awaforge

tableEblc

AGPL-3.0-onlyRelease 2L4

Table EBLC — Embedded Bitmap Location (OT §8.4).

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

Monochrome counterpart of cblc, with identical wire layout: a header followed by one 48-byte bitmapSizeTable per strike. It describes the strikes and where their index subtables live; the bitmaps themselves are in ebdt.

Exports

Symbol Type Description
parseEblc function (bytes: Uint8Array) => { majorVersion, minorVersion, sizes: BitmapSizeTable[] }.
tableEblc factory Factory { name, dependencies, factory }.

BitmapSizeTable

Field Type
indexSubTableArrayOffset, indexTablesSize, numberOfIndexSubTables uint32
colorRef uint32
hori, vert SbitLineMetrics
startGlyphIndex, endGlyphIndex uint16
ppemX, ppemY, bitDepth uint8
flags int8

SbitLineMetrics

Field Type
ascender, descender int8
widthMax uint8
caretSlopeNumerator, caretSlopeDenominator, caretOffset int8
minOriginSB, minAdvanceSB, maxBeforeBL, minAfterBL int8
pad1, pad2 int8

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 { parseEblc } = fw.runtime.resolve('tableEblc');

const sfnt = parseSfnt(bytes);   // bytes: Uint8Array of a font with EBLC + EBDT
const eblc = parseEblc(sfnt.tables.EBLC.bytes);
for (const s of eblc.sizes) console.log(s.ppemX, s.ppemY, s.startGlyphIndex, s.endGlyphIndex);

Notes

  • Both line-metrics blocks (hori, vert) are decoded for every strike.
  • The index subtable arrays are not followed: indexSubTableArrayOffset, indexTablesSize and numberOfIndexSubTables are returned as offsets and counts for the consumer to load from the same table bytes.
  • Errors (all ParseError): fonts/eblc-short (fewer than 8 bytes), fonts/eblc-version (major version is neither 2 nor 3).

See also

  • ebdt — the bitmap data located here
  • ebsc — strikes obtained by scaling
  • cblc — color bitmap location counterpart
  • cbdt — color bitmap data counterpart