Implement BQP Android UI using QR codes

briar-android/src/org/briarproject/android/util/QrCodeDecoder.java

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+package org.briarproject.android.util;
+
+import android.hardware.Camera;
+import android.hardware.Camera.PreviewCallback;
+import android.hardware.Camera.Size;
+import android.os.AsyncTask;
+
+import com.google.zxing.BinaryBitmap;
+import com.google.zxing.LuminanceSource;
+import com.google.zxing.PlanarYUVLuminanceSource;
+import com.google.zxing.Reader;
+import com.google.zxing.ReaderException;
+import com.google.zxing.Result;
+import com.google.zxing.common.HybridBinarizer;
+import com.google.zxing.qrcode.QRCodeReader;
+
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.INFO;
+
+@SuppressWarnings("deprecation")
+public class QrCodeDecoder implements PreviewConsumer, PreviewCallback {
+
+	private static final Logger LOG =
+			Logger.getLogger(QrCodeDecoder.class.getName());
+
+	private final Reader reader = new QRCodeReader();
+	private final ResultCallback callback;
+
+	private boolean stopped = false;
+
+	public QrCodeDecoder(ResultCallback callback) {
+		this.callback = callback;
+	}
+
+	public void start(Camera camera) {
+		stopped = false;
+		askForPreviewFrame(camera);
+	}
+
+	public void stop() {
+		stopped = true;
+	}
+
+	private void askForPreviewFrame(Camera camera) {
+		if (!stopped) camera.setOneShotPreviewCallback(this);
+	}
+
+	public void onPreviewFrame(byte[] data, Camera camera) {
+		if (!stopped) {
+			Size size = camera.getParameters().getPreviewSize();
+			new DecoderTask(camera, data, size.width, size.height).execute();
+		}
+	}
+
+	private class DecoderTask extends AsyncTask<Void, Void, Void> {
+
+		final Camera camera;
+		final byte[] data;
+		final int width, height;
+
+		DecoderTask(Camera camera, byte[] data, int width, int height) {
+			this.camera = camera;
+			this.data = data;
+			this.width = width;
+			this.height = height;
+		}
+
+		@Override
+		protected Void doInBackground(Void... params) {
+			long now = System.currentTimeMillis();
+			LuminanceSource src = new PlanarYUVLuminanceSource(data, width,
+					height, 0, 0, width, height, false);
+			BinaryBitmap bitmap = new BinaryBitmap(new HybridBinarizer(src));
+			Result result = null;
+			try {
+				result = reader.decode(bitmap);
+			} catch (ReaderException e) {
+				return null; // No barcode found
+			} finally {
+				reader.reset();
+			}
+			long duration = System.currentTimeMillis() - now;
+			if (LOG.isLoggable(INFO))
+				LOG.info("Decoding barcode took " + duration + " ms");
+			callback.handleResult(result);
+			return null;
+		}
+
+		@Override
+		protected void onPostExecute(Void result) {
+			askForPreviewFrame(camera);
+		}
+	}
+
+	public interface ResultCallback {
+
+		void handleResult(Result result);
+	}
+}