├── .gitignore
├── hook.c
└── README.md


/.gitignore:
--------------------------------------------------------------------------------
1 | hook.so
2 | 


--------------------------------------------------------------------------------
/hook.c:
--------------------------------------------------------------------------------
 1 | #define _GNU_SOURCE
 2 | #include <dlfcn.h>
 3 | #include <libinput.h>
 4 | 
 5 | typedef const char* (*orig_get_name_t)(struct libinput_device *device);
 6 | 
 7 | const char* libinput_device_get_name(struct libinput_device *device) {
 8 |   set_scroll_emulation(device); // Inject the code to set scrolling emulation
 9 |   orig_get_name_t orig_get_name;
10 |   orig_get_name = (orig_get_name_t) dlsym(RTLD_NEXT, "libinput_device_get_name");
11 |   return orig_get_name(device);
12 | }
13 | 
14 | void set_scroll_emulation(struct libinput_device *device) {
15 |   libinput_device_config_middle_emulation_set_enabled(device, LIBINPUT_CONFIG_MIDDLE_EMULATION_ENABLED);
16 |   libinput_device_config_scroll_set_method(device, LIBINPUT_CONFIG_SCROLL_ON_BUTTON_DOWN);
17 |   libinput_device_config_scroll_set_button(device, 273);
18 | }
19 | 


--------------------------------------------------------------------------------
/README.md:
--------------------------------------------------------------------------------
 1 | 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)
 2 | 
 3 | Simply clone this repo and run
 4 | 
 5 | ```bash
 6 | gcc -shared -ldl -linput -fPIC hook.c -o hook.so
 7 | ```
 8 | 
 9 | which will generate a `hook.so` in the current directory.
10 | 
11 | 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)
12 | 
13 | e.g. You could add content like this to `/etc/profile.d/libinput.sh`
14 | 
15 | ```bash
16 | export LD_PRELOAD="$LD_PRELOAD /path/to/your/hook.so"
17 | ```
18 | 
19 | replace `/path/to/your/hook.so` with the __absolute path__ to your `hook.so`.
20 | 
21 | Reboot and enjoy. (Press right button and move the cursor = scrolling)
22 | 
23 | How does it work
24 | ===
25 | 
26 | It is very simple. The `libinput` library itself already contains code to emulate scrolling. Under Xorg we can use configuration like this
27 | 
28 | ```
29 | Driver "libinput"
30 | Option "MiddleEmulation" "1"
31 | Option "ScrollButton" "3"
32 | Option "ScrollMethod" "button"
33 | ```
34 | 
35 | 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.
36 | 
37 | 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.
38 | 
39 | 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 :).
40 | 


--------------------------------------------------------------------------------