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/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
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**
** GNU Free Documentation License Usage
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** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: http://www.gnu.org/copyleft/fdl.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example qws/mousecalibration
\title Mouse Calibration Example
\brief 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.
*/
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