xterm-addon-ligatures

xterm-addon-ligatures

Add support for programming ligatures to xterm.js when running in environments with access to Node.js APIs (such as Electron).

Requirements

• Node.js 8.x or higher (present in Electron 1.8.3 or higher)
• xterm.js 3.6.0 or higher using the default canvas renderer

Usage

Install in your project by running:

npm install xterm-addon-ligatures

Then, modify the location where you initialize the terminal to enable ligature support after opening. If you enable ligatures prior to opening the terminal, they will not function properly.

Your code should look something like this:

import { Terminal } from 'xterm';
import * as ligatures from 'xterm-addon-ligatures';

Terminal.applyAddon(ligatures);

const terminal = new Terminal();
terminal.open(document.getElementById('terminal-mount'));
terminal.enableLigatures();

Importing in TypeScript

If you use TypeScript, you will need to cast the terminal variable as any when you enable ligatures because TypeScript does not know that the addon is available on the terminal object. It will look like this:

(terminal as any).enableLigatures()

Alternatively, you can import the addon directly as a function and pass the terminal as an argument:

import { Terminal } from 'xterm';
import { enableLigatures } from 'xterm-addon-ligatures';

const terminal = new Terminal();
terminal.open(document.getElementById('terminal-mount'));
enableLigatures(terminal);

How It Works

In a browser environment, font ligature information is read directly by the web browser and used to render text correctly without any intervention from the developer. As of version 3, xterm.js uses the canvas to render characters individually, resulting in a significant performance boost. However, this means that it can no longer lean on the browser to determine when to draw font ligatures.

This package locates the font file on disk for the font currently in use by the terminal and parses the ligature information out of it (via the font-ligatures package). As text is rendered in xterm.js, this package annotates it with the locations of ligatures, allowing xterm.js to render it correctly.

Since this package depends on being able to find and resolve a system font from disk, it has to have system access that isn't available in the web browser. As a result, this package is mainly useful in environments that combine browser and Node.js runtimes (such as Electron).

Fonts

This package makes use of the following fonts for testing:

• Fira Code - Licensed under the OFL by Nikita Prokopov, Mozilla Foundation with reserved names Fira Code, Fira Mono, and Fira Sans
• Iosevka - Licensed under the OFL by Belleve Invis with reserved name Iosevka