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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)
     {
         setRotation(qrand() % (360 * 16));
     }

     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::advance(int step)
     {
         if (!step)
             return;
         // 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;

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