Add performance stats overlay in status bar

Show FPS, frame time, visible/total objects, and visible/total
triangles in the status bar. Toggled via Settings > Show Performance
Stats, persisted in app settings.

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

src/ifcviewer/AppSettings.cpp

@@ -24,6 +24,7 @@
 namespace {
 constexpr const char* kGeometryLibraryKey = "geometry/library";
 constexpr const char* kGeometryLibraryDefault = "hybrid-cgal-simple-opencascade";
+constexpr const char* kShowStatsKey = "viewport/show_stats";
 }
 
 AppSettings& AppSettings::instance() {
@@ -46,12 +47,25 @@ void AppSettings::setGeometryLibrary(const QString& value) {
     emit geometryLibraryChanged(value);
 }
 
+bool AppSettings::showStats() const {
+    return show_stats_;
+}
+
+void AppSettings::setShowStats(bool value) {
+    if (show_stats_ == value) return;
+    show_stats_ = value;
+    persist();
+    emit showStatsChanged(value);
+}
+
 void AppSettings::load() {
     QSettings settings;
     geometry_library_ = settings.value(kGeometryLibraryKey, kGeometryLibraryDefault).toString();
+    show_stats_ = settings.value(kShowStatsKey, false).toBool();
 }
 
 void AppSettings::persist() {
     QSettings settings;
     settings.setValue(kGeometryLibraryKey, geometry_library_);
+    settings.setValue(kShowStatsKey, show_stats_);
 }

src/ifcviewer/AppSettings.h

@@ -34,8 +34,12 @@ public:
     QString geometryLibrary() const;
     void setGeometryLibrary(const QString& value);
 
+    bool showStats() const;
+    void setShowStats(bool value);
+
 signals:
     void geometryLibraryChanged(const QString& value);
+    void showStatsChanged(bool value);
 
 private:
     AppSettings();
@@ -43,6 +47,7 @@ private:
     void persist();
 
     QString geometry_library_;
+    bool show_stats_ = false;
 };
 
 #endif // APPSETTINGS_H

src/ifcviewer/MainWindow.cpp

@@ -18,6 +18,7 @@
  ********************************************************************************/
 
 #include "MainWindow.h"
+#include "AppSettings.h"
 #include "SettingsWindow.h"
 
 #include <QApplication>
@@ -43,6 +44,23 @@ MainWindow::MainWindow(QWidget* parent)
         QMessageBox::warning(this, "Error", msg);
     }, Qt::QueuedConnection);
 
+    connect(viewport_, &ViewportWindow::frameStatsUpdated, this, [this](const ViewportWindow::FrameStats& s) {
+        if (!stats_label_->isVisible()) return;
+        stats_label_->setText(
+            QString("%1 fps | %2 ms | %3/%4 obj | %5/%6 tri")
+                .arg(s.fps, 0, 'f', 1)
+                .arg(s.frame_time_ms, 0, 'f', 1)
+                .arg(s.visible_objects)
+                .arg(s.total_objects)
+                .arg(s.visible_triangles)
+                .arg(s.total_triangles));
+    });
+
+    connect(&AppSettings::instance(), &AppSettings::showStatsChanged, this, [this](bool show) {
+        stats_label_->setVisible(show);
+        if (!show) stats_label_->clear();
+    });
+
     connect(&element_poll_timer_, &QTimer::timeout, this, &MainWindow::pollNewElements);
     element_poll_timer_.setInterval(100);
 
@@ -91,7 +109,10 @@ void MainWindow::setupUi() {
     progress_bar_->setMaximumWidth(200);
     progress_bar_->setVisible(false);
     status_label_ = new QLabel("Ready");
+    stats_label_ = new QLabel();
+    stats_label_->setVisible(AppSettings::instance().showStats());
     statusBar()->addWidget(status_label_, 1);
+    statusBar()->addPermanentWidget(stats_label_);
     statusBar()->addPermanentWidget(progress_bar_);
 }
 

src/ifcviewer/MainWindow.h

@@ -66,6 +66,7 @@ private:
     QTableWidget* property_table_ = nullptr;
     QProgressBar* progress_bar_ = nullptr;
     QLabel* status_label_ = nullptr;
+    QLabel* stats_label_ = nullptr;
     QTimer element_poll_timer_;
     QElapsedTimer load_timer_;
 

src/ifcviewer/SettingsWindow.cpp

@@ -20,6 +20,7 @@
 #include "SettingsWindow.h"
 #include "AppSettings.h"
 
+#include <QCheckBox>
 #include <QDialogButtonBox>
 #include <QFormLayout>
 #include <QLineEdit>
@@ -40,6 +41,9 @@ void SettingsWindow::setupUi() {
     geometry_library_edit_->setMinimumWidth(280);
     form->addRow("Geometry Library", geometry_library_edit_);
 
+    show_stats_check_ = new QCheckBox(this);
+    form->addRow("Show Performance Stats", show_stats_check_);
+
     auto* button_box = new QDialogButtonBox(
         QDialogButtonBox::Ok | QDialogButtonBox::Cancel, this);
 
@@ -60,9 +64,11 @@ void SettingsWindow::showEvent(QShowEvent* event) {
 
 void SettingsWindow::syncFromSettings() {
     geometry_library_edit_->setText(AppSettings::instance().geometryLibrary());
+    show_stats_check_->setChecked(AppSettings::instance().showStats());
 }
 
 void SettingsWindow::onAccepted() {
     AppSettings::instance().setGeometryLibrary(geometry_library_edit_->text());
+    AppSettings::instance().setShowStats(show_stats_check_->isChecked());
     accept();
 }

src/ifcviewer/SettingsWindow.h

@@ -22,6 +22,7 @@
 
 #include <QDialog>
 
+class QCheckBox;
 class QLineEdit;
 class QShowEvent;
 
@@ -41,6 +42,7 @@ private:
     void syncFromSettings();
 
     QLineEdit* geometry_library_edit_ = nullptr;
+    QCheckBox* show_stats_check_ = nullptr;
 };
 
 #endif

src/ifcviewer/ViewportWindow.cpp

@@ -532,6 +532,7 @@ void ViewportWindow::updateCamera() {
 void ViewportWindow::buildVisibleList(const QMatrix4x4& vp) {
     visible_counts_.clear();
     visible_offsets_.clear();
+    visible_triangles_ = 0;
 
     std::lock_guard<std::mutex> lock(upload_mutex_);
     if (object_draw_info_.empty()) return;
@@ -582,6 +583,7 @@ void ViewportWindow::buildVisibleList(const QMatrix4x4& vp) {
             visible_counts_.push_back(static_cast<GLsizei>(obj.index_count));
             visible_offsets_.push_back(reinterpret_cast<const void*>(
                 static_cast<uintptr_t>(obj.index_offset)));
+            visible_triangles_ += obj.index_count / 3;
         }
     }
 }
@@ -617,6 +619,25 @@ void ViewportWindow::render() {
     renderAxisGizmo();
 
     context_->swapBuffers(this);
+
+    // Compute FPS (updated once per second to avoid flicker).
+    float dt = frame_clock_.restart() / 1000.0f;
+    accumulated_time_ += dt;
+    frame_count_++;
+    if (accumulated_time_ >= 1.0f) {
+        last_fps_ = static_cast<float>(frame_count_) / accumulated_time_;
+        frame_count_ = 0;
+        accumulated_time_ = 0.0f;
+
+        FrameStats stats;
+        stats.fps = last_fps_;
+        stats.frame_time_ms = 1000.0f / last_fps_;
+        stats.total_objects = static_cast<uint32_t>(object_draw_info_.size());
+        stats.visible_objects = static_cast<uint32_t>(visible_counts_.size());
+        stats.total_triangles = total_triangles_;
+        stats.visible_triangles = visible_triangles_;
+        emit frameStatsUpdated(stats);
+    }
 }
 
 void ViewportWindow::renderAxisGizmo() {

src/ifcviewer/ViewportWindow.h

@@ -65,9 +65,19 @@ public:
     void setSelectedObjectId(uint32_t id);
     uint32_t pickObjectAt(int x, int y);
 
+    struct FrameStats {
+        float fps;
+        float frame_time_ms;
+        uint32_t total_objects;
+        uint32_t visible_objects;
+        uint32_t total_triangles;
+        uint32_t visible_triangles;
+    };
+
 signals:
     void objectPicked(uint32_t object_id);
     void initialized();
+    void frameStatsUpdated(const ViewportWindow::FrameStats& stats);
 
 protected:
     void exposeEvent(QExposeEvent* event) override;
@@ -152,6 +162,10 @@ private:
 
     // Stats
     uint32_t total_triangles_ = 0;
+    uint32_t visible_triangles_ = 0;
+    int frame_count_ = 0;
+    float accumulated_time_ = 0.0f;
+    float last_fps_ = 0.0f;
 };
 
 #endif // VIEWPORTWINDOW_H