fix: persist user-selected preview view mode after first load (#13625)

fix: apply smart preview defaults per extruder count session

- Track last extruder count (1=single, 2+=multi) instead of boolean flag
- Apply appropriate default (ColorPrint/FeatureType) when count changes
- User selections persist within same extruder count
- Symmetric behavior: both single and multi actively apply defaults
- Delete duplicate dead code block (uncommented TODO scaffolding)

Behavior:
- First slice (any type) → appropriate default
- User changes view → persists on re-slice
- Switch single→single or multi→multi → persists
- Switch single↔multi → appropriate default applies

src/slic3r/GUI/GCodeViewer.cpp

@@ -1344,18 +1344,26 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
 
     // load_toolpaths(gcode_result, build_volume, exclude_bounding_box);
     
-    // ORCA: Only show filament/color print preview if more than one tool/extruder is actually used in the toolpaths.
-    // Only reset back to Toolpaths (FeatureType) if we are currently in ColorPrint and this load is single-tool.
-    if (m_viewer.get_used_extruders_count() > 1) {
-        auto it = std::find(view_type_items.begin(), view_type_items.end(), libvgcode::EViewType::ColorPrint);
-        if (it != view_type_items.end())
-            m_view_type_sel = std::distance(view_type_items.begin(), it);
-        set_view_type(libvgcode::EViewType::ColorPrint);
-    } else if (get_view_type() == libvgcode::EViewType::ColorPrint) {
-        auto it = std::find(view_type_items.begin(), view_type_items.end(), libvgcode::EViewType::FeatureType);
-        if (it != view_type_items.end())
-            m_view_type_sel = std::distance(view_type_items.begin(), it);
-        set_view_type(libvgcode::EViewType::FeatureType);
+    // ORCA: Apply smart default view type when extruder count changes.
+    // Multi-color: ColorPrint (Filament), Single-color: FeatureType (Line Type).
+    // User selections persist within same extruder count, defaults reapply on count change.
+    int current_count = m_viewer.get_used_extruders_count();
+    if (current_count > 1) {
+        if (m_last_extruder_count_default_applied != 2) {
+            auto it = std::find(view_type_items.begin(), view_type_items.end(), libvgcode::EViewType::ColorPrint);
+            if (it != view_type_items.end())
+                m_view_type_sel = std::distance(view_type_items.begin(), it);
+            set_view_type(libvgcode::EViewType::ColorPrint);
+            m_last_extruder_count_default_applied = 2;
+        }
+    } else {
+        if (m_last_extruder_count_default_applied != 1) {
+            auto it = std::find(view_type_items.begin(), view_type_items.end(), libvgcode::EViewType::FeatureType);
+            if (it != view_type_items.end())
+                m_view_type_sel = std::distance(view_type_items.begin(), it);
+            set_view_type(libvgcode::EViewType::FeatureType);
+            m_last_extruder_count_default_applied = 1;
+        }
     }
 
     // BBS: data for rendering color arrangement recommendation
@@ -1455,18 +1463,6 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
             m_viewer.set_time_mode(libvgcode::convert(PrintEstimatedStatistics::ETimeMode::Normal));
     }
 
-    // set to color print by default if use multi extruders
-    if (m_viewer.get_used_extruders_count() > 1) {
-        for (int i = 0; i < view_type_items.size(); i++) {
-            if (view_type_items[i] == libvgcode::EViewType::ColorPrint) {
-                m_view_type_sel = i;
-                break;
-            }
-        }
-
-        set_view_type(libvgcode::EViewType::ColorPrint);
-    }
-
     bool only_gcode_3mf = false;
     PartPlate* current_plate = wxGetApp().plater()->get_partplate_list().get_curr_plate();
     bool current_has_print_instances = current_plate->has_printable_instances();

src/slic3r/GUI/GCodeViewer.hpp

@@ -226,6 +226,7 @@ private:
     std::vector<libvgcode::EViewType> view_type_items;
     std::vector<std::string> view_type_items_str;
     int       m_view_type_sel = 0;
+    int       m_last_extruder_count_default_applied{0};  // 0=unset, 1=single, 2+=multi
     std::vector<EMoveType> options_items;
 
     bool m_legend_visible{ true };