content/browser/device_orientation/accelerometer_mac.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/browser/device_orientation/accelerometer_mac.h"
   6
   7 #include <math.h>
   8
   9 #include "base/logging.h"
  10 #include "content/browser/device_orientation/orientation.h"
  11 #include "third_party/sudden_motion_sensor/sudden_motion_sensor_mac.h"
  12
  13 namespace content {
  14
  15 // Create a AccelerometerMac object and return NULL if no valid sensor found.
  16 DataFetcher* AccelerometerMac::Create() {
  17   scoped_ptr<AccelerometerMac> accelerometer(new AccelerometerMac);
  18   return accelerometer->Init() ? accelerometer.release() : NULL;
  19 }
  20
  21 AccelerometerMac::~AccelerometerMac() {
  22 }
  23
  24 AccelerometerMac::AccelerometerMac() {
  25 }
  26
  27 const DeviceData* AccelerometerMac::GetDeviceData(DeviceData::Type type) {
  28   if (type != DeviceData::kTypeOrientation)
  29     return NULL;
  30   return GetOrientation();
  31 }
  32
  33 //  Retrieve per-axis orientation values.
  34 //
  35 //  Axes and angles are defined according to the W3C DeviceOrientation Draft.
  36 //  See here: http://dev.w3.org/geo/api/spec-source-orientation.html
  37 //
  38 //  Note: only beta and gamma angles are provided. Alpha is set to zero.
  39 //
  40 //  Returns false in case of error.
  41 //
  42 const Orientation* AccelerometerMac::GetOrientation() {
  43   DCHECK(sudden_motion_sensor_.get());
  44
  45   // Retrieve per-axis calibrated values.
  46   float axis_value[3];
  47   if (!sudden_motion_sensor_->ReadSensorValues(axis_value))
  48     return NULL;
  49
  50   // Transform the accelerometer values to W3C draft angles.
  51   //
  52   // Accelerometer values are just dot products of the sensor axes
  53   // by the gravity vector 'g' with the result for the z axis inverted.
  54   //
  55   // To understand this transformation calculate the 3rd row of the z-x-y
  56   // Euler angles rotation matrix (because of the 'g' vector, only 3rd row
  57   // affects to the result). Note that z-x-y matrix means R = Ry * Rx * Rz.
  58   // Then, assume alpha = 0 and you get this:
  59   //
  60   // x_acc = sin(gamma)
  61   // y_acc = - cos(gamma) * sin(beta)
  62   // z_acc = cos(beta) * cos(gamma)
  63   //
  64   // After that the rest is just a bit of trigonometry.
  65   //
  66   // Also note that alpha can't be provided but it's assumed to be always zero.
  67   // This is necessary in order to provide enough information to solve
  68   // the equations.
  69   //
  70   const double kRad2deg = 180.0 / M_PI;
  71
  72   scoped_refptr<Orientation> orientation(new Orientation());
  73
  74   orientation->set_beta(kRad2deg * atan2(-axis_value[1], axis_value[2]));
  75   orientation->set_gamma(kRad2deg * asin(axis_value[0]));
  76   // TODO(aousterh): should absolute_ be set to false here?
  77   // See crbug.com/136010.
  78
  79   // Make sure that the interval boundaries comply with the specification. At
  80   // this point, beta is [-180, 180] and gamma is [-90, 90], but the spec has
  81   // the upper bound open on both.
  82   if (orientation->beta() == 180.0) {
  83     orientation->set_beta(-180.0);  // -180 == 180 (upside-down)
  84   }
  85   if (orientation->gamma() == 90.0) {
  86     static double just_less_than_90 = nextafter(90, 0);
  87     orientation->set_gamma(just_less_than_90);
  88   }
  89
  90   // At this point, DCHECKing is paranoia. Never hurts.
  91   DCHECK_GE(orientation->beta(), -180.0);
  92   DCHECK_LT(orientation->beta(),  180.0);
  93   DCHECK_GE(orientation->gamma(), -90.0);
  94   DCHECK_LT(orientation->gamma(),  90.0);
  95
  96   orientation->AddRef();
  97   return orientation.get();
  98 }
  99
 100 bool AccelerometerMac::Init() {
 101   sudden_motion_sensor_.reset(SuddenMotionSensor::Create());
 102   return sudden_motion_sensor_.get() != NULL;
 103 }
 104
 105 }  // namespace content