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+/****************************************************************************
+**
+** Tutorial
+**
+** Copyright (C) 1992-2008 Trolltech ASA.  All rights reserved.
+**
+** This file is part of the Qt GUI Toolkit.
+**
+** This file may be used under the terms of the GNU General
+** Public License versions 2.0 or 3.0 as published by the Free
+** Software Foundation and appearing in the files LICENSE.GPL2
+** and LICENSE.GPL3 included in the packaging of this file.
+** Alternatively you may (at your option) use any later version
+** of the GNU General Public License if such license has been
+** publicly approved by Trolltech ASA (or its successors, if any)
+** and the KDE Free Qt Foundation.
+**
+** Please review the following information to ensure GNU General
+** Public Licensing requirements will be met:
+** http://trolltech.com/products/qt/licenses/licensing/opensource/.
+** If you are unsure which license is appropriate for your use, please
+** review the following information:
+** http://trolltech.com/products/qt/licenses/licensing/licensingoverview
+** or contact the sales department at sales@trolltech.com.
+**
+** This file may be used under the terms of the Q Public License as
+** defined by Trolltech ASA and appearing in the file LICENSE.QPL
+** included in the packaging of this file.  Licensees holding valid Qt
+** Commercial licenses may use this file in accordance with the Qt
+** Commercial License Agreement provided with the Software.
+**
+** This file is provided "AS IS" with NO WARRANTY OF ANY KIND,
+** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted
+** herein.
+**
+**********************************************************************/
+
+/*! \page tutorial.html
+
+\title Qt Tutorial #1 - The 14 Steps
+
+This tutorial gives an introduction to GUI programming using the Qt
+toolkit. It doesn't cover everything: the emphasis is on teaching the
+programming philosophy of GUI programming, and Qt's features are
+introduced as needed. Some commonly used features are never used in
+this tutorial.
+
+Chapter one starts with a ten-line hello-world and each subsequent
+chapter introduces one or a few more concepts. By Chapter 14, the ten
+lines from Chapter 1 have turned into a 650-line game.
+
+If you're completely new to Qt, please read \link how-to-learn-qt.html
+How to Learn Qt\endlink if you haven't already done so.
+
+Tutorial chapters:
+\list 1
+\i \link tutorial1-01.html Hello, World!\endlink
+\i \link tutorial1-02.html Calling it Quits\endlink
+\i \link tutorial1-03.html Family Values\endlink
+\i \link tutorial1-04.html Let There Be Widgets\endlink
+\i \link tutorial1-05.html Building Blocks\endlink
+\i \link tutorial1-06.html Building Blocks Galore!\endlink
+\i \link tutorial1-07.html One Thing Leads to Another\endlink
+\i \link tutorial1-08.html Preparing for Battle\endlink
+\i \link tutorial1-09.html With Cannon You Can\endlink
+\i \link tutorial1-10.html Smooth as Silk\endlink
+\i \link tutorial1-11.html Giving It a Shot\endlink
+\i \link tutorial1-12.html Hanging in the Air the Way Bricks Don't\endlink
+\i \link tutorial1-13.html Game Over\endlink
+\i \link tutorial1-14.html Facing the Wall\endlink
+\endlist
+
+This little game doesn't look much like a modern GUI application. It
+uses a good few of the GUI techniques, but after you've worked through
+it, we recommend reading \link tutorial2.html Tutorial #2\endlink. The
+second tutorial is a little more formal and covers the features of
+typical application including menubars, toolbars, loading and saving,
+dialogs, etc.
+
+*/
+
+/*! \page tutorial1-01.html
+
+\title Qt Tutorial - Chapter 1: Hello, World!
+
+\img t1.png Screenshot of tutorial one
+
+This first program is a simple hello-world example. It contains only
+the bare minimum you need to get a Qt application up and running.
+The picture above is a snapshot of this program.
+
+\include t1/main.cpp
+\quotefile t1/main.cpp
+
+\section1 Line-by-line Walkthrough
+
+\skipto include
+\printline qapp
+
+This line includes the QApplication class definition. There has to be
+exactly one QApplication object in every application that uses Qt.
+QApplication manages various application-wide resources, such as the
+default font and cursor.
+
+\printline qpushbutton
+
+This line includes the QPushButton class definition. The
+\link hierarchy.html reference documentation \endlink for each class
+mentions at the top which file needs to be included to use that class.
+
+QPushButton is a classical GUI push button that the user can press
+and release. It manages its own look and feel, like every other \l
+QWidget. A widget is a user interface object that can process user
+input and draw graphics. The programmer can change both the overall
+\link QApplication::setStyle() look and feel\endlink and many minor
+properties of it (such as color), as well as the widget's content. A
+QPushButton can show either a text or a \l QPixmap.
+
+\printline main
+\printline {
+
+The main() function is the entry point to the program. Almost always
+when using Qt, main() only needs to perform some kind of initialization
+before passing the control to the Qt library, which then tells the
+program about the user's actions via events.
+
+\c argc is the number of command-line arguments and \c argv is the
+array of command-line arguments. This is a C/C++ feature. It is not
+specific to Qt; however, Qt needs to process these arguments (see
+following).
+
+\printline QApplication
+
+\c a is this program's QApplication. Here it is created and processes
+some of the command-line arguments (such as -display under X Window).
+Note that all command-line arguments recognized by Qt are removed from
+\c argv (and \c argc is decremented accordingly). See the \l
+QApplication::argv() documentation for details.
+
+<strong>Note:</strong> It is essential that the QApplication object be
+created before any window-system parts of Qt are used.
+
+\printline QPushButton
+
+Here, \e after the QApplication, comes the first window-system code: A
+push button is created.
+
+The button is set up to display the text "Hello world!" and be a
+window of its own (because the constructor specifies 0 for the parent
+window, inside which the button should be located).
+
+\printline resize
+
+The button is set up to be 100 pixels wide and 30 pixels high (plus the
+window system frame). In this case we don't care about the button's
+position, and we accept the default value.
+
+\printline setMainWidget
+
+The push button is chosen as the main widget for the application. If
+the user closes a main widget, the application exits.
+
+You don't have to have a main widget, but most programs do have one.
+
+\printline show
+
+A widget is never visible when you create it. You must call show() to
+make it visible.
+
+\printline exec
+
+This is where main() passes control to Qt, and exec() will return when
+the application exits.
+
+In exec(), Qt receives and processes user and system events and passes
+these on to the appropriate widgets.
+
+\printline }
+
+You should now try to compile and run this program.
+
+\target compiling
+\section1 Compiling
+
+To compile a C++ application you need to create a makefile. The
+easiest way to create a makefile for Qt is to use the \link
+qmake-manual.book qmake\endlink build tool supplied with Qt. If you've
+saved \c main.cpp in its own directory, all you have to do is:
+\code
+qmake -project
+qmake
+\endcode
+
+The first command tells \link qmake-manual.book qmake\endlink to
+create a \c .pro (project) file. The second command tells it to create
+a (platform-specific) makefile based on the project file. You should
+now be able to type \c make (or \c nmake if you're using Visual
+Studio) and then run your first Qt application!
+
+\section1 Behavior
+
+When you run it, you will see a small window filled with a single
+button, and on it you can read the famous words, Hello World!
+
+\section1 Exercises
+
+Try to resize the window. Press the button. If you're running X
+Window, try running the program with the -geometry option
+(for example, \c {-geometry 100x200+10+20}).
+
+You're now ready for \link tutorial1-02.html Chapter 2.\endlink
+
+[\link tutorial1-02.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \page tutorial1-02.html
+
+\title Qt Tutorial - Chapter 2: Calling it Quits
+
+\img t2.png Screenshot of tutorial two
+
+Having created a window in \link tutorial1-01.html Chapter 1, \endlink we will
+now go on to make the application quit properly when the user tells it to.
+
+We will also use a font that is more exciting than the default one.
+
+\include t2/main.cpp
+\quotefile t2/main.cpp
+
+\section1 Line-by-line Walkthrough
+
+\skipto qfont
+\printline qfont
+
+Since this program uses QFont, it needs to include qfont.h. Qt's font
+abstraction is rather different from the horror provided by X, and
+loading and using fonts has been highly optimized.
+
+\skipto QPushButton
+\printline QPushButton
+
+This time, the button says "Quit" and that's exactly what the program
+will do when the user clicks the button. This is not a coincidence.
+We still pass 0 as the parent, since the button is a top-level window.
+
+\printline resize
+
+We've chosen another size for the button since the text is a bit
+shorter than "Hello world!". We could also have used \l QFontMetrics
+to set right size.
+
+\printline setFont
+
+Here we choose a new font for the button, an 18-point bold font from
+the Times family. Note that we create the font on the spot.
+
+It is also possible to change the default font (using \l
+QApplication::setFont()) for the whole application.
+
+\printline connect
+
+connect() is perhaps \e the most central feature of Qt.
+Note that connect() is a static function in QObject. Do not confuse it
+with the connect() function in the socket library.
+
+This line establishes a one-way connection between two Qt objects (objects
+that inherit QObject, directly or indirectly). Every Qt object can have
+both \c signals (to send messages) and \c slots (to receive messages). All
+widgets are Qt objects. They inherit QWidget which in turn inherits
+QObject.
+
+Here, the \e clicked() signal of \e quit is connected to the \e
+quit() slot of \e a, so that when the button is clicked, the
+application quits.
+
+The \link signalsandslots.html Signals and Slots\endlink documentation
+describes this topic in detail.
+
+\section1 Behavior
+
+When you run this program, you will see an even smaller window than in
+Chapter 1, filled with an even smaller button.
+
+(See \link tutorial1-01.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Try to resize the window. Press the button. Oops!  That connect()
+would seem to make some difference.
+
+Are there any other signals in QPushButton you can connect to quit?
+Hint: The QPushButton inherits most of its behavior from QButton.
+
+You're now ready for \link tutorial1-03.html Chapter 3.\endlink
+
+[\link tutorial1-01.html Previous tutorial\endlink]
+[\link tutorial1-03.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \page tutorial1-03.html
+
+\title Qt Tutorial - Chapter 3: Family Values
+
+\img t3.png Screenshot of tutorial three
+
+This example shows how to create parent and child widgets.
+
+We'll keep it simple and use just a single parent and a lone child.
+
+\include t3/main.cpp
+\quotefile t3/main.cpp
+
+\section1 Line-by-line Walkthrough
+
+\skipto qvbox.h
+\printline qvbox.h
+
+We add an include of qvbox.h to get the layout class we'll use.
+
+\skipto QVBox
+\printline QVBox
+
+Here we simply create a vertical box container. The QVBox arranges
+its child widgets in a vertical row, one above the other, handing out
+space according to each child's \l QWidget::sizePolicy().
+
+\printline resize
+
+We set its width to 200 pixels and the height to 120 pixels.
+
+\printline quit
+
+A child is born.
+
+This QPushButton is created with both a text ("Quit") and a parent
+(box). A child widget is always on top of its parent. When
+displayed, it is clipped by its parent's bounds.
+
+The parent widget, the QVBox, automatically adds the child centered in
+its box. Because nothing else is added, the button gets all the space
+the parent has.
+
+\skipto show
+\printline show
+
+When a parent widget is shown, it will call show for all its children
+(except those on which you have done an explicit \l QWidget::hide()).
+
+\section1 Behavior
+
+The button no longer fills the entire widget. Instead, it gets a
+"natural" size. This is because there is now a new top-level widget,
+which uses the button's size hint and size change policy to set the
+button's size and position. (See \l QWidget::sizeHint() and \l
+QWidget::setSizePolicy() for more information about these functions.)
+
+(See \link tutorial1-01.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Try resizing the window. How does the button change?  What is the
+button's size-change policy?  What happens to the button's height if
+you run the program with a bigger font?  What happens if you try to
+make the window \e really small?
+
+You're now ready for \link tutorial1-04.html Chapter 4.\endlink
+
+[\link tutorial1-02.html Previous tutorial\endlink]
+[\link tutorial1-04.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \page tutorial1-04.html
+
+\title Qt Tutorial - Chapter 4: Let There Be Widgets
+
+\img t4.png Screenshot of tutorial four
+
+This example shows how to create your own widget, describes how to control the
+minimum and maximum sizes of a widget, and introduces widget names.
+
+\include t4/main.cpp
+\quotefile t4/main.cpp
+
+\section1 Line-by-line Walkthrough
+
+\skipto MyWidget
+\printuntil }
+
+Here we create a new class. Because this class inherits from QWidget,
+the new class is a widget and may be a top level window or a child
+widget (like the push button in Chapter 3).
+
+This class has only one member, a constructor (in addition to the
+members it inherits from QWidget). The constructor is a standard Qt
+widget constructor; you should always include a similar constructor
+when you create widgets.
+
+The first argument is its parent widget. To create a top-level window
+you specify a null pointer as the parent. As you can see, this widget
+defaults to be a top-level window.
+
+The second argument is the widget's name. This is \e not the text
+that appears in the window's title bar or in the button. It is a name
+associated with a widget to make it possible to \link
+QObject::queryList() look up \endlink this widget later, and there is
+also a \link QObject::dumpObjectTree() handy debugging function
+\endlink that will list a complete widget hierarchy.
+
+\printline MyWidget
+\printline QWidget
+
+The implementation of the constructor starts here. Like most widgets,
+it just passes on the \c parent and \c name to the QWidget
+constructor.
+
+\printuntil setMaximumSize
+
+Because this widget doesn't know how to handle resizing, we fix its size
+by setting the minimum and maximum to be equal. In the next chapter
+we will show how a widget can respond to resize event from the user.
+
+\printuntil setFont
+
+Here we create and set up a child widget of this widget (the new widget's
+parent is \c this) which has the widget name "quit". The widget
+name has nothing to do with the button text; it just happens to be
+similar in this case.
+
+Note that \c quit is a local variable in the constructor. MyWidget
+does not keep track of it, but Qt does, and will by default delete it
+when MyWidget is deleted. This is why MyWidget doesn't need a
+destructor. (On the other hand, there is no harm in deleting a child
+when you choose to, the child will automatically tell Qt about its
+imminent death.)
+
+The setGeometry() call does the same as move() and resize() did in the
+previous chapters.
+
+\printline qApp
+\printline }
+
+Because the MyWidget class doesn't know about the application object, it
+has to connect to Qt's pointer to it, \c qApp.
+
+A widget is a software component and should know as little as possible
+about its environment in order to be as general and reusable as
+possible.
+
+Knowing the name of the application object would break this principle,
+so Qt offers an alias, qApp, for the cases in which a component such as
+MyWidget needs to talk to the application object.
+
+\printuntil }
+
+Here we instantiate our new child, set it to be the main widget, and
+execute the application.
+
+\section1 Behavior
+
+This program is very similar in behavior to the previous one. The
+difference lies in the way we have implemented it. It does behave
+slightly differently, however. Just try to resize it to see.
+
+(See \link tutorial1-01.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Try to create another MyWidget object in main(). What happens?
+
+Try to add more buttons or put in widgets other than QPushButton.
+
+You're now ready for \link tutorial1-05.html Chapter 5.\endlink
+
+[\link tutorial1-03.html Previous tutorial\endlink]
+[\link tutorial1-05.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \page tutorial1-05.html
+
+\title Qt Tutorial - Chapter 5: Building Blocks
+
+\img t5.png Screenshot of tutorial five
+
+This example shows how to create and connect together several widgets
+by using signals and slots, and how to handle resize events.
+
+\include t5/main.cpp
+\quotefile t5/main.cpp
+
+\section1 Line-by-line Walkthrough
+
+\skipto qapp
+\printuntil qvbox
+
+Three new include files are shown here. qslider.h and qlcdnumber.h are there
+because we use two new widgets, QSlider and QLCDNumber. qvbox.h is
+here because we use Qt's automatic layout support.
+
+\skipto MyWidget
+\printuntil }
+
+\target constructor
+\printuntil {
+
+MyWidget is now derived from QVBox instead of QWidget. That way we use
+the layout of the QVBox (which places all of its children vertically
+inside itself). Resizes are now handled automatically by the QVBox and
+therefore by MyWidget, too.
+
+\skipto lcd
+\printline lcd
+
+\c lcd is a QLCDNumber, a widget that displays numbers in an LCD-like
+fashion. This instance is set up to display two digits and to be a child of
+\e this. It is named "lcd".
+
+\printline QSlider
+\printline slider
+\printline slider
+
+QSlider is a classical slider; the user can use the widget to drag
+something to adjust an integer value in a range. Here we create a
+horizontal one, set its range to 0-99 (inclusive, see the \l
+QSlider::setRange() documentation) and its initial value to 0.
+
+\printline connect
+
+Here we use the \link signalsandslots.html signal/slot mechanism \endlink
+to connect the slider's valueChanged() signal to the LCD number's
+display() slot.
+
+Whenever the slider's value changes it broadcasts the new value by
+emitting the valueChanged() signal. Because that signal is connected to
+the LCD number's display() slot, the slot is called when the signal is
+broadcast. Neither of the objects knows about the other. This is
+essential in component programming.
+
+Slots are otherwise normal C++ member functions and follow the normal
+C++ access rules.
+
+\section1 Behavior
+
+The LCD number reflects everything you do to the slider, and the
+widget handles resizing well. Notice that the LCD number widget
+changes in size when the window is resized (because it can), but the
+others stay about the same (because otherwise they would look stupid).
+
+(See \link tutorial1-01.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Try changing the LCD number to add more digits or \link
+QLCDNumber::setMode() to change mode.\endlink You can even add four push
+buttons to set the number base.
+
+You can also change the slider's range.
+
+Perhaps it would have been better to use \l QSpinBox than a slider?
+
+Try to make the application quit when the LCD number overflows.
+
+You're now ready for \link tutorial1-06.html Chapter 6.\endlink
+
+[\link tutorial1-04.html Previous tutorial\endlink]
+[\link tutorial1-06.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \page tutorial1-06.html
+
+\title Qt Tutorial - Chapter 6: Building Blocks Galore!
+
+\img t6.png Screenshot of tutorial six
+
+This example shows how to encapsulate two widgets into a new component and
+how easy it is to use many widgets. For the first time, we use a custom
+widget as a child widget.
+
+\target main
+\include t6/main.cpp
+\quotefile t6/main.cpp
+
+\section1 Line-by-line Walkthrough
+
+\skipto LCDRange
+\printuntil };
+
+The LCDRange widget is a widget without any API. It just has a
+constructor. This sort of widget is not very useful, so we'll add some API later.
+
+\printuntil }
+
+This is lifted straight from the
+\link tutorial1-05.html#constructor MyWidget constructor \endlink in Chapter 5.
+The only differences are that the button is left out and the class
+is renamed.
+
+\printline MyWidget
+\printuntil }
+
+MyWidget, too, contains no API except a constructor.
+
+\printline MyWidget
+\printuntil connect
+
+The push button that used to be in what is now LCDRange has been
+separated so that we can have one "Quit" button and many LCDRange
+objects.
+
+\printline grid
+
+We create a QGrid object with four columns. The QGRid widget
+automatically arranges its children in rows and columns; you can
+specify the number of rows or of columns, and QGrid will discover its
+new children and fit them into the grid.
+
+\printline for
+\printline for
+\printline LCDRange
+
+Four columns, four rows.
+
+We create 4*4 LCDRanges, all of which are children of the grid object.
+The QGrid widget will arrange them.
+
+\printline }
+
+That's all.
+
+\section1 Behavior
+
+This program shows how easy it is to use many widgets at a time. Each
+one behaves like the slider and LCD number in the previous
+chapter. Again, the difference lies in the implementation.
+
+(See \link tutorial1-01.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Initialize each slider with a different/random value on startup.
+
+The source contains three occurrences of "4". What happens if you
+change the one in the \l QGrid constructor call?  What about the other
+two?  Why is this?
+
+You're now ready for \link tutorial1-07.html Chapter 7.\endlink
+
+[\link tutorial1-05.html Previous tutorial\endlink]
+[\link tutorial1-07.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t7/lcdrange.h */
+/*! \file t7/lcdrange.cpp */
+/*! \file t7/main.cpp */
+
+/*! \page tutorial1-07.html
+
+\title Qt Tutorial - Chapter 7: One Thing Leads to Another
+
+\img t7.png Screenshot of tutorial seven
+
+This example shows how to create custom widgets with signals and
+slots, and how to connect them together in more complex ways. For the
+first time, the source is split among several files which we've placed
+in the \c t7 subdirectory.
+
+\list
+\i \l t7/lcdrange.h contains the LCDRange class definition.
+\i \l t7/lcdrange.cpp contains the LCDRange implementation.
+\i \l t7/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+\section2 \l t7/lcdrange.h
+
+This file is mainly lifted from \link tutorial1-06.html#main main.cpp \endlink in
+Chapter 6; only the changes are noted here.
+
+\quotefile t7/lcdrange.h
+
+\skipto ifndef
+\printuntil define
+
+This is the classic C construction to avoid errors if a header file
+happens to be included more than once. If you don't use it already,
+it is a very good habit to develop. The #ifndef should enclose \e all of the
+header file.
+
+\printline include
+
+\c qvbox.h is included. LCDRange inherits QVBox, and the header file
+of a parent class must always be included. We cheated a bit in the
+previous chapters, and we let \c qwidget.h be included indirectly via
+other header files such as \c qpushbutton.h.
+
+\printline QSlider
+
+This is another classic trick, but one that's much less used often. Because
+we don't need QSlider in the \e interface of the class, only in the
+implementation, we use a forward declaration of the class in the
+header file and include the header file for QSlider in the .cpp
+file.
+
+This makes the compilation of big projects much faster, because when a
+header file has changed, fewer files need to be recompiled. It can
+often speed up big compilations by a factor of two or more.
+
+\skipto LCDRange
+\printuntil parent=0
+
+Note the Q_OBJECT. This macro must be included in \e all classes that
+contain signals and/or slots. If you are curious, it defines the
+functions that are implemented in the
+\link metaobjects.html meta object file \endlink.
+
+\printline value
+\printuntil valueChanged
+
+These three members make up an interface between this widget and other
+components in a program. Until now, LCDRange didn't really have an
+interface at all.
+
+value() is a public function for accessing the value of the LCDRange.
+setValue() is our first custom slot and valueChanged() is our first
+custom signal.
+
+Slots must be implemented in the normal way (remember that a slot is also
+a C++ member function). Signals are automatically implemented in the
+\link signalsandslots.html meta object\endlink file. Signals follow the
+access rules of protected C++ functions (i.e., they can be emitted only
+by the class they are defined in or by classes inheriting from it).
+
+The signal valueChanged() is used when the LCDRange's value has
+changed - just as you guessed from the name. This is not the last
+signal you'll see called <i>something</i>Changed().
+
+\section2 \l t7/lcdrange.cpp
+
+\quotefile t7/lcdrange.cpp
+
+This file is mainly lifted from \link tutorial1-06.html#main t6/main.cpp \endlink, and
+only the changes are noted here.
+
+\skipto connect
+\printline connect
+\printline display
+\printline connect
+\printline valueChanged
+
+This code is from the LCDRange constructor.
+
+The first connect is the same that you have seen in the previous chapter.
+The second is new; it connects slider's valueChanged() signal to this
+object's valueChanged \e signal. Connect() with 3 arguments always
+connects to signals or slots in \c this object.
+
+Yes, that's right. Signals can be connected to other signals. When
+the first is emitted, the second signal is also emitted.
+
+Let's look at what happens when the user operates the slider. The
+slider sees that its value has changed and emits the valueChanged()
+signal. That signal is connected both to the display() slot of the
+QLCDNumber and to the valueChanged() signal of the LCDRange.
+
+Thus, when the signal is emitted, LCDRange emits its own
+valueChanged() signal. In addition, QLCDNumber::display() is called
+and shows the new number.
+
+Note that you're not guaranteed any particular order of execution -
+LCDRange::valueChanged() may be emitted before or after
+QLCDNumber::display()and is entirely arbitrary.
+
+\skipto LCDRange::value
+\printuntil }
+
+The implementation of value() is straightforward; it simply returns
+the slider's value.
+
+\printline setValue
+\printuntil }
+
+The implementation of setValue() is equally straightforward. Note
+that because the slider and LCD number are connected, setting the
+slider's value automatically updates the LCD number as well. In
+addition, the slider will automatically adjust the value if it is
+outside its legal range.
+
+\section2 \l t7/main.cpp
+
+\quotefile t7/main.cpp
+
+\skipto previous
+\printline previous
+\printuntil setValue
+\printline previous
+\printline }
+\printline }
+
+All of main.cpp is copied from the previous chapter except in
+the constructor for MyWidget. When we create the 16 LCDRange object, we
+now connect them using the \link signalsandslots.html
+signal/slot\endlink mechanism. Each has its valueChanged() signal
+connected to the setValue() slot in the previous one. Because LCDRange
+emits the signal valueChanged() when its value changes (surprise!), we
+are here creating a "chain" of signals and slots.
+
+\target compiling
+\section1 Compiling
+
+Creating a makefile for a multi-file application is no different from
+creating one for a single-file application. If you've saved all the
+files in this example in their own directory, all you have to do is:
+\code
+qmake -project
+qmake
+\endcode
+
+The first command tells \link qmake-manual.book qmake\endlink to
+create a \c .pro (project) file. The second command tells it to create
+a (platform-specific) makefile based on the project file. You should
+now be able to type \c make (or \c nmake if you're using Visual
+Studio) to build your application.
+
+\section1 Behavior
+
+On startup, the program's appearance is identical to the previous one.
+Try operating the slider to the bottom right...
+
+\section1 Exercises
+
+Use the bottom right slider to set all LCDs to 50. Then set the top
+half to 40 by clicking once to the left of the slider handle. Now,
+use the one to the left of the last one operated to set the first
+seven LCDs back to 50.
+
+Click to the left of the handle on the bottom right slider. What
+happens?  Why is this the correct behavior?
+
+You're now ready for \link tutorial1-08.html Chapter 8.\endlink
+
+[\link tutorial1-06.html Previous tutorial\endlink]
+[\link tutorial1-08.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t8/lcdrange.h */
+/*! \file t8/lcdrange.cpp */
+/*! \file t8/cannon.h */
+/*! \file t8/cannon.cpp */
+/*! \file t8/main.cpp */
+
+/*! \page tutorial1-08.html
+
+\title Qt Tutorial - Chapter 8: Preparing for Battle
+
+\img t8.png Screenshot of tutorial eight
+
+In this example, we introduce the first custom widget that can paint
+itself. We also add a useful keyboard interface (with two lines of
+code).
+
+\list
+\i \l t8/lcdrange.h contains the LCDRange class definition.
+\i \l t8/lcdrange.cpp contains the LCDRange implementation.
+\i \l t8/cannon.h contains the CannonField class definition.
+\i \l t8/cannon.cpp contains the CannonField implementation.
+\i \l t8/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+\section2 \l t8/lcdrange.h
+
+This file is very similar to the lcdrange.h in Chapter 7. We have added
+one slot: setRange().
+
+\quotefile t8/lcdrange.h
+
+\skipto setRange
+\printline setRange
+
+We now add the possibility of setting the range of the LCDRange.
+Until now, it has been fixed at 0..99.
+
+\section2 \l t8/lcdrange.cpp
+
+\quotefile t8/lcdrange.cpp
+
+There is a change to the constructor (we'll discuss that later).
+
+\skipto ::setRange
+\printuntil slider
+\printline }
+
+SetRange() sets the range of the slider in the LCDRange. Because we
+have set up the QLCDNumber to always display two digits, we want to
+limit the possible range of \c minVal and \c maxVal to 0..99 to avoid
+overflow of the QLCDNumber. (We could have allowed values down to -9
+but chose not to.)  If the arguments are illegal, we use Qt's
+qWarning() function to issue a warning to the user and return
+immediately. qWarning() is a printf-like function that by default
+sends its output to \c stderr. If you want, you can install your own handler
+function using \l ::qInstallMsgHandler().
+
+\section2 \l t8/cannon.h
+
+CannonField is a new custom widget that knows how to display itself.
+
+\quotefile t8/cannon.h
+
+\skipto include
+\skipto class
+\printuntil parent=0
+
+CannonField inherits QWidget, and we use the same idiom as for LCDRange.
+
+\printuntil angleChanged
+
+For the time being, CannonField only contains an angle value for which we
+provide an interface using the same idiom as for value in LCDRange.
+
+\printline protected
+\printline paintEvent
+
+This is the second of the many event handlers in QWidget that we
+encounter. This virtual function is called by Qt whenever a widget needs
+to update itself (i.e., paint the widget's surface).
+
+
+\section2 \l t8/cannon.cpp
+
+\quotefile t8/cannon.cpp
+
+\skipto ::CannonField
+\printuntil {
+
+Again, we use the same idiom as for LCDRange in the previous chapter.
+
+\printuntil }
+
+The constructor initializes the angle value to 45 degrees and sets a
+custom palette for this widget.
+
+This palette uses the indicated color as background and picks other
+colors suitably. (For this widget only the background and text
+colors will actually be used.)
+
+\skipto ::setAngle
+\printuntil emit
+\printline }
+
+This function sets the angle value. We have chosen a legal range of
+5..70 and adjust the given number of degrees accordingly. We have
+chosen not to issue a warning if the new angle is out of range.
+
+If the new angle equals the old one, we return immediately. It is
+important to only emit the signal angleChanged() when the angle \e
+really has changed.
+
+Then we set the new angle value and repaint our widget. The \l
+QWidget::repaint() function clears the widget (usually filling it with
+its background color) and sends a paint event to the widget. This
+results in a call to the paint event function of the widget.
+
+Finally, we emit the angleChanged() signal to tell the outside world
+that the angle has changed. The \c emit keyword is unique to Qt and
+not regular C++ syntax. In fact, it is a macro.
+
+\skipto ::paintEvent
+\printuntil drawText
+\printline }
+
+This is our first attempt to write a paint event handler. The event
+argument contains a description of the paint event. \l QPaintEvent
+contains the region in the widget that must be updated. For the time
+being, we will be lazy and just paint everything.
+
+Our code displays the angle value in the widget at a fixed position.
+First we create a QString with some text and the angle; then we create
+a QPainter operating on this widget and use it to paint the string.
+We'll come back to QPainter later; it can do a great many things.
+
+
+\section2 \l t8/main.cpp
+
+\quotefile t8/main.cpp
+
+\skipto cannon.h
+\printline cannon.h
+
+We include our new class.
+
+\skipto MyWidget
+\printuntil };
+
+This time we include a single LCDRange and a CannonField in our top-level
+widget.
+
+\skipto angle
+\printline angle
+
+In the constructor, we create and set up our LCDRange.
+
+\printline setRange
+
+We set the LCDRange to accept ranges from 5 to 70 degrees.
+
+\printline cannonField
+\printline CannonField
+
+We create our CannonField.
+
+\printuntil setValue
+
+Here we connect the valueChanged() signal of the LCDRange to the
+setAngle() slot of the CannonField. This will update CannonField's angle
+value whenever the user operates the LCDRange. We also make the reverse
+connection so that changing the angle in the CannonField will update the
+LCDRange value. In our example we never change the angle of the
+CannonField directly; but by doing the last connect() we ensure that no
+future changes will disrupt the synchronization between those two values.
+
+This illustrates the power of component programming and proper
+encapsulation.
+
+Notice how important it is to emit the angleChanged() signal only when
+the angle actually changes. If both the LCDRange and the CannonField
+had omitted this check, the program would have entered an infinite
+loop upon the first change of one of the values.
+
+\printline QGridLayout
+\printline 2x2
+
+So far we have used the no-assembly-required QVBox and QGrid widgets
+for geometry management. Now, however, we want to have a little more
+control over the layout, and we switch to the more powerful QGridLayout
+class. QGridLayout isn't a widget; it is a different class that can
+manage the children of \e any widget.
+
+As the comment indicates, we create a two-by-two array with ten pixel
+borders. (The constructor for \l QGridLayout can be a little cryptic,
+so it's good to put in such comments.)
+
+\printline addWidget
+
+We add the Quit button in the top-left cell of the grid: 0, 0.
+
+\printline addWidget
+
+We put the angle LCDRange in the bottom-left cell, aligned to the top
+of its cell. (This alignment is one of the things QGridLayout allows
+but QGrid does not allow.)
+
+\printline addWidget
+
+We put the CannonField object in the bottom-right cell. (The top-
+right cell is empty.)
+
+\printline setColStretch
+
+We tell QGridLayout that the right column (column 1) is stretchable.
+Because the left column isn't (it has stretch factor 0, the default
+value), QGridLayout will try to let the left-hand widgets' sizes be
+unchanged and will resize just the CannonField when the MyWidget is
+resized.
+
+\printline setValue
+
+We set an initial angle value. Note that this will trigger the
+connection from LCDRange to CannonField.
+
+\printline setFocus
+
+Our last action is to set \c angle to have keyboard focus so that
+keyboard input will go to the LCDRange widget by default.
+
+LCDRange does not contain any keyPressEvent(), so that would seem not
+to be terribly useful. However, its constructor just got a new line:
+
+\quotefile t8/lcdrange.cpp
+\skipto setFocusProxy
+\printline setFocusProxy
+
+The LCDRange sets the slider to be its focus proxy. That means that
+when someone (the program or the user) wants to give the LCDRange
+keyboard focus, the slider should take care of it. QSlider has a decent
+keyboard interface, so with just one line of code we've given LCDRange
+one.
+
+\section1 Behavior
+
+The keyboard now does something - the arrow keys, Home, End, PageUp
+and PageDown all do something vaguely sensible.
+
+When the slider is operated, the CannonField displays the new angle
+value. Upon resizing, CannonField is given as much space as possible.
+
+On Windows machines with an 8-bit display the new background color is
+dithered to death. The next chapter works around this.
+
+(See \link tutorial1-07.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Try to resize the window. What happens if you make it really narrow
+or really squat?
+
+If you remove the AlignTop, what happens to the LCDRange's position
+and size?  Why?
+
+If you give the left-hand column a non-zero stretch factor, what
+happens when you resize the window?
+
+Leave out the setFocus() call. Which behavior do you prefer?
+
+Try to change "Quit" to "&Quit" in the QButton::setText() call. How
+does the button's look change?  What happens if you press Alt+Q while
+the program's running?  (It is Meta+Q on a few keyboards.)
+
+Center the text in the CannonField.
+
+You're now ready for \link tutorial1-09.html Chapter 9.\endlink
+
+[\link tutorial1-07.html Previous tutorial\endlink]
+[\link tutorial1-09.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t9/lcdrange.h */
+/*! \file t9/lcdrange.cpp */
+/*! \file t9/cannon.h */
+/*! \file t9/cannon.cpp */
+/*! \file t9/main.cpp */
+
+/*! \page tutorial1-09.html
+
+\title Qt Tutorial - Chapter 9: With Cannon You Can
+
+\img t9.png Screenshot of tutorial nine
+
+In this example we become graphic by drawing a cute little blue
+cannon. Only cannon.cpp differs from the previous chapter.
+
+\list
+\i \l t9/lcdrange.h contains the LCDRange
+class definition.
+\i \l t9/lcdrange.cpp contains the LCDRange
+implementation.
+\i \l t9/cannon.h contains the CannonField class
+definition.
+\i \l t9/cannon.cpp contains the CannonField
+implementation.
+\i \l t9/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+\section2 \l t9/cannon.cpp
+
+\quotefile t9/cannon.cpp
+
+\skipto ::paintEvent
+\printuntil QPainter
+
+We'll now start to use QPainter in earnest. We create a painter that
+operates on this widget.
+
+\printline setBrush
+
+When QPainter fills a rectangle, a circle, or whatever, it fills the
+shape using its brush. Here we set it to use a blue brush. (We
+could also use a pattern.)
+
+\printline setPen
+
+And the edges of what QPainter draws are drawn using the pen. Here we
+set it to NoPen, meaning that there will be no special edge when we
+draw something; the blue brush will go all the way to the edges of
+the things we draw.
+
+\skipto translate
+\printline translate
+
+The \l QPainter::translate() function translates the coordinate
+system of the QPainter; i.e., it moves it by an offset. Here we set
+the (0, 0) point to the bottom-left corner of the widget. The x and
+y directions remain unchanged, i.e., all the y coordinates inside the
+widget are now negative (see \link coordsys.html The Coordinate
+System\endlink for more information about Qt's coordinate system).
+
+\printline drawPie
+
+The drawPie() function draws a pie shape inside the specified
+rectangle using a start angle and an arc length. The angles are
+specified in 1/16th of a degree. Zero degrees is at the 3 o'clock
+position. The drawing direction is counter-clockwise. Here we draw a
+quarter of a circle in the bottom-left corner of the widget. The pie
+is filled with blue and has no outline.
+
+\printline rotate
+
+The QPainter::rotate() function rotates the coordinate system of the
+QPainter around the origin. The rotation argument is a \c float given
+in degrees (not given in 1/16th of a degree as above) and clockwise.
+Here we rotate the coordinate system \c ang degrees counter-clockwise.
+
+\printline drawRect
+
+The QPainter::drawRect() function draws the specified rectangle. Here
+we draw the barrel of the cannon.
+
+It can often be difficult to envision the resulting drawing when the
+coordinate system has been transformed (translated, rotated, scaled, or
+sheared) as above.
+
+In this case the coordinate system is first translated and then rotated.
+If the rectangle QRect(33, -4, 15, 8) had been drawn in the translated
+coordinate system, it would have looked like this:
+
+\img t9_1.png The cannon translated but not rotated
+
+Note that the rectangle is clipped by the border of the CannonField
+widget. When we rotate the coordinate system, for instance 60
+degrees, the rectangle will be rotated around (0, 0), which is the
+bottom-left corner because we have translated the coordinate system.
+The result looks like this:
+
+\img t9_2.png The cannon translated and rotated
+
+We're done, except that we haven't explained why Windows didn't dither
+this time.
+
+\quotefile t9/main.cpp
+\skipto main
+\printline main
+\printline {
+\printline CustomColor
+\printline QApplication
+
+We tell Qt that we want a different color-allocation strategy for this
+program. There is no single correct color-allocation strategy. Because
+this program uses an unusual yellow but not many colors, \c
+CustomColor is best. There are several other allocation strategies; you can read about them in the \l QApplication::setColorSpec()
+documentation.
+
+Mostly you can ignore this, since the default is good. Occasionally
+some applications with unusual color use look bad; changing the
+allocation strategy often helps then.
+
+\section1 Behavior
+
+When the slider is operated the angle of the drawn cannon changes
+accordingly.
+
+The Q on the Quit button is now underlined, and Alt+Q does what you
+think it does. If you do not know why, you didn't do the exercises in
+Chapter 8.
+
+You may notice that the cannon flickers annoyingly, especially on a
+slow machine. We'll fix this in the next chapter.
+
+(See \link tutorial1-07.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Set a different pen instead of NoPen. Set a patterned brush.
+
+Try "Q&uit" or "Qu&it" as button text instead of "&Quit". What
+happens?
+
+You're now ready for \link tutorial1-10.html Chapter 10.\endlink
+
+[\link tutorial1-08.html Previous tutorial\endlink]
+[\link tutorial1-10.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t10/lcdrange.h */
+/*! \file t10/lcdrange.cpp */
+/*! \file t10/cannon.h */
+/*! \file t10/cannon.cpp */
+/*! \file t10/main.cpp */
+
+/*! \page tutorial1-10.html
+
+\title Qt Tutorial - Chapter 10: Smooth as Silk
+
+\img t10.png Screenshot of tutorial ten
+
+In this example, we introduce painting in a pixmap to remove flickering.
+We also add a force control.
+
+\list
+\i \l t10/lcdrange.h contains the LCDRange
+class definition.
+\i \l t10/lcdrange.cpp contains the LCDRange
+implementation.
+\i \l t10/cannon.h contains the CannonField class
+definition.
+\i \l t10/cannon.cpp contains the CannonField
+implementation.
+\i \l t10/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+\section2 \l t10/cannon.h
+
+The CannonField now has a force value in addition to the angle.
+
+\quotefile t10/cannon.h
+
+\skipto angle
+\printuntil forceChanged
+
+The interface to the force follows the same practice as for the angle.
+
+\skipto private
+\printuntil cannonRect
+
+We have put the definition of the cannon's enclosing rectangle in a
+separate function.
+
+\skipto ang
+\printuntil };
+
+The force is stored in the integer \c f.
+
+\section2 \l t10/cannon.cpp
+
+\quotefile t10/cannon.cpp
+
+\skipto include
+\skipto pixmap
+\printline pixmap
+
+We include the QPixmap class definition.
+
+\skipto ::CannonField
+\printuntil }
+
+The force (\c f) is initialized to zero.
+
+\skipto ::setAngle
+\printuntil }
+
+We have made a slight change in the setAngle() function. It repaints
+only the portion of the widget that contains the cannon. The FALSE
+argument indicates that the specified rectangle should not be erased
+before a paint event is sent to the widget. This speeds up and smooths
+the drawing a little bit.
+
+\skipto ::setForce
+\printuntil }
+
+The implementation of setForce() is quite similar to that of
+setAngle(). The only difference is that because we don't show the force
+value, we don't need to repaint the widget.
+
+\skipto ::paintEvent
+\printuntil return
+
+We have now optimized the paint event to repaint only the parts of the
+widget that need updating. First we check whether we have to paint
+anything at all, and we return if we don't.
+
+\printline cannonRect
+\printline pix
+
+Then we create a temporary pixmap, which we use for flicker-free
+painting. All the painting operations are done into this pixmap, and
+then the pixmap is drawn on the screen in a single operation.
+
+This is the essence of flicker-free drawing: Draw on each pixel
+precisely once. Less, and you get drawing errors. More, and you get
+flicker. It doesn't matter much in this example - when the code was
+written there were still machines slow enough for it to flicker, but
+not any more. We've kept the code for educational purposes.
+
+\printline fill
+
+We fill the pixmap with the background from this widget.
+
+\printline QPainter
+\printuntil end
+
+We paint, as in Chapter 9, but now we paint in the pixmap.
+
+At this point, we have a painter variable and a pixmap that looks
+precisely right, but we still haven't painted on the screen.
+
+\printline begin
+\printline drawPixmap
+
+So we open the painter on the CannonField itself and then draw the pixmap.
+
+That's all. A couple of extra lines at the top and a couple at the
+bottom, and the code is 100% flicker-free.
+
+\skipto cannonRect
+\printuntil }
+
+This function returns the rectangle enclosing the cannon in widget
+coordinates. First we create a rectangle with the size 50x50 and then
+move it so its bottom left corner is equal to the widget's own bottom-
+left corner.
+
+The \l QWidget::rect() function returns the widget's enclosing
+rectangle in the widget's own coordinates (where the top left corner
+is 0, 0).
+
+\section2 \l t10/main.cpp
+
+\quotefile t10/main.cpp
+
+\skipto MyWidget::MyWidget
+\printuntil {
+
+The constructor is mostly the same, but some new bits have been added.
+
+\skipto force
+\printline force
+\printline force
+
+We add a second LCDRange, which will be used to set the force.
+
+\skipto force
+\printline connect
+\printline cannonField
+\printline connect
+\printline force
+
+We connect the \c force widget and the \c cannonField widget, just like
+we did for the \c angle widget.
+
+\skipto QVBoxLayout
+\printline QVBoxLayout
+\printline addLayout
+\printline addWidget
+\printline addWidget
+
+In Chapter 9 we put \c angle in the lower-left cell of the layout.
+Now we want to have two widgets in that cell, so we make a vertical
+box, put the vertical box in the grid cell, and put each of \c angle
+and \c range in the vertical box.
+
+\skipto force
+\printline setValue
+
+We initialize the force value to 25.
+
+\section1 Behavior
+
+The flicker has gone and we have a force control.
+
+(See \link tutorial1-07.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+
+\section1 Exercises
+
+Make the size of the cannon barrel be dependent on the force.
+
+Put the cannon in the bottom-right corner.
+
+Try adding a better keyboard interface. For example, make + and -
+increase and decrease the force and enter shoot. Hint: \l QAccel and
+new addStep() and subtractStep() slots in LCDRange, like \l
+QSlider::addStep(). If you're bothered by the way the left and right
+keys work (I am!), change that too.
+
+You're now ready for \link tutorial1-11.html Chapter 11.\endlink
+
+[\link tutorial1-09.html Previous tutorial\endlink]
+[\link tutorial1-11.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t11/lcdrange.h */
+/*! \file t11/lcdrange.cpp */
+/*! \file t11/cannon.h */
+/*! \file t11/cannon.cpp */
+/*! \file t11/main.cpp */
+
+/*! \page tutorial1-11.html
+
+\title Qt Tutorial - Chapter 11: Giving It a Shot
+
+\img t11.png Screenshot of tutorial eleven
+
+In this example we introduce a timer to implement animated shooting.
+
+\list
+\i \l t11/lcdrange.h contains the LCDRange
+class definition.
+\i \l t11/lcdrange.cpp contains the LCDRange
+implementation.
+\i \l t11/cannon.h contains the CannonField class
+definition.
+\i \l t11/cannon.cpp contains the CannonField
+implementation.
+\i \l t11/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+\section2 \l t11/cannon.h
+
+The CannonField now has shooting capabilities.
+
+\quotefile t11/cannon.h
+
+\skipto shoot
+\printline shoot
+
+Calling this slot will make the cannon shoot if a shot is not in the air.
+
+\printline private
+\printline moveShot
+
+This private slot is used to move the shot while it is in the air,
+using a \l QTimer.
+
+\skipto private
+\printline private
+\printline paintShot
+
+This private function paints the shot.
+
+\skipto shotRect
+\printline shotRect
+
+This private function returns the shot's enclosing rectangle if
+one is in the air; otherwise the returned rectangle is undefined.
+
+\skipto timerCount
+\printuntil shoot_f
+\printline };
+
+These private variables contain information that describes the shot. The
+\c timerCount keeps track of the time passed since the shot was fired.
+The \c shoot_ang is the cannon angle and \c shoot_f is the cannon force
+when the shot was fired.
+
+
+\section2 \l t11/cannon.cpp
+
+\quotefile t11/cannon.cpp
+
+\skipto include
+\skipto math
+\printline math
+
+We include the math library because we need the sin() and cos() functions.
+
+\skipto ::CannonField
+\printuntil }
+
+We initialize our new private variables and connect the \l
+QTimer::timeout() signal to our moveShot() slot. We'll move the
+shot every time the timer times out.
+
+\skipto ::shoot
+\printuntil start
+\printline }
+
+This function shoots a shot unless a shot is in the air. The \c timerCount
+is reset to zero. The \c shoot_ang and \c shoot_f are set to the current
+cannon angle and force. Finally, we start the timer.
+
+\skipto ::moveShot
+\printuntil repaint
+\printline }
+
+moveShot() is the slot that moves the shot, called every 50
+milliseconds when the QTimer fires.
+
+Its tasks are to compute the new position, repaint the screen with the
+shot in the new position, and if necessary, stop the timer.
+
+First we make a \l QRegion that holds the old shotRect(). A QRegion
+is capable of holding any sort of region, and we'll use it here to
+simplify the painting. ShotRect() returns the rectangle where the
+shot is now - it is explained in detail later.
+
+Then we increment the \c timerCount, which has the effect of moving the
+shot one step along its trajectory.
+
+Next we fetch the new shot rectangle.
+
+If the shot has moved beyond the right or bottom edge of the widget, we
+stop the timer or we add the new shotRect() to the QRegion.
+
+Finally, we repaint the QRegion. This will send a single paint event
+for just the one or two rectangles that need updating.
+
+\skipto ::paintEvent
+\printuntil }
+
+The paint event function has been split in two since the previous
+chapter. Now we fetch the bounding rectangle of the region that
+needs painting, check whether it intersects either the cannon and/or
+the shot, and if necessary, call paintCannon() and/or paintShot().
+
+\skipto ::paintShot
+\printuntil drawRect
+\printline }
+
+This private function paints the shot by drawing a black filled rectangle.
+
+We leave out the implementation of paintCannon(); it is the same as
+the paintEvent() from the previous chapter.
+
+\skipto ::shotRect
+\printuntil return
+\printline }
+
+This private function calculates the center point of the shot and returns
+the enclosing rectangle of the shot. It uses the initial cannon force and
+angle in addition to \c timerCount, which increases as time passes.
+
+The formula used is the classical Newtonian formula for frictionless
+movement in a gravity field. For simplicity, we've chosen to
+disregard any Einsteinian effects.
+
+We calculate the center point in a coordinate system where y
+coordinates increase upward. After we have calculated the center
+point, we construct a QRect with size 6x6 and move its center point to
+the point calculated above. In the same operation we convert the
+point into the widget's coordinate system (see \link coordsys.html The
+Coordinate System\endlink).
+
+The qRound() function is an inline function defined in qglobal.h (included
+by all other Qt header files). qRound() rounds a double to the closest
+integer.
+
+\section2 \l t11/main.cpp
+
+\quotefile t11/main.cpp
+
+\skipto class
+\printuntil };
+
+The only addition is the Shoot button.
+
+\skipto ::MyWidget
+\skipto shoot
+\printuntil setFont
+
+In the constructor we create and set up the Shoot button exactly like we
+did with the Quit button. Note that the first argument to the constructor
+is the button text, and the third is the widget's name.
+
+\skipto connect
+\printline connect
+
+Connects the clicked() signal of the Shoot button to the shoot() slot
+of the CannonField.
+
+
+\section1 Behavior
+
+The cannon can shoot, but there's nothing to shoot at.
+
+(See \link tutorial1-07.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+
+\section1 Exercises
+
+Make the shot a filled circle. Hint: \l QPainter::drawEllipse() may
+help.
+
+Change the color of the cannon when a shot is in the air.
+
+You're now ready for \link tutorial1-12.html Chapter 12.\endlink
+
+[\link tutorial1-10.html Previous tutorial\endlink]
+[\link tutorial1-12.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t12/lcdrange.h */
+/*! \file t12/lcdrange.cpp */
+/*! \file t12/cannon.h */
+/*! \file t12/cannon.cpp */
+/*! \file t12/main.cpp */
+
+/*! \page tutorial1-12.html
+
+\title Qt Tutorial - Chapter 12: Hanging in the Air the Way Bricks Don't
+
+\img t12.png Screenshot of tutorial twelve
+
+In this example, we extend our LCDRange class to include a text label.
+We also provide something to shoot at.
+
+\list
+\i \l t12/lcdrange.h contains the LCDRange
+class definition.
+\i \l t12/lcdrange.cpp contains the LCDRange
+implementation.
+\i \l t12/cannon.h contains the CannonField class
+definition.
+\i \l t12/cannon.cpp contains the CannonField
+implementation.
+\i \l t12/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+
+\section2 \l t12/lcdrange.h
+
+The LCDRange now has a text label.
+
+\quotefile t12/lcdrange.h
+
+\skipto QLabel
+\printline QLabel
+
+We name declare QLabel because we want to use a pointer to it in the class
+definition.
+
+\skipto class
+\printuntil parent=0
+\printline parent=0
+\printline name=0
+
+We have added a new constructor that sets the label text in addition to
+the parent and name.
+
+\skipto text
+\printline text
+
+This function returns the label text.
+
+\skipto setText
+\printline setText
+
+This slot sets the label text.
+
+\skipto private
+\printuntil init
+
+Because we now have two constructors, we have chosen to put the common
+initialization in the private init() function.
+
+\skipto QLabel
+\printline label
+
+We also have a new private variable: a QLabel. QLabel is one of Qt's
+standard widgets and can show a text or a pixmap with or without a
+frame.
+
+
+\section2 \l t12/lcdrange.cpp
+
+\quotefile t12/lcdrange.cpp
+
+\skipto qlabel
+\printline include
+
+Here we include the QLabel class definition.
+
+\skipto ::LCDRange
+\printuntil }
+
+This constructor calls the init() function, which contains the common
+initialization code.
+
+\skipto ::LCDRange
+\printuntil }
+
+This constructor first calls init() and then sets the label text.
+
+\skipto ::init
+\printuntil }
+
+The setup of \c lcd and \c slider is the same as in the previous
+chapter. Next we create a QLabel and tell it to align the contents
+centered (both vertically and horizontally). The connect() statements
+have also been taken from the previous chapter.
+
+\skipto ::text
+\printuntil }
+
+This function returns the label text.
+
+\skipto ::setText
+\printuntil }
+
+This function sets the label text.
+
+\section2 \l t12/cannon.h
+
+The CannonField now has two new signals: hit() and missed(). In addition
+it contains a target.
+
+\quotefile t12/cannon.h
+
+\skipto slots
+\skipto newTarget
+\printline newTarget
+
+This slot creates a target at a new position.
+
+\skipto signals
+\printuntil missed
+
+The hit() signal is emitted when a shot hits the target. The missed()
+signal is emitted when the shot moves beyond the right or bottom edge
+of the widget (i.e., it is certain that it has not and will not
+hit the target).
+
+\skipto paintTarget
+\printline paintTarget
+
+This private function paints the target.
+
+\skipto targetRect
+\printline targetRect
+
+This private function returns the enclosing rectangle of the target.
+
+\skipto target
+\printline target
+
+This private variable contains the center point of the target.
+
+
+\section2 \l t12/cannon.cpp
+
+\quotefile t12/cannon.cpp
+
+\skipto qdatetime
+\printline qdatetime
+
+We include the QDate, QTime, and QDateTime class definitions.
+
+\skipto stdlib
+\printline stdlib
+
+We include the stdlib library because we need the rand() function.
+
+\skipto newTarget
+\printline newTarget
+
+This line has been added to the constructor. It creates a "random"
+position for the target. In fact, the newTarget() function will try
+to paint the target. Because we are in a constructor, the CannonField
+widget is invisible. Qt guarantees that no harm is done when calling
+repaint() on a hidden widget.
+
+\skipto ::newTarget
+\printuntil repaint
+\printline }
+
+This private function creates a target center point at a new "random"
+position.
+
+We use the rand() function to fetch random integers. The rand() function
+normally returns the same series of numbers each time you run a program.
+This would make the target appear at the same position every time. To
+avoid this, we must set a random seed the first time this function is
+called. The random seed must also be random in order to avoid equal random
+number series. The solution is to use the number of seconds that have
+passed since midnight as a pseudo-random value.
+
+First we create a static bool local variable. A static variable like
+this one is guaranteed to keep its value between calls to the function.
+
+The \c if test will succeed only the first time this function is called
+because we set \c first_time to FALSE inside the \c if block.
+
+Then we create the QTime object \c midnight, which represents the time
+00:00:00. Next we fetch the number of seconds from midnight until
+now and use it as a random seed. See the documentation for \l QDate,
+\l QTime, and \l QDateTime for more information.
+
+Finally we calculate the target's center point. We keep it within
+the rectangle (x=200, y=35, width=190, height=255), (i.e., the
+possible x and y values are x = 200..389 and y = 35..289) in a
+coordinate system where we put y position 0 at the bottom edge of the
+widget and let y values increase upwards  X is as normal, with 0 at
+the left edge and with x values increasing to the right.
+
+By experimentation we have found this to always be in reach of the shot.
+
+Note that rand() returns a random integer >= 0.
+
+\skipto ::moveShot
+\printuntil QRect
+
+This part of the timer event has not changed from the previous chapter.
+
+\printuntil hit
+
+This \c if statement checks whether the shot rectangle intersects the
+target rectangle. If it does, the shot has hit the target (ouch!).
+We stop the shoot timer and emit the hit() signal to tell the outside
+world that a target was destroyed, and return.
+
+Note that we could have created a new target on the spot, but because the
+CannonField is a component we leave such decisions to the user of the
+component.
+
+\printuntil missed
+
+This \c if statement is the same as in the previous chapter, except that
+it now emits the missed() signal to tell the outside world about the
+failure.
+
+\printuntil }
+
+And the rest of the function is as before.
+
+CannonField::paintEvent() is as before, except that this has been
+added:
+
+\skipto ::paintEvent
+\skipto targetRect
+\printline updateR
+\printline paintTarget
+
+These two lines make sure that the target is also painted when necessary.
+
+\skipto ::paintTarget
+\printuntil }
+
+This private function paints the target; a rectangle filled with red and
+with a black outline.
+
+\skipto ::targetRect
+\printuntil }
+
+This private function returns the enclosing rectangle of the target.
+Remember from newTarget() that the \c target point uses y coordinate 0 at
+the bottom of the widget. We calculate the point in widget coordinates
+before we call \l QRect::moveCenter().
+
+The reason we have chosen this coordinate mapping is to fix the distance
+between the target and the bottom of the widget. Remember that the widget
+can be resized by the user or the program at any time.
+
+\section2 \l t12/main.cpp
+
+\quotefile t12/main.cpp
+
+There are no new members in the MyWidget class, but we have slightly
+changed the constructor to set the new LCDRange text labels.
+
+\skipto ::MyWidget
+\skipto angle
+\printline ANGLE
+
+We set the angle text label to "ANGLE".
+
+
+\skipto force
+\printline FORCE
+
+We set the force text label to "FORCE".
+
+
+\section1 Behavior
+
+The LCDRange widgets look a bit strange - the built-in layout
+management in QVBox gives the labels too much space and the rest not
+enough. We'll fix that in the next chapter.
+
+(See \link tutorial1-07.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+\section1 Exercises
+
+Make a cheat button that, when pressed, makes the CannonField display
+the shot trajectory for five seconds.
+
+If you did the "round shot" exercise from the previous chapter, try
+changing the shotRect() to a shotRegion() that returns a \l QRegion so
+you can have really accurate collision detection.
+
+Make a moving target.
+
+Make sure that the target is always created entirely on-screen.
+
+Make sure that the widget cannot be resized so that the target isn't
+visible. Hint: \l QWidget::setMinimumSize() is your friend.
+
+Not easy; make it possible to have several shots in the air at the
+same time. Hint: make a Shot object.
+
+You're now ready for \link tutorial1-13.html Chapter 13.\endlink
+
+[\link tutorial1-11.html Previous tutorial\endlink]
+[\link tutorial1-13.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t13/lcdrange.h */
+/*! \file t13/lcdrange.cpp */
+/*! \file t13/cannon.h */
+/*! \file t13/cannon.cpp */
+/*! \file t13/gamebrd.h */
+/*! \file t13/gamebrd.cpp */
+/*! \file t13/main.cpp */
+
+/*! \page tutorial1-13.html
+
+\title Qt Tutorial - Chapter 13: Game Over
+
+\img t13.png Screenshot of tutorial thirteen
+
+In this example we start to approach a real playable game with a
+score. We give MyWidget a new name (GameBoard) and add some slots.
+
+We put the definition in gamebrd.h and the implementation in gamebrd.cpp.
+
+The CannonField now has a game over state.
+
+The layout problems in LCDRange are fixed.
+
+\list
+\i \l t13/lcdrange.h contains the LCDRange
+class definition.
+\i \l t13/lcdrange.cpp contains the LCDRange
+implementation.
+\i \l t13/cannon.h contains the CannonField class
+definition
+\i \l t13/cannon.cpp contains the CannonField
+implementation.
+\i \l t13/gamebrd.h contains the GameBoard
+class definition.
+\i \l t13/gamebrd.cpp contains the GameBoard
+implementation.
+\i \l t13/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+
+\section2 \l t13/lcdrange.h
+
+\quotefile t13/lcdrange.h
+
+\skipto include
+\printuntil QWidget
+
+We inherit QWidget rather than QVBox. QVBox is very easy to use, but
+again it showed its limitations so we switch to the more powerful and
+slightly harder to use QVBoxLayout. (As you remember, QVBoxLayout is
+not a widget, it manages one.)
+
+\section2 \l t13/lcdrange.cpp
+
+\quotefile t13/lcdrange.cpp
+
+\skipto layout
+\printline layout
+
+We need to include qlayout.h now to get the other layout management
+API.
+
+\printline LCDRange
+\printline QWidget
+
+We inherit QWidget in the usual way.
+
+The other constructor has the same change. init() is unchanged,
+except that we've added some lines at the end:
+
+\skipto QVBoxLayout
+\printline QVBoxLayout
+
+We create a QVBoxLayout with all the default values, managing this
+widget's children.
+
+\printline addWidget
+
+At the top we add the QLCDNumber with a non-zero stretch.
+
+\printline addWidget
+\printline addWidget
+
+Then we add the other two, both with the default zero stretch.
+
+This stretch control is something QVBoxLayout (and QHBoxLayout, and
+QGridLayout) offers but classes like QVBox do not. In this case
+we're saying that the QLCDNumber should stretch and the others should
+not.
+
+\section2 \l t13/cannon.h
+
+The CannonField now has a game over state and a few new functions.
+
+\quotefile t13/cannon.h
+
+\skipto gameOver
+\printline gameOver
+
+This function returns TRUE if the game is over or FALSE if a game
+is going on.
+
+\skipto setGameOver
+\printuntil restartGame
+
+Here are two new slots: setGameOver() and restartGame().
+
+\skipto canShoot
+\printline canShoot
+
+This new signal indicates that the CannonField is in a state where the
+shoot() slot makes sense. We'll use it below to enable/disable the
+Shoot button.
+
+\skipto gameEnded
+\printline gameEnded
+
+This private variable contains the game state. TRUE means that the
+game is over, and FALSE means that a game is going on.
+
+\section2 \l t13/cannon.cpp
+
+\quotefile t13/cannon.cpp
+
+\skipto ::CannonField
+\skipto gameEnded
+\printline gameEnded
+
+This line has been added to the constructor. Initially, the game is not
+over (luckily for the player :-).
+
+\skipto ::shoot
+\printuntil }
+
+We added a new isShooting() function, so shoot() uses it instead of
+testing directly. Also, shoot tells the world that the CannonField
+cannot shoot now.
+
+\skipto ::setGameOver
+\printuntil }
+
+This slot ends the game. It must be called from outside CannonField,
+because this widget does not know when to end the game. This is an
+important design principle in component programming. We choose to
+make the component as flexible as possible to make it usable with
+different rules (for example, a multi-player version of this in which the
+first player to hit ten times wins could use the CannonField unchanged).
+
+If the game has already been ended we return immediately. If a game is
+going on we stop the shot, set the game over flag, and repaint the entire
+widget.
+
+\skipto ::restartGame
+\printuntil }
+
+This slot starts a new game. If a shot is in the air, we stop shooting.
+We then reset the \c gameEnded variable and repaint the widget.
+
+moveShot() too emits the new canShoot(TRUE) signal at the same time as
+either hit() or miss().
+
+Modifications in CannonField::paintEvent():
+
+\skipto ::paintEvent
+\printuntil }
+
+The paint event has been enhanced to display the text "Game Over" if
+the game is over, i.e.,  \c gameEnded is TRUE. We don't bother to
+check the update rectangle here because speed is not critical when
+the game is over.
+
+To draw the text we first set a black pen; the pen color is used
+when drawing text. Next we choose a 48 point bold font from the
+Courier family. Finally we draw the text centered in the widget's
+rectangle. Unfortunately, on some systems (especially X servers with
+Unicode fonts) it can take a while to load such a large font. Because
+Qt caches fonts, you will notice this only the first time the font is
+used.
+
+\printuntil }
+
+We draw the shot only when shooting and the target only when playing
+(that is, when the game is not ended).
+
+
+\section2 \l t13/gamebrd.h
+
+This file is new. It contains the definition of the GameBoard class,
+which was last seen as MyWidget.
+
+\quotefile t13/gamebrd.h
+
+\skipto include
+\skipto class
+\printuntil };
+
+We have now added four slots. These are protected and are used internally.
+We have also added two QLCDNumbers (\c hits and \c shotsLeft) which display
+the game status.
+
+
+\section2 \l t13/gamebrd.cpp
+
+This file is new. It contains the implementation of the GameBoard
+class, which was last seen as MyWidget.
+
+\quotefile t13/gamebrd.cpp
+
+We have made some changes in the GameBoard constructor.
+
+\skipto ::GameBoard
+\skipto cannonField
+\printline cannonField
+
+\c cannonField is now a member variable, so we carefully change the
+constructor to use it. (The \e good programmers at Trolltech never
+forget this, but I do. Caveat programmor - if "programmor" is Latin,
+at least. Anyway, back to the code.)
+
+\skipto hit
+\printline connect
+\printline hit
+\printline connect
+\printline missed
+
+This time we want to do something when the shot has hit or missed the
+target. Thus we connect the hit() and missed() signals of the
+CannonField to two protected slots with the same names in this class.
+
+\skipto shoot
+\skipto connect
+\printline fire
+
+Previously we connected the Shoot button's clicked() signal directly
+to the CannonField's shoot() slot. This time we want to keep track of
+the number of shots fired, so we connect it to a protected slot in
+this class instead.
+
+Notice how easy it is to change the behavior of a program when you are
+working with self-contained components.
+
+\printline connect
+\printline setEnabled
+
+We also use the cannonField's canShoot() signal to enable or disable
+the Shoot button appropriately.
+
+\skipto restart
+\printuntil connect
+
+We create, set up, and connect the New Game button as we have done
+with the other buttons. Clicking this button will activate the
+newGame() slot in this widget.
+
+\printuntil shotsLeftL
+\printline QLabel
+
+We create four new widgets. Note that we don't bother to keep the
+pointers to the QLabel widgets in the GameBoard class because there's
+nothing much we want to do with them. Qt will delete them when the
+GameBoard widget is destroyed, and the layout classes will resize them
+appropriately.
+
+\skipto QHBoxLayout
+\printuntil addStretch
+\printline addWidget
+
+The number of widgets in the top-right cell is getting large. Once it
+was empty; now it's full enough that we group together the layout
+setting for better overview.
+
+Notice that we let all the widgets have their preferred sizes, instead
+putting the stretch just to the left of the New Game button.
+
+\skipto newGame
+\printline newGame
+\printline }
+
+We're all done constructing the GameBoard, so we start it all using
+newGame(). (NewGame() is a slot, but as we said, slots can be used as
+ordinary functions, too.)
+
+\skipto ::fire
+\printuntil }
+
+This function fires a shot. If the game is over or if there is a shot in the
+air, we return immediately. We decrement the number of shots left and tell
+the cannon to shoot.
+
+\skipto ::hit
+\printuntil }
+
+This slot is activated when a shot has hit the target. We increment the
+number of hits. If there are no shots left, the game is over. Otherwise,
+we make the CannonField generate a new target.
+
+\skipto ::missed
+\printuntil }
+
+This slot is activated when a shot has missed the target. If there are no
+shots left, the game is over.
+
+\skipto ::newGame
+\printuntil }
+
+This slot is activated when the user clicks the Restart button. It is
+also called from the constructor. First it sets the number of shots
+to 15. Note that this is the only place in the program where we set
+the number of shots. Change it to whatever you like to change the
+game rules. Next we reset the number of hits, restart the game, and
+generate a new target.
+
+\section2 \l t13/main.cpp
+
+This file has just been on a diet. MyWidget is gone, and the only
+thing left is the main() function, unchanged except for the name
+change.
+
+
+\section1 Behavior
+
+The cannon can shoot at a target; a new target is automatically created
+when one has been hit.
+
+Hits and shots left are displayed and the program keeps track of them.
+The game can end, and there's a button to start a new game.
+
+(See \link tutorial1-07.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+
+\section1 Exercises
+
+Add a random wind factor and show it to the user.
+
+Make some splatter effects when the shot hits the target.
+
+Implement multiple targets.
+
+You're now ready for \link tutorial1-14.html Chapter 14.\endlink
+
+[\link tutorial1-12.html Previous tutorial\endlink]
+[\link tutorial1-14.html Next tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/
+
+/*! \file t14/lcdrange.h */
+/*! \file t14/lcdrange.cpp */
+/*! \file t14/cannon.h */
+/*! \file t14/cannon.cpp */
+/*! \file t14/gamebrd.h */
+/*! \file t14/gamebrd.cpp */
+/*! \file t14/main.cpp */
+
+/*! \page tutorial1-14.html
+
+\title Qt Tutorial - Chapter 14: Facing the Wall
+
+\img t14.png Screenshot of tutorial fourteen
+
+This is the final example: a complete game.
+
+We add keyboard accelerators and introduce mouse events to CannonField. We
+put a frame around the CannonField and add a barrier (wall) to make the
+game more challenging.
+
+\list
+\i \l t14/lcdrange.h contains the LCDRange
+class definition.
+\i \l t14/lcdrange.cpp contains the LCDRange
+implementation.
+\i \l t14/cannon.h contains the CannonField class
+definition.
+\i \l t14/cannon.cpp contains the CannonField
+implementation.
+\i \l t14/gamebrd.h contains the GameBoard
+class definition.
+\i \l t14/gamebrd.cpp contains the GameBoard
+implementation.
+\i \l t14/main.cpp contains MyWidget and main.
+\endlist
+
+\section1 Line-by-line Walkthrough
+
+\section2 \l t14/cannon.h
+
+The CannonField can now receive mouse events to make the user aim the
+barrel by clicking on it and dragging. CannonField also has a barrier
+wall.
+
+\quotefile t14/cannon.h
+
+\skipto CannonField
+\skipto protected
+\printuntil mouseReleaseEvent
+
+In addition to the familiar event handlers, CannonField implements
+three mouse event handlers. The names say it all.
+
+\skipto paintBarrier
+\printline paintBarrier
+
+This private function paints the barrier wall.
+
+\skipto barrierRect
+\printline barrierRect
+
+This private function returns the enclosing rectangle of the barrier.
+
+\skipto barrelHit
+\printline barrelHit
+
+This private function checks if a point is inside the barrel of the cannon.
+
+\skipto barrelPressed
+\printline barrelPressed
+
+This private variable is TRUE if the user has pressed the mouse on the
+barrel and not released it.
+
+
+\section2 \l t14/cannon.cpp
+
+\quotefile t14/cannon.cpp
+
+\skipto ::CannonField
+\skipto barrelPressed
+\printline barrelPressed
+
+This line has been added to the constructor. Initially, the mouse is
+not pressed on the barrel.
+
+\skipto ::moveShot
+\skipto else
+\printuntil {
+
+Now that we have a barrier, there are three ways to miss. We test for
+the third, too.
+
+\skipto ::mousePressEvent
+\printuntil }
+
+This is a Qt event handler. It is called when the user presses a
+mouse button when the mouse cursor is over the widget.
+
+If the event was not generated by the left mouse button, we return
+immediately. Otherwise, we check if the position of the mouse cursor
+is within the cannon's barrel. If it is, we set \c barrelPressed to
+TRUE.
+
+Notice that the pos() function returns a point in the widget's
+coordinate system.
+
+\skipto ::mouseMoveEvent
+\printuntil setAngle
+\printline }
+
+This is another Qt event handler. It is called when the user already
+has pressed the mouse button inside this widget and then moves/drags
+the mouse. (You can make Qt send mouse move events even when no
+buttons are pressed. See \l QWidget::setMouseTracking().)
+
+This handler repositions the cannon's barrel according to the position of
+the mouse cursor.
+
+First, if the barrel is not pressed, we return. Next, we fetch the
+mouse cursor's position. If the mouse cursor is to the left or below
+the widget, we adjust the point to be inside the widget.
+
+Then we calculate the angle between the bottom edge of the widget and
+the imaginary line between the bottom-left corner of the widget and
+the cursor position. Finally we set the cannon's angle to the new
+value converted to degrees.
+
+Remember that setAngle() redraws the cannon.
+
+\skipto ::mouseReleaseEvent
+\printuntil }
+
+This Qt event handler is called whenever the user releases a mouse
+button and it was pressed inside this widget.
+
+If the left button is released, we can be sure that the barrel is no
+longer pressed.
+
+The paint event has two extra lines:
+
+\skipto ::paintEvent
+\skipto barrierRect
+\printline barrierRect
+\printline paintBarrier
+
+paintBarrier() does the same sort of thing as paintShot(),
+paintTarget(), and paintCannon().
+
+\skipto ::paintBarrier
+\printuntil }
+
+This private function paints the barrier as a rectangle filled with
+yellow and with a black outline.
+
+\skipto ::barrierRect
+\printuntil }
+
+This private function returns the rectangle of the barrier. We fix
+the bottom edge of the barrier to the bottom edge of the widget.
+
+\skipto ::barrelHit
+\printuntil }
+
+This function returns TRUE if the point is in the barrel; otherwise it returns
+FALSE.
+
+Here we use the class \l QWMatrix. It is defined in the header file
+qwmatrix.h, which is included by qpainter.h.
+
+QWMatrix defines a coordinate system mapping. It can perform the same
+transformations as the QPainter.
+
+Here we perform the same transformation steps as we do when drawing
+the barrel in the paintCannon() function. First we translate the
+coordinate system and then we rotate it.
+
+Now we need to check whether the point \c p (in widget coordinates) lies
+inside the barrel. To do this, we invert the transformation matrix.
+The inverted matrix performs the inverse transformation that we used
+when drawing the barrel. We map the point \c p using the inverted
+matrix and return TRUE if it is inside the original barrel rectangle.
+
+
+\section2 \l t14/gamebrd.cpp
+
+\quotefile t14/gamebrd.cpp
+
+\skipto qaccel.h
+\printline qaccel.h
+
+We include the class definition of \l QAccel.
+
+\skipto ::GameBoard
+\skipto QVBox
+\printline QVBox
+\printline setFrameStyle
+\printline cannonField
+
+We create and set up a \l QVBox, set its frame style, and then create
+\c CannonField as a child of that box. Because nothing else is in the
+box, the effect is that the QVBox will put a frame around the
+CannonField.
+
+\skipto QAccel
+\printline accel
+\printline connectItem
+\printline fire
+\printline connectItem
+\printline fire
+
+Here we create and set up an accelerator. An accelerator is an object
+that intercepts keyboard events to an application and calls slots if
+certain keys are pressed. This mechanism is also called shortcut
+keys. Note that an accelerator is a child of a widget and will be
+destroyed when that widget is destroyed. QAccel is \e not a widget
+and has no visible effect on its parent.
+
+We define two shortcut keys. We want the slot fire() to be called
+when the user presses Enter, and we want the application to quit when
+key Ctrl+Q is pressed. Because Enter is sometimes Return and there
+are even keyboards with \e both keys, we make both Enter and Return
+invoke fire().
+
+\printline connectItem
+\printline quit
+
+And then we set up Ctrl+Q to do the same thing as Alt+Q. Some
+people are more used to Ctrl+Q (and anyway it shows how do do it).
+
+CTRL, Key_Enter, Key_Return and Key_Q are all constants provided by
+Qt. They're actually Qt::Key_Enter, etc., but practically all classes
+inherit the \l Qt namespace class.
+
+\printline QGridLayout
+\printline addWidget
+\printline addWidget
+\printline setColStretch
+
+We put \c box (the QVBox), not the CannonField, in the lower-right
+cell.
+
+\section1 Behavior
+
+The cannon now shoots when you press Enter. You can also position the
+cannon's angle using the mouse. The barrier makes it a little more
+challenging to play the game. We also have a nice looking frame
+around the CannonField.
+
+(See \link tutorial1-07.html#compiling Compiling\endlink for how to create a
+makefile and build the application.)
+
+
+\section1 Exercises
+
+Write a space invaders game.
+
+(This exercise was first done by
+\link mailto:igorr@ifi.uio.no Igor Rafienko\endlink. You can
+\link http://www.stud.ifi.uio.no/~igorr/download.html
+download his game\endlink.)
+
+The new exercise is: Write a Breakout game.
+
+Final exhortation: Go forth now and create \e {masterpieces of the
+programming art!}
+
+\omit
+Cf. Chapter 27 of The TeXbook
+\endomit
+
+[\link tutorial1-13.html Previous tutorial\endlink]
+[\link tutorial1-01.html First tutorial\endlink]
+[\link tutorial.html Main tutorial page\endlink]
+
+*/