Rotate frames correctly for back camera

media/capture/video/linux/video_capture_device_linux.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Linux specific implementation of VideoCaptureDevice.
 // V4L2 is used for capturing. V4L2 does not provide its own thread for
 // capturing so this implementation uses a Chromium thread for fetching frames
 // from V4L2.
 
 #ifndef MEDIA_CAPTURE_VIDEO_LINUX_VIDEO_CAPTURE_DEVICE_LINUX_H_
@@ skipping 32 matching lines @@
   void GetPhotoCapabilities(GetPhotoCapabilitiesCallback callback) override;
   void SetPhotoOptions(mojom::PhotoSettingsPtr settings,
                        SetPhotoOptionsCallback callback) override;
 
  protected:
   void SetRotation(int rotation);
 
  private:
   static int TranslatePowerLineFrequencyToV4L2(PowerLineFrequency frequency);
 
+  // Return true if the camera is back-facing.
+  bool GetCameraFacing(const VideoCaptureDeviceDescriptor& device_descriptor);
+
   // Internal delegate doing the actual capture setting, buffer allocation and
   // circulation with the V4L2 API. Created and deleted in the thread where
   // VideoCaptureDeviceLinux lives but otherwise operating on |v4l2_thread_|.
   scoped_refptr<V4L2CaptureDelegate> capture_impl_;
 
   base::Thread v4l2_thread_;  // Thread used for reading data from the device.
 
   const VideoCaptureDeviceDescriptor device_descriptor_;
 
+  bool is_back_camera_;

[wuchengli, 2016/11/16 12:15:19]

I think we need three states -- back facing, front facing, and unknown (or
external).

[shenghao, 2016/11/17 08:41:44]

But what we really cares is whether it is a back camera. For external and front
camera, we don't need to adjust the rotation value.

[wuchengli, 2016/11/17 09:26:04]

OK. Let's document it then.
// True if the camera is world-facing. False if the camera is user-facing,
external, or unknown.

[shenghao, 2016/11/17 10:15:55]

Done.

+
   DISALLOW_IMPLICIT_CONSTRUCTORS(VideoCaptureDeviceLinux);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_VIDEO_LINUX_VIDEO_CAPTURE_DEVICE_LINUX_H_