Implement DeviceMotionEvent API

content/browser/device_sensors/sensor_manager_chromeos.h

 // Copyright 2015 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 CONTENT_BROWSER_DEVICE_SENSORS_SENSOR_MANAGER_CHROMEOS_H_
 #define CONTENT_BROWSER_DEVICE_SENSORS_SENSOR_MANAGER_CHROMEOS_H_
 
 #include "base/macros.h"
 #include "base/synchronization/lock.h"
 #include "chromeos/accelerometer/accelerometer_reader.h"
 #include "chromeos/accelerometer/accelerometer_types.h"
 #include "content/common/content_export.h"
+#include "content/common/device_sensors/device_motion_hardware_buffer.h"
 #include "content/common/device_sensors/device_orientation_hardware_buffer.h"
+#include "ui/gfx/geometry/vector3d_f.h"
 
 namespace content {
 
 // Observes Chrome OS accelerometer sensors, and provides updated device
 // orientation information.
 class CONTENT_EXPORT SensorManagerChromeOS
     : public chromeos::AccelerometerReader::Observer {
  public:
   SensorManagerChromeOS();
   ~SensorManagerChromeOS() override;
 
+  // Begins monitoring of motion events, the shared memory of |buffer| will be
+  // updated upon subsequent events.
+  bool StartFetchingDeviceMotionData(DeviceMotionHardwareBuffer* buffer);
+
+  // Stops monitoring motion events. Returns true if there is an active
+  // |motion_buffer_| and fetching stops. Otherwise returns false.
+  bool StopFetchingDeviceMotionData();
+
   // Begins monitoring of orientation events, the shared memory of |buffer| will
   // be updated upon subsequent events.
   bool StartFetchingDeviceOrientationData(
       DeviceOrientationHardwareBuffer* buffer);
 
   // Stops monitoring orientation events. Returns true if there is an active
   // |orientation_buffer_| and fetching stops. Otherwise returns false.
   bool StopFetchingDeviceOrientationData();
 
   // chromeos::AccelerometerReader::Observer:
   void OnAccelerometerUpdated(
       const chromeos::AccelerometerUpdate& update) override;
 
  protected:
   // Begins/ends the observation of accelerometer events.
   virtual void StartObservingAccelerometer();
   virtual void StopObservingAccelerometer();
 
  private:
+  // Process accelerometer data and update according buffers.

[flackr, 2015/02/18 22:34:09]

Comment is a bit confusing, Perhaps "Updates |motion_buffer_| or
|orientation_buffer_| accordingly."?

[jonross, 2015/02/25 00:09:56]

Done.

+  void GenerateMotionEvent(double x, double y, double z);
+  void GenerateOrientationEvent(double x, double y, double z);
+
   // Shared memory to update.
+  DeviceMotionHardwareBuffer* motion_buffer_;
   DeviceOrientationHardwareBuffer* orientation_buffer_;
 
   // Synchronize orientation_buffer_ across threads.

[flackr, 2015/02/18 22:34:09]

nit: Two comments or convert into a single comment covering both like
"Synchronize buffer updates across threads."

On reading through the code, I don't understand why these locks are necessary.
Is StartFetchingDeviceMotionData not called on the UI thread? If it is,
OnAccelerometerUpdated is also called on the UI thread, so it seems that there
is no risk of motion_buffer_ updating while we're using it. If it's not, I don't
think it's safe to call AccelerometerReader::AddObserver from another thread.

[jonross, 2015/02/25 00:09:56]

StartFetchingDeviceMotionData is called from the IO thread.
OnAccelerometerUpdated is currently called from the UI thread.

However currently AccelerometerReader::AddObserver is not thread safe. An
upcoming patch to this review will address that.

This will have the benefit of performing all notifications to observers on their
calling threads. Thus making these locks redundant.

+  base::Lock motion_buffer_lock_;
   base::Lock orientation_buffer_lock_;
 
+  // The current component of accelerometer data associated to gravity.
+  gfx::Vector3dF gravity_;
+
   DISALLOW_COPY_AND_ASSIGN(SensorManagerChromeOS);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVICE_SENSORS_SENSOR_MANAGER_CHROMEOS_H_