WheelEvent zoom is getting weird if I enable other mouse events.

User Generated

tntna.zvfuen@tznvy.p

Programming

Description

I am stuck with this weird behavior where, if I enable rubberband drag, the wheel event doesn't zoom under mouse anymore. It does zooming but irrespective of mouse position. And if I disable other events, then wheelEvent works properly.

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Explanation & Answer

QGraphicsView::scale function's behaviour depends on the mouse position. It's performing automatically and internally by QGraphicsView. Since you don't pass mouse position to the scale function, I think QGraphicsView tracks the mouse and remembers the last position on its own.

By reimplementing mouse event handlers you have taken this ability from it. The view can't determine the mouse position anymore because its original handlers aren't called.

Luckily this issue can be easily fixed. You need to call base class implementation before your own:

void MyGraphics::mousePressEvent(QMouseEvent *event) {
QGraphicsView::mousePressEvent(event);
// your implementation goes here
}
It's an example for mousePressEvent but you should add similar statements to all your event handlers unless you need to disable some part of default behavior.


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