Tutorial: Implementing a Device Plug-in

Mouse Handler

The class definition for our mouse handler contains numerous data members which are used by the filtering code. The class definition is (examplemousehandler.h):

    #define TS_SAMPLES   5

    class ExampleMouseHandler : public QObject, public QWSCalibratedMouseHandler {
        Q_OBJECT
    public:
        ExampleMouseHandler(const QString &device = QString("/dev/input/event1"));
        ~ExampleMouseHandler();

        void suspend();
        void resume();

    private:
        int  nX, nY;
        int  sx[TS_SAMPLES+3], sy[TS_SAMPLES+3];
        int  index_x1, index_x2, index_y1, index_y2, min_x, min_y;
        int  mouseIdx;
        static const int mouseBufSize = 2048;
        uchar mouseBuf[mouseBufSize];
        QPoint oldmouse;

        QSocketNotifier *m_notify;
        int  mouseFd;

    private Q_SLOTS:
        void readMouseData();
    };

The constructor opens the mouse device, /dev/input/event1. A QSocketNotifier is used to get asynchronous notification on the availability of data from the device. The readMouseData() slot is connected tot he QSocketNotifier::activated() signal and will be called whenever data is available to be read from the device.

    ExampleMouseHandler::ExampleMouseHandler(const QString &device)
        : nX(0), nY(0), min_x(INT_MAX), min_y(INT_MAX), mouseIdx(0)
    {
        qLog(Input) << "Loaded Example touchscreen plugin!";
        setObjectName("Example Mouse Handler");
        mouseFd = ::open(device.toLocal8Bit().constData(), O_RDONLY | O_NDELAY);
        if (mouseFd >= 0) {
            qLog(Input) << "Opened" << device << "as touchscreen input";
            m_notify = new QSocketNotifier(mouseFd, QSocketNotifier::Read, this);
            connect(m_notify, SIGNAL(activated(int)), this, SLOT(readMouseData()));
        } else {
            qWarning("Cannot open %s for touchscreen input (%s)",
                     device.toLocal8Bit().constData(), strerror(errno));
            return;
        }
    }

In the destructor we close the device.

    ExampleMouseHandler::~ExampleMouseHandler()
    {
        if (mouseFd >= 0)
            ::close(mouseFd);
    }

The suspend() and resume() functions are called to stop and start the flow of mouse events to the system. We just enable and disable notifications from QSocketNotifier.

    void ExampleMouseHandler::suspend()
    {
        m_notify->setEnabled( false );
    }

    void ExampleMouseHandler::resume()
    {
        m_notify->setEnabled( true );
    }

The ExampleInput structure defines the format of the data read from the device. The Linux event interface uses 16 byte packets.

    struct ExampleInput {
        unsigned int   dummy1;
        unsigned int   dummy2;
        unsigned short type;
        unsigned short code;
        unsigned int   value;
    };

Whenever data is available to be read from the device the readMouseData() slot will be invoked by the QSocketNotifier. readMouseData() reads and processes all available mouse events.

    void ExampleMouseHandler::readMouseData()
    {
        if (!qt_screen)
            return;

        int n;

        do {
            n = read(mouseFd, mouseBuf+mouseIdx, mouseBufSize-mouseIdx);
            if (n > 0)
                mouseIdx += n;

Each packet read from the device only contains information on a single axis. Process packets until we have TS_SAMPLES complete sample.

            ExampleInput *data;
            int idx = 0;

            while (mouseIdx-idx >= (int)sizeof(ExampleInput)) {
                uchar *mb = mouseBuf+idx;
                data = (ExampleInput*)mb;
                if (data->code == 0) {
                    // x value
                    sx[nX] = data->value;
                    nX++;
                } else if (data->code == 1) {
                    // y value
                    sy[nY] = data->value;
                    nY++;
                }

Our simple filtering algorithm uses the average of the two closest points in the last TS_SAMPLES samples.

                if (nX >= TS_SAMPLES && nY >= TS_SAMPLES) {
                    int ss = (nX < nY) ? nX : nY;

                    for (int i = 0; i < ss - 1; i++) {
                        for (int j = i + 1; j < ss; j++) {
                            int dx = sx[i] - sx[j];
                            if (dx < 0)
                                dx = -dx;
                            int dy = sy[i] - sy[j];
                            if (dy < 0)
                                dy = -dy;
                            if (min_x > dx) {
                                min_x = dx;
                                index_x1 = i;
                                index_x2 = j;
                            }
                            if (min_y > dy) {
                                min_y = dy;
                                index_y1 = i;
                                index_y2 = j;
                            }
                        }
                    }

                    QPoint pos((sx[index_x1] + sx[index_x2])/2,
                               (sy[index_y1] + sy[index_y2])/2);

                    nX = 0;
                    nY = 0;
                    min_x = INT_MAX;
                    min_y = INT_MAX;

The filtered touchscreen sample is transformed from device coordinates to screen coordinates, and a mouseChanged() signal is emitted.

                    oldmouse = transform( pos );
                    if (oldmouse.x() < MOUSE_SAMPLE_MIN || oldmouse.x() > MOUSE_SAMPLE_MAX ||
                        oldmouse.y() < MOUSE_SAMPLE_MIN || oldmouse.y() > MOUSE_SAMPLE_MAX) {
                        qLog(Input) << "*BAD Mouse sample :x="
                                    << oldmouse.x() << ",y=" << oldmouse.y();
                        oldmouse.setX(0);
                        oldmouse.setY(0);
                    } else {
                        qLog(Input) << "Mouse Down:x="
                                    << oldmouse.x() << ",y=" << oldmouse.y();
                        emit mouseChanged(oldmouse, Qt::LeftButton);
                    }
                }

Emit mouseChanged() signal when the stylus is removed from the screen.

                if ((data->code == 24) && (data->value == 0)) {
                    // Removed pen from screen
                    qLog(Input) << "Mouse Up  :x=" << oldmouse.x() << ",y=" << oldmouse.y();
                    emit mouseChanged(oldmouse, 0);
                    nX = 0;
                    nY = 0;

Move pointers to process the next packet.

                }
                idx += sizeof(ExampleInput);
            }
            int surplus = mouseIdx - idx;
            for (int i = 0; i < surplus; i++)
                mouseBuf[i] = mouseBuf[idx+i];
            mouseIdx = surplus;
        } while (n > 0);
    }

    #include <QtGui/QWSMouseHandlerFactoryInterface>

    class ExampleMouseDriverPlugin : public QMouseDriverPlugin {
        Q_OBJECT
    public:
        ExampleMouseDriverPlugin( QObject *parent  = 0 );
        ~ExampleMouseDriverPlugin();

        QWSMouseHandler* create(const QString& driver);
        QWSMouseHandler* create(const QString& driver, const QString& device);
        QStringList keys()const;
    };

    QStringList ExampleMouseDriverPlugin::keys() const
    {
        return QStringList() << "examplemousehandler";
    }

    QWSMouseHandler* ExampleMouseDriverPlugin::create(const QString& driver, const QString& device)
    {
        if ( driver.toLower() == "examplemousehandler" ) {
            qLog(Input) << "Before call ExampleMouseHandler()";
            return new ExampleMouseHandler(device);
        }
        return 0;
    }

    QWSMouseHandler* ExampleMouseDriverPlugin::create(const QString& driver)
    {
        if( driver.toLower() == "examplemousehandler" ) {
            qLog(Input) << "Before call ExampleMouseHandler()";
            return new ExampleMouseHandler();
        }
        return 0;
    }

    QTOPIA_EXPORT_QT_PLUGIN(ExampleMouseDriverPlugin)

    requires(qws)
    TEMPLATE=plugin
    PLUGIN_FOR=qt
    PLUGIN_TYPE=mousedrivers

    TARGET=examplemousehandler

    CONFIG+=qtopia
    QTOPIA=base

    HEADERS=\
        examplemousedriverplugin.h\
        examplemousehandler.h

    SOURCES=\
        examplemousedriverplugin.cpp\
        examplemousehandler.cpp

    PROJECTS *= plugins/qtopiacore/mousedrivers/example

    export QWS_MOUSE_PROTO=examplemousehandler

    export QWS_MOUSE_PROTO=examplemousehandler:/dev/input/event2

        export QWS_DISPLAY=examplescreen