Qt Tutorial - Chapter 13: Game Over

This file is new. It contains the implementation of the GameBoard class, which was last seen as MyWidget.

We have made some changes in the GameBoard constructor.

        cannonField = new CannonField( this, "cannonField" );

cannonField is now a member 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()),
                 this, 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.

        QPushButton *restart
            = new QPushButton( "&New Game", this, "newgame" );
        restart->setFont( QFont( "Times", 18, QFont::Bold ) );

        connect( restart, SIGNAL(clicked()), this, 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 = new QLCDNumber( 2, this, "hits" );
        shotsLeft = new QLCDNumber( 2, this, "shotsleft" );
        QLabel *hitsL = new QLabel( "HITS", this, "hitsLabel" );
        QLabel *shotsLeftL
            = new QLabel( "SHOTS LEFT", this, "shotsleftLabel" );

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.

        QHBoxLayout *topBox = new QHBoxLayout;
        grid->addLayout( topBox, 0, 1 );
        topBox->addWidget( shoot );
        topBox->addWidget( hits );
        topBox->addWidget( 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();
    }

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.)

    void GameBoard::fire()
    {
        if ( cannonField->gameOver() || cannonField->isShooting() )
            return;
        shotsLeft->display( shotsLeft->intValue() - 1 );
        cannonField->shoot();
    }

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.

    void GameBoard::hit()
    {
        hits->display( hits->intValue() + 1 );
        if ( shotsLeft->intValue() == 0 )
            cannonField->setGameOver();
        else
            cannonField->newTarget();
    }

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.

    void GameBoard::missed()
    {
        if ( shotsLeft->intValue() == 0 )
            cannonField->setGameOver();
    }

This slot is activated when a shot has missed the target. If there are no shots left, the game is over.

    void GameBoard::newGame()
    {
        shotsLeft->display( 15 );
        hits->display( 0 );
        cannonField->restartGame();
        cannonField->newTarget();
    }

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.

t13/main.cpp