multi screen

[Thomas Feldman]

Hello,

i'm programming an application under Qt4/windows dedicated to multi screen video. I would like to render the content of a first widget in full screen mode to screen 1 and to render the content of the second widget in full screen mode to screen 2.

Does anyone knows how to do this with lowest CPU usage?

Thanks!

Thomas

[high_flyer]

Have a look at QDesktopWidget in order to target various screens.

Does anyone knows how to do this with lowest CPU usage?

Have a look here

[Thomas Feldman]

Have a look at QDesktopWidget in order to target various screens.

The trouble is that, as far as i understand, QDesktopWidget is an information class that enable to "retrieve" information about screens but doesn't allow to assign a particular widget to a particular screen..is that true?

[high_flyer]

Well, with QDesktopWidget you can get a pointer to the deskotop which is on the desired screen.
And you can use that pointer as a parent for the widget you want to place on that screen.
NOTE: on a virtual desktop it might not be possible to distiguish between physical screens shared by the same desktop, all though the docs say it should be.
I had that problem not long ago - but then you can use QWidget::move() to place your widget on the right physical screen.

[Thomas Feldman]

Thanks for this answer. I will indeed use QApplication::desktop()->screen(0 or 1) as the parent widget.

May I ask you another question. I planned to use a QLabel for displaying pixmaps (each 40 ms). From your experience, is it slower than your method, ie using QImage and QBrush-> fillRect? Either, did you try the drawPixmap function of Qpainter?

Thanks
Thomas

[high_flyer]

May I ask you another question. I planned to use a QLabel for displaying pixmaps (each 40 ms). From your experience, is it slower than your method, ie using QImage and QBrush-> fillRect? Either, did you try the drawPixmap function of Qpainter?

I didn't try that under Qt4 so I can't tell you how fast it is. (my method).
Or if it even works.
To what you had in mind:
In case you are getting a buffer from external source - like a camera, you will have to convert from QImager to QPixmap - and that is slow.
Your aim should be to feed your buffer as directly as you can to the paintEvent().