# Source code for tutorial 11: cannon.cpp

    /****************************************************************
    **
    ** Implementation CannonField class, Qt tutorial 11
    **
    ****************************************************************/

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

    #include <math.h>

    CannonField::CannonField( QWidget *parent, const char *name )
            : QWidget( parent, name )
    {
        ang           = 45;
        f             = 0;
        shooting      = FALSE;
        timerCount    = 0;
        shoot_ang     = 0;
        shoot_f       = 0;
    }

    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 ( shooting )
            return;
        timerCount = 0;
        shoot_ang  = ang;
        shoot_f    = f;
        shooting   = TRUE;
        startTimer( 50 );
    }

    void CannonField::timerEvent( QTimerEvent * )
    {
        erase( shotRect() );
        timerCount++;

        QRect shotR = shotRect();

        if ( shotR.x() > width() || shotR.y() > height() ) {
            stopShooting();
            return;
        }
        repaint( shotR, FALSE );
    }

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

        if ( updateR.intersects( cannonRect() ) )
            paintCannon( &p );
        if ( shooting &&  updateR.intersects( shotRect() ) )
            paintShot( &p );
        p.end();
    }

    void CannonField::stopShooting()
    {
        shooting = FALSE;
        killTimers();
    }

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

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

    void CannonField::paintCannon( QPainter *p )
    {
        QRect    cr = cannonRect();
        QPixmap  pix( cr.size() );
        QPainter tmp;

        pix.fill( this, cr.topLeft() );

        tmp.begin( &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( barrel_rect );
        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        = ( barrel_rect.right()  + 5 )*cos(radians);
        double y0        = ( barrel_rect.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;
    }