CODEWITHSUNDEEP
qt
Stefano Borini
Stefano Borini

Reputation: 143895

Qt mapToGlobal and multiple screens. How do they interact?

I don't understand how mapToGlobal interacts with a multiple screen setup. Is it returning the global position relative to that particular screen, or to the whole desktop?

If I invoke QCursor.setPos(widget.mapToGlobal(widget.geometry().topLeft()) will I always end up with the pointer in the top left corner of the widget, regardless of any multiscreen situation?

Upvotes: 2

Views: 2223

Answers (1)

TheDarkKnight
TheDarkKnight

Reputation: 27621

As the docs state for mapToGlobal: -

Translates the widget coordinate pos to global screen coordinates

Since you're mapping from local coordinates, you can actually just use: -

mapToGlobal(QPoint(0,0));

Rather than having to specify the widget's top left position of the geometry.

As for mapping to Global coordinates, from memory, I think the global space is extended across the screens, so two screens at a resolution of 1024 x 768 would give a screen space of 2048 x 768, if arranged side by side.

The docs also state: -

For desktops with multiple screens, the size of the desktop is the union of all the screen sizes

So I would expect mapToGlobal would return a value with respect to the total screen space available, rather than just the screen that the widget resides. If it didn't, it would be quite awkward to handle a widget that was placed between two screens.

Note that you can also use QDesktopWidget for information about the different screens and to check which screen a widget resides upon. It's also useful if you want to place a widget on a specific screen.

Finally, in Qt 5, there's also the QScreen class to query screen properties.

Upvotes: 3

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