Question

/****************************************************************
**
** Implementation CannonField class, Qt tutorial 13
**
****************************************************************/

#include "cannon.h"
#include <qtimer.h>
#include <qpainter.h>
#include <qpixmap.h>
#include <qdatetime.h>

#include <math.h>
#include <stdlib.h>


CannonField::CannonField( QWidget *parent, const char *name )
        : QWidget( parent, name )
{
    ang = 45;
    f = 0;
    timerCount = 0;
    autoShootTimer = new QTimer( this, "movement handler" );
    connect( autoShootTimer, SIGNAL(timeout()),
             this, SLOT(moveShot()) );
    shoot_ang = 0;
    shoot_f = 0;
    target = QPoint( 0, 0 );
    gameEnded = FALSE;
    setPalette( QPalette( QColor( 250, 250, 200) ) );
    newTarget();
}


void CannonField::setAngle( int degrees )
{
    if ( degrees < 5 )
        degrees = 5;
    if ( degrees > 70 )
        degrees = 70;
    if ( ang == degrees )
        return;
    ang = degrees;
    repaint( cannonRect(), FALSE );
    emit angleChanged( ang );
}


void CannonField::setForce( int newton )
{
    if ( newton < 0 )
        newton = 0;
    if ( f == newton )
        return;
    f = newton;
    emit forceChanged( f );
}


void CannonField::shoot()
{
    if ( isShooting() )
        return;
    timerCount = 0;
    shoot_ang = ang;
    shoot_f = f;
    autoShootTimer->start( 50 );
    emit canShoot( FALSE );
}


void  CannonField::newTarget()
{
    static bool first_time = TRUE;
    if ( first_time ) {
        first_time = FALSE;
        QTime midnight( 0, 0, 0 );
        srand( midnight.secsTo(QTime::currentTime()) );
    }
    QRegion r( targetRect() );
    target = QPoint( 200 + rand() % 190,
                     10  + rand() % 255 );
    repaint( r.unite( targetRect() ) );
}

void CannonField::setGameOver()
{
    if ( gameEnded )
        return;
    if ( isShooting() )
        autoShootTimer->stop();
    gameEnded = TRUE;
    repaint();
}

void CannonField::restartGame()
{
    if ( isShooting() )
        autoShootTimer->stop();
    gameEnded = FALSE;
    repaint();
    emit canShoot( TRUE );
}

void CannonField::moveShot()
{
    QRegion r( shotRect() );
    timerCount++;

    QRect shotR = shotRect();

    if ( shotR.intersects( targetRect() ) ) {
        autoShootTimer->stop();
        emit hit();
        emit canShoot( TRUE );
    } else if ( shotR.x() > width() || shotR.y() > height() ) {
        autoShootTimer->stop();
        emit missed();
        emit canShoot( TRUE );
    } else {
        r = r.unite( QRegion( shotR ) );
    }

    repaint( r );
}


void CannonField::paintEvent( QPaintEvent *e )
{
    QRect updateR = e->rect();
    QPainter p( this );

    if ( gameEnded ) {
        p.setPen( black );
        p.setFont( QFont( "Courier", 48, QFont::Bold ) );
        p.drawText( rect(), AlignCenter, "Game Over" );
    }
    if ( updateR.intersects( cannonRect() ) )
        paintCannon( &p );
    if ( isShooting() && updateR.intersects( shotRect() ) )
        paintShot( &p );
    if ( !gameEnded && updateR.intersects( targetRect() ) )
        paintTarget( &p );
}


void CannonField::paintShot( QPainter *p )
{
    p->setBrush( black );
    p->setPen( NoPen );
    p->drawRect( shotRect() );
}


void CannonField::paintTarget( QPainter *p )
{
    p->setBrush( red );
    p->setPen( black );
    p->drawRect( targetRect() );
}


const QRect barrelRect(33, -4, 15, 8);

void CannonField::paintCannon( QPainter *p )
{
    QRect cr = cannonRect();
    QPixmap pix( cr.size() );
    pix.fill( this, cr.topLeft() );

    QPainter tmp( &pix );
    tmp.setBrush( blue );
    tmp.setPen( NoPen );

    tmp.translate( 0, pix.height() - 1 );
    tmp.drawPie( QRect( -35,-35, 70, 70 ), 0, 90*16 );
    tmp.rotate( -ang );
    tmp.drawRect( barrelRect );
    tmp.end();

    p->drawPixmap( cr.topLeft(), pix );
}


QRect CannonField::cannonRect() const
{
    QRect r( 0, 0, 50, 50 );
    r.moveBottomLeft( rect().bottomLeft() );
    return r;
}


QRect CannonField::shotRect() const
{
    const double gravity = 4;

    double time      = timerCount / 4.0;
    double velocity  = shoot_f;
    double radians   = shoot_ang*3.14159265/180;

    double velx      = velocity*cos( radians );
    double vely      = velocity*sin( radians );
    double x0        = ( barrelRect.right()  + 5 )*cos(radians);
    double y0        = ( barrelRect.right()  + 5 )*sin(radians);
    double x         = x0 + velx*time;
    double y         = y0 + vely*time - 0.5*gravity*time*time;

    QRect r = QRect( 0, 0, 6, 6 );
    r.moveCenter( QPoint( qRound(x), height() - 1 - qRound(y) ) );
    return r;
}


QRect CannonField::targetRect() const
{
    QRect r( 0, 0, 20, 10 );
    r.moveCenter( QPoint(target.x(),height() - 1 - target.y()) );
    return r;
}


bool CannonField::isShooting() const
{
    return autoShootTimer->isActive();
}


QSizePolicy CannonField::sizePolicy() const
{
    return QSizePolicy( QSizePolicy::Expanding, QSizePolicy::Expanding );
}