QGraphicsView mousewheel zoom

Strangelove

For my application which uses QGraphicsView and QGraphicsScene, I am trying to implement a mousewheel zoom function. The best I've come up with is the following, which (kinda) works but has an annoying issue:

    # Method in QGraphicsView
    def wheelEvent(self, event):
        factor = 1 * (event.angleDelta().y() / 1000 + 1)

        view_rect = QRect(
            0, 0, self.viewport().width(), self.viewport().height())
        visible_scene_rect = QRectF(
            self.mapToScene(view_rect).boundingRect())

        view_width = visible_scene_rect.size().width()
        scene_width = self.sceneRect().size().width()
        view_height = visible_scene_rect.size().height()
        scene_height = self.sceneRect().size().height()

        if (0 < factor < 1) and (
            view_width < scene_width or view_height < scene_height):
            self.scale(factor, factor)
            self._zoom = self._zoom * factor
        elif factor > 1 and self._zoom < 3:
            self.scale(factor, factor)
            self._zoom = self._zoom * factor

(The scene's sceneRect() has been properly set beforehand).

The issue is that if the user is zooming out with a rapid gesture (e.g. on a trackpad), it is possible to zoom much farther than the scene's extents. The scene then becomes ridiculously small.

I feel the code is going through some convoluted calculations which should be handled in a simpler fashion, since this is such a common scenario, but I'm not sure how to achieve this.

Thanks for your help.

mrjj

Hi
This example also has zoom
https://doc.qt.io/qt-5/qtwidgets-graphicsview-chip-example.html

You code looks fine.