car.cpp Example File

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  #include "car.h"
  #include <QtWidgets/QtWidgets>
  #include <math.h>

  static const double Pi = 3.14159265358979323846264338327950288419717;

  QRectF Car::boundingRect() const
  {
      return QRectF(-35, -81, 70, 115);
  }

  Car::Car() : color(Qt::green), wheelsAngle(0), speed(0)
  {
      startTimer(1000 / 33);
      setFlag(QGraphicsItem::ItemIsMovable, true);
      setFlag(QGraphicsItem::ItemIsFocusable, true);
  }

  void Car::accelerate()
  {
      if (speed < 10)
          ++speed;
  }

  void Car::decelerate()
  {
      if (speed > -10)
          --speed;
  }

  void Car::turnLeft()
  {
      if (wheelsAngle > -30)
          wheelsAngle -= 5;
  }

  void Car::turnRight()
  {
      if (wheelsAngle < 30)
         wheelsAngle += 5;
  }

  void Car::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  {
      Q_UNUSED(option);
      Q_UNUSED(widget);

      painter->setBrush(Qt::gray);
      painter->drawRect(-20, -58, 40, 2); // front axel
      painter->drawRect(-20, 7, 40, 2); // rear axel

      painter->setBrush(color);
      painter->drawRect(-25, -79, 50, 10); // front wing

      painter->drawEllipse(-25, -48, 50, 20); // side pods
      painter->drawRect(-25, -38, 50, 35); // side pods
      painter->drawRect(-5, 9, 10, 10); // back pod

      painter->drawEllipse(-10, -81, 20, 100); // main body

      painter->drawRect(-17, 19, 34, 15); // rear wing

      painter->setBrush(Qt::black);
      painter->drawPie(-5, -51, 10, 15, 0, 180 * 16);
      painter->drawRect(-5, -44, 10, 10); // cocpit

      painter->save();
      painter->translate(-20, -58);
      painter->rotate(wheelsAngle);
      painter->drawRect(-10, -7, 10, 15); // front left
      painter->restore();

      painter->save();
      painter->translate(20, -58);
      painter->rotate(wheelsAngle);
      painter->drawRect(0, -7, 10, 15); // front left
      painter->restore();

      painter->drawRect(-30, 0, 12, 17); // rear left
      painter->drawRect(19, 0, 12, 17);  // rear right
  }

  void Car::timerEvent(QTimerEvent *event)
  {
      Q_UNUSED(event);

      const qreal axelDistance = 54;
      qreal wheelsAngleRads = (wheelsAngle * Pi) / 180;
      qreal turnDistance = ::cos(wheelsAngleRads) * axelDistance * 2;
      qreal turnRateRads = wheelsAngleRads / turnDistance;  // rough estimate
      qreal turnRate = (turnRateRads * 180) / Pi;
      qreal rotation = speed * turnRate;

      setTransform(QTransform().rotate(rotation), true);
      setTransform(QTransform::fromTranslate(0, -speed), true);
      update();
  }