QGraphicsItem使用

//重寫虛函數
QRectF boundingRect() const;//預計繪制的區域
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget /* = 0 */);//繪制

QRectF MyItem::boundingRect() const
{
    qreal adjust = 0.5;
    return QRectF(-100 - adjust, -100 - adjust, 200 + adjust, 200 + adjust);
}
void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QBrush brush(QColor(200,125,125));
    painter->setBrush(brush);
    painter->drawRect(-100, -100, 200, 200);
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QGraphicsScene scene;
    scene.setSceneRect(-300, -300, 600, 600);//場景大小
    scene.setItemIndexMethod(QGraphicsScene::NoIndex);//線性索引

    MyItem *item = new MyItem;
    scene.addItem(item);
    scene.addText("Hello World!");

    QGraphicsView view(&scene);
    view.setRenderHint(QPainter::Antialiasing);//指定Render標簽，抗鋸齒
    view.setCacheMode(QGraphicsView::CacheBackground);//緩存模式
    view.setViewportUpdateMode(QGraphicsView::BoundingRectViewportUpdate);//場景重繪更新方式
    view.setDragMode(QGraphicsView::ScrollHandDrag);//拖動模式，鼠標可拖動
    view.resize(400, 300);
    view.show();

    //scene.removeItem(scene.itemAt(-10, -10, view.transform()));
    return a.exec();
}