For anyone reading, this is a fork of the original but with everything except the vim homekeys commented out

Interception plugin for vimproved input

My hideous (but working and performant) C++ code to remap the keys on any input device that emits keys.

tl;dr;

• space cadet: Maps space key into modifier (layer) key when held for long that transforms hjkl (vim homerow) into arrows, number row into F-keys, and a bit more. Space still emits SPACE key when tapped without holding.
• caps2esc: Makes CAPS key send ESC when tapped and L_CTRL when held.
• return2ctrl: Makes RETURN key send RETURN when tapped and R_CTRL when held.

Requirements

Basically any OS that works with libevdev (linux with kernel newer than 2.6.36), no matter what desktop environment, or even if any DE is used (yes, it works the same in X server instead of xmodmap, but also in plain terminal without graphical environment).

Running

Use it with a job specification for udevmon (from Interception Tools). I install the binary to /opt/interception/interception-vimproved and use it like the following on Arch linux on Thinkpad x1c gen7.

- JOB:
    - "intercept -g $DEVNODE | /opt/interception/interception-vimproved | uinput -d $DEVNODE"
  DEVICE:
    NAME: ".*((k|K)(eyboard|EYBOARD)|TADA68).*"

That matches any udev devices containing keyboard in the name (or my external TADA68 keyboard).

Alternatively, you can run it with udevmon binary straight, just make sure to be negatively nice (nice -n -20 udevmon -c /etc/udevmon.yml) so your input is always available.

Configuration

Currently, there's no config file, but if you want to experiment with adding/removing/changing the mappings, take a look at the bottom of the ./interception-vimproved.cpp - initInterceptedKeys function has comments to guide you. Remember to make the project and replace the binary (or point to the new one from your udevmon config).

Testing

In case you want to edit the source code, kill the udevmon daemon, and manually try the following to avoid getting stuck with broken input. Trust me, you can get yourself in a dead end situation easily.

# sleep buys you some time to focus away from terminal to your playground, also you'll probably need to add a sudo
sleep 1 && timeout 10 udevmon -c /etc/udevmon.yml

Why make this

1. I have problems switching back and forth between my external keyboard and laptop keyboard. I customized my external keyboard with QMK to reduce my pinky strain and improve usability, but when I switch back to laptop keyboard, it's all lost, plus I have to fight my muscle memory.
2. I used to use X.Org server with xinput, where I had an xkbcomp based solution with xcape and xmodmap. However, since moving to wayland, that solution doesn't work anymore, and I needed to move to libevdev based solution.
3. Enter Interception Tools. It advertises itself as "a minimal composable infrastructure on top of libudev and libevdev". It, on one side, intercepts events from devices and writes them raw to stdout, and on the other side, it receives events from stdin and writes them to virtual input device.
4. This plugin sits piped between Interception Tool's intercept and uinput (intercept | interception-vimproved | uinput). It interprets input from intercept and maps it to desired events which are then passed to uinput for emitting.

• Other solutions I tried didn't behave as expected and produced unexpected artefacts.
• In this solution, the use of sleeps is eliminated, there's no buffers for input and the interaction with output is minimized to reduce extra costs of writing to it often.

Related work

• Interception Tools
• space2meta
• dual-function-keys
• interception-k2k