Awesome

A simple hack to use middle button scrolling emulation under GNOME Wayland (and other Wayland compositors that do not expose libinput configuration). This is tested with my GPD Pocket, whose trackpoint does not have a middle button thus cannot scroll by default (after applying this hook, I can use right button + cursor to emulate scrolling)

Simply clone this repo and run

gcc -shared -ldl -linput -fPIC hook.c -o hook.so

which will generate a hook.so in the current directory.

Then add this hook.so to your LD_PRELOAD (use /etc/profile.d or /etc/profile in order to make it usable to GNOME Wayland)

e.g. You could add content like this to /etc/profile.d/libinput.sh

export LD_PRELOAD="$LD_PRELOAD /path/to/your/hook.so"

replace /path/to/your/hook.so with the absolute path to your hook.so.

Reboot and enjoy. (Press right button and move the cursor = scrolling)

How does it work

It is very simple. The libinput library itself already contains code to emulate scrolling. Under Xorg we can use configuration like this

Driver "libinput"
Option "MiddleEmulation" "1"
Option "ScrollButton" "3"
Option "ScrollMethod" "button"

To enable this built-in feature. Even if some Wayland compositors do not expose such configuration, the functionality is still available thanks to libinput. All we need to do is to find a way to force apply these options to the devices.

Therefore, I tried to find a function that has libinput_device as a parameter and will be always called. One of them is libinput_device_get_name. This is what hook.c does: hook into this function and force set the needed configuration on every possible device. Since the compositors will load /etc/profile regardlessly, we will now have working scrolling emulation.

It might be better if something could be done to force expose those configuration options through LD_PRELOAD. This is not difficult, but I'm not doing it now because it seems enough for me right now :).