Created attachment 136118 [details] Screen shot of the Display Configuration panel. SUMMARY I have a laptop with a 14" HiDPI screen (2160x1440) on which I want to apply scaling. However, since Plasma 5.21 the scaling is apparently implemented by lowering the actual screen resolution, which results in a blurred screen. STEPS TO REPRODUCE 1. Open Display Configuration in Display Settings 2. Use the Scale slider to set scaling to 125% 3. Click Apply OBSERVED RESULT Everything on the screen is scaled up, but it is done at the expense of clarity. The whole screen looks blurred, not just some applications, but all applications. The picture of the screen in the settings dialog says "Laptop screen (1728x1152)" instead of "2160x1440". The Resolution drop-down menu says "2160x1440 (3:2)" as it should. Only Wayland is affected. Scaling works OK in X11. EXPECTED RESULT The expected result is that the text and screen elements would be scaled by 125% and look as crisp as before. This worked perfectly before Plasma 5.21.0. SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: Arch Linux (available in About System) KDE Plasma Version: 5.21.1 KDE Frameworks Version: 5.79.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION
The fact that setting a scale factor changes the logical resolution is expected. If you have a 2160x1440 screen and you want to apply a scale factor of 1.25, kwin will compute the logical size as follows * logical_width = mode_width / scale_factor = 2160 / 1.25 = 1728 * logical_height = mode_height / scale_factor = 1440 / 1.25 = 1152 Monitors don't have infinite number of pixels, so if the scale factor changes, the logical size will be changed with it. The kscreen kcm has to communicate the difference between native resolution and logical resolution in a better way.
(In reply to Vlad Zahorodnii from comment #1) > The fact that setting a scale factor changes the logical resolution is > expected. I would expect the number of pixels to stay the same. To me scaling means scaling the objects displayed on screen to be enlarged measured in pixels, so that they are just as big in millimeters as on a lower resolution display. This is how Plasma (Wayland) worked before version 5.21, this is the way Plasma (X11) still works in version 5.21, this is how Windows works when you apply scaling. What is the point of a HiDPI display if you get a *worse* picture on a 150% scaled 2160x1440 display than 100% on a native 1440x900 display? KDE Plasma 5.21 was supposed to improve Wayland support. "Plasma's KWin compositor / window manager features much better Wayland support." The fact is that 5.20 worked perfectly fine for me, but the 5.21 behavior is a showstopper for me. I had to go back to Plasma (X11) after using Plasma (Wayland) for several years.
https://www.reddit.com/r/kde/comments/lficfe/wayland_fractional_scaling_may_be_sort_of_a/
Why KDE/Wayland cannot have scaling without lowering resolution like in KDE/X11? Scaling on X11 is mostly works and similar to windows.
https://gitlab.freedesktop.org/wayland/wayland-protocols/-/issues/34
*** This bug has been marked as a duplicate of bug 437533 ***