#include "myitem.h"
#include<QtGui>

MyItem::MyItem()
{
    setFlags(ItemIsFocusable|ItemIsMovable);
    boundingRect();
    rect.setRect(-18,-18,36,36);
}
QRectF MyItem::boundingRect() const
{
    return QRectF(rect);
}

void MyItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    prepareGeometryChange();
    rect.moveCenter(event->pos()-offset);
    update();
}
void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    painter->drawRect(rect);
}
void MyItem::keyPressEvent(QKeyEvent *event)
{
    switch (event->key())
    {
    case Qt::Key_4 :
        rotate(-30);
        break;
    case Qt::Key_6 :
        rotate(30);
        break;
    case Qt::Key_Up:
        scale(1.2,1.2);
        break;
    case Qt::Key_Down:
        scale(1/1.2,1/1.2);
        break;
    }
}
void MyItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    setFocus();
    offset=event->pos()-rect.center();
}

正常item缩放旋转都是以图形项坐标原点变化的，为什么我这么一改就只能按item初始位置的坐标点变化了？
item.setPos(x,y); 就按(x,y)点旋转、缩放，如果没设置就是场景坐标的（0,0）点。我的boundingRect也跟着改变了位置，为什么不是按着图形项坐标原点变化？