ZXing源码解析三：相机的配置与数据的处理2

 Point theScreenResolution = new Point();
    display.getSize(theScreenResolution);
    screenResolution = theScreenResolution;
    Log.i(TAG, "Screen resolution in current orientation: " + screenResolution);
    cameraResolution = CameraConfigurationUtils.findBestPreviewSizeValue(parameters, screenResolution);
    Log.i(TAG, "Camera resolution: " + cameraResolution);
    bestPreviewSize = CameraConfigurationUtils.findBestPreviewSizeValue(parameters, screenResolution);
    Log.i(TAG, "Best available preview size: " + bestPreviewSize);
    boolean isScreenPortrait = screenResolution.x < screenResolution.y;
    boolean isPreviewSizePortrait = bestPreviewSize.x > bestPreviewSize.y;
    if (isScreenPortrait == isPreviewSizePortrait) {
      previewSizeOnScreen = bestPreviewSize;
    } else {
      previewSizeOnScreen = new Point(bestPreviewSize.y, bestPreviewSize.x);
    }

public static Point findBestPreviewSizeValue(Camera.Parameters parameters, Point screenResolution) {
    //获取相机支持的尺寸，手机不同会有不同的值
    List<Camera.Size> rawSupportedSizes = parameters.getSupportedPreviewSizes();
    if (rawSupportedSizes == null) {
      Log.w(TAG, "Device returned no supported preview sizes; using default");
      Camera.Size defaultSize = parameters.getPreviewSize();
      if (defaultSize == null) {
        throw new IllegalStateException("Parameters contained no preview size!");
      }
      return new Point(defaultSize.width, defaultSize.height);
    }
    if (Log.isLoggable(TAG, Log.INFO)) {
      StringBuilder previewSizesString = new StringBuilder();
      for (Camera.Size size : rawSupportedSizes) {
        previewSizesString.append(size.width).append('x').append(size.height).append(' ');
      }
      Log.i(TAG, "Supported preview sizes: " + previewSizesString);
    }
    //这句代码是获取屏幕宽高的比例
    double screenAspectRatio = screenResolution.x / (double) screenResolution.y;
    // Find a suitable size, with max resolution
    int maxResolution = 0;
    Camera.Size maxResPreviewSize = null;
    //for循环的作用是找到相机合适的尺寸和最大的分辨率，这里
    //合适的尺寸指的是和屏幕宽高比相同的尺寸。
    for (Camera.Size size : rawSupportedSizes) {
      int realWidth = size.width;
      int realHeight = size.height;
      int resolution = realWidth * realHeight;
      if (resolution < MIN_PREVIEW_PIXELS) {
        continue;
      }
      boolean isCandidatePortrait = realWidth < realHeight;
      int maybeFlippedWidth = isCandidatePortrait ? realHeight : realWidth;
      int maybeFlippedHeight = isCandidatePortrait ? realWidth : realHeight;
      double aspectRatio = maybeFlippedWidth / (double) maybeFlippedHeight;
      double distortion = Math.abs(aspectRatio - screenAspectRatio);
      if (distortion > MAX_ASPECT_DISTORTION) {
        continue;
      }
    //这句代码是找到与屏幕宽高比一致的尺寸，否则就用相机默认的尺寸
      if (maybeFlippedWidth == screenResolution.x && maybeFlippedHeight == screenResolution.y) {
        Point exactPoint = new Point(realWidth, realHeight);
        Log.i(TAG, "Found preview size exactly matching screen size: " + exactPoint);
        return exactPoint;
      }
      // Resolution is suitable; record the one with max resolution
      if (resolution > maxResolution) {
        maxResolution = resolution;
        maxResPreviewSize = size;
      }
    }
    // If no exact match, use largest preview size. This was not a great idea on older devices because
    // of the additional computation needed. We're likely to get here on newer Android 4+ devices, where
    // the CPU is much more powerful.
    if (maxResPreviewSize != null) {
      Point largestSize = new Point(maxResPreviewSize.width, maxResPreviewSize.height);
      Log.i(TAG, "Using largest suitable preview size: " + largestSize);
      return largestSize;
    }
    // If there is nothing at all suitable, return current preview size
    Camera.Size defaultPreview = parameters.getPreviewSize();
    if (defaultPreview == null) {
      throw new IllegalStateException("Parameters contained no preview size!");
    }
    Point defaultSize = new Point(defaultPreview.width, defaultPreview.height);
    Log.i(TAG, "No suitable preview sizes, using default: " + defaultSize);
    return defaultSize;
  }

@Override
  public void onPreviewFrame(byte[] data, Camera camera) {
    Point cameraResolution = configManager.getCameraResolution();
    Handler thePreviewHandler = previewHandler;
    if (cameraResolution != null && thePreviewHandler != null) {
      Point screenResolution = configManager.getScreenResolution();
      Message message;
      if (screenResolution.x < screenResolution.y){
        // 手机为竖屏时
        message = thePreviewHandler.obtainMessage(previewMessage, cameraResolution.y,
                cameraResolution.x, data);
      } else {
        // 手机为横屏时
        message = thePreviewHandler.obtainMessage(previewMessage, cameraResolution.x,
                cameraResolution.y, data);
      }
      message.sendToTarget();
      previewHandler = null;
    } else {
      Log.d(TAG, "Got preview callback, but no handler or resolution available");
    }

 //将原始图像传感器的数据转换为竖屏
    if (width < height) {
      // portrait
      byte[] rotatedData = new byte[data.length];
      for (int x = 0; x < width; x++) {
        for (int y = 0; y < height; y++)
          rotatedData[y * width + width - x - 1] = data[y + x * height];
      }
      data = rotatedData;
    }