如何在Qt环境中将鼠标光标限制为矩形（在Ubuntu 12.04中，不是Windows）

Question

there is a question confuse me a few days, that is how can I limit mouse cursor into a rectangle in Qt environment? And my OS is ubuntu 12.04, so Windows API ClipCursor() doesn't work. thank you very much.

Answer 1

this involving QGraphicsItem::itemChange() . If you have an item which you want to restrict to a certain area then reimplement itemChange() for that item and monitor QGraphicsItem::ItemPositionHasChanged changes to see whether the items wants to be placed outside your area of interest and prevent that by returning a position from inside that area. for example:

    QVariant QGraphicsItem::itemChange(GraphicsItemChange change, const QVariant &value)
{
    switch (change) {
    case ItemPositionHasChanged:
        if(x() < -200 || y() < -200 || x() > 200 || y() > 200)
            setPos(0, 0);
        graph->itemMoved();
        break;
    default:
        break;
    };

    return QGraphicsItem::itemChange(change, value);
}

If you don't have an item but rather want to force a user to click within the area then hide the mouse pointer (by setting it to a blank shape), create a dedicated item that will serve as a cursor, optionally grab the mouse to that shape and then use itemChange() like I described earlier.