fonttypes

This is fonttypes, a TypeScript library for font engineering. It will be primarily useful for people working with variable fonts, especially at the source level; it includes types for designspaces, coordinates, locations, variation models, and provides utility functions for OpenType interpolation.

Installation

npm install fonttypes

Usage

This library uses branded types to ensure that you don't mix up different coordinate spaces. For example, you can't pass a UserspaceCoordinate to a function that expects a DesignspaceCoordinate. It also provides functions to convert between these spaces, and to normalize locations for interpolation.

It provides a VariationModel class that can be used to perform interpolation given a set of master locations and corresponding values.

Here's an example of how to use the library to convert between coordinate spaces and interpolate a value in a variable font.

import {
  UserspaceCoordinate,
  DesignspaceLocation,
  UserspaceLocation,
  UserspaceToDesignspaceMapping,
  Axis,
  userspaceToDesignspace,
  normalizeLocation,
  VariationModel,
  NormalizedLocation,
} from "fonttypes";

// Define the axes for a variable font
let weightMap: UserspaceToDesignspaceMapping = [
  [100, 100],
  [400, 400],
  [700, 600],
  [900, 900],
];

let axisMin: DesignspaceCoordinate = 100;
const axes: Axis[] = [
  {
    tag: "wght",
    name: "Weight",
    min: axisMin, // Oops, this won't compile!
    default: 400,
    max: 900,
    map: weightMap,
  },
];

// Convert a userspace location to a designspace location
const userLocation: UserspaceLocation = { wght: 650 };
const designLocation: DesignspaceLocation = userspaceToDesignspace(
  userLocation,
  axes,
);
console.log("Designspace location:", designLocation);
// -> Designspace location: { wght: 550 }

// Normalize the designspace location
const normalizedLocation: NormalizedLocation = normalizeLocation(
  designLocation,
  axes,
);
console.log("Normalized location:", normalizedLocation);
// -> Normalized location: { wght: 0.3 }

// --- Interpolation ---

// Define master locations in normalized space
const masterLocations: NormalizedLocation[] = [
  { wght: 0.0 },
  { wght: -1.0 },
  { wght: 1.0 },
];

// Create a variation model
const model = new VariationModel(masterLocations, ["wght"]);

// Values for a glyph component's x-position at each master location
const masterValues = [150, 100, 250]; // Corresponds to default, min, max

// Interpolate the x-position at our normalized location
const interpolatedValue = model.interpolateFromMasters(
  normalizedLocation,
  masterValues,
);

console.log("Interpolated value:", interpolatedValue);
// -> Interpolated value: 180

Building and Testing

To build the library from source, run:

npm run build

To run the tests, use:

npm run test

API Documentation

Full API documentation is available at https://simoncozens.github.io/fonttypes/