Comments about adding tablet support to Wayland

[Dmitry Kazakov]

Hi, all!

I'd like to add about mapping of the tablet input.

In XInput one can assign a matrix transfromation for each tablet device,
which is exactly what people need. The usual usecase is the following:

A painter has a display + intuos tablet + cintiq. The external tablet is
mapped to the external display, the Cintiq, obviously, is mapped into
itself [0]. The external display can be (and probably will be) rotated on
90deg to have Portrait orientation.

Right now all the mappings for such configuration can be achieved with
xsetwacom/xinput calls.


[0] - No painters I know use mappings to the specific window. Mode switches
are troublesome.



On Mon, Jun 30, 2014 at 11:41 AM, Dmitry Kazakov <dimula73 at gmail.com> wrote:

> Hi, all!
>
> I will try to answer all your emails in one post.
>
> 1) Tablet vs. Touch. Basically what I am talking about is *not* touch
> arbitration and palm recognition. The Wacom driver itself blocks all the
> touch events when the stylus is in the proximity, so it performs the
> necessary arbitration. What we need is to block several kinds of actions
> (read "tools") when the user uses touch and unblock them when the user
> works with stylus or mouse. An exact usecase: we need to allow the user to
> zoom/pan on the canvas with his fingers, but at the same time real painting
> with fingers must be prohibited (it disturbs the painters). Right now it is
> almost impossible, because we get no touch events, and instead get
> synthesized MousePress/Release/Move events for finger actions, which are
> indistinguishable from real mouse events.
>
> 2) Buttons vs Tablet Press. Well, to tell you the truth we are not
> interested in whether the stylus touched the surface of not. At all. The
> stylus has 3 button: the tip itself, and two buttons. These three buttons
> can be remapped with the driver (xsetwacom) to any X11 button the user
> wants. Therefore, I have absolutely no interest in
> TabletTouch/TabletRelease if the only thing they tell me that the stylus
> has touched the surface of the tablet with the stylus or not. What I really
> need is the TabletButtonPress/Release event, which tells me:
>
> 1) Which button (of the three) is pressed
> 2) Exact position of the stylus
> 3) Pressure, Tilt, Z-coordinate if available (might be zero/unit for some
> of the buttons)
>
> The situation is getting even worse if you look at the feature which
> Windows' Wacom driver has (I'm not sure whether this feature is available
> in X11 Wacom driver, but it is highly requested by the painters). On
> Windows the buttons on the stylus can be switched into "modifier" mode.
> That is pressing the button doesn't produce a real button event. You need
> to press the  stylus button, and then touch the surface of the tablet with
> the tip: only then the app will get mouse button click (right or middle
> button usually). If this feature will ever be implemented in X11 Wacom
> driver (which is quite desirable), your protocol with TabletTouch/Press
> will not work. Please check Wintab protocol docs for more info,
> specifically, CSR_SYSBTNMAP attributes [0]
>
> 3) Axes resolution. Yes, it is perfectly ok to have a separate function
> which tells the physical limits of the axis. What I wanted to say is that
> min_value/max_value attributes, which are reported by XInput are not
> enough. For rotation I also need to know the mapping of the coordinate
> system origin and it's direction (clockwise/counterclockwise).
>
> PS:
> Please keep me in CC, I'm having troubles with keeping up with the traffic
> in this mailing list.
>
>
> [0] - http://www.wacomeng.com/windows/docs/Wintab_v140.htm
>
>
>
> On Fri, Jun 27, 2014 at 6:53 AM, Jason Gerecke <killertofu at gmail.com>
> wrote:
>
>> On Wed, Jun 25, 2014 at 5:50 PM, Peter Hutterer
>> <peter.hutterer at who-t.net> wrote:
>> > Replying to three emails at once here to keep the thread a bit more
>> > managable.
>> >
>> > On Wed, Jun 25, 2014 at 01:38:22PM -0700, Jason Gerecke wrote:
>> >> On Wed, Jun 25, 2014 at 12:38 AM, Lyude <thatslyude at gmail.com> wrote:
>> >> > On Wed, 2014-06-25 at 11:06 +0400, 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).
>> >> >
>> >> > Benjamin commented on this as I was writing this e-mail, and I
>> figured I
>> >> > should too: yes, it's awesome to see developers commenting on the
>> >> > protocol. A lot of the quirks around this protocol are going to be
>> >> > difficult to see without the help of people who have programmed on
>> the
>> >> > client side of things as opposed to the compositor side of things. So
>> >> > yes, your input is very much appreciated and I thank you for it!
>> >> >
>> >> >>
>> >> >> 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".
>> >> >
>> >> > Don't worry, we haven't forgotten about these. These will eventually
>> be
>> >> > added into the protocol. The reason why they're not in this draft is
>> >> > because I'm doing this as my Google Summer of Code project, and as
>> such
>> >> > I'm on a deadline and I have to focus on just getting the basics done
>> >> > first before I can focus on all of the other features.
>> >
>> > Our current approach, both in libinput and the WL protocol should make
>> these
>> > additions little more than adding a couple of enum, so I think we're
>> good
>> > here.
>> >
>> >> >> 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).
>> >> >
>> >> > Right now libinput handles the finger device as another touchpad,
>> since
>> >> > that's usually what it is. Your use-case sounds perfectly valid
>> though,
>> >> > but IMO a better approach would be to add something to the protocol
>> for
>> >> > touchpads on wayland so that it can be known that they belong to a
>> >> > tablet and provide any other sorts of data you might be need, so
>> >> > programs like yours can treat them differently.
>> >
>> > Dmitry, are you talking about pen/touch arbitration, i.e. don't send
>> touch
>> > events when the pen is in use. If so, that's definitely on the plan, we
>> need
>> > it for touchpads (disable while typing feature), and we need it for the
>> > pen/touch interference.
>> >
>> > This will be hidden away so you or event the compositor don't have to
>> worry
>> > about it.
>> >
>> >> >> 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'm not entirely sure that's a good idea. If I'm reading this right,
>> you
>> >> > mean that additional button presses should be sent when the tool
>> touches
>> >> > the surface of the tablet. [...]
>> >
>> > We're already sending out BTN_TOUCH when the tip touches the surface,
>> so I
>> > think we're good here. Unless Dmitry was referring to something else.
>> >
>> >
>> >> >> 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.
>> >> >
>> >> > We would all love for this to be the case I promise you, but
>> >> > unfortunately it's not that simple for all of the axes. The distance
>> >> > axis reports a seemingly meaningless value that can't be converted to
>> >> > millimeters very easily. That being said, I have come up with a few
>> ways
>> >> > that we could actually convert it to millimeters, but this will have
>> to
>> >> > wait until I've fulfilled the goals for my Google Summer of Code
>> Project
>> >> > (unless anyone else wants to implement this in the mean time in
>> libinput
>> >> > of course).
>> >> >
>> >> > I'll write up the method I've come up with for converting this wild
>> >> > value to actual millimeters at some point when I get the chance.
>> >> >
>> >> While I'm interested in seeing what you've come up with, I would be
>> >> very hesitant to integrate the code into libinput. We make *no* claims
>> >> about the physical resolution or accuracy of the distance axis. I've
>> >> seen the value change by more than 10 units just by switching to a
>> >> different pen... There's absolutely nothing stopping us from
>> >> introducing a tablet that invalidates any clever code you may come up
>> >> with.
>> >
>> > yeah, I agree with Jason here, let's not pretend we have data we don't
>> have.
>> > As much as I'd like to attach concrete physical information to all axes
>> we
>> > can't (well, shouldn't) make it up.
>> >
>> > Short of keeping a database of each tablet with the offsets and ratios
>> to
>> > convert distance values to mm I don't think this is doable, and I'm not
>> a
>> > big fan of that either.
>> >
>> >> > As for the tilt axes of the tools, this is something that could be
>> >> > represented in a more meaningful value. We could normalize it to a
>> >> > number between 0 and 180°, so you can get the actual tilt in degrees
>> as
>> >> > opposed to what we currently have. This is something we could pull
>> off
>> >> > rather easily, I'll make sure to discuss this with my mentor
>> tomorrow.
>> >> >
>> >> Alternatively, I would suggest adding an e.g.
>> >> `libinput_event_tablet_get_axis_resolution` function. To get a
>> >> physical value, a caller would just multiply whatever this function
>> >> returns for some axis by the current normalized unitless value for the
>> >> same. I suggest this for a few reasons: it is a fairly standard way of
>> >> doing things (HID, the kernel, and X all use the same system), is more
>> >> efficient (callers working in your preferred unit [e.g. Qt] are spared
>> >> doing the conversion but anyone else [e.g. GTK, EFL] will have to do a
>> >> second conversion to a different unit), and provides a way of getting
>> >> physical information for any axis (if we ever came out with a pen that
>> >> accurately measured distance, you wouldn't need to change the
>> >> semantics of how distance is reported or sacrifice the now-existant
>> >> physical translation information).
>> >
>> > Jason: how accurate is tilt, and are applications actually using it as
>> angle or
>> > just as normalized number anyway?
>> >
>>
>> I can't find a mention of the accuracy in any public docs, so I'm a
>> little hesitant to give numbers on the list. The spec sheet does show
>> it to be accurate to a handful of degrees though.
>>
>> The second part is a little complicated to answer. Every tilt-enabled
>> program I'm aware of uses the data to adjust the brush azimuth. The
>> goal is to have the virtual brush angled to be parallel with the
>> physical pen at all times. A few applications also calculate an
>> altitude angle, deforming the brush from circular to increasingly
>> eliptical as the pen becomes more horizontal. Qt and Android (and
>> likely EFL based on current discussions) have APIs that specify angles
>> in various physical forms: tilt-x/tilt-y in degrees, alt-az in
>> radians, etc. GTK on the other hand provides normalized data, but
>> neither provides resolution information nor information about what
>> "normalized" means. Because of the resulting ambiguity, GIMP and
>> Inkscape do their calculations on the assumption that [-1, 1] in GTK
>> corresponds to [-180 degrees, +180 degrees] in the physical world. GTK
>> actually does its normalization based on the device's min/max though
>> (so [-64 degrees, +63 degrees] for our hardware) meaning that GIMP and
>> Inkscape wind up calculating incorrect azimuth values. The results
>> aren't _that_ wrong though; I'm not aware of anyone having noticed or
>> filing a bug about it.
>>
>> tl;dr, Applications universally /try/ to use the physical angles. Not
>> all succeed.
>>
>> Jason
>> ---
>> Now instead of four in the eights place /
>> you’ve got three, ‘Cause you added one  /
>> (That is to say, eight) to the two,     /
>> But you can’t take seven from three,    /
>> So you look at the sixty-fours....
>>
>> >> > As for tangential pressure, this is a term I've never actually heard
>> of
>> >> > before. I don't know what the values from the tablet are supposed to
>> >> > correspond to in regards to pressure, so I've added two of our
>> friends
>> >> > at Wacom to the CC list help us out (I hope you two don't mind!) on
>> >> > this.
>> >> > (Jason and Ping, if you guys aren't on the list already, the original
>> >> > protocol this e-mail is discussing can be found here:
>> >> >
>> http://lists.freedesktop.org/archives/wayland-devel/2014-June/015583.html
>> >> > )
>> >> >
>> >> > In regards to rotation and any other axes, I haven't had any contact
>> >> > with these yet. So I can't really say much on them.
>> >
>> > Rotation exists on the mouse/lens cursor tool, but it's a calculation
>> based
>> > on the tilt x/y axes. For us it'd just be one more axis.
>> >
>> > Cheers,
>> >    Peter
>> >
>> >> I'm not sure where the term "tangential pressure" came from, but it
>> >> can refer either to the fingerwheel on the airbrush tool (expected to
>> >> be used to control ink flow rate; value is basically [0, 1]) or the
>> >> fingerwheel on the 4D Mouse tool (which is like a spring-loaded
>> >> mousewheel that reports how far forward or backward from the neutral
>> >> position the wheel is; value is basically [-1, 1]).
>> >>
>> >> Jason
>> >
>>
>
>
>
> --
> Dmitry Kazakov
>



-- 
Dmitry Kazakov
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