[Development] Confused about HiDPI scaling and fonts

Morten Sørvig Morten.Sorvig at qt.io
Wed Feb 10 12:53:27 CET 2021

It may be easier to show the expected behaviour with a video:


The important thing is that text visual size and window visual size is kept in sync as the system DPI changes. From the report I got the impression that this was maybe not the case - but that could be a misunderstanding.

>From there it's possible to go into the details: there are multiple coordinate systems, window and text sizes are (approximately) constant in one coordinate system but changes in another. Long discussions can be had :)

But fortunately, Qt apps can for the most part ignore this and continue to assume a single coordinate system at 96DPI. 

- Morten

> On 9 Feb 2021, at 18:17, Friedemann Kleint <Friedemann.Kleint at qt.io> wrote:
> Hi,
> it seems there is a misunderstanding here: Qt High  DPI scaling preserves the  point-size of the fonts; they are sized according to the system metrics.
> All it does is pretend a lower resolution to the application so that apps written for 96DPI continue to work.
> It is not a means of zooming the application (as opposed to QT_SCALE_FACTOR ).
> Regards, Friedemann
> -- 
> Friedemann Kleint
> The Qt Company GmbH
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