awaforge

tableHhea

AGPL-3.0-onlyRelease 2L4

Table hhea — Horizontal Header (OT §6.4.3), 36 bytes.

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

Drives how advance widths are interpreted in hmtx via numberOfHMetrics, which decides how many full records precede the lsb-only tail.

Resolve

const { parseHhea, encodeHhea } = runtime.resolve('tableHhea');

API

Method Signature Returns
parseHhea (bytes: Uint8Array) => HheaTable Throws if < 36 bytes.
encodeHhea (hhea: HheaTable) => Uint8Array Exactly 36 bytes.

HheaTable

Field Type
majorVersion, minorVersion uint16
ascender, descender, lineGap int16
advanceWidthMax uint16
minLeftSideBearing, minRightSideBearing, xMaxExtent int16
caretSlopeRise, caretSlopeRun, caretOffset int16
metricDataFormat int16
numberOfHMetrics uint16

Examples

const { parseHhea } = runtime.resolve('tableHhea');
const hhea = parseHhea(sfnt.tables.hhea.bytes);
console.log(hhea.ascender, hhea.numberOfHMetrics);

Notes

  • 4 reserved int16 records (between caretOffset and metricDataFormat) are read then discarded at parse time, written as zero at encode.
  • numberOfHMetrics must be ≥ 1 and ≤ maxp.numGlyphs — validated on the hmtx side.

See also

  • hmtx — depends on numberOfHMetrics
  • maxp