camtest: adapt to new api

internal_filesystem/apps/com.example.camtest/assets/camtest.py

@@ -95,7 +95,7 @@ def qr_button_click(e):
 def try_capture():
     global current_cam_buffer, image_dsc, image, use_webcam
     if use_webcam:
-        new_cam_buffer = webcam.capture_grayscale()
+        new_cam_buffer = cam.capture_grayscale()
     elif cam.frame_available():
         new_cam_buffer = cam.capture()  # Returns memoryview
     if len(new_cam_buffer):
@@ -193,12 +193,23 @@ def init_cam():
         return None
 
 
+import webcam
+
+class Webcam:
+    def __init__(self):
+        # webcam.init() returns (obj, capture_grayscale, deinit)
+        self.obj, self._capture_grayscale, self._deinit = webcam.init()
+    def capture_grayscale(self):
+        return self._capture_grayscale(self.obj)
+    def deinit(self):
+        return self._deinit(self.obj)
+
+
 cam = init_cam()
 if not cam:
     print("init cam failed, retrying with webcam...")
     try:
-        import webcam
-        current_cam_buffer = webcam.capture_grayscale()
+        cam = Webcam()
         use_webcam = True
     except Exception as e:
         print(f"camtest.py: webcam exception: {e}")