[hud] Implement FPS display as a HUD item

src/dxvk/hud/dxvk_hud.cpp

@@ -37,6 +37,7 @@ namespace dxvk::hud {
     addItem<HudVersionItem>("version");
     addItem<HudClientApiItem>("api", m_device);
     addItem<HudDeviceInfoItem>("devinfo", m_device);
+    addItem<HudFpsItem>("fps");
   }
   
   

src/dxvk/hud/dxvk_hud_item.cpp

@@ -147,4 +147,38 @@ namespace dxvk::hud {
     return position;
   }
 
+
+  HudFpsItem::HudFpsItem() { }
+  HudFpsItem::~HudFpsItem() { }
+
+
+  void HudFpsItem::update(dxvk::high_resolution_clock::time_point time) {
+    m_frameCount += 1;
+
+    auto elapsed = std::chrono::duration_cast<std::chrono::microseconds>(time - m_lastUpdate);
+
+    if (elapsed.count() >= UpdateInterval) {
+      int64_t fps = (10'000'000ll * m_frameCount) / elapsed.count();
+
+      m_frameRate = str::format("FPS: ", fps / 10, ".", fps % 10);
+      m_frameCount = 0;
+      m_lastUpdate = time;
+    }
+  }
+
+
+  HudPos HudFpsItem::render(
+          HudRenderer&      renderer,
+          HudPos            position) {
+    position.y += 16.0f;
+
+    renderer.drawText(16.0f,
+      { position.x, position.y },
+      { 1.0f, 1.0f, 1.0f, 1.0f },
+      m_frameRate);
+
+    position.y += 8.0f;
+    return position;
+  }
+
 }

src/dxvk/hud/dxvk_hud_item.h

@@ -160,4 +160,31 @@ namespace dxvk::hud {
   };
 
 
+  /**
+   * \brief HUD item to display the frame rate
+   */
+  class HudFpsItem : public HudItem {
+    constexpr static int64_t UpdateInterval = 500'000;
+  public:
+
+    HudFpsItem();
+
+    ~HudFpsItem();
+
+    void update(dxvk::high_resolution_clock::time_point time);
+
+    HudPos render(
+            HudRenderer&      renderer,
+            HudPos            position);
+
+  private:
+
+    uint32_t                                m_frameCount = 0;
+    dxvk::high_resolution_clock::time_point m_lastUpdate
+      = dxvk::high_resolution_clock::now();
+
+    std::string m_frameRate;
+
+  };
+
 }