SUMMARY Every hour or so after using touch for a while, it seems to permanently break with what window to send the touch to. This sadly affects even the plasma bottom bar, so that it becomes nearly impossible to do anything and it's pretty close in effect to the touch screen being plain dead. A video of this effect is attached. I've been using KDE for months at this point with a mouse and never saw this happening, so that suggests to me that it's likely to be a touch-related issue. This device doesn't have a mouse attached, hence I'm using touch input a lot. STEPS TO REPRODUCE 1. Set up KDE Plasma 6 and use touch heavily. May require no hardware mouse to be attached, not sure about that. 2. At some point it breaks, I wish I knew how or when. OBSERVED RESULT See video, all the touches seem to go to wrong windows and the bottom bar usually becomes dead too and it's chaos. The only workaround I've found is logging out and logging back in, which fixes it. EXPECTED RESULT Touch keeps working SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: postmarketOS Edge (available in About System) KDE Plasma Version: 6.1.2 KDE Frameworks Version: 6.3.0 Qt Version: 6.6.3 ADDITIONAL INFORMATION
Created attachment 171336 [details] Video that shows what happens when the touch suddenly breaks and it goes to the wrong windows
Do you have the "Slide Back" effect enabled?
I found a "Slide Back" in "Desktop Effects" via the search and it's not enabled. This is a pretty fresh install and all desktop effects should still be the default value.
okay
Could this possibly be XWayland related? I noticed Nheko, which can be seen in the video missing the touches despite being in the front, has been at that point in time cut off from the Wayland socket and forced to use XWayland, while Firefox which can be seen in the video receiving the the touches in the background, should be running with Wayland natively.
Maybe. There was X11-specific bug 478556 before
As for XWayland: After some more testing, at least once the bug hits it no longer seems to be XWayland related. Like, maybe an XWayland app might trigger it or maybe not, but then once the bug is "active" if I close all non-native-wayland app windows, I still can't tap anything. As for the issue generally: It seems like touch focus somehow becomes "sticky" and is glued to one app window, often Wayland firefox, and then tapping any other app window or any other item like the plasma bottom task bar is ignored like the touchscreen is dead. Even worse, if once that happens I close firefox and reopen it, then the touchscreen goes completely dead. So it seems like it's stuck to one specific window and when that window goes then no touch input is possible anymore. If I can provide any more logs I would love to do so, since this issue happens every few minutes and it's very disruptive, sadly.
The following doesn't repair the touchscreen once the bug hits: killall plasmashell kstart plasmashell The following DOES repair the touchscreen once the bug hits (while retaining all KDE windows, but all others are killed): killall -9 kwin_wayland That seems to confirm it's probably some sort of kwin bug and not a plasma bug.
This seems to be related to touch gestures, for sure drag and drop getting confused and maybe also this weird three finger window overview gesture getting confused and stuck. Here is one way I found that pretty reliably gets you into a broken state where touch is dead if you repeat it a few times: 1. Put your finger down on the icon only task switcher in the plasma bottom bar on some app icon, and do a long press. The menu will pop up but at the same time or just moments later or earlier, a small copy of the icon will show up next to your finger indicating you began drag and drop. 2. Move your finger wildly across the screen without lifting it (improtant!), with drag and drop ongoing. 3. Now still without lifting your finger, move it fast toward one of the screen edges to the side or the top, and move it out of the screen area. This may require a touch screen with a bezel. Repeat this a few times and suddenly touch will go dead, neither the bottom bar nor any app windows open at this time will still react. I also found a way to fix it again if you have a hardware keyboard attached: press Super+L to lock the screen. Now touch should work again, but you need to enter your password to unlock it again, of course.
It's also possible to make this more commonly happen by putting multiple fingers on the screen I think, in just the right or wrong ways. I have a hard time doing this with exact steps, but eventually I always run into it. So it seems to be connected to either global touch gestures, or touch drag and drop, or both. Possibly related to tracking which fingers are on the screen and how they are numbered, maybe.