Comments about adding tablet support to Wayland

[Dmitry Kazakov]

Hi, all!

I am a developer from Krita painting application team. We recently did
quite much work on incorporating better tablet support in Krita. I have
several comments about your proposal of the tablet protocol (sorry for nor
replying directly, since I wasn't subscribed to the list before).

1) Axes. There should also be an axis for rotation of the stylus (Artpen)
and Tangential Pressure (for the wheel of the Airbrush).
2) There is also Artpen type of stylus. In Qt it is called "Rotational
Stylus".
3) Fingers. There is a complication in XInput2 right now, since touch
enabled Wacom devices have a special Finger XInput2 device, which provides
both interfaces: tablet and touch and therefore generates both types of
events. Right now Qt5 still cannot handle it properly, but the work is in
progress. From Krita point of view, the main usecase for us is to
distinguish whether the user paints with a finger of with the stylus.
Because most of the users prefer to disable painting with fingers and use
it for gestures/UI only (yes, palm detection works with non-100%
probability).
4) Button Press/Release events should come in both cases: when the user
clicks on the stylus' buttons and when the stylus touches the surface of
the tablet.
6) It might be a good idea to define the physical properties of the axes.
E.g. for tilt, rotation and tangential pressure. Afair, Wacom driver for
XInput returns some not-very-obvious values right now. One would need to
experiment to know what these numbers mean.

Thanks!

-- 
Dmitry Kazakov
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