Support fonts that use MarkGlyphSets

[jakejackson1]

Summary

mPDF rejects any font whose GSUB lookups use a mark filtering set. That takes out every current release of Noto Sans Sinhala, among others, at any non-zero useOTL — the exception is Font "..." contains MarkGlyphSets which is not supported.

The support is already written. A GSUB lookup can set the UseMarkFilteringSet flag (0x0010) to ignore every mark except those in a GDEF mark glyph set; mPDF parses those sets when it reads GDEF, and both TTFontFile::_checkGSUBignore() and Otl::_checkGCOMignore() consult them. Only the two functions that build the ignore pattern refuse — and in both, the throw sits directly above a working implementation the author left unreachable, commented "Not tested yet" and "Change also in ttfontsuni.php".

This drops those two throws so the existing code runs, keeping a guard for the one case that is genuinely broken: a filtering set GDEF does not define. Four lines of src/.

This was originally committed to the Font Packages PR, where it does not belong — it is independent of font packages. It is split out here.

Try it

$mpdf = new \Mpdf\Mpdf([
    'fontDir'  => [__DIR__ . '/tests/data/ttf'],
    'fontdata' => ['sinhalasubset' => ['R' => 'NotoSansSinhala-Subset.ttf', 'useOTL' => 0xFF]],
    'default_font' => 'sinhalasubset',
]);

$mpdf->WriteHTML('<p>සිංහල අකුරු ශ්‍රී ලංකා</p>');
$mpdf->Output('sinhala.pdf', \Mpdf\Output\Destination::FILE);

On gravitypdf-7.0 that throws. On this branch it renders, and the ශ්‍රී conjunct matches what HarfBuzz produces for the same font and string.

Test plan

• composer test — 1000 tests, 2291 assertions, green.
• composer cs — clean.
• Both new tests fail without the src/ change, and they fail on different throws: reverting only Otl.php leaves TTFontFileTest::testGetMetricsWithMarkGlyphSets passing and MarkGlyphSetsTest failing. Neither change is redundant.

More info

The two call sites

Function	Was	Now
TTFontFile::_getGSUBignoreString() (src/TTFontFile.php)	throw new FontException('... contains MarkGlyphSets which is not supported'), with $str = $this->MarkGlyphSets[$MarkFilteringSet]; unreachable beneath it	assigns $str, throwing only if GDEF defines no such set
Otl::_getGCOMignoreString() (src/Otl.php)	throw new MpdfException('... contains MarkGlyphSets - Not tested yet'), with a $MarkFilteringSet == '' guard and the assignment unreachable beneath it	keeps the existing guard, widened to cover an undefined set, then assigns $str

$ignoreflag is dead in both functions — it survives only in the commented-out [IGNORE$ignoreflag] scheme the author never finished — so the assignment to $str is the whole behaviour.

Why this shows up now

fontmake sets the flag routinely, so it is not a corner case: it is most current Google/Noto releases with mark positioning. The existing tests/data/ttf/NotoSans-Regular.ttf fixture does define four mark glyph sets, but only its GPOS lookups reference them, and neither throw is on a GPOS path — which is why the suite has been green while the bug was live.

The fixture

tests/data/ttf/NotoSansSinhala-Subset.ttf is Noto Sans Sinhala (OFL 1.1, no reserved font name) subsetted with fontTools to the sample text with --layout-features='*'. 7,656 bytes, 32 glyphs, retaining 2 mark glyph sets and 7 GSUB lookups that carry the flag — an order of magnitude smaller than the other fixtures in that directory.