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# cannonfield.cpp Example File
tutorial/t11/cannonfield.cpp

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

        #include <QPaintEvent>
        #include <QPainter>
        #include <QTimer>

        #include <math.h>

        #include "cannonfield.h"

        CannonField::CannonField(QWidget *parent)
            : QWidget(parent)
        {
            ang = 45;
            f = 0;
            timerCount = 0;
            autoShootTimer = new QTimer(this);
            connect(autoShootTimer, SIGNAL(timeout()), this, SLOT(moveShot()));
            shoot_ang = 0;
            shoot_f = 0;
            setPalette(QPalette(QColor(250, 250, 200)));
        }

        void CannonField::setAngle(int angle)
        {
            if (angle < 5)
                angle = 5;
            if (angle > 70)
                angle = 70;
            if (ang == angle)
                return;
            ang = angle;
            update(cannonRect());
            emit angleChanged(ang);
        }

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

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

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

            QRect shotR = shotRect();

            if (shotR.x() > width() || shotR.y() > height()) {
                autoShootTimer->stop();
            } else {
                region = region.unite(shotR);
            }
            update(region);
        }

        void CannonField::paintEvent(QPaintEvent * /* event */)
        {
            QPainter painter(this);

            paintCannon(painter);
            if (autoShootTimer->isActive())
                paintShot(painter);
        }

        void CannonField::paintShot(QPainter &painter)
        {
            painter.setPen(Qt::NoPen);
            painter.setBrush(Qt::black);
            painter.drawRect(shotRect());
        }

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

        void CannonField::paintCannon(QPainter &painter)
        {
            painter.setPen(Qt::NoPen);
            painter.setBrush(Qt::blue);

            painter.save();
            painter.translate(0, height());
            painter.drawPie(QRect(-35, -35, 70, 70), 0, 90 * 16);
            painter.rotate(-ang);
            painter.drawRect(barrelRect);
            painter.restore();
        }

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

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