Virama conjunct+Mc width fix#223
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After careful review of Virama width calculation and study of uucode, two related changes:
- Bugfix Invisible_Stacker viramas now form conjuncts (Burmese, Khmer, etc.)
Discovered while analyzing Burmese, found in ``IndicSyllabicCategory.txt``, "causes conjunct
formation", added in Unicode 14.0:
# Indic_Syllabic_Category=Invisible_Stacker
#
# Invisible stacker (usually kills inherent vowel of consonant; is not visible
# by itself; causes conjunct formation or consonant
# stacking)
So this logically belongs with the others in ``_ISC_VIRAMA_SET``. Use code generation instead of
the copy and paste done before, this set would have changed in several past unicode releases and
so may change again in the future.
- Change Virama+consonant width calculation to match @jacobsandlund's uucode (ghostty)
Our previous implementation was perhaps too complex, but more "giving" for width compared to
uucode's implementation, and neither of ours really has any basis in standards, seems to be of
taste. contour's libunicode does not make concern for virama, and uucode's does, measurement
is simpler to implement and will probably improve performance, see code comment::
# Virama codepoints (Indic_Syllabic_Category=Virama|Invisible_Stacker)
# are treated as zero-width combining marks, matching Ghostty's uucode
# library. Whether a virama+consonant sequence should collapse to 1 or
# 2 cells is undefined by Unicode; we follow uucode's (1).
…idth Mc following a virama conjunct (C+V+C) was adding width +1. The Mc closes the conjunct and accounts for its 1-cell contribution, it should not add its own. I'm not sure this is directly spelled by any specification, following uucode/ghostty measurements, here.
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bugfix Virama conjunct: Mc following a conjunct adds no independent width
Mc following a virama conjunct (C+V+C) was adding width +1. The Mc
closes the conjunct and accounts for its 1-cell contribution, it should
not add its own. I'm not sure this is directly spelled by any
specification, following uucode/ghostty measurements, here.