source: trunk/doc/src/examples/mousecalibration.qdoc@ 550

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/*!
    \example qws/mousecalibration
    \title Mouse Calibration Example

    The Mouse Calibration example demonstrates how to write a simple
    program using the mechanisms provided by the QWSMouseHandler class
    to calibrate the mouse handler in \l{Qt for Embedded Linux}. 

    Calibration is the process of mapping between physical
    (i.e. device) coordinates and logical coordinates.

    The example consists of two classes in addition to the main program:

    \list
        \o \c Calibration is a dialog widget that retrieves the device coordinates.
        \o \c ScribbleWidget is a minimal drawing program used to let the user
            test the new mouse settings.
    \endlist

    First we will review the main program, then we will take a look at
    the \c Calibration class. The \c ScribbleWidget class is only a
    help tool in this context, and will not be covered here.

    \section1 The Main Program

    The program starts by presenting a message box informing the user
    of what is going to happen:

    \snippet examples/qws/mousecalibration/main.cpp 0

    The QMessageBox class provides a modal dialog with a range of
    different messages, roughly arranged along two axes: severity and
    complexity. The message box has a different icon for each of the
    severity levels, but the icon must be specified explicitly. In our
    case we use the default QMessageBox::NoIcon value. In addition we
    use the default complexity, i.e. a message box showing the given
    text and an \gui OK button.

    At this stage in the program, the mouse could be completely
    uncalibrated, making the user unable to press the \gui OK button. For
    that reason we use the static QTimer::singleShot() function to
    make the message box disappear after 10 seconds. The QTimer class
    provides repetitive and single-shot timers: The single shot
    function calls the given slot after the specified interval.

    \snippet examples/qws/mousecalibration/main.cpp 1

    Next, we create an instance of the \c Calibration class which is a
    dialog widget retrieving the required sample coordinates: The
    dialog sequentially presents five marks for the user to press,
    storing the device coordinates for the mouse press events.

    \snippet examples/qws/mousecalibration/main.cpp 2

    When the calibration dialog returns, we let the user test the new
    mouse settings by drawing onto a \c ScribbleWidget object. Since
    the mouse still can be uncalibrated, we continue to use the
    QMessageBox and QTimer classes to inform the user about the
    program's progress.

    An improved calibration tool would let the user choose between
    accepting the new calibration, reverting to the old one, and
    restarting the calibration.

    \section1 Calibration Class Definition

    The \c Calibration class inherits from QDialog and is responsible
    for retrieving the device coordinates from the user.

    \snippet examples/qws/mousecalibration/calibration.h 0

    We reimplement QDialog's \l {QDialog::exec()}{exec()} and \l
    {QDialog::accept()}{accept()} slots, and QWidget's \l
    {QWidget::paintEvent()}{paintEvent()} and \l
    {QWidget::mouseReleaseEvent()}{mouseReleaseEvent()} functions.

    In addition, we declare a couple of private variables, \c data and
    \c pressCount, holding the \c Calibration object's number of mouse
    press events and current calibration data. The \c pressCount
    variable is a convenience variable, while the \c data is a
    QWSPointerCalibrationData object (storing the physical and logical
    coordinates) that is passed to the mouse handler. The
    QWSPointerCalibrationData class is simply a container for
    calibration data.

    \section1 Calibration Class Implementation

    In the constructor we first ensure that the \c Calibration dialog
    fills up the entire screen, has focus and will receive mouse
    events (the latter by making the dialog modal):

    \snippet examples/qws/mousecalibration/calibration.cpp 0

    Then we initialize the \l{QWSPointerCalibrationData::}{screenPoints}
    array:

    \snippet examples/qws/mousecalibration/calibration.cpp 1

    In order to specify the calibration, the 
    \l{QWSPointerCalibrationData::screenPoints}{screenPoints} array must
    contain the screen coordinates for the logical positions
    represented by the QWSPointerCalibrationData::Location enum
    (e.g. QWSPointerCalibrationData::TopLeft).  Since non-linearity is
    expected to increase on the edge of the screen, all points are
    kept 10 percent within the screen. The \c qt_screen pointer is a
    reference to the screen device. There can only be one screen
    device per application.

    \snippet examples/qws/mousecalibration/calibration.cpp 2

    Finally, we initialize the variable which keeps track of the number of
    mouse press events we have received.

    \snippet examples/qws/mousecalibration/calibration.cpp 3

    The destructor is trivial.

    \snippet examples/qws/mousecalibration/calibration.cpp 4

    The reimplementation of the QDialog::exec() slot is called from
    the main program.

    First we clear the current calibration making the following mouse
    event delivered in raw device coordinates. Then we call the
    QWidget::grabMouse() function to make sure no mouse events are
    lost, and the QWidget::activateWindow() function to make the
    top-level widget containing this dialog, the active window. When
    the call to the QDialog::exec() base function returns, we call
    QWidget::releaseMouse() to release the mouse grab before the
    function returns.

    \snippet examples/qws/mousecalibration/calibration.cpp 5

    The QWidget::paintEvent() function is reimplemented to receive the
    widget's paint events. A paint event is a request to repaint all
    or parts of the widget. It can happen as a result of
    QWidget::repaint() or QWidget::update(), or because the widget was
    obscured and has now been uncovered, or for many other reasons.
    In our reimplementation of the function we simply draw a cross at
    the next point the user should press.

    \snippet examples/qws/mousecalibration/calibration.cpp 6

    We then reimplement the QWidget::mouseReleaseEvent() function to
    receive the widget's move events, using the QMouseEvent object
    passed as parameter to find the coordinates the user pressed, and
    update the QWSPointerCalibrationData::devPoints array.

    In order to complete the mapping between logical and physical
    coordinates, the \l
    {QWSPointerCalibrationData::devPoints}{devPoints} array must
    contain the raw device coordinates for the logical positions
    represented by the QWSPointerCalibrationData::Location enum
    (e.g. QWSPointerCalibrationData::TopLeft)

    We continue by drawing the next cross, or close the dialog by
    calling the QDialog::accept() slot if we have collected all the
    required coordinate samples.

    \snippet examples/qws/mousecalibration/calibration.cpp 7

    Our reimplementation of the QDialog::accept() slot simply activate
    the new calibration data using the QWSMouseHandler::calibrate()
    function. We also use the Q_ASSERT() macro to ensure that the number
    of required samples are present.
*/