awaforge

tableVhea

AGPL-3.0-onlyRelease 2L4

Table vhea — Vertical Header (OT §6.4.10), 36 bytes.

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

Vertical analogue of hhea. numOfLongVerMetrics decides how many full (advanceHeight, tsb) records precede the tsb-only tail of vmtx.

Exports

Symbol Type Description
parseVhea function (bytes: Uint8Array) => VheaTable. Throws ParseError fonts/vhea-short when fewer than 36 bytes are given.
encodeVhea function (h: VheaTable) => Uint8Array. Exactly 36 bytes; missing fields take defaults (see Notes).
tableVhea factory Factory { name, dependencies, factory }.

VheaTable

Field Type
majorVersion, minorVersion uint16
ascender, descender, lineGap int16
advanceHeightMax int16
minTopSideBearing, minBottomSideBearing, yMaxExtent int16
caretSlopeRise, caretSlopeRun, caretOffset int16
metricDataFormat int16
numOfLongVerMetrics uint16

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 { parseSfnt } = fw.runtime.resolve('fontSfnt');
const { parseVhea, encodeVhea } = fw.runtime.resolve('tableVhea');

const sfnt = parseSfnt(bytes);   // bytes: Uint8Array of a font with a vhea table
const vhea = parseVhea(sfnt.tables.vhea.bytes);
console.log(vhea.ascender, vhea.numOfLongVerMetrics);
const out = encodeVhea(vhea);    // 36 bytes

Notes

  • parseVhea skips the four reserved int16 fields between caretOffset and metricDataFormat; encodeVhea writes them as zero.
  • encodeVhea defaults: majorVersion 1, minorVersion 0, caretSlopeRun 1, every other field 0. parseVhea does not check the version.

See also

  • vmtx — the metrics array this header sizes
  • vorg — vertical origins
  • hhea — horizontal counterpart