On Tue, May 11, 2021 at 10:15:39AM +0200, Andrea Somaini wrote: > Thanks a lot for your detailed response, that blog post was amazing and it > made some things much more clearer. > > At the end, I managed to write a kernel driver that receives input through > a character device and sends raw input events, without ever knowing the > existence of evdev. It still need a lot of tweaking regarding resolution > and which events I should send and which not. (e.g. should I communicate > the pressure if my data does not contain information about it? What about > tool_width/major-axis and such?)
The only thing pressure is used for atm is for palm and thumb detection. Given you're writing a virtual touchpad, you shouldn't need either. Same for major/minor. Tool width is unused in libinput so I wouldn't bother with it either. > Anyway, with some trial and error the driver kinda works and I got to see > 1:1 multitouch gesture on GNOME 40 :) > > Regarding performance: I use a userspace process to write to a character > device which talks to my kernelspace code, maybe using evdev directly > avoids some layers of abstraction? And in this way I don’t have to write > any kernelspace code right? correct, uinput is a module supported everywhere and would not require a custom kernel module. Using it removes one moving part, you only need the userspace process because everything else is already there (and well-tested :) Cheers, Peter > > Repo with my code: https://github.com/thegoldgoat/toccami_driver > > Thank you so much, > Andrea > Il 11 mag 2021, 03:09 +0200, Peter Hutterer <peter.hutte...@who-t.net>, ha > scritto: > > On Sat, May 08, 2021 at 12:45:24PM +0200, Andrea Somaini wrote: > > > Hello, > > > I was thinking about creating a virtual touchpad device for Linux > > > I never worked on such low level software, so I feel kinda lost > > > Can someone please point me where should I start? > > > > The best option you have at this point is to emulate an evdev node that > > behaves like a touchpad. That's both straightforward and complicated at the > > same time. The code itself is trivial (use python-libevdev, check the > > examples directory) but getting touchpads right in evdev can be a bit > > tricky - you really need to know the details of the evdev protocol. > > > > If you look at the libinput test devices (e.g. > > test/litest-device-synaptics-rmi4.c) you get a **rough** idea of the events > > you need to send for a finger down event and a finger move event. > > You still need to handle BTN_TOOL_DOUBLETAP, etc. > > What I recommend is: use libinput record to record 1, 2, 3... finger > > interactions on your normal touchpad to get the set of data sent, then > > emulate that device. Axis ranges and coordinates can generally be changed > > at-will, but the set of events within each frame has to be correct (or > > correct enough) to be processed as expected. > > > > https://who-t.blogspot.com/2016/09/understanding-evdev.html has some > > explanations too. > > > > Cheers, > > Peter > > _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/wayland-devel
