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

src/kivy_garden/zbarcam/zbarcam.py

@@ -1,5 +1,7 @@
+import collections
 import os
-from collections import namedtuple
+import queue
+import threading
 
 import PIL
 from kivy.clock import Clock
@@ -21,7 +23,7 @@ class ZBarCam(AnchorLayout):
     resolution = ListProperty([640, 480])
 
     symbols = ListProperty([])
-    Symbol = namedtuple('Symbol', ['type', 'data'])
+    Symbol = collections.namedtuple('Symbol', ['type', 'data'])
     # checking all possible types by default
     code_types = ListProperty(set(pyzbar.ZBarSymbol))
 
@@ -30,6 +32,10 @@ def __init__(self, **kwargs):
         # that way the `XCamera` import doesn't happen too early
         Builder.load_file(os.path.join(MODULE_DIRECTORY, "zbarcam.kv"))
         super().__init__(**kwargs)
+
+        self._decoding_frame = threading.Event()
+        self._symbols_queue = queue.Queue()
+
         Clock.schedule_once(lambda dt: self._setup())
 
     def _setup(self):
@@ -49,6 +55,7 @@ def _on_camera_ready(self, xcamera):
         Starts binding when the `xcamera._camera` instance is ready.
         """
         xcamera._camera.bind(on_texture=self._on_texture)
+        Clock.schedule_interval(self._update_symbols, 0)
 
     def _remove_shoot_button(self):
         """
@@ -59,13 +66,32 @@ 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._threaded_detect_qrcode_frame,
+                args=(
+                    xcamera.texture,
+                    xcamera.texture.pixels,
+                    self.code_types,
+                ),
+            ).start()
+
+    def _threaded_detect_qrcode_frame(self, texture, pixels, code_types):
+        self._symbols_queue.put(
+            self._detect_qrcode_frame(texture, code_types, pixels)
+        )
+        self._decoding_frame.clear()
 
-    @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, code_types, pixels=None):
+        image_data = pixels or texture.pixels  # Use pixels kwarg for threading
         size = texture.size
         # Fix for mode mismatch between texture.colorfmt and data returned by
         # texture.pixels. texture.pixels always returns RGBA, so that should
@@ -76,9 +102,11 @@ 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
 
     @property

tests/kivy_garden/zbarcam/test_zbarcam.py

@@ -4,6 +4,7 @@
 
 from kivy.base import EventLoop
 from kivy.core.image import Image
+
 from kivy_garden.zbarcam import ZBarCam
 
 FIXTURE_DIR = os.path.join(