QGraphicsItem绘制重叠区域

效果如下：

我通过重写一个继承自QGraphicitem的类来实现上述功能，绘制重叠区域主要通过QPainterPath来实现，核心代码如下：

void myGraphicRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QPen mPen= QPen(Qt::yellow);
    painter->setPen(mPen);
    //绘制旋转后的矩形
    painter->drawPolygon(m_oldRectPolygon);
    //绘制旋转圆形
    mPen.setWidth(2);
    mPen.setColor(Qt::green);
    painter->setPen(mPen);
    QPointF pf = getSmallRotateRectCenter(m_oldRectPolygon[0],m_oldRectPolygon[1]);
    QRectF rect = QRectF(pf.x()-10,pf.y()-10,20,20);
    painter->drawEllipse(rect);//绘制圆形
    painter->drawPoint(pf);//绘制点
    //有重叠的情况
    if(!this->scene()->collidingItems(this).isEmpty())
    {
       QPainterPath path,pathOthers;
       QList<QGraphicsItem *> lstcolliItems = this->scene()->collidingItems(this);
       int nColliNum = lstcolliItems.count();
       for(int i = 0;i<nColliNum;i++)
       {
           QGraphicsItem* pTempItem = this->scene()->collidingItems(this)[i];
           QPainterPath tempPath = pTempItem->shape();
           tempPath.translate(pTempItem->pos());//转换到view中的坐标
           pathOthers += tempPath;//记录与本item重叠的item的路径
       }
       path.addPolygon(m_oldRectPolygon);
       path.translate(this->pos());//转换到view中的坐标
       path &= pathOthers;//计算重叠部分的路径path
       path.translate(-this->pos().x(),-this->pos().y());//转换回本Item中的坐标
       QBrush brush(Qt::cyan);
       mPen.setColor(Qt::blue);
       painter->setPen(mPen);
       painter->setBrush(brush);
       painter->drawPath(path);//绘制重叠区域
    }
}