Implement java-side browser sensor polling for device motion and device orientation DOM events.

content/public/android/java/src/org/chromium/content/browser/DeviceOrientation.java

-// Copyright (c) 2012 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.
-
-package org.chromium.content.browser;
-
-import android.content.Context;
-import android.hardware.Sensor;
-import android.hardware.SensorEvent;
-import android.hardware.SensorEventListener;
-import android.hardware.SensorManager;
-import android.os.Handler;
-import android.os.Looper;
-
-import org.chromium.base.CalledByNative;
-import org.chromium.base.JNINamespace;
-import org.chromium.base.WeakContext;
-
-import java.util.List;
-
-/**
- * Android implementation of the DeviceOrientation API.
- */
-@JNINamespace("content")
-class DeviceOrientation implements SensorEventListener {
-
-    // These fields are lazily initialized by getHandler().
-    private Thread mThread;
-    private Handler mHandler;
-
-    // The lock to access the mHandler.
-    private Object mHandlerLock = new Object();
-
-    // Non-zero if and only if we're listening for events.
-    // To avoid race conditions on the C++ side, access must be synchronized.
-    private int mNativePtr;
-
-    // The lock to access the mNativePtr.
-    private Object mNativePtrLock = new Object();
-
-    // The gravity vector expressed in the body frame.
-    private float[] mGravityVector;
-
-    // The geomagnetic vector expressed in the body frame.
-    private float[] mMagneticFieldVector;
-
-    // Lazily initialized when registering for notifications.
-    private SensorManager mSensorManager;
-
-    // The only instance of that class and its associated lock.
-    private static DeviceOrientation sSingleton;
-    private static Object sSingletonLock = new Object();
-
-    private DeviceOrientation() {
-    }
-
-    /**
-     * Start listening for sensor events. If this object is already listening
-     * for events, the old callback is unregistered first.
-     *
-     * @param nativePtr Value to pass to nativeGotOrientation() for each event.
-     * @param rateInMilliseconds Requested callback rate in milliseconds. The
-     *            actual rate may be higher. Unwanted events should be ignored.
-     * @return True on success.
-     */
-    @CalledByNative
-    public boolean start(int nativePtr, int rateInMilliseconds) {
-        synchronized (mNativePtrLock) {
-            stop();
-            if (registerForSensors(rateInMilliseconds)) {
-                mNativePtr = nativePtr;
-                return true;
-            }
-            return false;
-        }
-    }
-
-    /**
-     * Stop listening for sensor events. Always succeeds.
-     *
-     * We strictly guarantee that nativeGotOrientation() will not be called
-     * after this method returns.
-     */
-    @CalledByNative
-    public void stop() {
-        synchronized (mNativePtrLock) {
-            if (mNativePtr != 0) {
-                mNativePtr = 0;
-                unregisterForSensors();
-            }
-        }
-    }
-
-    @Override
-    public void onAccuracyChanged(Sensor sensor, int accuracy) {
-        // Nothing
-    }
-
-    @Override
-    public void onSensorChanged(SensorEvent event) {
-        switch (event.sensor.getType()) {
-            case Sensor.TYPE_ACCELEROMETER:
-                if (mGravityVector == null) {
-                    mGravityVector = new float[3];
-                }
-                System.arraycopy(event.values, 0, mGravityVector, 0, mGravityVector.length);
-                break;
-
-            case Sensor.TYPE_MAGNETIC_FIELD:
-                if (mMagneticFieldVector == null) {
-                    mMagneticFieldVector = new float[3];
-                }
-                System.arraycopy(event.values, 0, mMagneticFieldVector, 0,
-                                 mMagneticFieldVector.length);
-                break;
-
-            default:
-                // Unexpected
-                return;
-        }
-
-        getOrientationUsingGetRotationMatrix();
-    }
-
-    void getOrientationUsingGetRotationMatrix() {
-        if (mGravityVector == null || mMagneticFieldVector == null) {
-            return;
-        }
-
-        // Get the rotation matrix.
-        // The rotation matrix that transforms from the body frame to the earth
-        // frame.
-        float[] deviceRotationMatrix = new float[9];
-        if (!SensorManager.getRotationMatrix(deviceRotationMatrix, null, mGravityVector,
-                mMagneticFieldVector)) {
-            return;
-        }
-
-        // Convert rotation matrix to rotation angles.
-        // Assuming that the rotations are appied in the order listed at
-        // http://developer.android.com/reference/android/hardware/SensorEvent.html#values
-        // the rotations are applied about the same axes and in the same order as required by the
-        // API. The only conversions are sign changes as follows.  The angles are in radians
-
-        float[] rotationAngles = new float[3];
-        SensorManager.getOrientation(deviceRotationMatrix, rotationAngles);
-
-        double alpha = Math.toDegrees(-rotationAngles[0]);
-        while (alpha < 0.0) {
-            alpha += 360.0; // [0, 360)
-        }
-
-        double beta = Math.toDegrees(-rotationAngles[1]);
-        while (beta < -180.0) {
-            beta += 360.0; // [-180, 180)
-        }
-
-        double gamma = Math.toDegrees(rotationAngles[2]);
-        while (gamma < -90.0) {
-            gamma += 360.0; // [-90, 90)
-        }
-
-        gotOrientation(alpha, beta, gamma);
-    }
-
-    boolean registerForSensors(int rateInMilliseconds) {
-        if (registerForSensorType(Sensor.TYPE_ACCELEROMETER, rateInMilliseconds)
-                && registerForSensorType(Sensor.TYPE_MAGNETIC_FIELD, rateInMilliseconds)) {
-            return true;
-        }
-        unregisterForSensors();
-        return false;
-    }
-
-    private SensorManager getSensorManager() {
-        if (mSensorManager != null) {
-            return mSensorManager;
-        }
-        mSensorManager = (SensorManager)WeakContext.getSystemService(Context.SENSOR_SERVICE);
-        return mSensorManager;
-    }
-
-    void unregisterForSensors() {
-        SensorManager sensorManager = getSensorManager();
-        if (sensorManager == null) {
-            return;
-        }
-        sensorManager.unregisterListener(this);
-    }
-
-    boolean registerForSensorType(int type, int rateInMilliseconds) {
-        SensorManager sensorManager = getSensorManager();
-        if (sensorManager == null) {
-            return false;
-        }
-        List<Sensor> sensors = sensorManager.getSensorList(type);
-        if (sensors.isEmpty()) {
-            return false;
-        }
-
-        final int rateInMicroseconds = 1000 * rateInMilliseconds;
-        // We want to err on the side of getting more events than we need.
-        final int requestedRate = rateInMicroseconds / 2;
-
-        // TODO(steveblock): Consider handling multiple sensors.
-        return sensorManager.registerListener(this, sensors.get(0), requestedRate, getHandler());
-    }
-
-    void gotOrientation(double alpha, double beta, double gamma) {
-        synchronized (mNativePtrLock) {
-            if (mNativePtr != 0) {
-              nativeGotOrientation(mNativePtr, alpha, beta, gamma);
-            }
-        }
-    }
-
-    private Handler getHandler() {
-        synchronized (mHandlerLock) {
-            // If we don't have a background thread, start it now.
-            if (mThread == null) {
-                mThread = new Thread(new Runnable() {
-                    @Override
-                    public void run() {
-                        Looper.prepare();
-                        // Our Handler doesn't actually have to do anything, because
-                        // SensorManager posts directly to the underlying Looper.
-                        setHandler(new Handler());
-                        Looper.loop();
-                    }
-                });
-                mThread.start();
-            }
-            // Wait for the background thread to spin up.
-            while (mHandler == null) {
-                try {
-                    mHandlerLock.wait();
-                } catch (InterruptedException e) {
-                    // Somebody doesn't want us to wait! That's okay, SensorManager accepts null.
-                    return null;
-                }
-            }
-            return mHandler;
-        }
-    }
-
-    private void setHandler(Handler handler) {
-        synchronized (mHandlerLock) {
-            mHandler = handler;
-            mHandlerLock.notify();
-        }
-    }
-
-    @CalledByNative
-    private static DeviceOrientation getInstance() {
-        synchronized (sSingletonLock) {
-            if (sSingleton == null) {
-                sSingleton = new DeviceOrientation();
-            }
-            return sSingleton;
-        }
-    }
-
-    /**
-     * See chrome/browser/device_orientation/data_fetcher_impl_android.cc
-     */
-    private native void nativeGotOrientation(
-            int nativeDataFetcherImplAndroid,
-            double alpha, double beta, double gamma);
-}