added event-loop callback

ocv_rpicam.py

@@ -1,9 +1,11 @@
 #!/usr/bin/env python3
 from typing import Union, overload
-from picamera2 import Picamera2
+from picamera2 import Picamera2, MappedArray
 from pprint import pprint
 import json
 import cv2
+import time
+
 #import numpy as np
 #import argparse
 #import sys
@@ -73,6 +75,16 @@ def set_value(item: str, value):
 def get_value(item: str):
     return picam2.camera_controls[item]
     
+def process(request):
+    colour = (0, 255, 0)
+    origin = (0, 30)
+    font = cv2.FONT_HERSHEY_SIMPLEX
+    scale = 1
+    thickness = 2
+    timestamp = time.strftime("%Y-%m-%d %X")
+    with MappedArray(request, "main") as m:
+        cv2.putText(m.array, timestamp, origin, font, scale, colour, thickness)
+
 if __name__ == '__main__':
     for item in items:
         try:
@@ -97,6 +109,7 @@ if __name__ == '__main__':
     pprint(f"Camera config: {picam2.camera_configuration()}")
 
     # Start
+    picam2.pre_callback = process
     picam2.start()
     
     while True: