Generic Sensor API : Ambient Light Sensor API.

third_party/WebKit/Source/modules/sensor/AmbientLightSensorDispatcher.cpp

+// Copyright 2016 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 "modules/sensor/AmbientLightSensorDispatcher.h"
+
+#include "platform/MojoHelper.h"
+#include "public/platform/Platform.h"
+#include "public/platform/ServiceRegistry.h"
+#include "wtf/Assertions.h"
+#include "wtf/PassOwnPtr.h"
+
+namespace blink {
+
+AmbientLightSensorDispatcher& AmbientLightSensorDispatcher::instance()
+{
+    DEFINE_STATIC_LOCAL(Persistent<AmbientLightSensorDispatcher>, lightSensorDispatcher, (new AmbientLightSensorDispatcher()));
+    return *lightSensorDispatcher;
+}
+
+AmbientLightSensorDispatcher::AmbientLightSensorDispatcher()
+    : m_hasLatestData(false)
+{
+}
+
+void AmbientLightSensorDispatcher::queryNextReading()
+{
+    m_lightSensor->QueryNextReading(
+        sameThreadBindForMojo(&AmbientLightSensorDispatcher::onDidChange, this));
+}
+
+void AmbientLightSensorDispatcher::startReading()
+{
+    m_lightSensor->StartReading();
+}
+
+void AmbientLightSensorDispatcher::stopReading()
+{
+    m_lightSensor->StopReading();
+}
+
+void AmbientLightSensorDispatcher::onDidChange(device::AmbientLightSensorReadingPtr alsReading)
+{
+    queryNextReading();
+
+    ASSERT(alsReading);
+
+    updateSensorReading(AmbientLightSensorReadingProxy(
+        alsReading->timeStamp, alsReading->illuminance));
+}
+
+void AmbientLightSensorDispatcher::updateSensorReading(const AmbientLightSensorReadingProxy& alsReading)
+{
+    m_alsReading = alsReading;
+    m_hasLatestData = true;
+    notifyControllers();
+}
+
+void AmbientLightSensorDispatcher::startListening()
+{
+    ASSERT(!m_lightSensor.is_bound());
+    Platform::current()->serviceRegistry()->connectToRemoteService(mojo::GetProxy(&m_lightSensor));

[timvolodine, 2016/05/06 17:05:41]

does this mean that for for each blink instance we would have a separate mojo
service? i.e. multiple registrations for 'light sensor' on the platform side. if
so, are there any issues with that?

[riju_, 2016/05/16 16:58:51]

Isn't it the case that even for multiple blink instance of concrete sensors,
there is 1 dispatcher per sensor type ?
I think there is 1 interface_ptr, i.e m_lightSensor for all concrete sensor of
ALS, and if that is bound (connection exists), then we skip registration.

[timvolodine, 2016/05/17 17:46:18]

yeah sorry I wasn't clear, I meant there are multiple instances of mojo
implementations (i.e. sensorImpl in your case), but it looks like they all go to
a singleton SensorService anyway so you would not register multiple times on the
platform side. (Registering multiple times on platform side would probably work
as well, was just checking if there would be any issues with that). 

Looking ahead though looks like creating two ALS sensors in javascript with
different frequencies would be non-trivial to implement..

+    if (!m_hasLatestData)
+        startReading();
+
+    queryNextReading();
+}
+
+void AmbientLightSensorDispatcher::stopListening()
+{
+    stopReading();
+    m_lightSensor.reset();
+    m_hasLatestData = false;
+}
+
+} // namespace blink