awaforge

embedSubsetForPdf

AGPL-3.0-onlyRelease 2L4

Minimal TrueType subset for PDF Type0 / FontFile2 embedding.

Module embedSubsetForPdf | Source packages/front/office/fonts/src/embed-pdf/subsetForPdf.js | Deps fontErrors, fontSfnt, tableHead, tableHhea, tableMaxp, tableHmtx, tableLoca, embedFontDescriptor, cmapToUnicode, fontWriter, plus the sibling sub-modules embedClosure, embedCmapBuilder, embedGlyphRewriter, embedHash | Worker-safe yes

Computes the composite-glyph closure covering a set of code points, renumbers gids, re-encodes glyf/loca/hmtx/cmap/post/name/head, and also produces the FontDescriptor + ToUnicode CMap for the PDF Font dictionary.

Rewritten tables (vs. a verbatim copy of the source font's bytes):

  • glyf, loca, hmtx, cmap, head, hhea, maxp — recomputed for the renumbered/reduced glyph set (see Algorithm above).
  • post — the 32-byte header is preserved bit-for-bit for the fields shared across versions (italicAngle, underline, isFixedPitch, memory hints); the version tag itself is forced to 3.0 (no glyph names) unless the source is already 3.0, in which case the whole table is copied verbatim. A source post shorter than 32 bytes, or absent, yields no post table in the subset.
  • name, OS/2 — copied verbatim from the source font (unmodified).

Exports

Symbol Type Description
subsetForPdf function (font, codePoints, opts?) => { subsetBytes, gidMap, glyphMap, encoding, widths, toUnicodeCmap, postScriptName, fontDescriptor }.
embedSubsetForPdf factory Factory.

Usage

embedSubsetForPdf depends on four sub-modules (embedClosure, embedCmapBuilder, embedGlyphRewriter, embedHash). The package's modules array registers all four, placed before embedSubsetForPdf, so a runtime seeded with fw_require and modules resolves it with no further registration:

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

for (const m of [...fw_require, ...modules]) fw.runtime.register(m);
const font = fw.runtime.resolve('fonts').read(bytes);   // bytes: Uint8Array of a TrueType font
const { subsetForPdf } = fw.runtime.resolve('embedSubsetForPdf');
const subset = subsetForPdf(font, new Set([0x41, 0x42, 0x4F]));
// subset.subsetBytes ready for FontFile2

Notes

  • gid 0 (.notdef) is always kept.
  • A deterministic 6-letter prefix (e.g. ABCDEF+) is added to the PostScript name per PDF convention.
  • Composites are recursively expanded before renumbering.
  • encoding is always null — Type0/Identity-H addressing goes through the rebuilt cmap, not a PDF /Encoding entry.
  • widths is a per-new-gid advance-width array, in the same order as the renumbered glyphs (suitable for the PDF /W entry).
  • A font without glyf / loca tables (for example a CFF-flavoured OpenType font) is rejected with ContractError('fonts/subset-bad-font'); variable-font tables and the GSUB/GPOS layout tables are not carried through to the subset.
  • A source post table is never copied verbatim unless it is already version 3.0: a v1.0/v2.0/v4.0 post carries glyph-name data keyed to the SOURCE font's gid count/order, which the subset's renumbered/reduced glyph set invalidates — fonts.read() on the resulting bytes would otherwise throw fonts/post-num-mismatch.

See also