Move QWidget inside parent widget,but it delay

Joe Johnson

void ChildWidget::mousePressEvent(QMouseEvent *event)
{
    offset = event->pos();
}

void ChildWidget::mouseMoveEvent(QMouseEvent *event)
{
    //Using left mouse to move the control
    if (event->buttons() & Qt::LeftButton)
    {
        //Excute movement follow mouse position
        move(mapToParent(event->pos() - offset));
        //Make sure control do not move out parent size
        if (x() < 0)
            move(1, y());
        if (y() < 0)
            move(x(), 1);
        if (x() + width() > parentWidget()->width())
            move(parentWidget()->width() - 1 - width(), y());
        if (y() + height() > parentWidget()->height())
            move(x(), parentWidget()->height() - 1 - height());
    }
}

I have tried to make a child widget follow my mouse cursor and limit in into parent widget.It works,however,the child widget looks like to shrink when I move the child widget fast.According to Qt doc, the pos is the position of the last mouse move event.How can I make it looks "normal"?(no shrink)

JoeCFD

It looks like a few moves can happen:
first move: move(mapToParent(event->pos() - offset));
More possible moves could follow. Why do not you make one single move by combining all conditions together?

Joe Johnson

@JoeCFD thanks for your reply.Do you mean the follow part？

        //Make sure control do not move out parent size
        if (x() < 0)
            move(1, y());
        else if (y() < 0)
            move(x(), 1);
        else if (x() + width() > parentWidget()->width())
            move(parentWidget()->width() - 1 - width(), y());
        else if (y() + height() > parentWidget()->height())
            move(x(), parentWidget()->height() - 1 - height());
        else
            move(mapToParent(event->pos() - offset));

however,it still looks to shrink

JonB

@Joe-Johnson
No. You can't (necessarily) do it with else ifs anyway, as more than one condition might apply.

@JoeCFD is suggesting you use a couple of variables, say _x & _y. Do all your calculations first to set both of these. then do a single move(_x, _y) at the end. Whether it will help I'm not at all sure, but it would avoid multiple move()s if that is a problem.

Joe Johnson

@JonB thanks.```
QPoint point(mapToParent(event->pos() - offset));
//Make sure control do not move out parent size
if (x() < 0)
{
point.setX(1);
point.setY(y());
}
else if (y() < 0)
{
point.setX(x());
point.setY(1);
}
else if (x() + width() > parentWidget()->width())
{
point.setX(parentWidget()->width() - 1 - width());
point.setY(y());
}
else if (y() + height() > parentWidget()->height())
{
point.setX(x());
point.setY(parentWidget()->height() - 1 - height());
}
move(point);

however,maybe the multiple move()s is not the reason of the shrinking child widget

JonB

@Joe-Johnson said in Move QWidget inside parent widget,but it delay:

however,maybe the multiple move()s is not the reason of the shrinking child widget

That is probably correct! So this may be wasting your time. But your code is still not great with else ifs, e.g. look at what it would do if both x() & y() are less than zero....

JoeCFD

@Joe-Johnson add a print message in this func to check how many moves are done. This may not be the root cause. But I would clean this up first if I were you.

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Move QWidget inside parent widget,but it delay