QWidget - identify underlying wigets

Sam

Hi,

I have a frame with a number of widgets, on top of that frame lies a translucent Overlay widget (activated based on a property). I would like to know if there is way I can identify the underlying widgets under this Overlay widget on mousePress ( based on event->pos())

The fame itself can have multiple layers e.g with stackLayout and I would like to know the top level widgets from there.

alt text

I already tried widgetAt, topLevelAt and childAt but it doesn't full fill my requirement.

TIA
Sam

mrjj

Hi
Not sure why widgetAt did not work for you `?
http://doc.qt.io/qt-5/qapplication.html#widgetAt

Did you convert from event->pos that is in local coordinates to global coordinates
when using widgetAt?

raven-worx

@mrjj said in QWidget - identify underlying wigets:

Not sure why widgetAt did not work for you `?

because the overlay widget is returned in all times ;)

@Sam
eitherway you quickly hide the overlay for the childAt() call.
If there is noticeable flickering, you need to implement a custom recursive method to do what you want. It is pretty simple. Take a look at the source code of QWidget::childAt() and add a line to skip the child if it is your overlay.

mrjj

@raven-worx
Eh doh yes.. :)
My brain wanted the call to be like parentwidget->WidgetAt() as to skip Overlay. Missed it was QApp ;)

If we look at the function, it seems it can go through
WA_TransparentForMouseEvents ?
So if Overlay is marked with WA_TransparentForMouseEvents it should return the
widget beneath ? Or is "shoot a hole in the widget" not what i think :)

QWidget *QApplication::widgetAt(const QPoint &p)
1236{
1237    QWidget *window = QApplication::topLevelAt(p);
1238    if (!window)
1239        return 0;
1240
1241    QWidget *child = 0;
1242
1243    if (!window->testAttribute(Qt::WA_TransparentForMouseEvents))
1244        child = window->childAt(window->mapFromGlobal(p));
1245
1246    if (child)
1247        return child;
1248
1249    if (window->testAttribute(Qt::WA_TransparentForMouseEvents)) {
1250        //shoot a hole in the widget and try once again,
1251        //suboptimal on Qt for Embedded Linux where we do
1252        //know the stacking order of the toplevels.
1253        int x = p.x();
1254        int y = p.y();
1255        QRegion oldmask = window->mask();
1256        QPoint wpoint = window->mapFromGlobal(QPoint(x, y));
1257        QRegion newmask = (oldmask.isEmpty() ? QRegion(window->rect()) : oldmask)
1258                          - QRegion(wpoint.x(), wpoint.y(), 1, 1);
1259        window->setMask(newmask);
1260        QWidget *recurse = 0;
1261        if (QApplication::topLevelAt(p) != window) // verify recursion will terminate
1262            recurse = widgetAt(x, y);
1263        if (oldmask.isEmpty())
1264            window->clearMask();
1265        else
1266            window->setMask(oldmask);
1267        return recurse;
1268    }
1269    return window;
1270}

raven-worx

@mrjj
yes, but then you won't receive the mouseevent on the overlay again to trigger all this.

Edit:

but actually i think it can be made work with Qt::WA_TransparentForMouseEvents:

void OverlayWidget::mousePressEvent(QMouseEvent* event)
{
this->setAttribute( Qt::WA_TransparentForMouseEvents, true );
QWidget* childBeneath = this->childAt( event->pos() );
this->setAttribute( Qt::WA_TransparentForMouseEvents, false );
}

This should work.

Sam

@mrjj @raven-worx

void OverlayWidget::mousePressEvent(QMouseEvent* event)
{
this->setAttribute( Qt::WA_TransparentForMouseEvents, true );
QWidget* childBeneath = this->childAt( event->pos() );
this->setAttribute( Qt::WA_TransparentForMouseEvents, false );
}

Thanks a lot guys this works perfect :-) I just changed from childAt() to widgetAt()

qApp->widgetAt(mapToGlobal(e->pos()));

Solved QWidget - identify underlying wigets