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IME / tooling for remapping key combos to other key combos on Chrome OS
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README.md

chromeos-key-remapper

This repo contains:

  1. An unpublished Chrome OS IME that lets you use emacs-like cursor movement keys with a US English keyboard. C-a and C-k, to name a few.
  2. Tooling to build a custom IME that combines the remapper engine and other 3rd party IMEs.

Limitations

  • All the combined IMEs share the same JavaScript scope. Name collision can happen.
  • The options page of the custom IME can only display the options page of a single IME.
  • Keys can be only remapped to other key combinations. i.e. can't do things that the OS already supports through exiting key combos.
  • Only a single key combo can be mapped: no support for sequence of keys.

Prerequisites / assumptions

For the premade IME:

  • You don't want to remap when you're in crosh window

Additionally, for the make-your-own route:

  • python (I use 3.x; 2.x probably works)
  • waf command
    • waf* is gitignored in this repo; I have it downloaded to the root of my local clone
  • jscodeshift command
    • npm install in this repo and add ./node_module/.bin to $PATH when invoking waf
    • or: npm install -g jscodeshift

How to install

First, download this repo as a zip file and unpack it or clone the repo. Chrome OS needs to have access to the file system where your local copy resides.

Go to chrome://extensions and enable developer mode.

Using the premade IME

In chrome://extensions, click the "Load unpacked extension..." button and pick the remapper directory in your local copy of the repo.

Open Settings, then search for "manage input methods." Click the highlighted row with that label. There should be a row named "US x emacs"; check to enable it.

Now, pressing Ctrl-Shift-Space will cycle through all the IMEs that are enabled. Hit Ctrl-Space to switch back and forth between the previously selected IME.

There's an indicator next to the notification indicator that shows the active IME: make sure you've activated the IME you just installed and try out a few bindings like C-f, C-b in a text field.

See remapper/keymap.js for the keybindings. If you want different bindings, edit this file and reload the extension.

Making your own with a different language and/or layout

You need to create a config.ini file. config.ini.sample is a good starting point:

cp config.ini.sample config.ini

The config file can contain multiple sections. Each section, when built, will result in a directory under ./build that contains an IME extension. An IME extension can potentially hold multiple IMEs; however, this tooling only supports a single IME per extension.

Here's what a section looks like:

[us_emacs]
name = EN x emacs
description = US keyboard with emacs-like cursor movement
language = en-US
layout = us
fallback_imes =
options_page =

[us_emacs] is the section name, which will become the name of the directory.

name and description will become the name and description of both the extension and the IME you see in Settings.

language and layout dictate which language and layout the IME will be for. Change these to make an IME for your preferred language and layout. I'm not sure what values are accepted here. The extra keyboards repo may be a good resource.

fallback_imes and options_page are irrelevant to what we're doing now; we'll come back to it later.

To build an IME out of this config file, run waf:

python waf configure build

This should create a directory ./build/us_emacs/, which you can install like the premade one above.

Making your own by combining other IMEs

The basic steps are the same as the above: create config.ini and run waf.

This time, we actually make use of fallback_imes and options_page.

fallback_imes is a comma-separated list of directory names you put in ./imes. Said directories must contain an IME extension. All files in the directory will be copied to build/[config_section_name]/[fallback_ime_name]/, with .js files getting special treatment to make all this work.

options_page should be the path to the options page to use, relative to the built extension's root: [fallback_ime_name]/options.html, for example.

How you place an IME extension under ./imes is up to you. You could clone a repo there, or symlink to a directory outside the repo.

Let's see an example of how all this fits together.

I want to use my emacs keybindings on top of Chrome SKK, a Japanese IME, so here's what I do:

chrome-skk/
chrome-key-remapper/
  config.ini
  imes/
    skk -> ../../chrome-skk/extension
  remapper/
    ..

With a config like:

[skk_remapped]
name = SKK x emacs
description = SKK with emacs-like cursor movement
language = ja
layout = us
fallback_imes = skk
options_page = skk/options.html

When I invoke python waf configure build, an IME extension gets built in ./build/:

chrome-key-remapper/
  build/
    skk_remapped/
      manifest.json
      remapper/
        main.js
        ..
      skk/
        main.js
        ..

With this hybrid IME enabled and active, any key event not handled by the remapper will get passed onto SKK, enabling me to input Japanese text while enjoying the familiar emacs-like cursor movement keys.

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