Upcoming tablet input changes in Plasma Wayland

This blog post provides the heads-up about planned tablet input changes that are brewing for Plasma 6.3. KWin provides support for the tablet input protocol, but things are different on the client side. Some apps support it, some do not. If an application supports the tablet input protocol, great, it will receive tablet input events as is. On the other hand, if the application does not support the tablet input protocol, then KWin will fake tablet input as pointer input. In Plasma 6.3, KWin will stop doing that and I think that we should briefly talk what led us to such a decision and what impact it will have.

Originally, when the tablet input protocol support had landed in KWin, there were still pretty few applications and toolkits that supported it. Emulating tablet input was a fairly reasonable decision, otherwise you would have likely not been able to use tablet in the Plasma Wayland session at all. As time went by, more and more clients gained native support for the tablet protocol. Unfortunately, in meanwhile, we had also started noticing various issues with tablet emulation.

So, what’s the reasonable thing to do about it? Fix the bugs of course. And we did. But there is still a set of issues that cannot be addressed without bringing more complexity in already too complex code that we are struggling to keep afloat. Enough is enough.

Q: What’s new in 6.3?

A: Starting since 6.3, tablet input emulation will be deprecated and disabled by default. Note that you can enable it back by setting the KWIN_WAYLAND_EMULATE_TABLET=1 environment variable.

Q: When will tablet input emulation be dropped?

A: There is no concrete milestone at the moment.

Q: What does it mean to you? (as a user)

A: Hopefully, nothing. The major toolkits such as GTK, Qt, and SDL already provide support for the tablet protocol, so does Xwayland. So, you should be able to use tablet without any issues in X11 applications or Wayland native applications that use the aforementioned toolkits. Chromium/Electron still does not provide native support for tablet input on Wayland, but it’s also worth noting that most of those applications run through Xwayland by default unless the user sets some command-line arguments.

If your favorite application does not work with tablets, please tell it to the developers of that application so they know that there’s demand for such an operation mode.

Q: What should I do? (as a toolkit developer)

A: Please add support for tablets! If your toolkit already supports the tablet input protocol, wonderful, no work to do. \o/

Q: Is KWin alone by stopping emulating tablet input?

A: No, it is not. Mutter (the Wayland compositor in GNOME Shell) doesn’t emulate tablet input either.

Closing words

Deprecating tablet emulation is disappointing but the options that we have are not great either. It’s either bring in more complexity in order to fix the existing issues (plus even more code to ensure that the pointer focus is managed correctly when using both pointer and tablet) into an already too complex codebase or just do nothing special about applications that don’t opt in into tablet input. Hopefully, the remaining applications and toolkits that still miss tablet support add it in the near future. If you have more thoughts about it, please reach out to us at our matrix room.