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 #include <QPaintEvent>
 #include <QPainter>
 #include <QTimer>
 
 #include <math.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;
     setPalette(QPalette(QColor(250, 250, 200)));
     setAutoFillBackground(true);
 }
 
 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::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 &amp;painter)
 {
     painter.setPen(Qt::NoPen);
     painter.setBrush(Qt::black);
     painter.drawRect(shotRect());
 }
 
 const QRect barrelRect(30, -5, 20, 10);
 
 void CannonField::paintCannon(QPainter &amp;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;
 }