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Devanagari RA-appended half forms

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minjaesong
2026-02-26 09:08:39 +09:00
parent 08d1b41cc0
commit be1c8e2f79
4 changed files with 39 additions and 12 deletions
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1
OTFbuild/CLAUDE.md
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@@ -141,6 +141,7 @@ The bitmap font engine normalises Devanagari consonants to internal PUA forms be
| U+0915-0939 +48 | 0xF0170-0xF0194 | Nukta forms (consonant + U+093C) |
| U+0915-0939 +240 | 0xF0230-0xF0254 | Half forms (consonant + virama) |
| U+0915-0939 +480 | 0xF0320-0xF0404 | RA-appended forms (consonant + virama + RA) |
| U+0915-0939 +720 | 0xF0410-0xF04F4 | RA-appended half forms (consonant + virama + RA + virama) |
Mapping formula: `to_deva_internal(c)` = `c - 0x0915 + 0xF0140` for U+0915-0939.

44
OTFbuild/opentype_features.py
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@@ -627,11 +627,13 @@ def _generate_devanagari(glyphs, has, replacewith_subs=None):
# --- half: consonant (PUA) + virama -> half form ---
# After ccmp, consonants are in PUA form, so reference PUA here.
# Conjuncts are NOT here because half uses per-glyph masking (only
# pre-base consonants), preventing 3-glyph matches across the base.
# Covers all PUA consonants including conjuncts produced by akhn
# (e.g. DD.G + virama -> half-DD.G). The half feature uses
# per-glyph masking (only pre-base consonants get the mask), so
# conjunct glyphs formed by akhn inherit the pre-base mask and
# their following virama also has the pre-base mask.
half_subs = []
for uni_cp in range(0x0915, 0x093A):
internal = SC.to_deva_internal(uni_cp)
for internal in SC.DEVANAGARI_PRESENTATION_CONSONANTS:
half_form = internal + 240
if has(internal) and has(SC.DEVANAGARI_VIRAMA) and has(half_form):
half_subs.append(
@@ -668,15 +670,39 @@ def _generate_devanagari(glyphs, has, replacewith_subs=None):
# with the preceding consonant to produce the ra-appended glyph.
# Covers all PUA consonants: basic, nukta forms, AND conjuncts
# (e.g. DD.G + rakaar -> DD.G.RA).
cjct_subs = []
#
# A second lookup converts RA-appended + virama -> RA-appended half,
# since the half feature has already run before cjct.
cjct_lines = []
# Lookup 1: consonant + rakaar -> RA-appended form
ra_append_subs = []
for internal in SC.DEVANAGARI_PRESENTATION_CONSONANTS:
ra_form = internal + 480
if has(internal) and has(ra_sub) and has(ra_form):
cjct_subs.append(
f" sub {glyph_name(internal)} {glyph_name(ra_sub)} by {glyph_name(ra_form)};"
ra_append_subs.append(
f" sub {glyph_name(internal)} {glyph_name(ra_sub)} by {glyph_name(ra_form)};"
)
if cjct_subs:
features.append("feature cjct {\n script dev2;\n" + '\n'.join(cjct_subs) + "\n} cjct;")
if ra_append_subs:
cjct_lines.append(" lookup CjctRaAppend {")
cjct_lines.extend(ra_append_subs)
cjct_lines.append(" } CjctRaAppend;")
# Lookup 2: RA-appended + virama -> RA-appended half form
ra_half_subs = []
for ra_form in SC.DEVANAGARI_PRESENTATION_CONSONANTS_WITH_RA:
ra_half = ra_form + 240 # +240 from RA-appended = +720 from base
if has(ra_form) and has(SC.DEVANAGARI_VIRAMA) and has(ra_half):
ra_half_subs.append(
f" sub {glyph_name(ra_form)} {glyph_name(SC.DEVANAGARI_VIRAMA)} by {glyph_name(ra_half)};"
)
if ra_half_subs:
cjct_lines.append(" lookup CjctRaHalf {")
cjct_lines.extend(ra_half_subs)
cjct_lines.append(" } CjctRaHalf;")
if cjct_lines:
features.append("feature cjct {\n script dev2;\n" + '\n'.join(cjct_lines) + "\n} cjct;")
# --- blws: RA/RRA/HA (PUA) + U/UU -> special syllables ---
blws_subs = []