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

= How to use Maemo 5 specific APIs from Qt application =

== Accelometer ==

=== Introduction ===

This section explains how to use the [[Accelerometers | accelerometer]] D-Bus interface in a 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 is up to each application how to organize interactions with the [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, as demonstrated in our example.
We've moved D-Bus related functionality and orientation based calculations to a separate library that implements `DeviceOrientationNotifier' class. 
Our notifier asks MCE about orientation parameters with a certain period, 
 void DeviceOrientationNotifier::timerEvent(QTimerEvent *)
 {
   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 the application with the 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 a `SceneTuner', whose slot can be connected to an appropriate signal in order to setup these scene properties.
 DeviceOrientationNotifier notifier(100);
 SceneTuner tuner(&scene, TimerInterval);
 QObject::connect(&notifier, SIGNAL(deviceOrientation(qreal, qreal)), &tuner, SLOT(setProps(qreal, qreal)));
Based on that each mouse can take into account the gravity effect, see `Mouse::advance' for details.

== Using Zoom In and Zoom Out keys ==

This section uses the same qt-maemo-gravity-example to explain how to use Zoom In and Out keys in a Qt application. They are used to set the application window to fullscreen and normal modes like in the GTK+ example [[Documentation/Maemo 5 Developer Guide/Porting Software/Porting Existing GTK+ Application to Maemo 5|Maemo Sliders]].

First, the keys are released from maemo-status-volume by using <code>XChangeProperty()</code>.

hardkeyhandler.cpp:
 void HardkeyHandler::grabIncreaseDecreaseKeys(QWidget* window, bool grab)
 {
     // Tell maemo-status-volume to grab/ungrab increase/decrease keys
     unsigned long val = (grab==true)?1:0;
     Atom atom;
     atom = XInternAtom( QX11Info::display(), "_HILDON_ZOOM_KEY_ATOM", 0);
     XChangeProperty (QX11Info::display(),
                      window->winId(),
                      atom,
                      XA_INTEGER,
                      32,
                      PropModeReplace,
                      (unsigned char *) &val,
                      1);
}


Next, a handler for keypresses is created. 73 and 74 are the keycodes for F7/F8 in the SDK and Zoom In/Out buttons in the device. Handler functions emit corresponding signals when called.

hardkeyhandler.cpp
 bool HardkeyHandler::processX11Event(XEvent* event)
 {
     if ( event->type == KeyPress )
     {
         if (event->xkey.keycode == 73 || event->xkey.keycode == QKeySequence::ZoomOut)
         {
             emit decreaseKeyPressed();
             return true;
         } 
         else if (event->xkey.keycode == 74  || event->xkey.keycode ==  QKeySequence::ZoomIn)
         {
             emit increaseKeyPressed();
             return true;
         }
     }
 
     return false;
 }


Signals need slots, of course. They are located to myapplication.h and myapplication.cpp files. Here changing to fullscreen and back are done by <code>showFullScreen()</code> and <code>showNormal()</code>.

myapplication.cpp
 void MyApplication::increaseKeyPressed()
 {
     qDebug("MyApplication::increaseKeyPressed");
     view.showFullScreen();
 
 }
 
 void MyApplication::decreaseKeyPressed()
 {
     qDebug("MyApplication::decreaseKeyPressed");
     view.showNormal();
 }


The new signals are connected to corresponding slots in <code>main()</code>.

main.cpp
 QObject::connect(app.keyHandler(), SIGNAL(decreaseKeyPressed()), &app, SLOT(decreaseKeyPressed()));
 QObject::connect(app.keyHandler(), SIGNAL(increaseKeyPressed()), &app, SLOT(increaseKeyPressed()));

Finally, gtk-x11 library and the new source and header files (hardkeyhandler.* and myapplication.*) are added to the Qt project file:

collidingmice-gravity.pro:
 LIBS += -ldevornot-qt-maemo -L/usr/local/lib -lgtk-x11-2.0
 
 HEADERS += \
     mouse.h \
     hardkeyhandler.h \
     myapplication.h \
     scenetuner.h
 SOURCES += \
     main.cpp \
     hardkeyhandler.cpp \
     myapplication.cpp \
     mouse.cpp