Get mouse event for widget with trasparent background

Unick

Hello.

Is there a way to get mouse event in widget with transparent background, if mouse cursor is under transparent part of widgets.

I have main Qt window, this window has one child, which is third-party non-Qt window. Above i have panel (QWindow), which is owned by main window. This panel has Qt::Window flag and parent is main widnow.

My panel have attributes:

setAttribute(Qt::WA_NoSystemBackground, true);
setAttribute(Qt::WA_TranslucentBackground, true);

On panel i have non-trasparent child widgets. I able to get mouse events only if mouse cursor is under child widget. I know if my transparent panel did not get event, a widget under it get event. But under my widget third-party window is located. I cannot modify his code. My goal to intercept mouse event and implement drag&drop and third-party window should not get mouse event in this case.

I tested under Windows Qt 5.3.

Under mac all mouse events under transparent part of panel i can get in main window mouse event function. It does not work the same under Windows.

Unick

I found one solution, which works for me. But it looks like a hack :)

I added child QWidget to my panel. I added QGraphicsOpacityEffect for this QWidget and set opacity value to 0.01. As the results widget is invisible, but my panel is started to get mouse events. One remark: QWidget should fill full panel.

mrjj

Hi
You can have a go with event filter and see what flows around of events.
http://doc.qt.io/qt-5/eventsandfilters.html

bool MainView::eventFilter(QObject *obj, QEvent *event)
{
if (event->type() == QEvent::MouseButtonPress)
  {
    QMouseEvent *mouseEvent = static_cast<QMouseEvent*>(event);
    int mx=mouseEvent->pos().x(),my=mouseEvent->pos().y();

    qDebug() << QString::number(mx)<<" "<<QString::number(my);
...
  }
}

Unick

You can have a go with event filter and see what flows around of events.

Unfortunately it does not work. Also i tried to use nativeEvent method, but it does not work too.

mrjj

@Unick
Ok but what did you learn?
I never tested what WA_TranslucentBackground will do to the event flow but
an event filer would cast some light over that.
So such windows do not get any mouse events?

Unick

Looks like my third-party window gets mouse event first and process it. And event filter is not called for mouse events for transparent parts of my panel.

I learned MSDN and looks like it is feature of Windows: [https://msdn.microsoft.com/en-us/library/ms997507.aspx#layerwin_topic2b](link url)

Hit testing of a layered window is based on the shape and transparency of the window. This means that the areas of the window that are color-keyed or whose alpha value is zero will let the mouse messages through.
If the layered window has the WS_EX_TRANSPARENT extended window style, the shape of the layered window will be ignored and the mouse events will be passed to the other windows underneath the layered window.

But i will investigate more and post message if i find solution. Maybe i can use event hook.

Unick

I found one solution, which works for me. But it looks like a hack :)

I added child QWidget to my panel. I added QGraphicsOpacityEffect for this QWidget and set opacity value to 0.01. As the results widget is invisible, but my panel is started to get mouse events. One remark: QWidget should fill full panel.