Rotate frames correctly for back camera

media/capture/video/linux/camera_facing_chromeos.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_FACING_CHROMEOS_H_
+#define MEDIA_CAPTURE_VIDEO_LINUX_CAMERA_FACING_CHROMEOS_H_
+
+#include <stddef.h>
+
+#include <string>
+#include <unordered_map>
+
+#include <base/strings/string_piece.h>
+
+namespace media {
+
+// CameraFacingChromeOS reads the file /etc/camera/camera_characteristics.conf
+// 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 CameraFacingChromeOS {
+ public:
+  enum LensFacing { FRONT = 0, BACK = 1 };
+
+  CameraFacingChromeOS();
+  CameraFacingChromeOS(const std::string& config_file_path);
+  ~CameraFacingChromeOS();
+
+  // 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 LensFacing::FRONT or LensFacing::BACK.
+  // Default is LensFacing::FRONT.
+  LensFacing GetCameraFacing(const std::string& device_id,
+                             const std::string& model_id) const;
+
+  static const LensFacing kLensFacingDefault = LensFacing::FRONT;
+
+ private:
+  std::string GetUsbId(const std::string& device_id) const;
+  // Read file content and populate |camera_id_to_facing_|,
+  // |usb_id_to_camera_id_| and |model_id_to_camera_id_|.
+  void InitializeDeviceInfo(const std::string& config_file_path);
+
+  std::unordered_map<int, 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 media
+
+#endif  // MEDIA_CAPTURE_VIDEO_LINUX_CAMERA_FACING_CHROMEOS_H_