View source for Documentation/Maemo 5 Developer Guide/Development Environment/Maemo Programming Environments/Using Maemo 5 specific APIs in Qt application

== Introduction ==

This section explains how to use [[Accelerometers | accelerometer]] D-Bus interface in Maemo 5 Qt application.

The following code examples are used in this section:
* [https://garage.maemo.org/svn/maemoexamples/trunk/qt-maemo-gravity-example/ qt-maemo-gravity-example]

== D-Bus interface ==

It's up to each application how to organize interactions with [http://maemo.org/api_refs/5.0/beta/mce-dev/ MCE] orientation interface. In [[Documentation/Maemo 5 Developer Guide/Porting Software/Porting Existing GTK+ Application to Maemo 5#Portrait Mode | some cases]] catching orientation signal can be enough, but if e.g. more frequent updates are needed you might want to use method calls, that demonstrated in our example.
We've moved D-Bus related functionality and orientation based calculations to separate library, that implements `DeviceOrientationNotifier' class. 
Our notifier asks MCE about orientation parameters with certain period, 
 void DeviceOrientationNotifier::mceOrientationCall()
 {
   QDBusMessage msg = QDBusMessage::createMethodCall(MCE_SERVICE, MCE_REQUEST_PATH, MCE_REQUEST_IF, MCE_DEVICE_ORIENTATION_GET);
   bool sent = QDBusConnection::systemBus().callWithCallback(msg, this, SLOT(mceOrientationSlot(QString, QString, QString, int, int, int)));
 }
processes answers in `mceOrientationSlot' and emits data needed by application with following signal.
 void deviceOrientation(qreal pitch, qreal roll);

== Example application ==

We've modified [http://qt.nokia.com/doc/4.5/graphicsview-collidingmice.html one of Qt4 Examples] in order to show how device orientation can be used.
In our case pitch and roll are scene's characteristics, so we've implemented `SceneTuner', that's slot can be connected to appropriate signal in order to setup these scene's properties.
 DeviceOrientationNotifier notifier(100);
 SceneTuner tuner(&scene);
 QObject::connect(&notifier, SIGNAL(deviceOrientation(qreal, qreal)), &tuner, SLOT(setProps(qreal, qreal)));

Based on that each mouse can take into account gravity effect, see `Mouse::timerEvent' for details.