feat(perf): Implement Input Lag estimation logic

gui.py

@@ -1698,6 +1698,11 @@ class App:
             )
 
     def _build_ui(self):
+        # Performance tracking handlers
+        with dpg.handler_registry():
+            dpg.add_mouse_click_handler(callback=lambda: self.perf_monitor.record_input_event())
+            dpg.add_key_press_handler(callback=lambda: self.perf_monitor.record_input_event())
+
         with dpg.viewport_menu_bar():
             with dpg.menu(label="Windows"):
                 for label, tag in self.window_info.items():

performance_monitor.py

@@ -13,6 +13,10 @@ class PerformanceMonitor:
         self._cpu_usage = 0.0
         self._cpu_lock = threading.Lock()
         
+        # Input lag tracking
+        self._last_input_time = None
+        self._input_lag_ms = 0.0
+        
         # Start CPU usage monitoring thread
         self._stop_event = threading.Event()
         self._cpu_thread = threading.Thread(target=self._monitor_cpu, daemon=True)
@@ -29,6 +33,9 @@ class PerformanceMonitor:
     def start_frame(self):
         self._start_time = time.time()
 
+    def record_input_event(self):
+        self._last_input_time = time.time()
+
     def end_frame(self):
         if self._start_time is None:
             return
@@ -37,6 +44,11 @@ class PerformanceMonitor:
         self._last_frame_time = (end_time - self._start_time) * 1000.0
         self._frame_count += 1
         
+        # Calculate input lag if an input occurred during this frame
+        if self._last_input_time is not None:
+            self._input_lag_ms = (end_time - self._last_input_time) * 1000.0
+            self._last_input_time = None
+        
         elapsed_since_fps = end_time - self._fps_last_time
         if elapsed_since_fps >= 1.0:
             self._fps = self._frame_count / elapsed_since_fps
@@ -50,7 +62,8 @@ class PerformanceMonitor:
         return {
             'last_frame_time_ms': self._last_frame_time,
             'fps': self._fps,
-            'cpu_percent': cpu_usage
+            'cpu_percent': cpu_usage,
+            'input_lag_ms': self._input_lag_ms
         }
 
     def stop(self):

tests/test_performance_monitor.py

@@ -23,5 +23,15 @@ class TestPerformanceMonitor(unittest.TestCase):
         self.assertIn('cpu_percent', metrics)
         self.assertIsInstance(metrics['cpu_percent'], float)
 
+    def test_input_lag_collection(self):
+        self.monitor.start_frame()
+        self.monitor.record_input_event()
+        time.sleep(0.02)  # 20ms lag
+        self.monitor.end_frame()
+        
+        metrics = self.monitor.get_metrics()
+        self.assertGreaterEqual(metrics['input_lag_ms'], 20)
+        self.assertLess(metrics['input_lag_ms'], 40)
+
 if __name__ == '__main__':
     unittest.main()