1.5 fractional scale isn't crisp and clear with Qt6 applications

[zvova7890]

Please fill out the following:

• Sway Version:

  • 1.9.0

• wlroots version:

  • 0.17.2

• Description:

  • It is exposing the fractional value as 180 in the preferred_scale event. Qt sets the scale factor as 180/120 = 1.5. But it is blurred until I set the scale factor as 1.500586, which is the result of dividing physical/logical width.

> 2560/1706
1.5005861664712778

It seems Sway doing surface transformation despite client is using a correct scale factor that comes with fractional_scale_v1 protocol. Is that intentional or just a bug?

BTW, The Chromium project is also relying on that result of division, and it's crisp and clear with Sway, but blurry with KDE(which is strictly following the fractional_scale_v1 protocol). See related links:
https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/297
https://chromium-review.googlesource.com/c/chromium/src/+/5404799