Re: Help writing a virtual touchpad
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 , 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
Re: Help writing a virtual touchpad
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?) 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? Repo with my code: https://github.com/thegoldgoat/toccami_driver Thank you so much, Andrea Il 11 mag 2021, 03:09 +0200, Peter Hutterer , 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
Re: Help writing a virtual touchpad
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
