add to gui

gui/gui.cpp

@@ -136,17 +136,41 @@ void Gui::render(const EngineStats& stats) {
 
     ImGui::Columns(2, "main_columns");
 
-    // --- Left column: primary live readouts ---
+    // --- (0,0): primary live readouts — tach + throttle lever side by side ---
     DrawTachGauge(static_cast<float>(stats.rpm), static_cast<float>(stats.max_rpm),
                   static_cast<float>(stats.redline_rpm), 220.0f);
 
+    ImGui::SameLine();
+    ImGui::VSliderFloat("##throttle_lever", ImVec2(40, 160), &m_throttle_lever, 0.0f, 1.0f, "");
+    // VSliderFloat is only "active" while the mouse is down on it, so
+    // this is the spring-back: anything other than an active drag
+    // resets the lever to closed, including on release.
+    if (!ImGui::IsItemActive()) {
+        m_throttle_lever = 0.0f;
+    }
+    ImGui::SameLine();
+    ImGui::Text("Throttle\n%.0f%%", m_throttle_lever * 100.0f);
+
+    // Row 1 starts here in both columns, so column 1's content below
+    // lines up with column 0's regardless of which column is taller.
+    float row1_y = ImGui::GetCursorPosY();
+
+    // --- (1,0): fuel/power readouts + accessory toggles ---
     ImGui::Text("Fuel Consumption: %.2f L/h", stats.fuel_consumption_lph);
     ImGui::Text("Crank Power: %.2f kW", stats.crank_power_kw);
     ImGui::Text("Output Heat: %.1f J", stats.output_heat_j);
 
+    ImGui::Spacing();
+    ImGui::Separator();
+    ImGui::Text("Accessories");
+    ImGui::Checkbox("Alternator", &m_accessories.alternator);
+    ImGui::Checkbox("A/C", &m_accessories.ac);
+    ImGui::Checkbox("Power Steering", &m_accessories.power_steering);
+
     ImGui::NextColumn();
 
-    // --- Right column: extensible stats list (oil temp, coolant temp, ...) ---
+    // --- (1,1): extensible stats list (oil temp, coolant temp, ...) ---
+    ImGui::SetCursorPosY(row1_y);
     ImGui::Text("Stats");
     ImGui::Separator();
     for (const StatEntry& s : stats.extra_stats) {

gui/gui.h

@@ -28,6 +28,15 @@ struct EngineStats {
     std::vector<StatEntry> extra_stats;
 };
 
+// Which parasitic-load accessories are toggled on, via checkboxes drawn
+// in the left column by render(). Placeholders (Alternator, A/C, Power
+// Steering) until there's an actual load model behind them.
+struct AccessoryState {
+    bool alternator = false;
+    bool ac = false;
+    bool power_steering = false;
+};
+
 class Gui {
 public:
     bool init();                     // create window + ImGui context
@@ -36,6 +45,20 @@ public:
     void end_frame();                 // swap buffers
     void shutdown();
 
+    // Reflects the throttle lever as of the most recent render() call.
+    // Spring-loaded: holds whatever value the drag left it at only
+    // while the mouse is down, and snaps back to 0 the instant it's
+    // released. Read it any time after render() this frame, or before
+    // render() next frame, to feed it into the engine.
+    double throttle() const { return static_cast<double>(m_throttle_lever); }
+
+    // Reflects the checkbox state as of the most recent render() call —
+    // read it any time after render() this frame, or before render()
+    // next frame, to feed accessory load into the engine.
+    const AccessoryState& accessories() const { return m_accessories; }
+
 private:
     GLFWwindow* m_window = nullptr;
+    float m_throttle_lever = 0.0f;
+    AccessoryState m_accessories;
 };