使用QGraphicsView,QGraphicsScene,QGraphicsPixmapItem,能在场景中根据鼠标当前位置对图片进行缩放，是图片始终相对于鼠标位置固定。(QGraphicsViewSceneQGraphicsPixmapItem. can zoom the picture according to the current position of the mouse in the scene, so the picture is always fixed relative t