A second mark stacked on a letter now rides on the letter as well as on the
mark before it; a mark drawn up to an em above or below its letter stays on
the letter's line, and the glyph after it continues from the letter; marks in
a zero-width run are ordered by their letter; and a word gap after a mark is
measured from the letter's advance, not the mark's offset start.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq7HyCHD1R3rywQBPCHXZA
Text drawn one glyph per show operation, with zero-advance Thai tone marks
starting a hair past their base's advance, came out with the mark after the
next letter ("ห้อง" read "หอ้ง") because a line's glyphs were sorted by x
alone. A combining mark (Mn/Me) of a left-to-right script drawn right after
the glyph it sits over now rides on that glyph: placement sorts clusters, so
the mark keeps its content-stream place. Word gaps are measured between
clusters, and the tight-cluster rule now guards only loose combining signs,
so a Thai or Indic word gap with no space glyph reads as a space.
Fixes#6517
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq7HyCHD1R3rywQBPCHXZA
mtlcl410andClaude Opus 5.5
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jonathanwxh-cell
Dylan M. Taylor
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