DeviceOrientation API on ChromeOS

content/browser/device_sensors/sensor_manager_chromeos.cc

+// Copyright 2014 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.
+
+#include "content/browser/device_sensors/sensor_manager_chromeos.h"
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/memory/singleton.h"
+#include "content/public/browser/sensor_manager_delegate.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::GetInstance() {
+  return Singleton<SensorManagerChromeOS,
+                   LeakySingletonTraits<SensorManagerChromeOS>>::get();
+}
+
+bool SensorManagerChromeOS::StartFetchingDeviceOrientationData(
+    DeviceOrientationHardwareBuffer* buffer) {
+  DCHECK(buffer);
+  if (!SensorManagerDelegate::HasInstance())
+    return false;
+
+  {
+    // Lock must be released before providing the callback to prevent potential
+    // deadlock.
+    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();
+  }
+
+  base::Callback<void(double, double, double)> callback = base::Bind(
+      &SensorManagerChromeOS::OnAccelerationIncludingGravity, callback_ref_);
+  SensorManagerDelegate::GetInstance()->StartFetchingDeviceOrientationData(
+      callback);
+
+  return true;
+}
+
+void SensorManagerChromeOS::StopFetchingDeviceOrientationData() {
+  if (!SensorManagerDelegate::HasInstance())
+    return;
+  SensorManagerDelegate::GetInstance()->StopFetchingDeviceOrientationData();
+  base::AutoLock autolock(orientation_buffer_lock_);
+  if (!orientation_buffer_)
+    return;
+  // Null message to signify that sensors are no longer available
+  orientation_buffer_->seqlock.WriteBegin();
+  orientation_buffer_->data.allAvailableSensorsAreActive = false;
+  orientation_buffer_->seqlock.WriteEnd();
+  orientation_buffer_ = nullptr;
+}
+
+SensorManagerChromeOS::~SensorManagerChromeOS() {
+}
+
+SensorManagerChromeOS::SensorManagerChromeOS()
+    : orientation_buffer_(nullptr), callback_ref_(this) {
+}
+
+void SensorManagerChromeOS::OnAccelerationIncludingGravity(double x,
+                                                           double y,
+                                                           double z) {
+  base::AutoLock autolock(orientation_buffer_lock_);
+  if (!orientation_buffer_)
+    return;
+  // Create a unit vector to remove gravity.

[flackr, 2014/11/13 00:07:34]

Did you mean for a TODO? It doesn't look like gravity's being removed.

[jonross, 2014/11/13 01:34:05]

Poor comment, as this smooths out all acceleration. The unit vector was to
simply the trig.

+  // TODO(jonross): Stop reversing signs for vector components once
+  // accelerometer values have been reversed.
+  gfx::Vector3dF data(x, y ? -y : 0.0f, z ? -z : 0.0f);

[flackr, 2014/11/13 00:07:34]

Isn't this just the following? (i.e. why the ternary's?)
gfx::Vector3dF data(x, -y, -z);

[jonross, 2014/11/13 01:34:05]

Comment added, as -0.0f messed up trig

+  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());
+
+  // Have the interval boundaries comply with the specification. Beta is

[flackr, 2014/11/13 00:07:34]

nit: Convert beta and gamma to fit the intervals in specification.

[jonross, 2014/11/13 01:34:05]

Done.

+  // [-180,180) and gamma is [-90, 90).

[flackr, 2014/11/13 00:07:34]

nit: [-180, 180)

[jonross, 2014/11/13 01:34:05]

Done.

+  if (beta >= 180.0f)
+    beta = -180.0f;
+  if (gamma >= 90.0f)
+    gamma = -90.0f;
+  orientation_buffer_->seqlock.WriteBegin();

[flackr, 2014/11/13 00:07:34]

Should we be moving this to accelerometer_reader.cc to avoid passing values
through the UI thread? Maybe a TODO.

[jonross, 2014/11/13 01:34:05]

TODO added

+  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();
+}
+
+}  // namespace content