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mouse.cpp Example File
^{graphicsview/collidingmice/mouse.cpp}

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 #include "mouse.h"

 #include <QGraphicsScene>
 #include <QPainter>
 #include <QStyleOption>

 #include <math.h>

 static const double Pi = 3.14159265358979323846264338327950288419717;
 static double TwoPi = 2.0 * Pi;

 static qreal normalizeAngle(qreal angle)
 {
     while (angle < 0)
         angle += TwoPi;
     while (angle > TwoPi)
         angle -= TwoPi;
     return angle;
 }

 Mouse::Mouse()
     : angle(0), speed(0), mouseEyeDirection(0),
       color(qrand() % 256, qrand() % 256, qrand() % 256)
 {
     rotate(qrand() % (360 * 16));
     startTimer(1000 / 33);
 }

 QRectF Mouse::boundingRect() const
 {
     qreal adjust = 0.5;
     return QRectF(-18 - adjust, -22 - adjust,
                   36 + adjust, 60 + adjust);
 }

 QPainterPath Mouse::shape() const
 {
     QPainterPath path;
     path.addRect(-10, -20, 20, 40);
     return path;
 }

 void Mouse::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
 {
     // Body
     painter->setBrush(color);
     painter->drawEllipse(-10, -20, 20, 40);

     // Eyes
     painter->setBrush(Qt::white);
     painter->drawEllipse(-10, -17, 8, 8);
     painter->drawEllipse(2, -17, 8, 8);

     // Nose
     painter->setBrush(Qt::black);
     painter->drawEllipse(QRectF(-2, -22, 4, 4));

     // Pupils
     painter->drawEllipse(QRectF(-8.0 + mouseEyeDirection, -17, 4, 4));
     painter->drawEllipse(QRectF(4.0 + mouseEyeDirection, -17, 4, 4));

     // Ears
     painter->setBrush(scene()->collidingItems(this).isEmpty() ? Qt::darkYellow : Qt::red);
     painter->drawEllipse(-17, -12, 16, 16);
     painter->drawEllipse(1, -12, 16, 16);

     // Tail
     QPainterPath path(QPointF(0, 20));
     path.cubicTo(-5, 22, -5, 22, 0, 25);
     path.cubicTo(5, 27, 5, 32, 0, 30);
     path.cubicTo(-5, 32, -5, 42, 0, 35);
     painter->setBrush(Qt::NoBrush);
     painter->drawPath(path);
 }

 void Mouse::timerEvent(QTimerEvent *)
 {
     // Don't move too far away
     QLineF lineToCenter(QPointF(0, 0), mapFromScene(0, 0));
     if (lineToCenter.length() > 150) {
         qreal angleToCenter = ::acos(lineToCenter.dx() / lineToCenter.length());
         if (lineToCenter.dy() < 0)
             angleToCenter = TwoPi - angleToCenter;
         angleToCenter = normalizeAngle((Pi - angleToCenter) + Pi / 2);

         if (angleToCenter < Pi && angleToCenter > Pi / 4) {
             // Rotate left
             angle += (angle < -Pi / 2) ? 0.25 : -0.25;
         } else if (angleToCenter >= Pi && angleToCenter < (Pi + Pi / 2 + Pi / 4)) {
             // Rotate right
             angle += (angle < Pi / 2) ? 0.25 : -0.25;
         }
     } else if (::sin(angle) < 0) {
         angle += 0.25;
     } else if (::sin(angle) > 0) {
         angle -= 0.25;
     }

     // Try not to crash with any other mice
     QList<QGraphicsItem *> dangerMice = scene()->items(QPolygonF()
                                                        << mapToScene(0, 0)
                                                        << mapToScene(-30, -50)
                                                        << mapToScene(30, -50));
     foreach (QGraphicsItem *item, dangerMice) {
         if (item == this)
             continue;

         QLineF lineToMouse(QPointF(0, 0), mapFromItem(item, 0, 0));
         qreal angleToMouse = ::acos(lineToMouse.dx() / lineToMouse.length());
         if (lineToMouse.dy() < 0)
             angleToMouse = TwoPi - angleToMouse;
         angleToMouse = normalizeAngle((Pi - angleToMouse) + Pi / 2);

         if (angleToMouse >= 0 && angleToMouse < Pi / 2) {
             // Rotate right
             angle += 0.5;
         } else if (angleToMouse <= TwoPi && angleToMouse > (TwoPi - Pi / 2)) {
             // Rotate left
             angle -= 0.5;
         }
     }

     // Add some random movement
     if (dangerMice.size() > 1 && (qrand() % 10) == 0) {
         if (qrand() % 1)
             angle += (qrand() % 100) / 500.0;
         else
             angle -= (qrand() % 100) / 500.0;
     }

     speed += (-50 + qrand() % 100) / 100.0;

     qreal dx = ::sin(angle) * 10;
     mouseEyeDirection = (qAbs(dx / 5) < 1) ? 0 : dx / 5;

     rotate(dx);
     setPos(mapToParent(0, -(3 + sin(speed) * 3)));
 }