QGraphicsItem使用

//重写虚函数
QRectF boundingRect() const;//预计绘制的区域
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget /* = 0 */);//绘制

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);//场景大小
    scene.setItemIndexMethod(QGraphicsScene::NoIndex);//线性索引
    MyItem *item = new MyItem;
    scene.addItem(item);
    scene.addText("Hello World!");
    QGraphicsView view(&scene);
    view.setRenderHint(QPainter::Antialiasing);//指定Render标签，抗锯齿
    view.setCacheMode(QGraphicsView::CacheBackground);//缓存模式
    view.setViewportUpdateMode(QGraphicsView::BoundingRectViewportUpdate);//场景重绘更新方式
    view.setDragMode(QGraphicsView::ScrollHandDrag);//拖动模式，鼠标可拖动
    view.resize(400, 300);
    view.show();
    //scene.removeItem(scene.itemAt(-10, -10, view.transform()));
    return a.exec();
}