I don't know why that variable exists. It's useless as far as I can tell. Maybe it means that you are being scaled?
I use Screen.pixelDensity. Which varies as you think it should, but is spec'd in px per mm, not DPI. That pixelRatio is either 1 or 0, I don't think it is ever in between. In theory on a 2x device the pixelDenisty will be 2x the 1x. Meanwhile pixel ratio is: old (10yr) monitor: 4.x Samsung Note 2: 10.x Moto X: 16.x > Sent: Thursday, February 05, 2015 at 5:29 PM > From: "John Weeks" <j...@wavemetrics.com> > To: "interest@qt-project.org" <interest@qt-project.org> > Subject: [Interest] hi-res drawing on Windows > > Is there a comprehensive overview of drawing for monitors at various > resolutions on Windows? > > I am trying to get our application to work correctly on a hi-res monitor on > Windows. In particular, I have a QToolButton-derived class that makes a > button that is just the icon, with no visible frame. It overrides sizeHint(), > maximumSize() and paintEvent() to do this. Instances of the button are given > icons from PNG resources that have both standard and "@2x" versions. > > One point of this class is to size the button based on the size of the icon. > Thus, sizeHint() and maximumSize() both return iconSize(). In the > paintEvent(), I get the icon out of the button using icon(), get the QWindow > for the window hosting the button and then use QIcon::pixmap(QWindow *, > iconSize(), ...) to get the appropriate QPixmap to draw. > > On Macintosh this works great. On my 5k iMac I get the correct size and > hi-res pixmap. Slide the window over to my external standard-res monitor and > it redraws with the standard res pixmap. > > On Windows, I don't have a hi-res monitor. I'm faking it by setting "Change > the size of all items" to Larger 150%. That's another way to say, "Make my > large monitor small" :) Not ideal, and it's not 2x, so I don't really expect > the 2x icons. What I DO expect is the QWindow::devicePixelRatio() might > return 1.5, but all I get is 1.0 at all settings of "size of all items". > > I found this: > http://doc-snapshot.qt-project.org/qt5-5.4/highdpi.html > > Since I'm on Windows 8.1 I should be in "Per-Monitor DPI Aware" mode. It > seems like I shouldn't have to intervene in order to get > resolution-independent pixel drawing. > > If I do this before creating my QApplication instance: > qputenv("QT_DEVICE_PIXEL_RATIO", "2") > then I get 2.0 from devicePixelRatio(), as expected. I also get my hi-res > icons. > > If I do this instead: > qputenv("QT_DEVICE_PIXEL_RATIO", "1.5") > then devicePixelRatio returns 1.0, not 1.5. > > And it doesn't seem like I should have to set this myself, anyway. > > Thanks for any insight you might be able to offer! > > -John Weeks > > _______________________________________________ > Interest mailing list > Interest@qt-project.org > http://lists.qt-project.org/mailman/listinfo/interest > _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
