[Development] Respecting QGuiApplication::highDpiScaleFactorRoundingPolicy on Wayland

[Ilya Fedin]

On Mon, 9 Sep 2024 11:03:04 +0400
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?
> 
> The code changes are quite small actually: the main patch changing
> mostly qhighdpiscaling.cpp is 179 lines long. The auxiliary qtwayland
> patch to provide fractional QWaylandScreen::devicePixelRatio
> (currently it provides only fractional
> QWaylandWindow::devicePixelRatio) is 111 lines long.

Anyone? Morten Sørvig? Or is mailing list not the right place to discuss
this?