_width", "support_transition_speed", "bed_temperature", "bed_temperature_initial_layer",
         "can_switch_nozzle_type", "can_add_auxiliary_fan", "extra_flush_volume", "spaghetti_detector", "adaptive_layer_height"

src/libslic3r/PrintConfig.hpp

@@ -619,6 +619,7 @@ PRINT_CONFIG_CLASS_DEFINE(
     ((ConfigOptionBool,                support_on_build_plate_only))
     ((ConfigOptionBool,                support_critical_regions_only))
     ((ConfigOptionFloat,               support_top_z_distance))
+    ((ConfigOptionFloat,               support_bottom_z_distance))
     ((ConfigOptionInt,                 enforce_support_layers))
     ((ConfigOptionInt,                 support_filament))
     ((ConfigOptionFloat,               support_line_width))

src/libslic3r/PrintObject.cpp

@@ -707,6 +707,7 @@ bool PrintObject::invalidate_state_by_config_options(
 		} else if (
                opt_key == "elefant_foot_compensation"
             || opt_key == "support_top_z_distance"
+            || opt_key == "support_bottom_z_distance"
             || opt_key == "xy_hole_compensation"
             || opt_key == "xy_contour_compensation") {
             steps.emplace_back(posSlice);

src/libslic3r/Slicing.cpp

@@ -113,8 +113,7 @@ SlicingParameters SlicingParameters::create_from_config(
     if (! soluble_interface) {
         params.gap_raft_object    = object_config.raft_contact_distance.value;
         //BBS
-        //params.gap_object_support = object_config.support_bottom_z_distance.value;
-        params.gap_object_support = object_config.support_top_z_distance.value;
+        params.gap_object_support = object_config.support_bottom_z_distance.value; 
         params.gap_support_object = object_config.support_top_z_distance.value;
         if (params.gap_object_support <= 0)
             params.gap_object_support = params.gap_support_object;

src/libslic3r/TreeSupport.cpp

@@ -2150,9 +2150,12 @@ void TreeSupport::draw_circles(const std::vector<std::vector<Node*>>& contact_no
                 {
                     if (layer_nr >= bottom_interface_layers + bottom_gap_layers)
                     {
-                        const Layer* below_layer = m_object->get_layer(layer_nr - bottom_interface_layers);
-                        ExPolygons bottom_interface = std::move(intersection_ex(base_areas, below_layer->lslices));
-                        floor_areas.insert(floor_areas.end(), bottom_interface.begin(), bottom_interface.end());
+                        for (size_t i = 0; i <= bottom_gap_layers; i++)
+                        {
+                            const Layer* below_layer = m_object->get_layer(layer_nr - bottom_interface_layers - i);
+                            ExPolygons bottom_interface = std::move(intersection_ex(base_areas, below_layer->lslices));
+                            floor_areas.insert(floor_areas.end(), bottom_interface.begin(), bottom_interface.end());
+                        }
                     }
                     if (floor_areas.empty() == false) {
                         floor_areas = std::move(diff_ex(floor_areas, avoid_region_interface));