Sometimes we want to adjust the preview direction of Camera according to our own needs. Which API can we call to achieve our goal?

Let's take a look at some cute photos taken in the following picture, which are taken in normal direction, 180 degree rotation and 90 degree rotation.

(normal direction) (rotate 180 °) (rotate 90 °)

1, Camera API

On Camera1, we can set the direction of camera preview through setdisplay orientation (int degree).

mCamera.setDisplayOrientation(Surface.ROTATION_180);

Here is also a detailed description of the setDisplayOrientaion interface in the source code.

 /**
     * Set the clockwise rotation of preview display in degrees. This affects
     * the preview frames and the picture displayed after snapshot. This method
     * is useful for portrait mode applications. Note that preview display of
     * front-facing cameras is flipped horizontally before the rotation, that
     * is, the image is reflected along the central vertical axis of the camera
     * sensor. So the users can see themselves as looking into a mirror.
     *
     * <p>This does not affect the order of byte array passed in {@link
     * PreviewCallback#onPreviewFrame}, JPEG pictures, or recorded videos. This
     * method is not allowed to be called during preview.
     *
     * <p>If you want to make the camera image show in the same orientation as
     * the display, you can use the following code.
     * <pre>
     * public static void setCameraDisplayOrientation(Activity activity,
     *         int cameraId, android.hardware.Camera camera) {
     *     android.hardware.Camera.CameraInfo info =
     *             new android.hardware.Camera.CameraInfo();
     *     android.hardware.Camera.getCameraInfo(cameraId, info);
     *     int rotation = activity.getWindowManager().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;
     *     }
     *
     *     int result;
     *     if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
     *         result = (info.orientation + degrees) % 360;
     *         result = (360 - result) % 360;  // compensate the mirror
     *     } else {  // back-facing
     *         result = (info.orientation - degrees + 360) % 360;
     *     }
     *     camera.setDisplayOrientation(result);
     * }
     * </pre>
     *
     * <p>Starting from API level 14, this method can be called when preview is
     * active.
     *
     * <p><b>Note: </b>Before API level 24, the default value for orientation is 0. Starting in
     * API level 24, the default orientation will be such that applications in forced-landscape mode
     * will have correct preview orientation, which may be either a default of 0 or
     * 180. Applications that operate in portrait mode or allow for changing orientation must still
     * call this method after each orientation change to ensure correct preview display in all
     * cases.</p>
     *
     * @param degrees the angle that the picture will be rotated clockwise.
     *                Valid values are 0, 90, 180, and 270.
     * @throws RuntimeException if setting orientation fails; usually this would
     *    be because of a hardware or other low-level error, or because
     *    release() has been called on this Camera instance.
     * @see #setPreviewDisplay(SurfaceHolder)
     */
    public native final void setDisplayOrientation(int degrees);

2, Camera2 API

On the API of Camera2, I found that the preview direction can be set through a similar interface, but it can be achieved by adjusting the display of textureView through TextureView.setTransform(matrix).

  public void openCamera(){
    	CameraManager manager = (CameraManager) mContext.getSystemService(Context.CAMERA_SERVICE);
        try {
           ......
//Adjust the display direction of preview screen
configureTextureViewTransform(mTextureView.getWidth(),mTextureView.getHeight());
            manager.openCamera(cameraId, mStateCallback, null);
           ......
        }
}

private void configureTextureViewTransform(int viewWidth, int viewHeight) {
        if (null == mTextureView) {
            return;
        }
        int rotation = 0 ;/*activity.getWindowManager().getDefaultDisplay().getRotation();*/
        Matrix matrix = new Matrix();
        RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
        RectF bufferRect = new RectF(0, 0, mPreviewSize.getHeight(), mPreviewSize.getWidth());
        float centerX = viewRect.centerX();
        float centerY = viewRect.centerY();
        if (Surface.ROTATION_90 == rotation || Surface.ROTATION_270 == rotation) {
            bufferRect.offset(centerX - bufferRect.centerX(), centerY - bufferRect.centerY());
            matrix.setRectToRect(viewRect, bufferRect, Matrix.ScaleToFit.FILL);
            float scale = Math.max(
                    (float) viewHeight / mPreviewSize.getHeight(),
                    (float) viewWidth / mPreviewSize.getWidth());
            matrix.postScale(scale, scale, centerX, centerY);
            matrix.postRotate(90 * (rotation - 2), centerX, centerY);
        }else if (Surface.ROTATION_180 == rotation) {
            matrix.postRotate(180, centerX, centerY);
        }
        mTextureView.setTransform(matrix);
    }

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