Belt printer: bring back the raw G-code view in the canvas view menu (#16241)

The *Show raw G-code (belt only)* toggle retired in #16236 returns, as
an item of the Preview canvas view menu (the eye-icon popup, after
*Labels*) with its `B` shortcut, and only there: no legend checkbox.
Unlit, the preview shows the designed (upright) view; lit, the raw
machine-frame G-code, which is what to look at when checking the machine
frame transforms. The item only appears on a belt printer in Preview.

The toggle is view only (exported G-code is byte-identical either way),
and the layer slider now keeps its layer index across the reload (the
layer Z values differ between the two views, so the old keep-by-Z lost
the position).

## Verification
- Scripted GUI pass: item present only in the belt Preview menu (absent
in Prepare and on a non-belt printer), toggles from the menu and from
`B` with the eye following the state, legend has no belt entry, exported
G-code identical with the view on and off, slider stays at its layer
through toggles, 3MF reopen and printer switch unaffected.
- `fff_print_tests` 355 passed, `libslic3r_tests` 1116 passed;
`scripts/clang_tidy_diff.py --base upstream/belt-printer`: no findings.

Wiki: OrcaSlicer/OrcaSlicer_WIKI#374 documents the menu item and
shortcut with screenshots.

src/slic3r/GUI/GCodeViewer.cpp

@@ -1387,7 +1387,11 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
     m_viewer.set_dim_previous_layers_brightness(0.01f * std::stoi(get_app_config()->get("preview_dim_previous_layers_brightness")));
 
     // avoid processing if called with the same gcode_result.
-    if (m_last_result_id == gcode_result.id && wxGetApp().is_editor()) {
+    // On a belt printer the toolpath geometry fed to libvgcode also depends on the
+    // designed/raw view state (the back-transform is applied in convert), so the
+    // same result is converted again only when that view has been toggled.
+    const bool same_belt_view = !m_belt_view_enabled || m_last_belt_show_designed == m_belt_show_designed;
+    if (m_last_result_id == gcode_result.id && wxGetApp().is_editor() && same_belt_view) {
         //BBS: add logs
         BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << boost::format(": the same id %1%, return directly, result %2% ") % m_last_result_id % (&gcode_result);
 
@@ -1429,20 +1433,22 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
     }
 
     // convert data from PrusaSlicer format to libvgcode format.
-    // Belt printers: back-transform the toolpath geometry into model/Cartesian
-    // space using the general belt inverse (handles the mesh rotation, shear and
-    // axis remap), so the part is shown upright, the way it was designed.
+    // Belt printers: when the designed (upright) view is active, back-transform
+    // the toolpath geometry into model/Cartesian space using the general belt
+    // inverse (handles the mesh rotation, shear and axis remap). When off, the
+    // raw machine-frame G-code is shown (useful for checking the transform itself).
     const bool is_belt = m_belt_view_enabled && print.config().belt_printer.value;
-    Transform3d belt_inv = is_belt ? compute_belt_back_transform(print.config()) : Transform3d::Identity();
+    Transform3d belt_inv = (is_belt && m_belt_show_designed)
+        ? compute_belt_back_transform(print.config()) : Transform3d::Identity();
     // Belt: move positions are stored as gcode_Z + belt_z_origin (the start G-code's
     // purge-blob advance baked into the machine-Z origin by its G92 Z0 resets). Subtract
     // that constant before the linear back-transform so every toolpath maps to the model's
     // belt coordinate. Without it the back-transform mixes the offset with the gantry-Y
     // term, leaving a per-move designed-Y error that min-corner anchoring cannot remove
     // when a bridge/keel move happens to cancel it at the bbox minimum.
-    if (is_belt && gcode_result.belt_z_origin != 0.0f)
+    if (is_belt && m_belt_show_designed && gcode_result.belt_z_origin != 0.0f)
         belt_inv = belt_inv * Transform3d(Eigen::Translation3d(Vec3d(0.0, 0.0, -double(gcode_result.belt_z_origin))));
-    const bool apply_belt = is_belt
+    const bool apply_belt = is_belt && m_belt_show_designed
         && !belt_inv.matrix().isApprox(Transform3d::Identity().matrix());
     if (apply_belt) {
         // The linear belt back-transform recovers the print's shape and orientation but not
@@ -1679,6 +1685,7 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
 
     //BBS: move the id to the end of reset
     m_last_result_id = gcode_result.id;
+    m_last_belt_show_designed = m_belt_show_designed;
     m_gcode_result = &gcode_result;
     m_move_type_counts.fill(0);
     for (auto& move_type_times : m_move_type_times)

src/slic3r/GUI/GCodeViewer.hpp

@@ -199,6 +199,8 @@ private:
     std::vector<int> m_plater_extruder;
     bool m_gl_data_initialized{ false };
     unsigned int m_last_result_id{ 0 };
+    // Belt printers: the view the loaded result was converted for (see load_as_gcode).
+    bool m_last_belt_show_designed{ true };
     //BBS: save m_gcode_result as well
     const GCodeProcessorResult* m_gcode_result;
     std::array<unsigned int, static_cast<size_t>(EMoveType::Count)> m_move_type_counts{};
@@ -262,6 +264,8 @@ mutable bool m_no_render_path { false };
     bool m_is_dark = false;
 
     bool  m_belt_view_enabled = false;
+    bool  m_belt_show_designed = true;   // Designed (upright, back-transformed) view by default; off shows
+                                         // the raw machine-frame G-code (canvas view menu, hotkey B).
     float m_belt_angle_deg = 0.f;
 
     libvgcode::Viewer m_viewer;
@@ -402,6 +406,8 @@ public:
 
     void set_belt_printer(bool enabled, float angle_deg) { m_belt_view_enabled = enabled; m_belt_angle_deg = angle_deg; }
     bool is_belt_view() const { return m_belt_view_enabled && m_belt_angle_deg > 0.f; }
+    void toggle_belt_show_designed() { if (m_belt_view_enabled) m_belt_show_designed = !m_belt_show_designed; }
+    bool is_belt_show_designed() const { return m_belt_show_designed; }
 
     size_t get_extruders_count() { return m_extruders_count; }
     void push_combo_style();

src/slic3r/GUI/GLCanvas3D.cpp

@@ -3804,6 +3804,16 @@ bool GLCanvas3D::handle_shortcut(const KeyChord& chord)
         get_gcode_viewer().get_layers_slider()->switch_one_layer_mode();
         m_dirty = true;
         break;
+    case Shortcut::ToggleBeltRawGcode:
+        // Same state as the canvas view menu item. The designed-view back-transform is
+        // baked into the toolpaths at load time, so the preview is re-converted.
+        if (m_gcode_viewer.is_belt_view()) {
+            m_gcode_viewer.toggle_belt_show_designed();
+            if (Plater* plater = wxGetApp().plater())
+                plater->refresh_belt_view();
+            m_dirty = true;
+        }
+        break;
     case Shortcut::GoToLayer:
         if (!m_gizmos.is_enabled()) {
             get_gcode_viewer().get_layers_slider()->show_go_to_layer(true);
@@ -10334,6 +10344,22 @@ void GLCanvas3D::_render_canvas_toolbar()
             [p]{p->show_view3D_labels(!p->are_view3D_labels_shown());}
         );
 
+        // Belt printers, G-code preview only: show the raw machine-frame G-code instead of
+        // the designed (upright) view. This menu is the only place the toggle lives (plus
+        // its shortcut); the reload is deferred (CallAfter) so the preview is not rebuilt
+        // mid-render.
+        if (m_canvas_type == ECanvasType::CanvasPreview && m_gcode_viewer.is_belt_view()) {
+            ImGui::Separator();
+            create_menu_item( _utf8(L("Show raw G-code (belt only)")),
+                true,
+                !m_gcode_viewer.is_belt_show_designed(), // eye lit = raw machine-frame G-code (designed view off)
+                [this, p]{
+                    m_gcode_viewer.toggle_belt_show_designed();
+                    p->CallAfter([p]{ p->refresh_belt_view(); });
+                }
+            );
+        }
+
         ImGui::PopItemFlag();
         ImGui::EndPopup();
     }

src/slic3r/GUI/GUI_Preview.cpp

@@ -369,6 +369,25 @@ void Preview::reload_print(bool only_gcode)
     m_only_gcode = only_gcode;
 }
 
+void Preview::refresh_belt_view()
+{
+    // Re-run the G-code preview conversion so the belt "designed view" toggle takes effect
+    // (the back-transform is baked into the toolpath geometry in GCodeViewer::load_as_gcode,
+    // whose same-result cache also keys on the view state, so the re-convert runs).
+    // Reset m_loaded_print to bypass the "already loaded" guard the way reload_print does, but
+    // keep the current layer range and only-gcode mode so the view doesn't jump on toggle.
+    // The layer Z values differ between the designed and the raw view (the raw view's are
+    // machine-frame heights), so keep_z_range alone cannot find the old span: carry the
+    // slider over by layer index instead.
+    IMSlider *layers_slider = m_canvas->get_gcode_viewer().get_layers_slider();
+    const int lower  = layers_slider->GetLowerValue();
+    const int higher = layers_slider->GetHigherValue();
+    m_loaded_print = nullptr;
+    load_print(true /*keep_z_range*/, m_only_gcode);
+    if (higher <= layers_slider->GetMaxValue())
+        layers_slider->SetSelectionSpan(lower, higher);
+}
+
 //BBS: always load shell at preview
 void Preview::load_shells(const Print& print, bool force_previewing)
 {

src/slic3r/GUI/GUI_Preview.hpp

@@ -149,6 +149,7 @@ public:
     void load_print(bool keep_z_range = false, bool only_gcode = false);
     void reload_print(bool only_gcode = false);
     // Belt printers: re-convert the G-code preview so the "designed view" toggle takes effect.
+    void refresh_belt_view();
     //BBS: always load shell at preview
     void load_shells(const Print& print, bool force_previewing = false);
     void reset_shells();

src/slic3r/GUI/Plater.cpp

@@ -17885,6 +17885,11 @@ void Plater::reload_print()
     p->preview->reload_print();
 }
 
+void Plater::refresh_belt_view()
+{
+    p->preview->refresh_belt_view();
+}
+
 // BBS
 wxString Plater::get_project_name()
 {

src/slic3r/GUI/Plater.hpp

@@ -387,6 +387,7 @@ public:
     void reload_print();
     // Belt printers: re-run the G-code preview conversion so the "designed view" toggle
     // (hotkey B / legend checkbox) takes effect; the back-transform is applied to the
+    void refresh_belt_view();
     // toolpath geometry at load time. Keeps the current layer range and only-gcode mode.
 
     // SoftFever

src/slic3r/GUI/Shortcuts.cpp

@@ -149,6 +149,7 @@ constexpr std::array<ShortcutInfo, size_t(Shortcut::Count)> shortcut_table = {{
     SHORTCUT(ShowWireframe,     "show_wireframe",     L("Show/Hide wireframe"),                                  CANVAS,  { WXK_RETURN, CTRL_SHIFT }),
     SHORTCUT(ToggleGcodeWindow,   "toggle_gcode_window",   L("On/Off G-code window"),                            PREVIEW, { 'C' }),
     SHORTCUT(ToggleOneLayerMode,  "toggle_one_layer_mode", L("On/Off one layer mode of the vertical slider"),    PREVIEW, { 'L' }),
+    SHORTCUT(ToggleBeltRawGcode,  "toggle_belt_raw_gcode", L("Show raw G-code (belt only)"),                     PREVIEW, { 'B' }),
 
     // Application
     SHORTCUT(Preferences,       "preferences",        L("Preferences"),                                          GLOBAL, PREFERENCES_CHORD),

src/slic3r/GUI/Shortcuts.hpp

@@ -46,7 +46,7 @@ enum class Shortcut : uint8_t {
     // Camera
     ViewDefault, ViewTop, ViewBottom, ViewFront, ViewRear, ViewLeft, ViewRight, ViewPlate, ZoomIn, ZoomOut, Mouse3DSettings,
     // Display
-    ShowLabels, ShowWireframe, ToggleGcodeWindow, ToggleOneLayerMode,
+    ShowLabels, ShowWireframe, ToggleGcodeWindow, ToggleOneLayerMode, ToggleBeltRawGcode,
     // Application
     Preferences, Search, SwitchView, CollapseSidebar, ReloadDevicePage, KeyboardShortcuts,
     // Speed Dial