High DPI scaling detection

jazzco2

Hi all,

I would like to detect the scaling rate of the current display. I checked several values but couldn't find anything helpful:

DisplayZoom   pixelRatio   physicalDPI   logicalDPI   screenSize   fontSize
  100%            1          108.888         96       2560x1400        8
  125%            1          108.888        120       2560x1390        8
  150%            2           54.4438        96       1280x 690        8
  175%            2           54.4438        96       1280x 685        8
  200%            2           54.4438        96       1280x 680        8

Unlike the menu bar that's scaling correctly several elements like the status bar and text's in the tab widget tend to break out being too big or to small on several systems (Windows, Mac, Linux).

I read the chapter about High DPI Displays but there's nothing I didn't already tried out.

Best regards
Jazzco

jazzco2

Update:

The font size of the QMenu and the QTabBar do not differ in the main windows constructor. But after waiting for the followup events to be processed these fonts differ in fact.

To get the QTabBar having the same font size as the QMenu it doesn't help to just assign the menus font to the it. It is necessary to explicitly assign the pointSize to the font before assigning it to the destination widget (here the QTabBar).

Additionally one can get the QFontMetrics::height() for concrete values.

I mark this solved.

Best
Jazzco

SGaist

Hi,

You should add which Qt version as well.

jazzco2

Ah right, it's Qt 5.15.2 - and several versions before that. We won't change to current Qt 6 until the WebEngine is part of it.

Pl45m4

@jazzco2

Have a look here and here.

jazzco2

@Pl45m4 said in High DPI scaling detection:

@jazzco2

Have a look here and here.

As I told, I already worked through that page. The problems still exist. Therefore the question if there is any value in the libraries of Qt telling what scaling is active on the current display.

Pl45m4

@jazzco2 said in High DPI scaling detection:

As I told, I already worked through that page. The problems still exist

So you must have missed something :)

Device Pixel Ratio	The scale factor that either the operating system or Qt applies.

This is obtainable from every QWindow as well as from QScreen

https://doc.qt.io/qt-5/qscreen.html#devicePixelRatio-prop

Edit:

Isn't the pixelRatio already listed in your table? Or am I missing something now? Or I am not getting what you mean?!

From documentation:

Common values are 1.0 on normal displays and 2.0 on "retina" displays. Higher values are also possible.

jazzco2

@Pl45m4 said in High DPI scaling detection:

Isn't the pixelRatio already listed in your table?

Correct, but as you can see that value doesn't tell what scaling is set up on Windows. There is just a point where it switches from one to two - and there the resolution of the screen is halfed.

On startup the QGuiApplication get a font with a pixel-size that somehow reflects the scaling of the primary screen. But that font size isn't updated when the application is moved to a screen with a different scaling factor. Even more puzzling: The texts in the tab-bar and in the menu-bar appear in obvious different sizes - but asking them programatically they claim to have the same point size (the initial point-size of the app)

jazzco2

Update:

The font size of the QMenu and the QTabBar do not differ in the main windows constructor. But after waiting for the followup events to be processed these fonts differ in fact.

To get the QTabBar having the same font size as the QMenu it doesn't help to just assign the menus font to the it. It is necessary to explicitly assign the pointSize to the font before assigning it to the destination widget (here the QTabBar).

Additionally one can get the QFontMetrics::height() for concrete values.

I mark this solved.

Best
Jazzco