Using Soft Keys with Weston & Libinput

Ucan, Emre (ADITG/SW1) eucan at
Fri Feb 5 10:19:55 UTC 2016

Hello Peter,

Thank you for your answer. My comments are below.

> -----Original Message-----
> From: Peter Hutterer [mailto:peter.hutterer at]
> Sent: Freitag, 5. Februar 2016 07:16
> To: Ucan, Emre (ADITG/SW1)
> Cc: wayland-devel at; Friedrich, Eugen (ADITG/SW1)
> Subject: Re: Using Soft Keys with Weston & Libinput
> On Thu, Feb 04, 2016 at 10:38:18AM +0000, Ucan, Emre (ADITG/SW1) wrote:
> > Hi,
> >
> > We want to use soft keys with weston.
> >
> > The use-case is very similar to android that the touch panel is bigger than
> the display.
> > The out of display touch events should be routed to the clients as key
> events.
> >
> > As far as I understood, It is not possible to realize this use-case in
> > current weston implementation, because the coordinates of touch events
> are scaled to width and height of the display with
> libinput_event_touch_get_x(y)_transformed API.
> >
> > For example, when I touch a soft key (outside of display), the grab
> > interface will still get a touch event in the range of display width and height,
> and It will wrongly route this event to a wl_surface which is on the edge of
> the display. Weston cannot recognize that the event happened outside of
> the display.
> >
> > Is there a way to realize this use-case that I do not know ?
> short answer: you'll need code in weston to handle this.
> libinput doesn't care about the display, it merely takes the touch coordinates,
> the API then tells libinput to scale the range into that coordinate set. If you
> screen has an offset, you need to detect that and handle it separately but
> that is not something weston currently does.
> with the current APIs what you'll need to do is check the mm value for the
> display, calculate if it is outside the boundary you want and handle it
> accordingly. if it is within the display boundary, then you can pass it on
> normally.

I think it is not correct to solve this problem in weston. How will I get mm value for the display in input.c ?
I am not sure but we can get DPI information maybe from DRM. This would not work in current architecture of weston, because only drm backend plugin has access to drm device.

I am sending a picture of a head-unit for visualization of the use-case:
	- On the left upper corner there is the shutdown soft key
	- On the left side of display there is the volume slider which should send axis events.
	- On the right side there are other soft keys.

A similar problem is solved in libinput for touchpads:

	- If specific parts of touchpad is pressed, a button event is sent via evdev-mt-touchpad-buttons.c
	- If specific parts of touchpad is pressed, an axis event is sent via evdev-mt-touchpad-edge-scroll.c

My idea is to extend this implementation to support key events (i.e evdev-mt-touchpad-keys.c) and configure location of soft keys via udev-rules.

The soft-keys is a very important use-case for embedded devices, and I know that libinput is a DE oriented project.
But  I want to share this implementation (when it is finished), if it is interesting for the community.

> Cheers,
>    Peter

Best regards

Emre Ucan
Software Group I (ADITG/SW1)

Tel. +49 5121 49 6937
-------------- next part --------------
A non-text attachment was scrubbed...
Name: suzuki-ertiga-india-head-unit-630x350.jpg
Type: image/jpeg
Size: 64222 bytes
Desc: suzuki-ertiga-india-head-unit-630x350.jpg
URL: <>

More information about the wayland-devel mailing list