Device Orientation API on Chrome OS

content/browser/device_sensors/sensor_manager_chromeos.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.

[timvolodine, 2015/01/26 15:29:07]

nit: 2015?

[jonross, 2015/01/26 16:40:04]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/device_sensors/sensor_manager_chromeos.h"
+
+#include "base/logging.h"
+#include "chromeos/accelerometer/accelerometer_reader.h"
+#include "ui/gfx/geometry/vector3d_f.h"
+
+namespace {
+// Conversion ratio from radians to degrees.
+const double kRad2deg = 180.0 / M_PI;
+}
+
+namespace content {
+
+SensorManagerChromeOS::SensorManagerChromeOS() : orientation_buffer_(nullptr) {
+}
+
+SensorManagerChromeOS::~SensorManagerChromeOS() {
+}
+
+bool SensorManagerChromeOS::StartFetchingDeviceOrientationData(
+    DeviceOrientationHardwareBuffer* buffer) {
+  DCHECK(buffer);

[timvolodine, 2015/01/26 15:29:07]

what happens if StartFetchingDeviceOrientationData is called twice in
succession? maybe return early when orientation_buffer_ is not null (like in
Stop)?

[jonross, 2015/01/26 16:40:04]

Done.

+  {
+    base::AutoLock autolock(orientation_buffer_lock_);
+    orientation_buffer_ = buffer;
+
+    // No compass information, so we cannot provide absolute orientation.
+    orientation_buffer_->seqlock.WriteBegin();
+    orientation_buffer_->data.absolute = false;
+    orientation_buffer_->data.hasAbsolute = true;
+    orientation_buffer_->seqlock.WriteEnd();
+  }
+
+  StartObservingAccelerometer();
+  return true;
+}
+
+bool SensorManagerChromeOS::StopFetchingDeviceOrientationData() {
+  base::AutoLock autolock(orientation_buffer_lock_);

[timvolodine, 2015/01/26 15:29:07]

nit: do you need a lock to hold over the whole body? i.e. can
StopObservingAccelerometer be placed outside the lock?

[jonross, 2015/01/26 16:40:04]

Done.

+  if (!orientation_buffer_)
+    return false;
+  // Make sure to indicate that the sensor data is no longer available.
+  orientation_buffer_->seqlock.WriteBegin();
+  orientation_buffer_->data.allAvailableSensorsAreActive = false;
+  orientation_buffer_->seqlock.WriteEnd();
+  orientation_buffer_ = nullptr;
+
+  StopObservingAccelerometer();
+  return true;
+}
+
+void SensorManagerChromeOS::OnAccelerometerUpdated(
+    const ui::AccelerometerUpdate& update) {
+  base::AutoLock autolock(orientation_buffer_lock_);
+  if (!orientation_buffer_)
+    return;
+
+  ui::AccelerometerSource source;
+  if (update.has(ui::ACCELEROMETER_SOURCE_SCREEN)) {
+    source = ui::ACCELEROMETER_SOURCE_SCREEN;
+  } else if (update.has(ui::ACCELEROMETER_SOURCE_ATTACHED_KEYBOARD)) {
+    source = ui::ACCELEROMETER_SOURCE_ATTACHED_KEYBOARD;
+  } else {
+    return;
+  }
+
+  double x = update.get(source).x();
+  double y = update.get(source).y();
+  double z = update.get(source).z();
+
+  // Create a unit vector for trigonometry
+  // TODO(jonross): Stop reversing signs for vector components once
+  // accelerometer values have been fixed. crbug.com/431391
+  // Ternaries are to remove -0.0f which gives incorrect trigonometrical
+  // results.
+  gfx::Vector3dF data(x, y ? -y : 0.0f, z ? -z : 0.0f);
+  data.Scale(1.0f / data.Length());
+
+  // Transform accelerometer to W3C angles, using the Z-X-Y Eulerangles matrix.
+  // x = sin(gamma)
+  // y = -cos(gamma) * sin(beta)
+  // z = cos(beta) * cos(gamma)
+  // With only accelerometer alpha cannot be provided.
+  double beta = kRad2deg * atan2(data.y(), data.z());
+  double gamma = kRad2deg * asin(data.x());
+
+  // Convert beta and gamma to fit the intervals in the specification. Beta is
+  // [-180, 180) and gamma is [-90, 90).
+  if (beta >= 180.0f)
+    beta = -180.0f;
+  if (gamma >= 90.0f)
+    gamma = -90.0f;
+  orientation_buffer_->seqlock.WriteBegin();
+  orientation_buffer_->data.beta = beta;
+  orientation_buffer_->data.hasBeta = true;
+  orientation_buffer_->data.gamma = gamma;
+  orientation_buffer_->data.hasGamma = true;
+  orientation_buffer_->data.allAvailableSensorsAreActive = true;
+  orientation_buffer_->seqlock.WriteEnd();
+}
+
+void SensorManagerChromeOS::StartObservingAccelerometer() {
+  chromeos::AccelerometerReader::GetInstance()->AddObserver(this);
+}
+
+void SensorManagerChromeOS::StopObservingAccelerometer() {
+  chromeos::AccelerometerReader::GetInstance()->RemoveObserver(this);
+}
+
+}  // namespace content