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

Warning: You are not logged in. Your IP address will be recorded in this page's edit history.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.

Learn more about Contributing to the wiki.

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

== Accelometer ==

=== Introduction ===

This section explains how to use the [[N900 accelerometer|accelerometer]] D-Bus interface in a Maemo 5 Qt application.

The following code examples are used in this section:
* [https://vcs.maemo.org/svn/maemoexamples/tags/maemo_5.0/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 more frequent updates are needed, for example, 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 <code>DeviceOrientationNotifier</code> class. 
Our notifier asks MCE about orientation parameters with a certain period, 
<source lang="cpp">
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)));
}
</source>
processes answers in `mceOrientationSlot', and emits data needed by the application with the following signal:
<source lang="cpp">
void deviceOrientation(qreal pitch, qreal roll);
</source>

=== 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.
<source lang="cpp">
DeviceOrientationNotifier notifier(100);
SceneTuner tuner(&scene, TimerInterval);
QObject::connect(&notifier, SIGNAL(deviceOrientation(qreal, qreal)), &tuner, SLOT(setProps(qreal, qreal)));
</source>
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:
<source lang="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);
}
</source>

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:
<source lang="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;
}
</source>

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

myapplication.cpp:
<source lang="cpp">
void MyApplication::increaseKeyPressed()
{
    qDebug("MyApplication::increaseKeyPressed");
    view.showFullScreen();

}

void MyApplication::decreaseKeyPressed()
{
    qDebug("MyApplication::decreaseKeyPressed");
    view.showNormal();
}
</source>

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

main.cpp:
<source lang="cpp">
QObject::connect(app.keyHandler(), SIGNAL(decreaseKeyPressed()), &app, SLOT(decreaseKeyPressed()));
QObject::connect(app.keyHandler(), SIGNAL(increaseKeyPressed()), &app, SLOT(increaseKeyPressed()));
</source>

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

collidingmice-gravity.pro:
<pre>
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
</pre>

[[Category:Development]]
[[Category:Documentation]]
[[Category:Fremantle]]

Please note that all contributions to maemo.org wiki may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see maemo.org wiki:Copyrights for details). Do not submit copyrighted work without permission!

Summary:

Cancel | Editing help (opens in new window)

Retrieved from "http://wiki.maemo.org/Documentation/Maemo_5_Developer_Guide/Development_Environment/Maemo_Programming_Environments/Using_Maemo_5_specific_APIs_in_Qt_application"

Personal tools

Navigation

Views

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

@@ Line 15: / Line 15: @@
 We've moved D-Bus related functionality and orientation based calculations to a separate library that implements <code>DeviceOrientationNotifier</code> class.
 Our notifier asks MCE about orientation parameters with a certain period,
-<source lang="cpp-qt">
+<source lang="cpp">
 void DeviceOrientationNotifier::timerEvent(QTimerEvent *)
 {
@@ Line 23: / Line 23: @@
 </source>
 processes answers in `mceOrientationSlot', and emits data needed by the application with the following signal:
-<source lang="cpp-qt">
+<source lang="cpp">
 void deviceOrientation(qreal pitch, qreal roll);
 </source>
@@ Line 31: / Line 31: @@
 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.
-<source lang="cpp-qt">
+<source lang="cpp">
 DeviceOrientationNotifier notifier(100);
 SceneTuner tuner(&scene, TimerInterval);
@@ Line 45: / Line 45: @@
 hardkeyhandler.cpp:
-<source lang="cpp-qt">
+<source lang="cpp">
 void HardkeyHandler::grabIncreaseDecreaseKeys(QWidget* window, bool grab)
 {
@@ Line 66: / Line 66: @@
 hardkeyhandler.cpp:
-<source lang="cpp-qt">
+<source lang="cpp">
 bool HardkeyHandler::processX11Event(XEvent* event)
 {
@@ Line 90: / Line 90: @@
 myapplication.cpp:
-<source lang="cpp-qt">
+<source lang="cpp">
 void MyApplication::increaseKeyPressed()
 {
@@ Line 108: / Line 108: @@
 main.cpp:
-<source lang="cpp-qt">
+<source lang="cpp">
 QObject::connect(app.keyHandler(), SIGNAL(decreaseKeyPressed()), &app, SLOT(decreaseKeyPressed()));
 QObject::connect(app.keyHandler(), SIGNAL(increaseKeyPressed()), &app, SLOT(increaseKeyPressed()));