Hide the Design tab behind an experimental CAD preference

The tab is now gated on a new enable_cad_feature app-config key, off by
default, exposed in Preferences under General > Features. When off, the
page is never created, so the Design-only camera option is hidden too.
Takes effect on restart, like the other feature toggles.

src/libslic3r/AppConfig.cpp

@@ -311,6 +311,11 @@ void AppConfig::set_defaults()
         set_bool("zoom_to_mouse", false);
 
 #ifdef SLIC3R_CAD
+    // Experimental parametric Design tab. Off by default: the tab is not created at all
+    // until this is turned on, so nothing it builds reaches an unsuspecting user.
+    if (get("enable_cad_feature").empty())
+        set_bool("enable_cad_feature", false);
+
     // Design tab: draw a mate connector as a face rather than as the abstract disc + roll
     // quadrant. Defaults ON — face orientation is hardwired perception, so the roll and the
     // verse read without being learned, which no abstract glyph achieves. Turning it off

src/slic3r/GUI/GUI_App.hpp

@@ -349,6 +349,9 @@ public:
     int             OnExit() override;
     bool            initialized() const { return m_initialized; }
     inline bool     is_enable_multi_machine() { return this->app_config&& this->app_config->get("enable_multi_machine") == "true"; }
+#ifdef SLIC3R_CAD
+    inline bool     is_enable_cad_feature() { return this->app_config && this->app_config->get_bool("enable_cad_feature"); }
+#endif
 
     std::map<std::string, bool> test_url_state;
 

src/slic3r/GUI/MainFrame.cpp

@@ -1025,8 +1025,11 @@ void MainFrame::update_layout()
         size_t prepare_pos = (home_idx == wxNOT_FOUND) ? 0 : static_cast<size_t>(home_idx) + 1;
 #ifdef SLIC3R_CAD
         // Design sits between Home and Prepare, so it goes in first and pushes Prepare along.
-        m_design_page->Reparent(m_tabpanel);
-        m_tabpanel->InsertPage(prepare_pos++, TAB_ID_DESIGN, m_design_page, _L("Design"), "tab_design_active");
+        // The page only exists when the experimental CAD feature is enabled.
+        if (m_design_page != nullptr) {
+            m_design_page->Reparent(m_tabpanel);
+            m_tabpanel->InsertPage(prepare_pos++, TAB_ID_DESIGN, m_design_page, _L("Design"), "tab_design_active");
+        }
 #endif
         m_tabpanel->InsertPage(prepare_pos, TAB_ID_PREPARE, m_plater, _L("Prepare"), "tab_3d_active");
         m_tabpanel->InsertPage(prepare_pos + 1, TAB_ID_PREVIEW, m_plater, _L("Preview"), "tab_preview_active");
@@ -1299,7 +1302,7 @@ void MainFrame::init_tabpanel() {
         //else if (panel == m_param_panel)
         //    m_param_panel->OnActivate();
 #ifdef SLIC3R_CAD
-        else if (panel == m_design_page) {
+        else if (m_design_page != nullptr && panel == m_design_page) {
             // Built on first activation, never at startup: the panel creates several hundred
             // controls and its own GL canvas, which a user who does not open the tab should
             // not pay for.
@@ -1351,11 +1354,15 @@ void MainFrame::init_tabpanel() {
 #ifdef SLIC3R_CAD
     // Stand-in page for the Design tab. The real DesignPanel is built into it the first time
     // the tab is selected (see the page-changed handler above), so nothing it constructs sits
-    // on the startup path.
-    m_design_page = new wxPanel(this);
-    m_design_page->SetSizer(new wxBoxSizer(wxVERTICAL));
-    m_design_page->Hide();
-    start_mcp_control_if_enabled();   // opens the MCP socket iff SNAPORCA_MCP is set
+    // on the startup path. The experimental feature is off by default, and when it is off the
+    // page is never created, so the tab does not appear at all (the preference takes effect on
+    // the next start, like the other feature toggles).
+    if (wxGetApp().is_enable_cad_feature()) {
+        m_design_page = new wxPanel(this);
+        m_design_page->SetSizer(new wxBoxSizer(wxVERTICAL));
+        m_design_page->Hide();
+        start_mcp_control_if_enabled();   // opens the MCP socket iff SNAPORCA_MCP is set
+    }
 #endif
 
     create_preset_tabs();

src/slic3r/GUI/Preferences.cpp

@@ -1741,6 +1741,14 @@ void PreferencesDialog::create_items()
     auto item_multi_machine    = create_item_checkbox(_L("Multi device management"), _L("With this option enabled, you can send a task to multiple devices at the same time and manage multiple devices."), "enable_multi_machine", _L("(Requires restart)"));
     g_sizer->Add(item_multi_machine);
 
+#ifdef SLIC3R_CAD
+    auto item_cad_feature      = create_item_checkbox(_L("CAD feature (experimental)"),
+        _L("With this option enabled, the Design tab is shown, where models can be built and edited "
+           "parametrically. This feature is experimental and still under development."),
+        "enable_cad_feature", _L("(Requires restart)"));
+    g_sizer->Add(item_cad_feature);
+#endif
+
 #if 0
     g_sizer->Add(create_item_title(_L("Filament Grouping")), 1, wxEXPAND);
     //temporarily disable it
@@ -1818,11 +1826,14 @@ void PreferencesDialog::create_items()
     g_sizer->Add(reverse_mouse_zoom);
 
 #ifdef SLIC3R_CAD
-    auto item_connector_face_glyph = create_item_checkbox(_L("Draw mate connectors as a face"),
-        _L("In the Design tab, draw a mate connector as a small face instead of the conventional "
-           "disc with a roll quadrant. A face's orientation is read without being learned. "
-           "Turn this off for the conventional CAD representation."), "design_connector_face_glyph");
-    g_sizer->Add(item_connector_face_glyph);
+    // Design-tab only, so it stays out of the way while the CAD feature is switched off.
+    if (wxGetApp().is_enable_cad_feature()) {
+        auto item_connector_face_glyph = create_item_checkbox(_L("Draw mate connectors as a face"),
+            _L("In the Design tab, draw a mate connector as a small face instead of the conventional "
+               "disc with a roll quadrant. A face's orientation is read without being learned. "
+               "Turn this off for the conventional CAD representation."), "design_connector_face_glyph");
+        g_sizer->Add(item_connector_face_glyph);
+    }
 #endif
 
     std::vector<wxString> ButtonDragActions = {_L("None"), _L("Pan"), _L("Rotate")};