I’ve also verified that newly created JavaFX windows are not being centered correctly under KDE (tested on Ubuntu 22 and 24). Looks like this is already fixed in PR 1789.
> On Nov 23, 2025, at 4:30 PM, Martin Fox <[email protected]> wrote: > > Thanks for the detailed information. It’s very helpful. > > KDE + multiple monitors + fractional scale + JavaFX. A perfect storm. In an > effort to get certain legacy applications to scale KDE is setting the old > “scaling-factor” to the floor of the actual scale. JavaFX is reading that > faulty value which is preventing it from computing the correct UI scale on a > per-monitor basis. Things go downhill from there. (For the record that’s what > KDE in Ubuntu 24 is doing. In Ubuntu 22 it’s setting GDK_SCALE instead.) > > The GDK_SCALE and “scaling-factor” settings are obsolete within their > respective toolkits and for some time they were never set. KDE resurrected > them and now they’re interfering with fractional scaling and multiple monitor > support in JavaFX. I’m putting together a PR to de-emphasize them. > > (Along those lines we should probably deprecate “glass.gtk.uiScale” since it > doesn’t work well with multiple monitors. A better approach would be to allow > the user to specify a multiplier to be applied to the per-monitor scales that > JavaFX computes internally.) > >> On Nov 22, 2025, at 12:57 PM, Chad Preisler <[email protected]> wrote: >> >> I'm running on a brand new Infinity Book Pro from Tuxedo Computers. Here is >> the system info. >> >> DISTRIB_ID=Ubuntu >> DISTRIB_RELEASE=24.04 >> DISTRIB_CODENAME=noble >> DISTRIB_DESCRIPTION="TUXEDO OS 24.04.3 LTS" >> NAME="TUXEDO OS" >> VERSION="24.04.3 LTS" >> ID=tuxedo >> ID_LIKE="ubuntu debian" >> PRETTY_NAME="TUXEDO OS" >> VERSION_ID="24.04" >> >> KDE Plasma Version: 6.4.5 >> KDE Frameworks Version: 6.17.0 >> Qt Version: 6.8.2 >> Kernel: 6.14.0-116036-tuxedo (64-bit) >> Graphics: Wayland >> >> I did some more testing and found that the scaling issues happen in a dual >> monitor environment where the scaling factor is different between the two >> monitors. Here is my setup. >> >> Built-in Screen: 2653x1600, 130% >> Samsung Odyssey G5 2560x1440, 0% >> >> When running with two monitors with "Scaled by system" off: >> - Things look sharp on the monitor with scaling (Built-in). However, fonts >> get pretty blurry on the unscaled monitor (G5). >> - If I scale up the unscaled monitor (G5) to 130%, things look sharp. >> However, everything is huge on the huge monitor. Not ideal. >> - As a side note, Netbeans exhibits the same behavior. It's sharp with tiny >> fonts on the scaled monitor and looks terrible on the unscaled. >> >> Running the app on a single screen (built-in) with "Scaled by system" off, >> the fonts are sharp, but they are also very small. >> Running the app on a single screen (built-in) with "Scaled by system" on, >> the font size is larger (perfect in my opinion) but it's not as sharp. >> >> The pop-up is probably not an issue. It seems like it always appears in >> about the middle of the screen. I don't use a lot of pop-ups, but a quick >> search said that is the default behavior. At some point my app was probably >> off center when I noticed the behavior. >> >
