import com.google.zxing.client.android.camera.open.CameraFacing; //导入依赖的package包/类
/**
 * Reads, one time, values from the camera that are needed by the app.
 */
void initFromCameraParameters(OpenCamera camera) {
    Camera.Parameters parameters = camera.getCamera().getParameters();
    WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    Display display = manager.getDefaultDisplay();

    int displayRotation = display.getRotation();
    int cwRotationFromNaturalToDisplay;
    switch (displayRotation) {
        case Surface.ROTATION_0:
            cwRotationFromNaturalToDisplay = 0;
            break;
        case Surface.ROTATION_90:
            cwRotationFromNaturalToDisplay = 90;
            break;
        case Surface.ROTATION_180:
            cwRotationFromNaturalToDisplay = 180;
            break;
        case Surface.ROTATION_270:
            cwRotationFromNaturalToDisplay = 270;
            break;
        default:
            // Have seen this return incorrect values like -90
            if (displayRotation % 90 == 0) {
                cwRotationFromNaturalToDisplay = (360 + displayRotation) % 360;
            } else {
                throw new IllegalArgumentException("Bad rotation: " + displayRotation);
            }
    }
    Log.i(TAG, "Display at: " + cwRotationFromNaturalToDisplay);

    int cwRotationFromNaturalToCamera = camera.getOrientation();
    Log.i(TAG, "Camera at: " + cwRotationFromNaturalToCamera);

    // Still not 100% sure about this. But acts like we need to flip this:
    if (camera.getFacing() == CameraFacing.FRONT) {
        cwRotationFromNaturalToCamera = (360 - cwRotationFromNaturalToCamera) % 360;
        Log.i(TAG, "Front camera overriden to: " + cwRotationFromNaturalToCamera);
    }

    cwRotationFromDisplayToCamera =
            (360 + cwRotationFromNaturalToCamera - cwRotationFromNaturalToDisplay) % 360;
    Log.i(TAG, "Final display orientation: " + cwRotationFromDisplayToCamera);
    if (camera.getFacing() == CameraFacing.FRONT) {
        Log.i(TAG, "Compensating rotation for front camera");
        cwNeededRotation = (360 - cwRotationFromDisplayToCamera) % 360;
    } else {
        cwNeededRotation = cwRotationFromDisplayToCamera;
    }
    Log.i(TAG, "Clockwise rotation from display to camera: " + cwNeededRotation);

    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);
    }
    Log.i(TAG, "Preview size on screen: " + previewSizeOnScreen);
}