awaforge

tableLoca

AGPL-3.0-onlyRelease 2L4

Table loca — Index to Location (OT §6.4.13).

Module tableLoca | Source packages/front/office/fonts/src/table/loca.js | Deps fontErrors, fontReader, fontWriter | Worker-safe yes

Array of numGlyphs + 1 offsets into glyf. The format is driven by head.indexToLocFormat:

  • short (0) — uint16, offset stored as bytes / 2 (limit: 128 KiB of glyf).
  • long (1) — uint32, offset in raw bytes.

Glyph N occupies [offsets[N], offsets[N+1]); an empty glyph has offsets[N] === offsets[N+1].

Resolve

const { parseLoca, encodeLoca } = runtime.resolve('tableLoca');

API

Method Signature Returns
parseLoca (bytes, numGlyphs, indexToLocFormat) => Uint32Array numGlyphs + 1 offsets in bytes.
encodeLoca (offsets: Uint32Array | number[]) => { bytes, indexToLocFormat } Picks short if all offsets are ≤ 0x1FFFE and even.

Examples

const { parseLoca } = runtime.resolve('tableLoca');
const loca = parseLoca(sfnt.tables.loca.bytes, maxp.numGlyphs, head.indexToLocFormat);
// loca[gid+1] - loca[gid] === glyph size in bytes

const { encodeLoca } = runtime.resolve('tableLoca');
const { bytes, indexToLocFormat } = encodeLoca(offsets);
head.indexToLocFormat = indexToLocFormat;   // keep in sync

Notes

  • The encoder selects short only if every offset is even AND ≤ 0x1FFFE — a single failure falls back to long.
  • The caller must propagate indexToLocFormat back into head after encoding.
  • A format outside {0,1} throws ParseError('fonts/loca-bad-format').
  • parseLoca also validates the offsets are non-decreasing; a drop throws ParseError('fonts/loca-non-monotonic').

See also

  • head — provides indexToLocFormat
  • glyf — consumer of the offsets