Qt编程之通过鼠标滚轮事件缩放QGraphicsView里面的Item

 

 

首先自己subclass QGraphicsView的一个类，叫DiagramView，然后重新实现它的滚轮事件函数，然后发送一个缩放信号：

 1 oid DiagramView::wheelEvent(QWheelEvent * event){

 2 

 3     if (event->delta() > 0)

 4     {

 5         emit mouseWheelZoom(true);

 6     }

 7     else

 8     {

 9         emit mouseWheelZoom(false);

10     }

11 

12 }

View Code

 

然后用connect把这个信号连接到要实现的槽函数上（ScaleFactor初始化为30）：

 1 void TopologyEditor::Zoom(bool zoom){

 2 

 3     

 4 

 5     

 6 

 7     if (zoom && scaleFactor >= 0)

 8     {

 9         

10         scaleFactor += 10;

11         QMatrix old_matrix;

12         old_matrix = view->matrix();

13         view->resetMatrix();

14         view->translate(old_matrix.dx(), old_matrix.dy());

15         view->scale(scaleFactor/100.0, scaleFactor/100.0);

16     }

17     else if (!zoom && scaleFactor >= 0)

18     {

19         scaleFactor -= 10;

20         QMatrix old_matrix;

21         old_matrix = view->matrix();

22         view->resetMatrix();

23         view->translate(old_matrix.dx(), old_matrix.dy());

24         

25         view->scale( scaleFactor/100.0,  scaleFactor/100.0);

26 

27     }

28 

29     else if (scaleFactor < 0){

30     

31         scaleFactor = 0.0;

32     }

33 

34 }

View Code

 

 

 

references：

http://stackoverflow.com/questions/19113532/qgraphicsview-zooming-in-and-out-under-mouse-position-using-mouse-wheel

http://www.qtcentre.org/threads/52603-Zoom-effect-by-mouse-Wheel-in-QGraphicsview