WebKit & WebCore part of the device motion implementation using the platform layer.

Source/WebCore/platform/chromium/support/WebDeviceMotionEventPump.cpp

+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.
+ *
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+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
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+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
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+ * in the documentation and/or other materials provided with the
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+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "WebDeviceMotionEventPump.h"
+
+#include <public/Platform.h>
+#include <public/WebDeviceMotionData.h>
+#include <public/WebDeviceMotionReader.h>
+
+namespace WebKit {
+
+// static
+WebDeviceMotionEventPump& WebDeviceMotionEventPump::shared()
+{
+    DEFINE_STATIC_LOCAL(WebDeviceMotionEventPump, webDeviceMotionEventPump, (kPumpDelayMilliSeconds / 1000.0f));
+    return webDeviceMotionEventPump;
+}
+
+WebDeviceMotionEventPump::WebDeviceMotionEventPump(double delay_seconds) :

[Peter Beverloo, 2013/04/17 19:08:23]

nit: WebKit uses camelCase, not hacker_case (for delay_seconds).

[timvolodine, 2013/04/18 12:37:38]

Done.

+    m_delaySeconds(delay_seconds),
+    m_lastFireEventTimeMonotonic(0),
+    m_stopped(true),
+    m_lastDeviceMotionData(0),
+    m_pumpTimer(this, &WebDeviceMotionEventPump::fireEvent)
+{
+}
+
+void WebDeviceMotionEventPump::fireEvent(Timer<WebDeviceMotionEventPump>*)
+{
+    if (m_stopped)
+        return;
+
+    m_lastFireEventTimeMonotonic = monotonicallyIncreasingTime();
+    WebDeviceMotionReader* reader = WebKit::Platform::current()->deviceMotionReader();
+    WebDeviceMotionData data;
+    reader->lastDeviceMotionData(data);

[Peter Beverloo, 2013/04/17 19:08:23]

hmm. Hypothetical situation: what if there is no latest device motion data?
Should lastDeviceMotionData() maybe return a boolean to indicate whether there
is anything at all?

[timvolodine, 2013/04/18 12:37:38]

Done.

+    m_lastDeviceMotionData = PassRefPtr<WebCore::DeviceMotionData>(data);
+
+    if (shouldFireEvent()) {
+        Vector<RefPtr<DeviceMotionController> > listenerVector;
+        copyToVector(m_listeners, listenerVector);
+        for (size_t i = 0;i < listenerVector.size(); ++i) {
+            listenerVector[i]->didChangeDeviceMotion(m_lastDeviceMotionData.get());
+        }
+    }
+
+    scheduleFireEvent();
+}
+
+void WebDeviceMotionEventPump::scheduleFireEvent()
+{
+    if (m_pumpTimer.isActive())
+        return;
+
+    double scheduleDelay = std::max<double>(m_delaySeconds - (monotonicallyIncreasingTime() - m_lastFireEventTimeMonotonic), 0);
+    m_pumpTimer.startOneShot(scheduleDelay);
+}
+
+WebCore::DeviceMotionData* WebDeviceMotionEventPump::latestDeviceMotionData()
+{
+    return m_lastDeviceMotionData.get();
+}
+
+bool WebDeviceMotionEventPump::shouldFireEvent()
+{
+    // FIXME motion event should be fired only when values are different from the values
+    // of the previously fired event.

[Peter Beverloo, 2013/04/17 19:08:23]

Is that so? In either case, I'd argue that this is more of a job for the
controller to do, given that the pump just... pumps, and shouldn't have any
further logic.

[timvolodine, 2013/04/18 12:37:38]

hmm, I was looking at the semantics for orientation, where the event is only
fired when sufficiently different from the previous one. The main reason to have
the shouldFireEvent() here is because the pump owns the lastDeviceMotionData,
hence in order to compare this would be the best place to do so.

[Peter Beverloo, 2013/04/18 13:56:06]

Where does the Device Orientation specification say that only firing the event
if it has changed enough should also apply to the devicemotion event? Do other
browsers do this?

I'm still not sure about the layering. It feels wrong for a pump to have logic a
controller should care about.

[timvolodine, 2013/04/18 14:55:37]

ok the spec does not say anything about firing the motion event, probably it
expects to do so with the delay specified in the interval property..
Anyway this will be needed for device orientation, and the pump is probably the
only reasonable place to do so. The controller does not own the data and is not
singleton anymore, I see it playing more of a dispatcher role.

+    return true;
+}
+
+void WebDeviceMotionEventPump::addListener(DeviceMotionController* controller)
+{
+    bool wasEmpty = m_listeners.isEmpty();
+    m_listeners.add(controller);
+    if (wasEmpty)
+        start();
+}
+
+void WebDeviceMotionEventPump::removeListener(DeviceMotionController* controller)
+{
+    m_listeners.remove(controller);
+    if (m_listeners.isEmpty())
+        stop();
+}
+
+void WebDeviceMotionEventPump::start()
+{
+    WebDeviceMotionReader* reader = WebKit::Platform::current()->deviceMotionReader();
+    ASSERT(reader);
+    reader->startUpdating();
+    m_stopped = false;
+    scheduleFireEvent();
+}
+
+void WebDeviceMotionEventPump::stop()
+{
+    WebDeviceMotionReader* reader = WebKit::Platform::current()->deviceMotionReader();
+    ASSERT(reader);
+    reader->stopUpdating();
+    m_stopped = true;
+}
+
+} // namespace WebKit