回复: Re: get input device in wayland

[Peter Hutterer]

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.

Cheers,
  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 lists.freedesktop.org
> 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 who-t.net> 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
>