[Development] Respecting QGuiApplication::highDpiScaleFactorRoundingPolicy on Wayland

[Ilya Fedin]

On Wed, 11 Sep 2024 10:53:33 +0000
Tor Arne Vestbø <Tor.arne.Vestbo at qt.io> wrote:

> > On Sep 9, 2024, at 9:03 AM, Ilya Fedin <fedin-ilja2010 at ya.ru> wrote:
> > 
> > While most platforms seem to have fractional scaling via
> > QHighDpiScaling, Wayland is the first (and the only right now)
> > platform that got fractional devicePixelRatio on QPA level.
> > QHighDpiScaling doesn't handle that and the Wayland QPA just
> > disables fractional scaling support when it sees the policy is not
> > PassThrough.
> > 
> > It's good that it does that at least but I believe this could be
> > done better. I have patches that make High DPI rounding policy to
> > behave on Wayland the same as on other platforms, allowing
> > applications using a rounding policy to render 1:1 with crsip fonts
> > (currently the compositor downscales as QPA disables fractional
> > scaling support) and actually respect the policy (downscaling means
> > it's effectively always Ceil).
> > 
> > Is there any interest in those changes?  
> 
> Yep, please share the patches. Doing so makes it easier to see how
> this fits within the existing architecture :)
> 
> Cheers,
> Tor Arne
> 

https://codereview.qt-project.org/c/qt/qtbase/+/590171
https://codereview.qt-project.org/c/qt/qtwayland/+/590173
https://codereview.qt-project.org/c/qt/qtwayland/+/590174

The qtwayland patches are meant to work in conjunction with the qtbase
patch.