Terminal: count East Asian Wide characters as two columns - #2894
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The emulator assumed every character occupies one cell, so Hangul, Han and Kana text, fullwidth forms and emoji were placed one column short per character and the screen fell apart as soon as a program laid text out for a real terminal (line editors, curses UIs, Ink based CLIs). Add CharWidth, a UAX eclipse-platform#11 East Asian Width lookup: Wide and Fullwidth count as two columns, combining marks and controls as zero, Ambiguous as one, as UAX eclipse-platform#11 recommends outside an East Asian legacy context. The emulator advances the cursor by that width and stores a NUL filler in the second cell of a wide character, never splits one across the right margin, blanks the other half when either half is overwritten and counts insert mode in cells. The renderer skips the fillers so a fixed width font draws a wide glyph over both cells, falls back to placing each character at its own cell when the font does not advance exactly one cell per column, and draws a character beyond the BMP whole. A partial repaint that starts on the second cell of a wide character is widened to its first, and copying drops the fillers. Tests cover the width table, placement, the margin, overwriting halves and insert mode.
This was referenced Sep 3, 2026
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The terminal emulator assumes every character occupies one cell. Hangul, Han and Kana text, fullwidth forms and emoji are East Asian Wide and occupy two, so every such character put the cursor one column short and the screen fell apart as soon as a program laid text out for a real terminal — line editors, curses UIs, Ink-based CLIs.
This adds
CharWidth, a UAX #11 East Asian Width lookup (Wide/Fullwidth = 2, combining marks and controls = 0, Ambiguous = 1 as UAX #11 recommends outside an East Asian legacy context), and makes the emulator and renderer follow it:Tests:
CharWidthTest(width table) and four cases inVT100EmulatorBackendTest(placement, margin, overwriting halves, insert mode). All existing terminal tests pass.Verified on Windows 11 with a Korean shell session, vim, htop and Claude Code inside the Eclipse Terminal; compared against Windows Terminal for column alignment.