Comments about adding tablet support to Wayland

[Ping Cheng]

On Mon, Jun 30, 2014 at 1:03 AM, Dmitry Kazakov <dimula73 at gmail.com> wrote:
> 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.

If we support matrix transformation in libinput/Wayland, all "tablet
to screen" mapping requests would be met, including my mapping to
windows.

> 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.

You work with painters directly. I believe you know more of what they
use. I am only a driver developer. I can not draw a straight line on
paper or on computer ;).

> Mode switches are troublesome.

My mapping/display toggle/mode toggle experience was from animation
artists' requests. What kind of trouble do you usually see from mode
switch/toggle? I want to see if we have a solution.

Thank you for sharing your ideas. We desperately needed feedback like yours.

Ping

> 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