# Source code for tutorial 10: cannon.cpp

    /****************************************************************
    **
    ** Implementation CannonField class, Qt tutorial 10
    **
    ****************************************************************/

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

    CannonField::CannonField( QWidget *parent, const char *name )
            : QWidget( parent, name )
    {
        ang = 45;
        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::paintEvent( QPaintEvent *e )
    {
        QRect updateR = e->rect();
        QPainter p;

        p.begin( this );
        if ( updateR.intersects( cannonRect() ) )
            paintCannon( &p );
        p.end();
    }

    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;
    }