awaforge

layoutClassDefinitions

AGPL-3.0-onlyRelease 2L4

Coverage + ClassDef — GSUB/GPOS/GDEF indexing primitives (OT §6.2).

Module layoutClassDefinitions | Source packages/front/office/fonts/src/layout/classDefinitions.js | Deps fontErrors, fontReader | Worker-safe yes

Two indexing tables used by every OpenType lookup:

  • Coverage: glyph → coverage index (or null). Formats 1 (list) / 2 (ranges).
  • ClassDef: glyph → class number uint16, default 0. Formats 1 (array) / 2 (ranges).

Each result exposes an ergonomic lookup(gid) helper.

Exports

Symbol Type Description
parseCoverage function (bytes) => { format, ..., lookup(gid) }.
parseClassDef function (bytes) => { format, ..., lookup(gid) }.
layoutClassDefinitions factory Factory.

Usage

import fw from '@awacloud/fw';
import { fw_require, modules } from '@awacloud/fonts';

for (const m of [...fw_require, ...modules]) fw.runtime.register(m);
const { parseCoverage } = fw.runtime.resolve('layoutClassDefinitions');
const cov = parseCoverage(subtableSlice);
const idx = cov.lookup(42); // null if not covered

Notes

  • Ranges are sorted — lookup uses a binary search.
  • Unknown format → ParseError fonts/coverage-format / fonts/classdef-format.

See also