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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 implementation in gamebrd.rb.
The CannonField now has a game over state.
The layout problems in LCDRange are fixed.
class LCDRange < Qt::Widget
We inherit Qt::Widget rather than Qt::VBox. Qt::VBox is very easy to use, but again it showed its limitations so we switch to the more powerful and slightly harder to use Qt::VBoxLayout. (As you remember, Qt::VBoxLayout is not a widget, it manages one.)
def initialize(s, parent, name)
super(parent, name)
We inherit Qt::Widget in the usual way.
init() is unchanged, except that we've added some lines at the end:
l = Qt::VBoxLayout.new( self )
We create a Qt::VBoxLayout with all the default values, managing this widget's children.
l.addWidget( lcd, 1 )
At the top we add the Qt::LCDNumber with a non-zero stretch.
l.addWidget( @slider )
l.addWidget( label )
Then we add the other two, both with the default zero stretch.
This stretch control is something Qt::VBoxLayout (and Qt::HBoxLayout, and Qt::GridLayout) offers but classes like Qt::VBox do not. In this case we're saying that the Qt::LCDNumber should stretch and the others should not.
The CannonField now has a game over state and a few new methods.
gameOver()
This method returns true if the game is over or false if a game is going on.
setGameOver()
restartGame()
Here are two new slots: setGameOver() and restartGame().
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.
@gameEnded
This instance variable contains the game state. true means that the game is over, and false means that a game is going on.
@gameEnded = false
This line has been added to the constructor. Initially, the game is not over (luckily for the player :-).
def shoot()
if isShooting()
return
end
@timerCount = 0
@shoot_ang = @ang
@shoot_f = @f
@autoShootTimer.start( 50 )
emit canShoot( false )
end
We added a new isShooting() method, so shoot() uses it instead of testing directly. Also, shoot tells the world that the CannonField cannot shoot now.
def setGameOver()
if @gameEnded
return
end
if isShooting()
@autoShootTimer.stop()
end
@gameEnded = true
repaint()
end
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.
def restartGame()
if isShooting()
@autoShootTimer.stop()
end
@gameEnded = false
repaint()
emit canShoot( true )
end
This slot starts a new game. If a shot is in the air, we stop shooting. We then reset the @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 paintEvent():
def paintEvent( e )
updateR = e.rect()
p = Qt::Painter.new( self )
if @gameEnded
p.setPen( black )
p.setFont( Qt::Font.new( "Courier", 48, QFont::Bold ) )
p.drawText( rect(), AlignCenter, "Game Over" )
end
The paint event has been enhanced to display the text "Game Over" if the game is over, i.e., @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.
if updateR.intersects( cannonRect() )
paintCannon( p )
end
if isShooting() && updateR.intersects( shotRect() )
paintShot( p )
end
if !@gameEnded && updateR.intersects( targetRect() )
paintTarget( p )
end
p.end()
end
We draw the shot only when shooting and the target only when playing (that is, when the game is not ended).
This file is new. It contains the definition of the GameBoard class, which was last seen as MyWidget.
class GameBoard < Qt::Widget
slots 'fire()', 'hit()', 'missed()', 'newGame()'
@hits
@shotsLeft
@cannonField
We have now added four slots. These are protected and are used internally. We have also added two Qt::LCDNumbers (@hits and @shotsLeft) which display the game status.
We have made some changes in the GameBoard constructor.
@cannonField = CannonField.new( self, "cannonField" )
cannonField is now an instance variable, so we carefully change the constructor to use it. (The good programmers at Trolltech never forget this, but I do. Caveat programmor - if "programmor" is Latin, at least. Anyway, back to the code.)
connect( @cannonField, SIGNAL('hit()'),
self, SLOT('hit()') )
connect( @cannonField, SIGNAL('missed()'),
this, SLOT('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.
connect( shoot, SIGNAL('clicked()'), SLOT('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.
connect( @cannonField, SIGNAL('canShoot(bool)'),
shoot, SLOT('setEnabled(bool)') )
We also use the cannonField's canShoot() signal to enable or disable the Shoot button appropriately.
restart = Qt::PushButton.new( "&New Game", self, "newgame" )
restart.setFont( Qt::Font.new( "Times", 18, Qt::Font::Bold ) )
connect( restart, SIGNAL('clicked()'), self, SLOT('newGame()') )
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.
@hits = Qt::LCDNumber.new( 2, self, "hits" )
@shotsLeft = Qt::LCDNumber.new( 2, self, "shotsleft" )
hitsL = Qt::Label.new( "HITS", self, "hitsLabel" )
shotsLeftL = Qt::Label.new( "SHOTS LEFT", self, "shotsleftLabel" )
We create four new widgets. Note that we don't bother to keep the references to the Qt::Label 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.
topBox = Qt::HBoxLayout.new
grid.addLayout( topBox, 0, 1 )
topBox.( shoot )
topBox.( @hits )
topBox.( hitsL )
topBox.addWidget( @shotsLeft )
topBox.addWidget( shotsLeftL )
topBox.addStretch( 1 )
topBox.addWidget( restart )
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.
newGame()
end
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 methods, too.)
def fire()
if @cannonField.gameOver() || @cannonField.isShooting()
return
end
@shotsLeft.display( @shotsLeft.intValue() - 1 )
@cannonField.shoot()
end
This method 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.
def hit()
@hits.display( @hits.intValue() + 1 )
if @shotsLeft.intValue() == 0
@cannonField.setGameOver()
else
@cannonField.newTarget()
end
end
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.
def missed()
if @shotsLeft.intValue() == 0
@cannonField.setGameOver()
end
end
This slot is activated when a shot has missed the target. If there are no shots left, the game is over.
def newGame()
@shotsLeft.display( 15.0 )
@hits.display( 0 )
@cannonField.restartGame()
@cannonField.newTarget()
end
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.
This file has just been on a diet. MyWidget is gone, and the only thing left is the top level code, unchanged except for the name change.
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.
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 Chapter 14.
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