src/com/android/settings/wifi/qrcode/QrCamera.java - platform/packages/apps/Settings - Git at Google

 /*
  * Copyright (C) 2018 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License
  */

 package com.android.settings.wifi.qrcode;

 import android.content.Context;
 import android.content.res.Configuration;
 import android.graphics.Matrix;
 import android.graphics.Rect;
 import android.graphics.SurfaceTexture;
 import android.hardware.Camera;
 import android.hardware.Camera.CameraInfo;
 import android.hardware.Camera.Parameters;
 import android.os.AsyncTask;
 import android.os.Handler;
 import android.os.Message;
 import android.util.ArrayMap;
 import android.util.Log;
 import android.util.Size;
 import android.view.Surface;
 import android.view.WindowManager;

 import androidx.annotation.VisibleForTesting;

 import com.google.zxing.BarcodeFormat;
 import com.google.zxing.BinaryBitmap;
 import com.google.zxing.DecodeHintType;
 import com.google.zxing.MultiFormatReader;
 import com.google.zxing.ReaderException;
 import com.google.zxing.Result;
 import com.google.zxing.common.HybridBinarizer;

 import java.io.IOException;
 import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Semaphore;

 /**
  * Manage the camera for the QR scanner and help the decoder to get the image inside the scanning
  * frame. Caller prepares a {@link SurfaceTexture} then call {@link #start(SurfaceTexture)} to
  * start QR Code scanning. The scanning result will return by ScannerCallback interface. Caller
  * can also call {@link #stop()} to halt QR Code scanning before the result returned.
  */
 public class QrCamera extends Handler {
     private static final String TAG = "QrCamera";

     private static final int MSG_AUTO_FOCUS = 1;

     /**
      * The max allowed difference between picture size ratio and preview size ratio.
      * Uses to filter the picture sizes of similar preview size ratio, for example, if a preview
      * size is 1920x1440, MAX_RATIO_DIFF 0.1 could allow picture size of 720x480 or 352x288 or
      * 176x44 but not 1920x1080.
      */
     private static final double MAX_RATIO_DIFF = 0.1;

     private static final long AUTOFOCUS_INTERVAL_MS = 1500L;

     private static Map<DecodeHintType, List<BarcodeFormat>> HINTS = new ArrayMap<>();
     private static List<BarcodeFormat> FORMATS = new ArrayList<>();

     static {
         FORMATS.add(BarcodeFormat.QR_CODE);
         HINTS.put(DecodeHintType.POSSIBLE_FORMATS, FORMATS);
     }

     @VisibleForTesting
     Camera mCamera;
     private Size mPreviewSize;
     private WeakReference<Context> mContext;
     private ScannerCallback mScannerCallback;
     private MultiFormatReader mReader;
     private DecodingTask mDecodeTask;
     private int mCameraOrientation;
     @VisibleForTesting
     Camera.Parameters mParameters;

     public QrCamera(Context context, ScannerCallback callback) {
         mContext =  new WeakReference<Context>(context);
         mScannerCallback = callback;
         mReader = new MultiFormatReader();
         mReader.setHints(HINTS);
     }

     /**
      * The function start camera preview and capture pictures to decode QR code continuously in a
      * background task.
      *
      * @param surface The surface to be used for live preview.
      */
     public void start(SurfaceTexture surface) {
         if (mDecodeTask == null) {
             mDecodeTask = new DecodingTask(surface);
             // Execute in the separate thread pool to prevent block other AsyncTask.
             mDecodeTask.executeOnExecutor(Executors.newSingleThreadExecutor());
         }
     }

     /**
      * The function stop camera preview and background decode task. Caller call this function when
      * the surface is being destroyed.
      */
     public void stop() {
         removeMessages(MSG_AUTO_FOCUS);
         if (mDecodeTask != null) {
             mDecodeTask.cancel(true);
             mDecodeTask = null;
         }
         if (mCamera != null) {
             mCamera.stopPreview();
         }
     }

     /** The scanner which includes this QrCamera class should implement this */
     public interface ScannerCallback {

         /**
          * The function used to handle the decoding result of the QR code.
          *
          * @param result the result QR code after decoding.
          */
         void handleSuccessfulResult(String result);

         /** Request the QR code scanner to handle the failure happened. */
         void handleCameraFailure();

         /**
          * The function used to get the background View size.
          *
          * @return Includes the background view size.
          */
         Size getViewSize();

         /**
          * The function used to get the frame position inside the view
          *
          * @param previewSize Is the preview size set by camera
          * @param cameraOrientation Is the orientation of current Camera
          * @return The rectangle would like to crop from the camera preview shot.
          */
         Rect getFramePosition(Size previewSize, int cameraOrientation);

         /**
          * Sets the transform to associate with preview area.
          *
          * @param transform The transform to apply to the content of preview
          */
         void setTransform(Matrix transform);

         /**
          * Verify QR code is valid or not. The camera will stop scanning if this callback returns
          * true.
          *
          * @param qrCode The result QR code after decoding.
          * @return Returns true if qrCode hold valid information.
          */
         boolean isValid(String qrCode);
     }

     @VisibleForTesting
     void setCameraParameter() {
         mParameters = mCamera.getParameters();
         mPreviewSize = getBestPreviewSize(mParameters);
         mParameters.setPreviewSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
         Size pictureSize = getBestPictureSize(mParameters);
         mParameters.setPictureSize(pictureSize.getWidth(), pictureSize.getHeight());

         final List<String> supportedFlashModes = mParameters.getSupportedFlashModes();
         if (supportedFlashModes != null &&
                 supportedFlashModes.contains(Parameters.FLASH_MODE_OFF)) {
             mParameters.setFlashMode(Parameters.FLASH_MODE_OFF);
         }

         final List<String> supportedFocusModes = mParameters.getSupportedFocusModes();
         if (supportedFocusModes.contains(Parameters.FOCUS_MODE_CONTINUOUS_PICTURE)) {
             mParameters.setFocusMode(Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
         } else if (supportedFocusModes.contains(Parameters.FOCUS_MODE_AUTO)) {
             mParameters.setFocusMode(Parameters.FOCUS_MODE_AUTO);
         }
         mCamera.setParameters(mParameters);
     }

     private boolean startPreview() {
         if (mContext.get() == null) {
             return false;
         }

         final WindowManager winManager =
                 (WindowManager) mContext.get().getSystemService(Context.WINDOW_SERVICE);
         final int rotation = winManager.getDefaultDisplay().getRotation();
         int degrees = 0;
         switch (rotation) {
             case Surface.ROTATION_0:
                 degrees = 0;
                 break;
             case Surface.ROTATION_90:
                 degrees = 90;
                 break;
             case Surface.ROTATION_180:
                 degrees = 180;
                 break;
             case Surface.ROTATION_270:
                 degrees = 270;
                 break;
         }
         final int rotateDegrees = (mCameraOrientation - degrees + 360) % 360;
         mCamera.setDisplayOrientation(rotateDegrees);
         mCamera.startPreview();
         if (Parameters.FOCUS_MODE_AUTO.equals(mParameters.getFocusMode())) {
             mCamera.autoFocus(/* Camera.AutoFocusCallback */ null);
             sendMessageDelayed(obtainMessage(MSG_AUTO_FOCUS), AUTOFOCUS_INTERVAL_MS);
         }
         return true;
     }

     private class DecodingTask extends AsyncTask<Void, Void, String> {
         private QrYuvLuminanceSource mImage;
         private SurfaceTexture mSurface;

         private DecodingTask(SurfaceTexture surface) {
             mSurface = surface;
         }

         @Override
         protected String doInBackground(Void... tmp) {
             if (!initCamera(mSurface)) {
                 return null;
             }

             final Semaphore imageGot = new Semaphore(0);
             while (true) {
                 // This loop will try to capture preview image continuously until a valid QR Code
                 // decoded. The caller can also call {@link #stop()} to interrupts scanning loop.
                 mCamera.setOneShotPreviewCallback(
                         (imageData, camera) -> {
                             mImage = getFrameImage(imageData);
                             imageGot.release();
                         });
                 try {
                     // Semaphore.acquire() blocking until permit is available, or the thread is
                     // interrupted.
                     imageGot.acquire();
                     Result qrCode = null;
                     try {
                         qrCode =
                                 mReader.decodeWithState(
                                         new BinaryBitmap(new HybridBinarizer(mImage)));
                     } catch (ReaderException e) {
                         // No logging since every time the reader cannot decode the
                         // image, this ReaderException will be thrown.
                     } finally {
                         mReader.reset();
                     }
                     if (qrCode != null) {
                         if (mScannerCallback.isValid(qrCode.getText())) {
                             return qrCode.getText();
                         }
                     }
                 } catch (InterruptedException e) {
                     Thread.currentThread().interrupt();
                     return null;
                 }
             }
         }

         @Override
         protected void onPostExecute(String qrCode) {
             if (qrCode != null) {
                 mScannerCallback.handleSuccessfulResult(qrCode);
             }
         }

         private boolean initCamera(SurfaceTexture surface) {
             final int numberOfCameras = Camera.getNumberOfCameras();
             Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
             try {
                 for (int i = 0; i < numberOfCameras; ++i) {
                     Camera.getCameraInfo(i, cameraInfo);
                     if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) {
                         releaseCamera();
                         mCamera = Camera.open(i);
                         mCameraOrientation = cameraInfo.orientation;
                         break;
                     }
                 }
                 if (mCamera == null && numberOfCameras > 0) {
                     Log.i(TAG, "Can't find back camera. Opening a different camera");
                     Camera.getCameraInfo(0, cameraInfo);
                     releaseCamera();
                     mCamera = Camera.open(0);
                     mCameraOrientation = cameraInfo.orientation;
                 }
             } catch (RuntimeException e) {
                 Log.e(TAG, "Fail to open camera: " + e);
                 mCamera = null;
                 mScannerCallback.handleCameraFailure();
                 return false;
             }

             try {
                 if (mCamera == null) {
                     throw new IOException("Cannot find available camera");
                 }
                 mCamera.setPreviewTexture(surface);
                 setCameraParameter();
                 setTransformationMatrix();
                 if (!startPreview()) {
                     throw new IOException("Lost contex");
                 }
             } catch (IOException ioe) {
                 Log.e(TAG, "Fail to startPreview camera: " + ioe);
                 mCamera = null;
                 mScannerCallback.handleCameraFailure();
                 return false;
             }
             return true;
         }
     }

     private void releaseCamera() {
         if (mCamera != null) {
             mCamera.release();
             mCamera = null;
         }
     }

     /** Set transform matrix to crop and center the preview picture */
     private void setTransformationMatrix() {
         final boolean isPortrait = mContext.get().getResources().getConfiguration().orientation
                 == Configuration.ORIENTATION_PORTRAIT;

         final int previewWidth = isPortrait ? mPreviewSize.getWidth() : mPreviewSize.getHeight();
         final int previewHeight = isPortrait ? mPreviewSize.getHeight() : mPreviewSize.getWidth();
         final float ratioPreview = (float) getRatio(previewWidth, previewHeight);

         // Calculate transformation matrix.
         float scaleX = 1.0f;
         float scaleY = 1.0f;
         if (previewWidth > previewHeight) {
             scaleY = scaleX / ratioPreview;
         } else {
             scaleX = scaleY / ratioPreview;
         }

         // Set the transform matrix.
         final Matrix matrix = new Matrix();
         matrix.setScale(scaleX, scaleY);
         mScannerCallback.setTransform(matrix);
     }

     private QrYuvLuminanceSource getFrameImage(byte[] imageData) {
         final Rect frame = mScannerCallback.getFramePosition(mPreviewSize, mCameraOrientation);
         final QrYuvLuminanceSource image = new QrYuvLuminanceSource(imageData,
                 mPreviewSize.getWidth(), mPreviewSize.getHeight());
         return (QrYuvLuminanceSource)
                 image.crop(frame.left, frame.top, frame.width(), frame.height());
     }

     @Override
     public void handleMessage(Message msg) {
         switch (msg.what) {
             case MSG_AUTO_FOCUS:
                 // Calling autoFocus(null) will only trigger the camera to focus once. In order
                 // to make the camera continuously auto focus during scanning, need to periodically
                 // trigger it.
                 mCamera.autoFocus(/* Camera.AutoFocusCallback */ null);
                 sendMessageDelayed(obtainMessage(MSG_AUTO_FOCUS), AUTOFOCUS_INTERVAL_MS);
                 break;
             default:
                 Log.d(TAG, "Unexpected Message: " + msg.what);
         }
     }

     /** Get best preview size from the list of camera supported preview sizes. Compares the
      * preview size and aspect ratio to choose the best one. */
     private Size getBestPreviewSize(Camera.Parameters parameters) {
         final double minRatioDiffPercent = 0.1;
         final Size windowSize = mScannerCallback.getViewSize();
         final double winRatio = getRatio(windowSize.getWidth(), windowSize.getHeight());
         double bestChoiceRatio = 0;
         Size bestChoice = new Size(0, 0);
         for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
             double ratio = getRatio(size.width, size.height);
             if (size.height * size.width > bestChoice.getWidth() * bestChoice.getHeight()
                     && (Math.abs(bestChoiceRatio - winRatio) / winRatio > minRatioDiffPercent
                     || Math.abs(ratio - winRatio) / winRatio <= minRatioDiffPercent)) {
                 bestChoice = new Size(size.width, size.height);
                 bestChoiceRatio = getRatio(size.width, size.height);
             }
         }
         return bestChoice;
     }

     /** Get best picture size from the list of camera supported picture sizes. Compares the
      *  picture size and aspect ratio to choose the best one. */
     private Size getBestPictureSize(Camera.Parameters parameters) {
         final Camera.Size previewSize = parameters.getPreviewSize();
         final double previewRatio = getRatio(previewSize.width, previewSize.height);
         List<Size> bestChoices = new ArrayList<>();
         final List<Size> similarChoices = new ArrayList<>();

         // Filter by ratio
         for (Camera.Size size : parameters.getSupportedPictureSizes()) {
             double ratio = getRatio(size.width, size.height);
             if (ratio == previewRatio) {
                 bestChoices.add(new Size(size.width, size.height));
             } else if (Math.abs(ratio - previewRatio) < MAX_RATIO_DIFF) {
                 similarChoices.add(new Size(size.width, size.height));
             }
         }

         if (bestChoices.size() == 0 && similarChoices.size() == 0) {
             Log.d(TAG, "No proper picture size, return default picture size");
             Camera.Size defaultPictureSize = parameters.getPictureSize();
             return new Size(defaultPictureSize.width, defaultPictureSize.height);
         }

         if (bestChoices.size() == 0) {
             bestChoices = similarChoices;
         }

         // Get the best by area
         int bestAreaDifference = Integer.MAX_VALUE;
         Size bestChoice = null;
         final int previewArea = previewSize.width * previewSize.height;
         for (Size size : bestChoices) {
             int areaDifference = Math.abs(size.getWidth() * size.getHeight() - previewArea);
             if (areaDifference < bestAreaDifference) {
                 bestAreaDifference = areaDifference;
                 bestChoice = size;
             }
         }
         return bestChoice;
     }

     private double getRatio(double x, double y) {
         return (x < y) ? x / y : y / x;
     }

     @VisibleForTesting
     protected void decodeImage(BinaryBitmap image) {
         Result qrCode = null;

         try {
             qrCode = mReader.decodeWithState(image);
         } catch (ReaderException e) {
         } finally {
             mReader.reset();
         }

         if (qrCode != null) {
             mScannerCallback.handleSuccessfulResult(qrCode.getText());
         }
     }

     /**
      * After {@link #start(SurfaceTexture)}, DecodingTask runs continuously to capture images and
      * decode QR code. DecodingTask become null After {@link #stop()}.
      *
      * Uses this method in test case to prevent power consumption problem.
      */
     public boolean isDecodeTaskAlive() {
         return mDecodeTask != null;
     }
 }
	/*
	* Copyright (C) 2018 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License
	*/

	package com.android.settings.wifi.qrcode;

	import android.content.Context;
	import android.content.res.Configuration;
	import android.graphics.Matrix;
	import android.graphics.Rect;
	import android.graphics.SurfaceTexture;
	import android.hardware.Camera;
	import android.hardware.Camera.CameraInfo;
	import android.hardware.Camera.Parameters;
	import android.os.AsyncTask;
	import android.os.Handler;
	import android.os.Message;
	import android.util.ArrayMap;
	import android.util.Log;
	import android.util.Size;
	import android.view.Surface;
	import android.view.WindowManager;

	import androidx.annotation.VisibleForTesting;

	import com.google.zxing.BarcodeFormat;
	import com.google.zxing.BinaryBitmap;
	import com.google.zxing.DecodeHintType;
	import com.google.zxing.MultiFormatReader;
	import com.google.zxing.ReaderException;
	import com.google.zxing.Result;
	import com.google.zxing.common.HybridBinarizer;

	import java.io.IOException;
	import java.lang.ref.WeakReference;
	import java.util.ArrayList;
	import java.util.List;
	import java.util.Map;
	import java.util.concurrent.Executors;
	import java.util.concurrent.Semaphore;

	/**
	* Manage the camera for the QR scanner and help the decoder to get the image inside the scanning
	* frame. Caller prepares a {@link SurfaceTexture} then call {@link #start(SurfaceTexture)} to
	* start QR Code scanning. The scanning result will return by ScannerCallback interface. Caller
	* can also call {@link #stop()} to halt QR Code scanning before the result returned.
	*/
	public class QrCamera extends Handler {
	private static final String TAG = "QrCamera";

	private static final int MSG_AUTO_FOCUS = 1;

	/**
	* The max allowed difference between picture size ratio and preview size ratio.
	* Uses to filter the picture sizes of similar preview size ratio, for example, if a preview
	* size is 1920x1440, MAX_RATIO_DIFF 0.1 could allow picture size of 720x480 or 352x288 or
	* 176x44 but not 1920x1080.
	*/
	private static final double MAX_RATIO_DIFF = 0.1;

	private static final long AUTOFOCUS_INTERVAL_MS = 1500L;

	private static Map<DecodeHintType, List<BarcodeFormat>> HINTS = new ArrayMap<>();
	private static List<BarcodeFormat> FORMATS = new ArrayList<>();

	static {
	FORMATS.add(BarcodeFormat.QR_CODE);
	HINTS.put(DecodeHintType.POSSIBLE_FORMATS, FORMATS);
	}

	@VisibleForTesting
	Camera mCamera;
	private Size mPreviewSize;
	private WeakReference<Context> mContext;
	private ScannerCallback mScannerCallback;
	private MultiFormatReader mReader;
	private DecodingTask mDecodeTask;
	private int mCameraOrientation;
	@VisibleForTesting
	Camera.Parameters mParameters;

	public QrCamera(Context context, ScannerCallback callback) {
	mContext = new WeakReference<Context>(context);
	mScannerCallback = callback;
	mReader = new MultiFormatReader();
	mReader.setHints(HINTS);
	}

	/**
	* The function start camera preview and capture pictures to decode QR code continuously in a
	* background task.
	*
	* @param surface The surface to be used for live preview.
	*/
	public void start(SurfaceTexture surface) {
	if (mDecodeTask == null) {
	mDecodeTask = new DecodingTask(surface);
	// Execute in the separate thread pool to prevent block other AsyncTask.
	mDecodeTask.executeOnExecutor(Executors.newSingleThreadExecutor());
	}
	}

	/**
	* The function stop camera preview and background decode task. Caller call this function when
	* the surface is being destroyed.
	*/
	public void stop() {
	removeMessages(MSG_AUTO_FOCUS);
	if (mDecodeTask != null) {
	mDecodeTask.cancel(true);
	mDecodeTask = null;
	}
	if (mCamera != null) {
	mCamera.stopPreview();
	}
	}

	/** The scanner which includes this QrCamera class should implement this */
	public interface ScannerCallback {

	/**
	* The function used to handle the decoding result of the QR code.
	*
	* @param result the result QR code after decoding.
	*/
	void handleSuccessfulResult(String result);

	/** Request the QR code scanner to handle the failure happened. */
	void handleCameraFailure();

	/**
	* The function used to get the background View size.
	*
	* @return Includes the background view size.
	*/
	Size getViewSize();

	/**
	* The function used to get the frame position inside the view
	*
	* @param previewSize Is the preview size set by camera
	* @param cameraOrientation Is the orientation of current Camera
	* @return The rectangle would like to crop from the camera preview shot.
	*/
	Rect getFramePosition(Size previewSize, int cameraOrientation);

	/**
	* Sets the transform to associate with preview area.
	*
	* @param transform The transform to apply to the content of preview
	*/
	void setTransform(Matrix transform);

	/**
	* Verify QR code is valid or not. The camera will stop scanning if this callback returns
	* true.
	*
	* @param qrCode The result QR code after decoding.
	* @return Returns true if qrCode hold valid information.
	*/
	boolean isValid(String qrCode);
	}

	@VisibleForTesting
	void setCameraParameter() {
	mParameters = mCamera.getParameters();
	mPreviewSize = getBestPreviewSize(mParameters);
	mParameters.setPreviewSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
	Size pictureSize = getBestPictureSize(mParameters);
	mParameters.setPictureSize(pictureSize.getWidth(), pictureSize.getHeight());

	final List<String> supportedFlashModes = mParameters.getSupportedFlashModes();
	if (supportedFlashModes != null &&
	supportedFlashModes.contains(Parameters.FLASH_MODE_OFF)) {
	mParameters.setFlashMode(Parameters.FLASH_MODE_OFF);
	}

	final List<String> supportedFocusModes = mParameters.getSupportedFocusModes();
	if (supportedFocusModes.contains(Parameters.FOCUS_MODE_CONTINUOUS_PICTURE)) {
	mParameters.setFocusMode(Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
	} else if (supportedFocusModes.contains(Parameters.FOCUS_MODE_AUTO)) {
	mParameters.setFocusMode(Parameters.FOCUS_MODE_AUTO);
	}
	mCamera.setParameters(mParameters);
	}

	private boolean startPreview() {
	if (mContext.get() == null) {
	return false;
	}

	final WindowManager winManager =
	(WindowManager) mContext.get().getSystemService(Context.WINDOW_SERVICE);
	final int rotation = winManager.getDefaultDisplay().getRotation();
	int degrees = 0;
	switch (rotation) {
	case Surface.ROTATION_0:
	degrees = 0;
	break;
	case Surface.ROTATION_90:
	degrees = 90;
	break;
	case Surface.ROTATION_180:
	degrees = 180;
	break;
	case Surface.ROTATION_270:
	degrees = 270;
	break;
	}
	final int rotateDegrees = (mCameraOrientation - degrees + 360) % 360;
	mCamera.setDisplayOrientation(rotateDegrees);
	mCamera.startPreview();
	if (Parameters.FOCUS_MODE_AUTO.equals(mParameters.getFocusMode())) {
	mCamera.autoFocus(/* Camera.AutoFocusCallback */ null);
	sendMessageDelayed(obtainMessage(MSG_AUTO_FOCUS), AUTOFOCUS_INTERVAL_MS);
	}
	return true;
	}

	private class DecodingTask extends AsyncTask<Void, Void, String> {
	private QrYuvLuminanceSource mImage;
	private SurfaceTexture mSurface;

	private DecodingTask(SurfaceTexture surface) {
	mSurface = surface;
	}

	@Override
	protected String doInBackground(Void... tmp) {
	if (!initCamera(mSurface)) {
	return null;
	}

	final Semaphore imageGot = new Semaphore(0);
	while (true) {
	// This loop will try to capture preview image continuously until a valid QR Code
	// decoded. The caller can also call {@link #stop()} to interrupts scanning loop.
	mCamera.setOneShotPreviewCallback(
	(imageData, camera) -> {
	mImage = getFrameImage(imageData);
	imageGot.release();
	});
	try {
	// Semaphore.acquire() blocking until permit is available, or the thread is
	// interrupted.
	imageGot.acquire();
	Result qrCode = null;
	try {
	qrCode =
	mReader.decodeWithState(
	new BinaryBitmap(new HybridBinarizer(mImage)));
	} catch (ReaderException e) {
	// No logging since every time the reader cannot decode the
	// image, this ReaderException will be thrown.
	} finally {
	mReader.reset();
	}
	if (qrCode != null) {
	if (mScannerCallback.isValid(qrCode.getText())) {
	return qrCode.getText();
	}
	}
	} catch (InterruptedException e) {
	Thread.currentThread().interrupt();
	return null;
	}
	}
	}

	@Override
	protected void onPostExecute(String qrCode) {
	if (qrCode != null) {
	mScannerCallback.handleSuccessfulResult(qrCode);
	}
	}

	private boolean initCamera(SurfaceTexture surface) {
	final int numberOfCameras = Camera.getNumberOfCameras();
	Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
	try {
	for (int i = 0; i < numberOfCameras; ++i) {
	Camera.getCameraInfo(i, cameraInfo);
	if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) {
	releaseCamera();
	mCamera = Camera.open(i);
	mCameraOrientation = cameraInfo.orientation;
	break;
	}
	}
	if (mCamera == null && numberOfCameras > 0) {
	Log.i(TAG, "Can't find back camera. Opening a different camera");
	Camera.getCameraInfo(0, cameraInfo);
	releaseCamera();
	mCamera = Camera.open(0);
	mCameraOrientation = cameraInfo.orientation;
	}
	} catch (RuntimeException e) {
	Log.e(TAG, "Fail to open camera: " + e);
	mCamera = null;
	mScannerCallback.handleCameraFailure();
	return false;
	}

	try {
	if (mCamera == null) {
	throw new IOException("Cannot find available camera");
	}
	mCamera.setPreviewTexture(surface);
	setCameraParameter();
	setTransformationMatrix();
	if (!startPreview()) {
	throw new IOException("Lost contex");
	}
	} catch (IOException ioe) {
	Log.e(TAG, "Fail to startPreview camera: " + ioe);
	mCamera = null;
	mScannerCallback.handleCameraFailure();
	return false;
	}
	return true;
	}
	}

	private void releaseCamera() {
	if (mCamera != null) {
	mCamera.release();
	mCamera = null;
	}
	}

	/** Set transform matrix to crop and center the preview picture */
	private void setTransformationMatrix() {
	final boolean isPortrait = mContext.get().getResources().getConfiguration().orientation
	== Configuration.ORIENTATION_PORTRAIT;

	final int previewWidth = isPortrait ? mPreviewSize.getWidth() : mPreviewSize.getHeight();
	final int previewHeight = isPortrait ? mPreviewSize.getHeight() : mPreviewSize.getWidth();
	final float ratioPreview = (float) getRatio(previewWidth, previewHeight);

	// Calculate transformation matrix.
	float scaleX = 1.0f;
	float scaleY = 1.0f;
	if (previewWidth > previewHeight) {
	scaleY = scaleX / ratioPreview;
	} else {
	scaleX = scaleY / ratioPreview;
	}

	// Set the transform matrix.
	final Matrix matrix = new Matrix();
	matrix.setScale(scaleX, scaleY);
	mScannerCallback.setTransform(matrix);
	}

	private QrYuvLuminanceSource getFrameImage(byte[] imageData) {
	final Rect frame = mScannerCallback.getFramePosition(mPreviewSize, mCameraOrientation);
	final QrYuvLuminanceSource image = new QrYuvLuminanceSource(imageData,
	mPreviewSize.getWidth(), mPreviewSize.getHeight());
	return (QrYuvLuminanceSource)
	image.crop(frame.left, frame.top, frame.width(), frame.height());
	}

	@Override
	public void handleMessage(Message msg) {
	switch (msg.what) {
	case MSG_AUTO_FOCUS:
	// Calling autoFocus(null) will only trigger the camera to focus once. In order
	// to make the camera continuously auto focus during scanning, need to periodically
	// trigger it.
	mCamera.autoFocus(/* Camera.AutoFocusCallback */ null);
	sendMessageDelayed(obtainMessage(MSG_AUTO_FOCUS), AUTOFOCUS_INTERVAL_MS);
	break;
	default:
	Log.d(TAG, "Unexpected Message: " + msg.what);
	}
	}

	/** Get best preview size from the list of camera supported preview sizes. Compares the
	* preview size and aspect ratio to choose the best one. */
	private Size getBestPreviewSize(Camera.Parameters parameters) {
	final double minRatioDiffPercent = 0.1;
	final Size windowSize = mScannerCallback.getViewSize();
	final double winRatio = getRatio(windowSize.getWidth(), windowSize.getHeight());
	double bestChoiceRatio = 0;
	Size bestChoice = new Size(0, 0);
	for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
	double ratio = getRatio(size.width, size.height);
	if (size.height * size.width > bestChoice.getWidth() * bestChoice.getHeight()
	&& (Math.abs(bestChoiceRatio - winRatio) / winRatio > minRatioDiffPercent
	\|\| Math.abs(ratio - winRatio) / winRatio <= minRatioDiffPercent)) {
	bestChoice = new Size(size.width, size.height);
	bestChoiceRatio = getRatio(size.width, size.height);
	}
	}
	return bestChoice;
	}

	/** Get best picture size from the list of camera supported picture sizes. Compares the
	* picture size and aspect ratio to choose the best one. */
	private Size getBestPictureSize(Camera.Parameters parameters) {
	final Camera.Size previewSize = parameters.getPreviewSize();
	final double previewRatio = getRatio(previewSize.width, previewSize.height);
	List<Size> bestChoices = new ArrayList<>();
	final List<Size> similarChoices = new ArrayList<>();

	// Filter by ratio
	for (Camera.Size size : parameters.getSupportedPictureSizes()) {
	double ratio = getRatio(size.width, size.height);
	if (ratio == previewRatio) {
	bestChoices.add(new Size(size.width, size.height));
	} else if (Math.abs(ratio - previewRatio) < MAX_RATIO_DIFF) {
	similarChoices.add(new Size(size.width, size.height));
	}
	}

	if (bestChoices.size() == 0 && similarChoices.size() == 0) {
	Log.d(TAG, "No proper picture size, return default picture size");
	Camera.Size defaultPictureSize = parameters.getPictureSize();
	return new Size(defaultPictureSize.width, defaultPictureSize.height);
	}

	if (bestChoices.size() == 0) {
	bestChoices = similarChoices;
	}

	// Get the best by area
	int bestAreaDifference = Integer.MAX_VALUE;
	Size bestChoice = null;
	final int previewArea = previewSize.width * previewSize.height;
	for (Size size : bestChoices) {
	int areaDifference = Math.abs(size.getWidth() * size.getHeight() - previewArea);
	if (areaDifference < bestAreaDifference) {
	bestAreaDifference = areaDifference;
	bestChoice = size;
	}
	}
	return bestChoice;
	}

	private double getRatio(double x, double y) {
	return (x < y) ? x / y : y / x;
	}

	@VisibleForTesting
	protected void decodeImage(BinaryBitmap image) {
	Result qrCode = null;

	try {
	qrCode = mReader.decodeWithState(image);
	} catch (ReaderException e) {
	} finally {
	mReader.reset();
	}

	if (qrCode != null) {
	mScannerCallback.handleSuccessfulResult(qrCode.getText());
	}
	}

	/**
	* After {@link #start(SurfaceTexture)}, DecodingTask runs continuously to capture images and
	* decode QR code. DecodingTask become null After {@link #stop()}.
	*
	* Uses this method in test case to prevent power consumption problem.
	*/
	public boolean isDecodeTaskAlive() {
	return mDecodeTask != null;
	}
	}