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# cannonfield.cpp Example File
tutorial/t12/cannonfield.cpp

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        **
        ** This file is part of the documentation of the Qt Toolkit.
        **
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        ** License version 2.0 as published by the Free Software Foundation
        ** and appearing in the file LICENSE.GPL included in the packaging of
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        #include <QDateTime>
        #include <QPaintEvent>
        #include <QPainter>
        #include <QTimer>

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

        #include "cannonfield.h"

        CannonField::CannonField(QWidget *parent)
            : QWidget(parent)
        {
            currentAngle = 45;
            currentForce = 0;
            timerCount = 0;
            autoShootTimer = new QTimer(this);
            connect(autoShootTimer, SIGNAL(timeout()), this, SLOT(moveShot()));
            shootAngle = 0;
            shootForce = 0;
            target = QPoint(0, 0);
            setPalette(QPalette(QColor(250, 250, 200)));
            setAutoFillBackground(true);
            newTarget();
        }

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

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

        void CannonField::shoot()
        {
            if (autoShootTimer->isActive())
                return;
            timerCount = 0;
            shootAngle = currentAngle;
            shootForce = currentForce;
            autoShootTimer->start(5);
        }

        void CannonField::newTarget()
        {
            static bool firstTime = true;

            if (firstTime) {
                firstTime = false;
                QTime midnight(0, 0, 0);
                srand(midnight.secsTo(QTime::currentTime()));
            }
            target = QPoint(200 + rand() % 190, 10 + rand() % 255);
            update();
        }

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

            QRect shotR = shotRect();

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

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

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

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

        void CannonField::paintTarget(QPainter &painter)
        {
            painter.setPen(Qt::black);
            painter.setBrush(Qt::red);
            painter.drawRect(targetRect());
        }

        const QRect barrelRect(30, -5, 20, 10);

        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(-currentAngle);
            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 / 20.0;
            double velocity = shootForce;
            double radians = shootAngle * 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;
        }

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