cannonfield.cpp Example File
^{tutorial/t13/cannonfield.cpp}

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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);
     gameEnded = false;
     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 (isShooting())
         return;
     timerCount = 0;
     shootAngle = currentAngle;
     shootForce = currentForce;
     autoShootTimer->start(5);
     emit canShoot(false);
 }

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

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

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

 void CannonField::restartGame()
 {
     if (isShooting())
         autoShootTimer->stop();
     gameEnded = false;
     update();
     emit canShoot(true);
 }

 void CannonField::moveShot()
 {
     QRegion region = 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 {
         region = region.unite(shotR);
     }
     update(region);
 }

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

     if (gameEnded) {
         painter.setPen(Qt::black);
         painter.setFont(QFont("Courier", 48, QFont::Bold));
         painter.drawText(rect(), Qt::AlignCenter, tr("Game Over"));
     }
     paintCannon(painter);
     if (isShooting())
         paintShot(painter);
     if (!gameEnded)
         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;
 }

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