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| author | Timothy Pearson <kb9vqf@pearsoncomputing.net> | 2011-07-10 15:24:15 -0500 |
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| committer | Timothy Pearson <kb9vqf@pearsoncomputing.net> | 2011-07-10 15:24:15 -0500 |
| commit | bd0f3345a938b35ce6a12f6150373b0955b8dd12 (patch) | |
| tree | 7a520322212d48ebcb9fbe1087e7fca28b76185c /doc/html/tutorial1-12.html | |
| download | qt3-bd0f3345a938b35ce6a12f6150373b0955b8dd12.tar.gz qt3-bd0f3345a938b35ce6a12f6150373b0955b8dd12.zip | |
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diff --git a/doc/html/tutorial1-12.html b/doc/html/tutorial1-12.html new file mode 100644 index 0000000..6964044 --- /dev/null +++ b/doc/html/tutorial1-12.html @@ -0,0 +1,328 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial.doc:1711 --> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>Qt Tutorial - Chapter 12: Hanging in the Air the Way Bricks Don't</title> +<style type="text/css"><!-- +fn { margin-left: 1cm; text-indent: -1cm; } +a:link { color: #004faf; text-decoration: none } +a:visited { color: #672967; text-decoration: none } +body { background: #ffffff; color: black; } +--></style> +</head> +<body> + +<table border="0" cellpadding="0" cellspacing="0" width="100%"> +<tr bgcolor="#E5E5E5"> +<td valign=center> + <a href="index.html"> +<font color="#004faf">Home</font></a> + | <a href="classes.html"> +<font color="#004faf">All Classes</font></a> + | <a href="mainclasses.html"> +<font color="#004faf">Main Classes</font></a> + | <a href="annotated.html"> +<font color="#004faf">Annotated</font></a> + | <a href="groups.html"> +<font color="#004faf">Grouped Classes</font></a> + | <a href="functions.html"> +<font color="#004faf">Functions</font></a> +</td> +<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Qt Tutorial - Chapter 12: Hanging in the Air the Way Bricks Don't</h1> + + +<p> <center><img src="t12.png" alt="Screenshot of tutorial twelve"></center> +<p> In this example, we extend our LCDRange class to include a text label. +We also provide something to shoot at. +<p> <ul> +<li> <a href="t12-lcdrange-h.html">t12/lcdrange.h</a> contains the LCDRange +class definition. +<li> <a href="t12-lcdrange-cpp.html">t12/lcdrange.cpp</a> contains the LCDRange +implementation. +<li> <a href="t12-cannon-h.html">t12/cannon.h</a> contains the CannonField class +definition. +<li> <a href="t12-cannon-cpp.html">t12/cannon.cpp</a> contains the CannonField +implementation. +<li> <a href="t12-main-cpp.html">t12/main.cpp</a> contains MyWidget and main. +</ul> +<p> <h2> Line-by-line Walkthrough +</h2> +<a name="1"></a><p> <h3> <a href="t12-lcdrange-h.html">t12/lcdrange.h</a> +</h3> +<a name="1-1"></a><p> The LCDRange now has a text label. +<p> + +<p> <pre> class QLabel; +</pre> +<p> We name declare <a href="qlabel.html">QLabel</a> because we want to use a pointer to it in the class +definition. +<p> <pre> class LCDRange : public <a href="qvbox.html">QVBox</a> + { + <a href="metaobjects.html#Q_OBJECT">Q_OBJECT</a> + public: + LCDRange( <a href="qwidget.html">QWidget</a> *parent=0, const char *name=0 ); + LCDRange( const char *s, QWidget *parent=0, + const char *name=0 ); +</pre> +<p> We have added a new constructor that sets the label text in addition to +the parent and name. +<p> <pre> const char *text() const; +</pre> +<p> This function returns the label text. +<p> <pre> void setText( const char * ); +</pre> +<p> This slot sets the label text. +<p> <pre> private: + void init(); +</pre> +<p> Because we now have two constructors, we have chosen to put the common +initialization in the private init() function. +<p> <pre> <a href="qlabel.html">QLabel</a> *label; +</pre> +<p> 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. +<p> <h3> <a href="t12-lcdrange-cpp.html">t12/lcdrange.cpp</a> +</h3> +<a name="1-2"></a><p> + +<p> <pre> #include <<a href="qlabel-h.html">qlabel.h</a>> +</pre> +<p> Here we include the <a href="qlabel.html">QLabel</a> class definition. +<p> <pre> LCDRange::LCDRange( <a href="qwidget.html">QWidget</a> *parent, const char *name ) + : <a href="qvbox.html">QVBox</a>( parent, name ) + { + init(); + } +</pre> +<p> This constructor calls the init() function, which contains the common +initialization code. +<p> <pre> LCDRange::LCDRange( const char *s, QWidget *parent, + const char *name ) + : <a href="qvbox.html">QVBox</a>( parent, name ) + { + init(); + setText( s ); + } +</pre> +<p> This constructor first calls init() and then sets the label text. +<p> <pre> void LCDRange::init() + { + <a href="qlcdnumber.html">QLCDNumber</a> *lcd = new <a href="qlcdnumber.html">QLCDNumber</a>( 2, this, "lcd" ); + slider = new <a href="qslider.html">QSlider</a>( Horizontal, this, "slider" ); + <a name="x2387"></a> slider-><a href="qrangecontrol.html#setRange">setRange</a>( 0, 99 ); + <a name="x2388"></a> slider-><a href="qslider.html#setValue">setValue</a>( 0 ); + + label = new <a href="qlabel.html">QLabel</a>( " ", this, "label" ); + <a name="x2383"></a> label-><a href="qlabel.html#setAlignment">setAlignment</a>( AlignCenter ); + + <a name="x2389"></a> <a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), + <a name="x2386"></a> lcd, SLOT(<a href="qlcdnumber.html#display">display</a>(int)) ); + <a href="qobject.html#connect">connect</a>( slider, SIGNAL(<a href="qslider.html#valueChanged">valueChanged</a>(int)), + SIGNAL(valueChanged(int)) ); + + <a href="qwidget.html#setFocusProxy">setFocusProxy</a>( slider ); + } +</pre> +<p> The setup of <tt>lcd</tt> and <tt>slider</tt> is the same as in the previous +chapter. Next we create a <a href="qlabel.html">QLabel</a> and tell it to align the contents +centered (both vertically and horizontally). The connect() statements +have also been taken from the previous chapter. +<p> <pre> const char *LCDRange::text() const + { + <a name="x2385"></a> return label-><a href="qlabel.html#text">text</a>(); + } +</pre> +<p> This function returns the label text. +<p> <pre> void LCDRange::setText( const char *s ) + { + <a name="x2384"></a> label-><a href="qlabel.html#setText">setText</a>( s ); + } +</pre> +<p> This function sets the label text. +<p> <h3> <a href="t12-cannon-h.html">t12/cannon.h</a> +</h3> +<a name="1-3"></a><p> The CannonField now has two new signals: hit() and missed(). In addition +it contains a target. +<p> + +<p> <pre> void newTarget(); +</pre> +<p> This slot creates a target at a new position. +<p> <pre> signals: + void hit(); + void missed(); +</pre> +<p> 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). +<p> <pre> void paintTarget( <a href="qpainter.html">QPainter</a> * ); +</pre> +<p> This private function paints the target. +<p> <pre> <a href="qrect.html">QRect</a> targetRect() const; +</pre> +<p> This private function returns the enclosing rectangle of the target. +<p> <pre> <a href="qpoint.html">QPoint</a> target; +</pre> +<p> This private variable contains the center point of the target. +<p> <h3> <a href="t12-cannon-cpp.html">t12/cannon.cpp</a> +</h3> +<a name="1-4"></a><p> + +<p> <pre> #include <<a href="qdatetime-h.html">qdatetime.h</a>> +</pre> +<p> We include the <a href="qdate.html">QDate</a>, <a href="qtime.html">QTime</a>, and <a href="qdatetime.html">QDateTime</a> class definitions. +<p> <pre> #include <stdlib.h> +</pre> +<p> We include the stdlib library because we need the rand() function. +<p> <pre> newTarget(); +</pre> +<p> 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. +<p> <pre> void CannonField::newTarget() + { + static bool first_time = TRUE; + if ( first_time ) { + first_time = FALSE; + <a href="qtime.html">QTime</a> midnight( 0, 0, 0 ); + <a name="x2399"></a><a name="x2398"></a> srand( midnight.<a href="qtime.html#secsTo">secsTo</a>(QTime::<a href="qtime.html#currentTime">currentTime</a>()) ); + } + <a href="qregion.html">QRegion</a> r( targetRect() ); + target = QPoint( 200 + rand() % 190, + 10 + rand() % 255 ); + <a name="x2395"></a> <a href="qwidget.html#repaint">repaint</a>( r.<a href="qrect.html#unite">unite</a>( targetRect() ) ); + } +</pre> +<p> This private function creates a target center point at a new "random" +position. +<p> 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. +<p> 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. +<p> The <tt>if</tt> test will succeed only the first time this function is called +because we set <tt>first_time</tt> to FALSE inside the <tt>if</tt> block. +<p> Then we create the <a href="qtime.html">QTime</a> object <tt>midnight</tt>, 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 <a href="qdate.html">QDate</a>, +<a href="qtime.html">QTime</a>, and <a href="qdatetime.html">QDateTime</a> for more information. +<p> 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. +<p> By experimentation we have found this to always be in reach of the shot. +<p> Note that rand() returns a random integer >= 0. +<p> <pre> void CannonField::moveShot() + { + <a href="qregion.html">QRegion</a> r( shotRect() ); + timerCount++; + + <a href="qrect.html">QRect</a> shotR = shotRect(); +</pre> +<p> This part of the timer event has not changed from the previous chapter. +<p> <pre> if ( shotR.<a href="qrect.html#intersects">intersects</a>( targetRect() ) ) { + <a name="x2400"></a> autoShootTimer-><a href="qtimer.html#stop">stop</a>(); + emit hit(); +</pre> +<p> This <tt>if</tt> 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. +<p> 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. +<p> <pre> <a name="x2397"></a><a name="x2396"></a> } else if ( shotR.<a href="qrect.html#x">x</a>() > width() || shotR.<a href="qrect.html#y">y</a>() > height() ) { + autoShootTimer-><a href="qtimer.html#stop">stop</a>(); + emit missed(); +</pre> +<p> This <tt>if</tt> 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. +<p> <pre> } else { +</pre> +<p> And the rest of the function is as before. +<p> CannonField::paintEvent() is as before, except that this has been +added: +<p> <pre> <a name="x2393"></a> if ( updateR.<a href="qrect.html#intersects">intersects</a>( targetRect() ) ) + paintTarget( &p ); +</pre> +<p> These two lines make sure that the target is also painted when necessary. +<p> <pre> void CannonField::paintTarget( <a href="qpainter.html">QPainter</a> *p ) + { + p-><a href="qpainter.html#setBrush">setBrush</a>( red ); + p-><a href="qpainter.html#setPen">setPen</a>( black ); + p-><a href="qpainter.html#drawRect">drawRect</a>( targetRect() ); + } +</pre> +<p> This private function paints the target; a rectangle filled with red and +with a black outline. +<p> <pre> QRect CannonField::targetRect() const + { + <a href="qrect.html">QRect</a> r( 0, 0, 20, 10 ); + <a name="x2394"></a> r.<a href="qrect.html#moveCenter">moveCenter</a>( QPoint(target.x(),height() - 1 - target.y()) ); + return r; + } +</pre> +<p> This private function returns the enclosing rectangle of the target. +Remember from newTarget() that the <tt>target</tt> point uses y coordinate 0 at +the bottom of the widget. We calculate the point in widget coordinates +before we call <a href="qrect.html#moveCenter">QRect::moveCenter</a>(). +<p> 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. +<p> <h3> <a href="t12-main-cpp.html">t12/main.cpp</a> +</h3> +<a name="1-5"></a><p> + +<p> There are no new members in the MyWidget class, but we have slightly +changed the constructor to set the new LCDRange text labels. +<p> <pre> LCDRange *angle = new LCDRange( "ANGLE", this, "angle" ); +</pre> +<p> We set the angle text label to "ANGLE". +<p> <pre> LCDRange *force = new LCDRange( "FORCE", this, "force" ); +</pre> +<p> We set the force text label to "FORCE". +<p> <h2> Behavior +</h2> +<a name="2"></a><p> The LCDRange widgets look a bit strange - the built-in layout +management in <a href="qvbox.html">QVBox</a> gives the labels too much space and the rest not +enough. We'll fix that in the next chapter. +<p> (See <a href="tutorial1-07.html#compiling">Compiling</a> for how to create a +makefile and build the application.) +<p> <h2> Exercises +</h2> +<a name="3"></a><p> Make a cheat button that, when pressed, makes the CannonField display +the shot trajectory for five seconds. +<p> If you did the "round shot" exercise from the previous chapter, try +changing the shotRect() to a shotRegion() that returns a <a href="qregion.html">QRegion</a> so +you can have really accurate collision detection. +<p> Make a moving target. +<p> Make sure that the target is always created entirely on-screen. +<p> Make sure that the widget cannot be resized so that the target isn't +visible. Hint: <a href="qwidget.html#setMinimumSize">QWidget::setMinimumSize</a>() is your friend. +<p> Not easy; make it possible to have several shots in the air at the +same time. Hint: make a Shot object. +<p> You're now ready for <a href="tutorial1-13.html">Chapter 13.</a> +<p> [<a href="tutorial1-11.html">Previous tutorial</a>] +[<a href="tutorial1-13.html">Next tutorial</a>] +[<a href="tutorial.html">Main tutorial page</a>] +<p> +<!-- eof --> +<p><address><hr><div align=center> +<table width=100% cellspacing=0 border=0><tr> +<td>Copyright © 2007 +<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a> +<td align=right><div align=right>Qt 3.3.8</div> +</table></div></address></body> +</html> |