Comments about adding tablet support to Wayland

[Hans de Goede]

Hi,

On 06/25/2014 09:06 AM, Dmitry Kazakov wrote:
> 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).

I just want to say that it is great to see a developer of a tablet using
app get involved in this discussion, and I also your timing is excellent,
joining the discussion while we are still actually discussing thanks.

Thanks your input is very much appreciated.

> 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.

I'll leave commenting on the above up to the real experts on this topic.

> 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.

AFAIK the plan is to normalize all the axis values, so for most axis they would
get a value of 0.0 - 1.0, where some axis may be -1.0 - 1.0, e.g. pressure, with
0.0 - 1.0 being barely touching - max-pressure and negative values meaning in
proximity but not touching.

Regards,

Hans