Add Thai shaper, ported from HarfBuzz#376
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- Decompose SARA AM (U+0E33) into NIKHAHIT + SARA AA and reorder NIKHAHIT past above-base marks, matching `preprocess_text_thai` - Apply PUA tone/vowel shift fallback for legacy fonts without Thai GSUB, mirroring `do_thai_pua_shaping` (above/below state machines + Windows/Mac PUA mapping tables) - Fall back to the buffer's Unicode script in OTLayoutEngine when neither GSUB nor GPOS picks an OT script — lets script-specific shapers run on fonts without matching GSUB/GPOS so the Thai PUA fallback is actually reachable - Fix typo in `UnicodeLayoutEngine` Thai mark classification: `0x0E3D` (unassigned) → `0x0E4D` (NIKHAHIT) - Register `thai` and `'lao '` (the 4-char OT tag with trailing space), add Noto Sans Thai + Noto Sans Lao (OFL) as test fixtures with 8 shaping tests
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fontkit currently has no dedicated Thai shaper — Thai (
thaiscript) falls through toDefaultShaper, which leaves SARA AM (U+0E33) intact. This breaks the GSUB chain rules every modern Thai font ships: with the buffer in[base, tone, SARA_AM]order the tone-mark-shiftingccmplookups don't fire, so e.g.น้ำkeeps the regularuni0E49instead of theuni0E49.smallHarfBuzz produces.This PR ports
hb-ot-shaper-thai.cc:[base, tone, SARA_AM]becomes[base, NIKHAHIT, tone, SARA_AA], which is the shape the font'sccmpwas designed to match.do_thai_pua_shaping: an above/below state machine assigns one ofNOP/SD/SL/SDL/RDactions to each tone or vowel mark, then we remap the codepoint to its Windows or Mac PUA variant if the font ships one. Gated on the absence of a Thai script in GSUB.Also folds in a one-character typo fix in
UnicodeLayoutEngine.js's Thai mark classification:0x0E3D(an unassigned codepoint in the Thai block) was sitting in theAbove_Rightswitch where0x0E4D(NIKHAHIT) belongs. Both NIKHAHIT and the surrounding cases (MAI HAN-AKAT, SARA I/II/UE/UEE, MAITAIKHU, THANTHAKHAT, YAMAKKAN) are classified asTopin Unicode's IndicPositionalCategory.Tests
Four tests added under
test/shaping.js, ported from HarfBuzz'ssara-am.testsand hand-picked Thai phrases. Test fixture is the hinted Noto Sans Thai from googlefonts (SIL OFL). Three of the four exercise the SARA AM path and fail without this shaper registered.Lao (
laoscript) is mapped to the same shaper since the reorder applies identically (codepoints offset by 0x80).Closes #134, closes #133.