Re:Re: 回复: Re: get input device in wayland

weinan wang weinan97 at
Fri Nov 24 03:00:34 UTC 2023

Thank you, I think I understand why the wayland-protocol is designed the way it is.
Finally, I would like to ask if there is a input mapping protocol upstream is
considering to add like "xinput map-to-output".
Tablet, touch screen, and other absolute device mapping functions
are currently implemented separately in different compositors,
such as kwin has added related functions in dbus

At 2023-11-24 09:11:34, "Peter Hutterer" <peter.hutterer at> wrote:
>On Wed, Nov 22, 2023 at 06:52:47PM +0800, WeiWei wrote:
>> Thank you very much, I will discuss this idea with the designer.
>> I'd like to ask, why the underlying device is not exposed in
>> current wayland-protocols, what are the benefits of doing this.
>The overwhelmingly vast majority of applications don't need to know
>about the specifics of the device, so exposing it is both not necessary
>and may also lead to interference if the applications try to do things
>based on assumptions that a compositor may not meet.
>X did expose the devices and in addition to making it a nightmare to
>maintain it is also effectively unused. Plus there's a whole can of
>niche bugs that can get exposed that way - e.g. if you're listening for
>button events on a specific device you can get out of sync with what the
>compositor treats as logical button state.
>> With keyboard and pointer, we don't usually care about 
>> physical device, but for touch devices, each touch device
>> will work independently and need input mapping and calibration,
>> is it possible to consider adding some device information
>> in wl_touch in the future.
>The general consensus is that touch mapping and calibration should be
>part of the compositor and/or a side-channel to the compositor if the
>calibration needs to be done in an external application.
>  Peter
>> 从 Windows 版邮件发送
>> 发件人: Peter Hutterer
>> 发送时间: 2023年11月22日 14:45
>> 收件人: weinan wang
>> 抄送: wayland-devel at
>> 主题: Re: Re: get input device in wayland
>> On Wed, Nov 22, 2023 at 09:22:56AM +0800, weinan wang wrote:
>> > Thanks for reply,
>> > We want to achieve an application for touch input map,
>> > it will map touch input to a output device when we have multi-screen.
>> > 
>> > The input map need provide a input device and a output device,
>> > in our design, we will traversal all screen to ask user "is this screen you
>> > want to map", and user choice a touch device by tap on a touch device,
>> > just like "touch config" feature in Windows11.
>> > 
>> > All in all, we want to achieve an application for touch input map, if have a batter
>> > design, i will discuss it with the designer.
>> There is no absolutely surefire way to do this as a pure Wayland
>> application but one possible UI flow would be:
>> - getting the list of touchscreens from udev [1]
>> - printing something like "Mapping screen 'Foo Vendor Touchscreen'" 
>> - display on output A with icons "this one", "nah, next one please"
>> - rotate through outputs until "this one" is clicked
>> You don't need to care whether the confirmation even comes from the
>> touchscreen.
>> Alternatively you can display on all screens simultaneously and assume
>> the button + screen that receives the "Yes" click are the one that want
>> the touchscreen.
>> Cheers,
>>   Peter
>> [1] slightly unreliable since there's no guarantee they're all handled
>> but most likely good enough
>> > At 2023-11-22 06:31:07, "Peter Hutterer" <peter.hutterer at> wrote:
>> > >On Tue, Nov 21, 2023 at 04:20:10PM +0800, weinan wang wrote:
>> > >> Hey Guys,
>> > >> We have an application that needs to get the touch device
>> > >> corresponding to the touch event, and on X11, we can get the device ID
>> > >> that sends this event according to the XI_Touch events, and then find
>> > >> the device we want according to this ID.  But on Wayland, it seems
>> > >> that neither wl_seat nor wl_touch can get device-related information,
>> > >> this application is a user permission, so we can't use libinput to get
>> > >> more low-level events.
>> > >> Please ask if there is any other way to get the device that sends the
>> > >> event?
>> > >
>> > >This is not possible in wayland, physical devices are abstracted into
>> > >wl_pointer/wl_keyboard/wl_touch and the underlying device is not exposed
>> > >anywhere through wayland or even current wayland-protocols.
>> > >
>> > >The sole exception is the wl_tablet protocol which is per physical
>> > >device but that's due to how tablets are being used.
>> > >
>> > >You don't usually have access to the libinput context inside the
>> > >compositor either (because Wayland itself doesn't require libinput, it's
>> > >an implementation detail).
>> > >
>> > >The question here is: what are you trying to achieve? maybe there's a
>> > >different way to do it than having access to the specific physical
>> > >device.
>> > >
>> > >Cheers,
>> > >  Peter
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