Keep mixed-color filaments intact when the extruder count changes (#15385)

* Keep mixed-color filaments intact when the extruder count changes

The extruder-count spinner resized the filament arrays in bulk at the tail,
which is where mixed-color slots live, so a new filament landed behind the
mix and the sidebar skipped a slot number. It now adds and removes one slot
at a time through the same calls the sidebar's +/- buttons use, so a new
slot opens ahead of the mixed tail and a removal renumbers object filament
ids, painted facets, custom g-code and mixed components rather than
clamping them away.

Drops the vector overload of set_num_filaments(), which this leaves without
callers.

src/slic3r/GUI/GUI_App.cpp

@@ -8906,10 +8906,16 @@ void GUI_App::load_current_presets(bool active_preset_combox/*= false*/, bool ch
         auto* nozzle_diameter = edited_printer_preset.config.option<ConfigOptionFloats>("nozzle_diameter");
         if (nozzle_diameter) {
             // Mixed-color slots are virtual filaments kept at the tail of the list, so they have no
-            // nozzle of their own. Sizing to the nozzle count alone would silently drop the mixes of
-            // a just-loaded project, and update_extruder_count() would then strip the facets painted
-            // with them.
-            preset_bundle->set_num_filaments(nozzle_diameter->values.size() + preset_bundle->num_mixed_filaments());
+            // nozzle of their own and the count has to allow for them. Only ever grow: this sizes
+            // the list so the combo boxes have something to bind to, and set_num_filaments() trims
+            // at the raw tail, so shrinking here would eat the mixes rather than the surplus
+            // physical slots. A list longer than the nozzle count is a state the app reaches
+            // legitimately - raising the extruder count and not saving the printer preset leaves
+            // exactly that on the next start - and losing the project's mixes to it is worse than
+            // carrying a filament the printer has no nozzle for until the count is next changed.
+            const size_t target = nozzle_diameter->values.size() + preset_bundle->num_mixed_filaments();
+            if (target > preset_bundle->filament_presets.size())
+                preset_bundle->set_num_filaments(target);
         }
     }
 	this->plater()->set_printer_technology(printer_technology);

src/slic3r/GUI/Plater.cpp

@@ -5506,12 +5506,15 @@ void Sidebar::add_custom_filament(wxColour new_col, const std::string& preset_na
 
     // Mixed-color slots are kept at the tail of the filament arrays, so a new physical
     // filament has to be inserted just after the last physical one rather than appended.
-    // total == every slot (physical + mixed); insert_pos == the physical slot count.
-    size_t      total          = wxGetApp().preset_bundle->filament_presets.size();
-    size_t      insert_pos     = p->combos_filament.size();
+    // Count off filament_is_mixed, not filament_presets or the combos: the extruder-count spinner
+    // reaches this before the sidebar has rebuilt, and update_multi_material_filament_presets()
+    // can have grown filament_presets alone.
+    auto       *bundle         = wxGetApp().preset_bundle;
+    size_t      insert_pos     = bundle->num_physical_filaments();
+    size_t      total          = insert_pos + bundle->num_mixed_filaments();
     int         filament_count = (int)(total + 1);
     std::string new_color      = new_col.GetAsString(wxC2S_HTML_SYNTAX).ToStdString();
-    wxGetApp().preset_bundle->set_num_filaments(filament_count, new_color);
+    bundle->set_num_filaments(filament_count, new_color);
 
     // Maintain physical-first ordering: rotate the new slot from end to insert_pos.
     // No mixed slots -> insert_pos == total -> every rotate below is a no-op.

src/slic3r/GUI/Tab.cpp

@@ -2174,21 +2174,25 @@ void Tab::on_value_change(const std::string& opt_key, const boost::any& value)
 
     //Orca: sync filament num if it's a multi tool printer
     if (opt_key == "extruders_count" && !m_config->opt_bool("single_extruder_multi_material")){
-        auto num_extruder = boost::any_cast<size_t>(value);
-        int         old_filament_size = wxGetApp().preset_bundle->filament_presets.size();
-        std::vector<std::string> new_colors;
-        for (int i = old_filament_size; i < num_extruder; ++i) {
-            wxColour    new_col   = Plater::get_next_color_for_filament();
-            std::string new_color = new_col.GetAsString(wxC2S_HTML_SYNTAX).ToStdString();
-            new_colors.push_back(new_color);
+        const size_t num_extruder = boost::any_cast<size_t>(value);
+        auto        *bundle       = wxGetApp().preset_bundle;
+        Sidebar     &sidebar      = wxGetApp().plater()->sidebar();
+        // A tool changer feeds filament N from nozzle N, so the extruder count sizes the physical
+        // run only; mixed slots are virtual and keep the tail. Go one slot at a time through the
+        // sidebar's own +/- calls: they insert ahead of the mixed tail and renumber filament ids,
+        // painted facets, custom g-code and mixed components, which a bulk resize clamps away.
+        // Both also refresh the print tab and export the selections, so nothing to do afterwards.
+        size_t physical = bundle->num_physical_filaments();
+        while (physical != num_extruder) {
+            if (physical < num_extruder)
+                sidebar.add_custom_filament(Plater::get_next_color_for_filament());
+            else
+                sidebar.delete_filament(physical - 1);   // physical > num_extruder >= 1
+            const size_t updated = bundle->num_physical_filaments();
+            if (updated == physical)
+                break;   // the call declined, e.g. the total slot limit - do not spin
+            physical = updated;
         }
-        // Mixed-color slots are virtual filaments at the tail of the list with no nozzle of their
-        // own, so they are carried on top of the new extruder count instead of being truncated.
-        const size_t total_filaments = num_extruder + wxGetApp().preset_bundle->num_mixed_filaments();
-        wxGetApp().preset_bundle->set_num_filaments(total_filaments, new_colors);
-        wxGetApp().plater()->on_filament_count_change(total_filaments);
-        wxGetApp().get_tab(Preset::TYPE_PRINT)->update();
-        wxGetApp().preset_bundle->export_selections(*wxGetApp().app_config);
     }
 
     //Orca: disable purge_in_prime_tower if single_extruder_multi_material is disabled