Make QRcode decoding non-blocking by doing it in a thread

src/kivy_garden/zbarcam/zbarcam.py

@@ -1,4 +1,6 @@
 import os
+import threading
+import queue
 from collections import namedtuple
 
 import PIL
@@ -49,6 +51,9 @@ def _on_camera_ready(self, xcamera):
         Starts binding when the `xcamera._camera` instance is ready.
         """
         xcamera._camera.bind(on_texture=self._on_texture)
+        self._decoding_frame = threading.Event()
+        self._symbols_queue = queue.Queue()
+        Clock.schedule_interval(self._update_symbols, 0)
 
     def _remove_shoot_button(self):
         """
@@ -59,13 +64,26 @@ def _remove_shoot_button(self):
         shoot_button = xcamera.children[0]
         xcamera.remove_widget(shoot_button)
 
-    def _on_texture(self, instance):
-        self.symbols = self._detect_qrcode_frame(
-            texture=instance.texture, code_types=self.code_types)
+    def _on_texture(self, xcamera):
+        if not self._decoding_frame.is_set():
+            self._decoding_frame.set()
+            threading.Thread(
+                target=self._detect_qrcode_frame,
+                args=(
+                    xcamera.texture,
+                    xcamera.texture.pixels,
+                    self.code_types,
+                ),
+            ).start()
 
-    @classmethod
-    def _detect_qrcode_frame(cls, texture, code_types):
-        image_data = texture.pixels
+    def _update_symbols(self, *args):
+        try:
+            self.symbols = self._symbols_queue.get_nowait()
+        except queue.Empty:
+            return
+
+    def _detect_qrcode_frame(self, texture, pixels, code_types):
+        image_data = pixels
         size = texture.size
         # Fix for mode mismatch between texture.colorfmt and data returned by
         # texture.pixels. texture.pixels always returns RGBA, so that should
@@ -76,10 +94,13 @@ def _detect_qrcode_frame(cls, texture, code_types):
         pil_image = fix_android_image(pil_image)
         symbols = []
         codes = pyzbar.decode(pil_image, symbols=code_types)
+
         for code in codes:
             symbol = ZBarCam.Symbol(type=code.type, data=code.data)
             symbols.append(symbol)
-        return symbols
+
+        self._symbols_queue.put(symbols)
+        self._decoding_frame.clear()
 
     @property
     def xcamera(self):