https://bugs.kde.org/show_bug.cgi?id=466373
Bug ID: 466373 Summary: Qt apps don't use wp-fractional-scale-v1 for hidpi fractional scaling on Wayland Classification: KDE Neon Product: neon Version: unspecified Platform: Neon OS: Linux Status: REPORTED Severity: normal Priority: NOR Component: Packages Testing Edition Assignee: neon-b...@kde.org Reporter: edoubray...@gmail.com CC: j...@jriddell.org, neon-b...@kde.org, sit...@kde.org Target Milestone: --- SUMMARY Qt client apps using system Qt 5.15.8 still use the old downscaling mechanism to deal with fractional scaling, instead of wp-fractional-scale-v1, leading to visual artefacts. STEPS TO REPRODUCE 1. Set "Scale" to fractional eg 135% in Display Configuration 2. Open a Qt app OBSERVED RESULT App is upscaled to 2x then downscaled. This produces aliasing artifacts as detailed previously here [1] EXPECTED RESULT Native scaling... like what is done by XWayland in "Apply scaling themselves" mode. See attached picture. On the left is XWayland (Platfom=xcb) and on the right Wayland. SOFTWARE/OS VERSIONS KDE Neon based on ubuntu 22.04.2 (available in About System) KDE Plasma Version: 5.27.1 KDE Frameworks Version: 5.104.0 Qt Version: 5.15.8 libqt5core5a Version: 5.15.8+p22.04+tunstable+git20230209.0323-0 python3-pyqt5 Version: 5.15.9+dfsg-1+22.04+jammy+unstable+build21 ADDITIONAL INFORMATION I believe the previous scaling is offered by Qt since 5.6 and is described here [2] and [3]. And the new one was announced by Nate here [4]. I think the KWin part landed: ``` > wayland-info | rg frac interface: 'wp_fractional_scale_manager_v1', version: 1, name: 10 ``` but maybe the Qt patches were not added to Neon's patch collection? Is this [5] related? how can I verify if the Qt5 client libs have support? I attach the small PyQt sample [6] used to show that the scale given to the app is 2x and the screen geometry and physicalDotsPerInch is fake (dpi 115.834 instead of 163), with system Qt 5.15.8. [1]: https://www.reddit.com/r/kde/comments/lficfe/wayland_fractional_scaling_may_be_sort_of_a/ [2]: https://www.qt.io/blog/2015/01/27/qt-weekly-24-high-dpi-qtwayland [3]: https://www.qt.io/blog/2016/01/26/high-dpi-support-in-qt-5-6 [4]: https://pointieststick.com/2022/12/16/this-week-in-kde-wayland-fractional-scaling-oh-and-we-also-fixed-multi-screen/ [5]: https://invent.kde.org/qt/qt/qtwayland/-/commit/23d3fc7 [6]: https://gist.github.com/eddy-geek/2a682a415abb5d351537ae3fc865dffd -- You are receiving this mail because: You are watching all bug changes.