I am a pen display owner, and with the release of Plasma 5.24 I am looking to switch from x11 to Wayland.
During my tests I encountered problems with the userspace tablet driver I am using, which is OpenTabletDriver. I outlined them in detail in the project's GitHub issue tracker, believing it was a matter of "just adding support for Plasma Wayland" (and I suggested a couple of ways to do so), but turned out the developers felt it wasn't really their problem, since other Wayland implementations work well and they didn't feel the need to make a special use case just for Plasma.
Now, this could be the end of the story, but it really outlines a problem: KWin maps virtual tablet input as if it were a real tablet, therefore causing mapping problems for end users.
I don't know if the second problem is a bug to be reported on KDE bugzilla or just a shortcoming, but either way this is breaking my use case and for the time being I cannot really switch to Wayland; and I feel like other people who draw with the help of userspace drivers can also be held back by such thing.
I think there should be at least a setting in `kcm_tablet` that disables all internal mapping and "just accepts the input"; that, or a DBus call that the userspace driver can make, or (better) both things.
STEPS TO REPRODUCE
1. Use OpenTabletDriver as an userspace tablet driver / configuration solution
2. Try to actually use the tablet under the Wayland session
3. Notice that the output is not what you expected
KWin maps the virtual tablet input as if it was a real tablet plugged in and using a kernel driver.
KWin won't map input coming from a virtual input device by default.
Linux/KDE Plasma: Artix Linux, 5.24.2
(available in About System)
KDE Plasma Version: 5.24.2
KDE Frameworks Version: 5.91.0
Qt Version: 5.15.2
I don't follow what you mean by " KWin maps virtual tablet input as if it were a real tablet"
(In reply to David Edmundson from comment #1)
> I don't follow what you mean by " KWin maps virtual tablet input as if it
> were a real tablet"
As far as I know, the program I use has to use `uinput` to pass input events the way I want them to be to programs. Since `uinput` creates virtual input devices from the userspace, KWin seems to not be currently able to distinguish between them and real input devices. That was my point.
>KWin seems to not be currently able to distinguish between them and real input devices
Why do we need to distinguish them from real input devices. What's the user-facing impact of this?
(In reply to David Edmundson from comment #3)
> What's the user-facing impact of this?
As I said, some users use third party programs to get their tablets working. When they do so, it's up to this program to map the handedness, orientation and input/output area of the tablet. Right now, this cannot properly function because `kcm_tablet` also provides handedness and orientation settings; but the most important user-facing impact of this is being unable to map the output to a certain display area, such as a window, a window region, or a region between two displays (if for some reason there's someone with this kinda use case). `kcm_tablet` doesn't support any of those use cases, and third party software like OpenTabletDriver usually factor in all the monitors' position, orientation and size to calculate display areas, X11-style, and therefore the input will be spit out in absolute coordinates relative to the total graphical real estate available to the user. When KWin maps this "absolute input" to be relative to just a display, things break and the user (me) gets really confused.
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A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/3070
A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/1216
I think this is similar to this bug report - https://bugs.kde.org/show_bug.cgi?id=457703 ?
Git commit 36e7eaf13a92f432573f13439155009e6aa02d7b by Joshua Goins, on behalf of Aki Sakurai.
Committed on 01/11/2023 at 18:42.
Pushed by redstrate into branch 'master'.
Add option to map tablet to full desktop area.
Some users might want to map the tablet to full desktop area.
M +12 -9 src/backends/libinput/connection.cpp
M +11 -0 src/backends/libinput/device.cpp
M +16 -0 src/backends/libinput/device.h