在QGraphicsView中创建自动滚动功能

我有一个 QGraphicsView 和一个 QGraphicsScene 。根据用户输入 QGraphicsItem 可以放置在场景上。此项目既可选择也可移动。

当场景大于视图滚动条时,将显示滚动条(设置为在必要时显示)。

当用户将项目移动到视图边缘附近时,场景的宽度/高度会相应地拉伸——我正在使场景变大。

问题是 当项目靠近视图边界时,如何强制滚动条与场景一起滚动? 功能我认为在任何图形编辑器中都很常见。在 MouseMoveEvent 在场景中,我正在使场景变大,迫使滑块移动并相应地更新可见的矩形。

这并没有达到预期效果。即使考虑到滚动正在调整到新的场景大小,视图中也没有平滑的移动。有更好的方法吗?

一些解释:

    itemUnderCursor = currently slected QGraphicsItem
    qgv = QGraphicsView

代码段:

    // check if item is near the border
    QPointF point = itemUnderCursor->mapToScene(itemUnderCursor->boundingRect().topLeft());
    double delta = 0;

    if(point.x() < visibleRect.left())
    {
        // prevent from drawing outside the scene
        itemUnderCursor->setPos(visibleRect.left(), itemUnderCursor->scenePos().y());

        if(event->scenePos().x() < oldMousePos.x()-3)
        {
            // stretch the scene
            if(qgv->horizontalScrollBar()->value() <= 0)
                setSceneRect(QRectF(QPointF(sceneRect().x() - 3, sceneRect().y()), sceneRect().bottomRight()));
            /*
             * disable signals from DrawingArea in order to avoid
             * recursive calls of mouseMoveEvent then enabling them
             * back to handle the rest of events
             */
            this->blockSignals(true);
            delta = point.x() - originalRect.left();
            qgv->horizontalScrollBar()->setValue(hScrollOriginalValue + delta);
        }
        oldMousePos = event->scenePos();
        this->blockSignals(false);

        // update the visible rectangle
        visibleRect = getVisibleRect(qgv);
    }

    if(point.x() + itemUnderCursor->boundingRect().width() > visibleRect.right())
    {
        // prevent from drawing outside the scene
        itemUnderCursor->setPos(visibleRect.right() - itemUnderCursor->boundingRect().width(), itemUnderCursor->scenePos().y());
        if(event->scenePos().x() > oldMousePos.x()+3)
        {
            // stretch the scene
            if(qgv->horizontalScrollBar()->value() >= 0)
                setSceneRect(QRectF(sceneRect().topLeft(), QPointF(sceneRect().bottomRight().x() + 3, sceneRect().bottomRight().y())));

            /*
             * disable signals from DrawingArea in order to avoid
             * recursive calls of mouseMoveEvent then enabling them
             * back to handle the rest of events
             */
           delta = point.x() + itemUnderCursor->boundingRect().width() - originalRect.right();
           this->blockSignals(true);
           qgv->horizontalScrollBar()->setValue(hScrollOriginalValue + delta);
        }
        oldMousePos = event->scenePos();
        this->blockSignals(false);

        // update the visible rectangle
        visibleRect = getVisibleRect(qgv);
    }

我正在对的顶部和底部边界执行相同的操作 Q图形视图 .