Add gear icon toolbar button with viewport options dropdown

Adds a ⚙ icon button to the right of the AA toggle in each viewport
tile's compact toolbar.  Clicking it opens a dropdown with:
  - Shading submenu: Smooth Shaded / Flat Shaded / Wireframe on Surface /
    Wireframe / Unlit  (new ShadingMode enum driving UsdImagingGLDrawMode)
  - Lighting submenu: Camera Headlight / Scene Lights + Dome Light toggle
  - Show Grid and Anti-Aliasing toggles (mirrored from icon buttons)
  - Bounding Box submenu: None / Per Object / All Selection
  - Background submenu: Dark Gray / Black / Light Gray / Midnight Blue

ShadingMode is persisted in viewport_settings.ini alongside the existing
per-tile settings (saved on shutdown, restored on startup).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

resources/icons/gear.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <path fill="white" d="M495.9 166.6c3.2 8.7.5 18.4-6.4 24.6l-43.3 39.4c1.1 8.3 1.7 16.8 1.7 25.4s-.6 17.1-1.7 25.4l43.3 39.4c6.9 6.2 9.6 15.9 6.4 24.6-4.4 11.9-9.7 23.3-15.8 34.3l-4.7 8.1c-6.6 11-14 21.4-22.1 31.2-5.9 7.2-15.7 9.6-24.5 6.8l-55.7-17.7c-13.4 10.3-28.2 18.9-44 25.4l-12.5 57.1c-2 9.1-9 16.3-18.2 17.8C283.7 510.8 269.5 512 255 512s-28.7-1.2-42.5-3.5c-9.2-1.5-16.2-8.7-18.2-17.8l-12.5-57.1c-15.8-6.5-30.6-15.1-44-25.4l-55.7 17.7c-8.8 2.8-18.6.3-24.5-6.8-8.1-9.8-15.5-20.2-22.1-31.2l-4.7-8.1C25.1 368.8 19.8 357.4 15.4 345.5c-3.2-8.7-.5-18.4 6.4-24.6l43.3-39.4C64.0 273.1 63.4 264.6 63.4 256s.6-17.1 1.7-25.4L21.8 191.2c-6.9-6.2-9.6-15.9-6.4-24.6 4.4-11.9 9.7-23.3 15.8-34.3l4.7-8.1c6.6-11 14-21.4 22.1-31.2 5.9-7.2 15.7-9.6 24.5-6.8l55.7 17.7c13.4-10.3 28.2-18.9 44-25.4l12.5-57.1C196.5 12.3 203.5 5.1 212.7 3.6 226.5 1.2 240.7 0 255.2 0s28.7 1.2 42.5 3.5c9.2 1.5 16.2 8.7 18.2 17.8l12.5 57.1c15.8 6.5 30.6 15.1 44 25.4l55.7-17.7c8.8-2.8 18.6-.3 24.5 6.8 8.1 9.8 15.5 20.2 22.1 31.2l4.7 8.1c6.1 11 11.4 22.4 15.8 34.3zM255.2 336a80 80 0 1 0 0-160 80 80 0 1 0 0 160z"/>
+</svg>

src/core/UsdSceneRenderer.cpp

@@ -131,6 +131,7 @@ UsdSceneRenderer::UsdSceneRenderer()
     : m_showGrid(true)
     , m_aaEnabled(false)
     , m_backgroundColor(0.15f, 0.15f, 0.15f)
+    , m_shadingMode(ShadingMode::SmoothShaded)
     , m_ambientLightOnly(true)
     , m_domeLightEnabled(false)
     , m_stageIsZup(false)
@@ -616,11 +617,27 @@ void UsdSceneRenderer::Render(int width, int height)
     m_renderParams = pxr::UsdImagingGLRenderParams();
     m_renderParams.frame                    = m_currentTime;
     m_renderParams.complexity               = 1.0f;
-    m_renderParams.drawMode                 = pxr::UsdImagingGLDrawMode::DRAW_SHADED_SMOOTH;
+    // Apply shading mode → drawMode + enableLighting
+    switch (m_shadingMode) {
+        case ShadingMode::FlatShaded:
+            m_renderParams.drawMode     = pxr::UsdImagingGLDrawMode::DRAW_SHADED_FLAT;
+            m_renderParams.enableLighting = true;  break;
+        case ShadingMode::WireframeOnSurface:
+            m_renderParams.drawMode     = pxr::UsdImagingGLDrawMode::DRAW_WIREFRAME_ON_SURFACE;
+            m_renderParams.enableLighting = true;  break;
+        case ShadingMode::Wireframe:
+            m_renderParams.drawMode     = pxr::UsdImagingGLDrawMode::DRAW_WIREFRAME;
+            m_renderParams.enableLighting = false; break;
+        case ShadingMode::Unlit:
+            m_renderParams.drawMode     = pxr::UsdImagingGLDrawMode::DRAW_SHADED_SMOOTH;
+            m_renderParams.enableLighting = false; break;
+        default: // SmoothShaded
+            m_renderParams.drawMode     = pxr::UsdImagingGLDrawMode::DRAW_SHADED_SMOOTH;
+            m_renderParams.enableLighting = true;  break;
+    }
     m_renderParams.showGuides               = true;
     m_renderParams.showProxy                = true;
     m_renderParams.showRender               = false;
-    m_renderParams.enableLighting           = true;
     m_renderParams.enableSampleAlphaToCoverage = true;
     m_renderParams.gammaCorrectColors       = false;
     m_renderParams.cullStyle                = pxr::UsdImagingGLCullStyle::CULL_STYLE_BACK_UNLESS_DOUBLE_SIDED;

src/core/UsdSceneRenderer.h

@@ -31,6 +31,15 @@ enum class BBoxMode {
     AllSelection    ///< One combined box for the entire selection
 };
 
+/// Surface shading mode — maps to UsdImagingGLDrawMode + enableLighting.
+enum class ShadingMode {
+    SmoothShaded,        ///< Smooth shading with materials (default)
+    FlatShaded,          ///< Flat shading with materials
+    WireframeOnSurface,  ///< Wireframe overlay on solid surface
+    Wireframe,           ///< Wireframe only, no fill
+    Unlit,               ///< Smooth geometry, lighting disabled
+};
+
 class UsdSceneRenderer {
 public:
     UsdSceneRenderer();
@@ -199,6 +208,9 @@ public:
     bool GetDomeLightEnabled()              const { return m_domeLightEnabled; }
     void SetDomeLightEnabled(bool val)            { m_domeLightEnabled = val; }
 
+    ShadingMode GetShadingMode()             const { return m_shadingMode; }
+    void        SetShadingMode(ShadingMode m)     { m_shadingMode = m; m_forceRefresh = true; }
+
     /// Default material ambient (kA, default 0.2 — matches viewSettingsDataModel.py).
     float GetDefaultMaterialAmbient()       const { return m_defaultMaterialAmbient; }
     void  SetDefaultMaterialAmbient(float v)      { m_defaultMaterialAmbient = v; }
@@ -298,6 +310,7 @@ private:
     pxr::GfVec3f    m_backgroundColor;
 
     // Lighting settings (mirrors stageView.py viewSettings)
+    ShadingMode     m_shadingMode;            // draw mode + lighting flags
     bool            m_ambientLightOnly;       // camera headlight
     bool            m_domeLightEnabled;       // dome/IBL light
     bool            m_stageIsZup;             // used for dome light rotation

src/ui/IconManager.cpp

@@ -60,6 +60,7 @@ static const char* IconFilename(Icon icon) {
         case Icon::Refresh:      return "arrows-rotate.svg";
         case Icon::FilePlus:     return "file-plus.svg";
         case Icon::Pen:          return "pen.svg";
+        case Icon::Settings:     return "gear.svg";
         default:                return nullptr;
     }
 }
@@ -75,7 +76,7 @@ static constexpr Icon kAllIcons[] = {
     Icon::LayoutSingle, Icon::LayoutHSplit, Icon::LayoutVSplit, Icon::LayoutQuad,
     Icon::SkipBack, Icon::StepBack, Icon::PlayBack, Icon::Play, Icon::Pause,
     Icon::StepForward, Icon::SkipEnd, Icon::Loop, Icon::Bounce,
-    Icon::Refresh, Icon::FilePlus, Icon::Pen,
+    Icon::Refresh, Icon::FilePlus, Icon::Pen, Icon::Settings,
 };
 
 // ---------------------------------------------------------------------------

src/ui/IconManager.h

@@ -54,6 +54,7 @@ enum class Icon {
     Refresh,      // reload / refresh
     FilePlus,     // create new file
     Pen,          // edit / edit target
+    Settings,     // gear / viewport options
 };
 
 /// Loads SVG files from disk, rasterizes them with NanoSVG, uploads them as

src/ui/ViewportPanel.cpp

@@ -635,6 +635,7 @@ void ViewportPanel::SaveSettings(const std::string& path) const
         f << "BBoxMode="        << s.bboxMode            << "\n";
         f << "AmbientLightOnly=" << (s.ambientLightOnly  ? 1 : 0) << "\n";
         f << "DomeLightEnabled=" << (s.domeLightEnabled  ? 1 : 0) << "\n";
+        f << "ShadingMode="      << s.shadingMode                  << "\n";
     }
 }
 
@@ -700,6 +701,7 @@ void ViewportPanel::LoadSettings(const std::string& path)
             else if (key == "BBoxMode")         ts.bboxMode         = toInt(val, ts.bboxMode);
             else if (key == "AmbientLightOnly") ts.ambientLightOnly = (val == "1");
             else if (key == "DomeLightEnabled") ts.domeLightEnabled = (val == "1");
+            else if (key == "ShadingMode")      ts.shadingMode      = toInt(val, ts.shadingMode);
         }
     }
 

src/ui/ViewportTile.cpp

@@ -99,6 +99,7 @@ ViewportTileSettings ViewportTile::GetSettings() const
     s.bboxMode         = static_cast<int>(m_renderer.GetBBoxMode());
     s.ambientLightOnly = m_renderer.GetAmbientLightOnly();
     s.domeLightEnabled = m_renderer.GetDomeLightEnabled();
+    s.shadingMode      = static_cast<int>(m_renderer.GetShadingMode());
     return s;
 }
 
@@ -112,6 +113,7 @@ void ViewportTile::ApplySettings(const ViewportTileSettings& s)
     m_renderer.SetBBoxMode(static_cast<BBoxMode>(s.bboxMode));
     m_renderer.SetAmbientLightOnly(s.ambientLightOnly);
     m_renderer.SetDomeLightEnabled(s.domeLightEnabled);
+    m_renderer.SetShadingMode(static_cast<ShadingMode>(s.shadingMode));
 }
 
 // ---------------------------------------------------------------------------
@@ -963,6 +965,100 @@ void ViewportTile::RenderCompactToolbar(int tileIndex)
     if (iconToggle(aaId.c_str(), "AA", Icon::Antialias, aa, "Toggle anti-aliasing"))
         m_renderer.SetAAEnabled(!aa);
 
+    ImGui::SameLine();
+    ImGui::TextDisabled("|");
+    ImGui::SameLine();
+
+    // -- Gear / viewport options popup ---------------------------------------
+    {
+        std::string gearId      = "##gear_" + std::to_string(tileIndex);
+        std::string gearPopupId = "GearPopup_" + std::to_string(tileIndex);
+
+        if (m_iconManager) {
+            ImTextureID tex = m_iconManager->Get(Icon::Settings);
+            ImGui::ImageButton(gearId.c_str(), ImTextureRef(tex), ImVec2(16.f, 16.f));
+        } else {
+            ImGui::Button("*");
+        }
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("Viewport options");
+
+        if (ImGui::BeginPopupContextItem(gearPopupId.c_str(),
+                ImGuiPopupFlags_MouseButtonLeft))
+        {
+            // -- Shading mode ------------------------------------------------
+            if (ImGui::BeginMenu("Shading")) {
+                ShadingMode cur = m_renderer.GetShadingMode();
+                auto shadingItem = [&](const char* label, ShadingMode mode) {
+                    if (ImGui::MenuItem(label, nullptr, cur == mode))
+                        m_renderer.SetShadingMode(mode);
+                };
+                shadingItem("Smooth Shaded",       ShadingMode::SmoothShaded);
+                shadingItem("Flat Shaded",          ShadingMode::FlatShaded);
+                shadingItem("Wireframe on Surface", ShadingMode::WireframeOnSurface);
+                shadingItem("Wireframe",            ShadingMode::Wireframe);
+                shadingItem("Unlit",                ShadingMode::Unlit);
+                ImGui::EndMenu();
+            }
+
+            // -- Lighting ----------------------------------------------------
+            if (ImGui::BeginMenu("Lighting")) {
+                bool ambient = m_renderer.GetAmbientLightOnly();
+                if (ImGui::MenuItem("Camera Headlight", nullptr,  ambient))
+                    m_renderer.SetAmbientLightOnly(true);
+                if (ImGui::MenuItem("Scene Lights",     nullptr, !ambient))
+                    m_renderer.SetAmbientLightOnly(false);
+                ImGui::Separator();
+                bool dome = m_renderer.GetDomeLightEnabled();
+                if (ImGui::MenuItem("Dome Light", nullptr, dome))
+                    m_renderer.SetDomeLightEnabled(!dome);
+                ImGui::EndMenu();
+            }
+
+            ImGui::Separator();
+
+            // -- Display toggles ---------------------------------------------
+            {
+                bool grid = m_renderer.ShowGrid();
+                if (ImGui::MenuItem("Show Grid", nullptr, grid))
+                    m_renderer.SetShowGrid(!grid);
+
+                bool aaItem = m_renderer.GetAAEnabled();
+                if (ImGui::MenuItem("Anti-Aliasing", nullptr, aaItem))
+                    m_renderer.SetAAEnabled(!aaItem);
+            }
+
+            ImGui::Separator();
+
+            // -- BBox --------------------------------------------------------
+            if (ImGui::BeginMenu("Bounding Box")) {
+                BBoxMode bbox = m_renderer.GetBBoxMode();
+                if (ImGui::MenuItem("None",          nullptr, bbox == BBoxMode::None))
+                    m_renderer.SetBBoxMode(BBoxMode::None);
+                if (ImGui::MenuItem("Per Object",    nullptr, bbox == BBoxMode::PerObject))
+                    m_renderer.SetBBoxMode(BBoxMode::PerObject);
+                if (ImGui::MenuItem("All Selection", nullptr, bbox == BBoxMode::AllSelection))
+                    m_renderer.SetBBoxMode(BBoxMode::AllSelection);
+                ImGui::EndMenu();
+            }
+
+            // -- Background --------------------------------------------------
+            if (ImGui::BeginMenu("Background")) {
+                auto& bg = m_renderer.GetBackgroundColor();
+                if (ImGui::MenuItem("Dark Gray",     nullptr, bg == pxr::GfVec3f(0.15f, 0.15f, 0.15f)))
+                    m_renderer.SetBackgroundColor(pxr::GfVec3f(0.15f, 0.15f, 0.15f));
+                if (ImGui::MenuItem("Black",         nullptr, bg == pxr::GfVec3f(0.0f, 0.0f, 0.0f)))
+                    m_renderer.SetBackgroundColor(pxr::GfVec3f(0.0f, 0.0f, 0.0f));
+                if (ImGui::MenuItem("Light Gray",    nullptr, bg == pxr::GfVec3f(0.45f, 0.45f, 0.45f)))
+                    m_renderer.SetBackgroundColor(pxr::GfVec3f(0.45f, 0.45f, 0.45f));
+                if (ImGui::MenuItem("Midnight Blue", nullptr, bg == pxr::GfVec3f(0.1f, 0.1f, 0.2f)))
+                    m_renderer.SetBackgroundColor(pxr::GfVec3f(0.1f, 0.1f, 0.2f));
+                ImGui::EndMenu();
+            }
+
+            ImGui::EndPopup();
+        }
+    }
+
     ImGui::PopStyleVar(); // ItemSpacing
 }
 

src/ui/ViewportTile.h

@@ -28,6 +28,7 @@ struct ViewportTileSettings {
     int         bboxMode         = 0;     ///< BBoxMode cast to int
     bool        ambientLightOnly = false;
     bool        domeLightEnabled = false;
+    int         shadingMode      = 0;     ///< ShadingMode cast to int (0 = SmoothShaded)
 };
 
 /// Named orthographic view directions.