Rotate frames correctly for back camera

media/capture/video/linux/camera_characteristics.h

+// Copyright 2016 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.
+
+#ifndef MEDIA_CAPTURE_VIDEO_LINUX_CAMERA_CHARACTERISTICS_H_
+#define MEDIA_CAPTURE_VIDEO_LINUX_CAMERA_CHARACTERISTICS_H_
+
+#include <stddef.h>
+
+#include <string>
+#include <unordered_map>
+
+#include <base/strings/string_piece.h>
+
+namespace media {
+
+// DeviceInfo can be found in /etc/camera/camera_characteristics.conf on device.
+struct CameraDeviceInfo {

[mcasas, 2016/11/29 19:12:56]

Make this struct public inside CameraCharacteristics.

[shenghao, 2016/12/01 07:34:21]

Done.

+  enum class LensFacing { kFront = 0, kBack = 1 };

[mcasas, 2016/11/29 19:12:56]

Enum members should be uppercase see, e.g. [1]
and not have the leading "k".

[1]
https://cs.chromium.org/chromium/src/content/browser/service_worker/service_w...

[kcwu, 2016/11/30 03:04:53]

FYI, chromium's style guide explicitly override the general style guide for enum
naming.
https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md

[shenghao, 2016/12/01 07:34:21]

Done.

+  static const LensFacing kLensFacingDefault = LensFacing::kFront;
+  // USB vender id and product id in "pid:vid" format.
+  std::string vid_pid;

[mcasas, 2016/11/29 19:12:56]

This member is unused.

[shenghao, 2016/12/01 07:34:21]

Done.

+  // Direction the camera faces relative to device screen.
+  LensFacing lens_facing;

[mcasas, 2016/11/29 19:12:56]

This member is unused.

[shenghao, 2016/12/01 07:34:21]

Done.

+};
+
+// CameraCharacteristics reads the file /etc/camera/camera_characteristics.conf

[mcasas, 2016/11/29 19:12:56]

I wonder if this file format is public or is specific for CrOs.
If the former, we should link to its documentation, but
if the latter, then these 2 files should have the suffix
 _chromeos.h (e.g. [1]), so they're pulled out of builds
automatically.

[1]
https://cs.chromium.org/chromium/src/media/capture/video/linux/video_capture_...

[shenghao, 2016/12/01 07:34:21]

Done.

+// and populates |camera_id_to_facing_|, |usb_id_to_camera_id_| and
+// |model_id_to_camera_id_|.
+//
+// Each line in the config file can be:
+// 1. Empty line
+// 2. Line starts with '#': comments
+// 3. Line follows the format:
+// camera[camera_id].[root_level_attribute]=[value] OR
+// camera[camera_id].module[module_id].[module_level_attribute]=[value]
+//
+// There are several assumptions of the config file:
+//  1. One camera ID has exactly one lens_facing attribute, at root level.
+//  2. usb_path is specified at module level. usb_path may not present at all,
+//  but if it presents, the same usb_path does not appear accross different
+//  camera IDs.
+//  3. usb_vid_pid is specified at module level. If usb_path does not present,
+//  each module needs to have one unique usb_vid_pid.
+//
+// Example of the config file:
+//  camera0.lens_facing=0
+//  camera0.sensor_orientation=0
+//  camera0.module0.usb_vid_pid=0123:4567
+//  camera0.module0.horizontal_view_angle=68.4
+//  camera0.module0.lens_info_available_focal_lengths=1.64
+//  camera0.module0.lens_info_minimum_focus_distance=0.22
+//  camera0.module0.lens_info_optimal_focus_distance=0.5
+//  camera0.module0.vertical_view_angle=41.6
+//  camera0.module1.usb_vid_pid=89ab:cdef
+//  camera0.module1.lens_info_available_focal_lengths=1.69,2
+//  camera1.lens_facing=1
+//  camera1.sensor_orientation=180
+class CameraCharacteristics {

[mcasas, 2016/11/29 19:12:56]

This class is now only used for parsing a file to extract 
and keep camera lens facing info, so the name isn't 
accurate. I propose calling it LensFacing or CameraFacing
or similar. Following my comment before, 
CameraDeviceInfo should  be inside this class, but 
CameraFacing::CameraDeviceInfo would be too verbose 
a name, so just change it to CameraFacing::DeviceInfo
or such.


On further thoughts, you don't seem to use the member
fields of said Struct, so just remove it, move the enum
class (corrected) to inside this class and hold on to the
values as you do now in l.82 |camera_id_to_facing_|.

[shenghao, 2016/12/01 07:34:21]

Done.

+ public:
+  CameraCharacteristics();
+  ~CameraCharacteristics();
+
+  // Get camera facing by specifying USB vid and pid and device path. |model_id|
+  // should be formatted as "vid:pid". |device_id| is something like
+  // "/dev/video2". It first tries to match usb path, obtained from |device_id|.
+  // If fails, |model_id| is then used.
+  // Returns CameraDeviceInfo::LensFacing::kFacingFront or
+  // CameraDeviceInfo::LensFacing::kFacingBack.
+  // Default is CameraDeviceInfo::LensFacing::kFacingFront.
+  CameraDeviceInfo::LensFacing GetCameraFacing(
+      const std::string& device_id,
+      const std::string& model_id) const;
+
+ private:
+  std::string GetUsbId(const std::string& device_id) const;
+  bool GetCameraId(const base::StringPiece& sub_key, int* camera_id);
+  // Read file content and populate |camera_id_to_facing_|,
+  // |usb_id_to_camera_id_| and |model_id_to_camera_id_|.
+  void InitializeDeviceInfo();
+
+  std::unordered_map<int, CameraDeviceInfo::LensFacing> camera_id_to_facing_;
+  std::unordered_map<std::string, int> usb_id_to_camera_id_;
+  std::unordered_map<std::string, int> model_id_to_camera_id_;
+};
+
+}  // namespace arc
+
+#endif  // MEDIA_CAPTURE_VIDEO_LINUX_CAMERA_CHARACTERISTICS_H_