fix: scroll offset_x by visual width, not char count, in focus() - #16
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fix: scroll offset_x by visual width, not char count, in focus()#16slaptijack wants to merge 1 commit into
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focus() compared the cursor's raw character-count column against the viewport width when deciding whether to scroll horizontally. For lines with double-width glyphs (CJK, emoji), character count under-estimates the true display width, so focus() could decide no scroll was needed while the cursor was actually off-screen — disagreeing with get_visible_cursor(), which already computes visual columns correctly via grapheme widths. focus() now computes cursor/offset_x visual columns the same way get_visible_cursor() does, and resolves scroll targets back to a char index via a new char_idx_for_visual_col() helper. Fixes vipmax#15
This was referenced Aug 27, 2026
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## Summary
- Qualifies the unconditional viewport guarantee in `docs/TUI_DESIGN.md`
("The vertical and horizontal viewport auto-scrolls to keep the cursor
visible...") with the accepted, temporary `ratatui-code-editor` 0.0.6
wide-glyph limitation already characterized in
`tests/editor_foundation_contract.rs`.
- Adds a new "Known limitation: wide-glyph cursor visibility" subsection
distinguishing affected behavior (long lines of wide/double-width glyphs
requiring horizontal scroll) from unaffected behavior (ASCII long lines,
short wide-glyph content, combining marks, exact Unicode round-trip),
each backed by an existing test.
- Links the upstream tracking issue
([vipmax/ratatui-code-editor#15](vipmax/ratatui-code-editor#15))
and proposed fix
([vipmax/ratatui-code-editor#16](vipmax/ratatui-code-editor#16)).
- Spells out the future resolution procedure (dependency-upgrade issue →
upgrade → flip the characterization assertion → verify via foundation
contract + Controller `TestBackend` → remove this doc section).
- Documentation-only; no source or test changes.
`known_limitation_wide_glyph_line_can_leave_cursor_offscreen_after_focus`
already fails conspicuously (per its own comment) once the upstream
behavior changes.
Closes #125
## Test plan
- [x] `cargo fmt --check`
- [x] `cargo clippy --locked --all-targets --all-features -- -D
warnings`
- [x] `cargo test --locked --all-targets --all-features`
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Summary
Editor::focus()decided whether to scroll horizontally by comparing the cursor's raw character-count column against the viewport width, which under-counts the true display width of lines containing double-width glyphs (CJK, emoji). This could leave the cursor off-screen whilefocus()believed no scroll was needed, disagreeing withget_visible_cursor(), which already accounts for grapheme display width.focus()now computes the cursor's andoffset_x's visual columns the same wayget_visible_cursor()does (summing grapheme widths), and resolves scroll targets back to a character index via a newchar_idx_for_visual_col()helper.Fixes #15
Test plan
focus_scrolls_horizontally_for_wide_glyph_linesintests/input.rs, reproducing the issue's repro case (a 20-character line of界, 40-cell-wide viewport) — cursor now stays visible afterfocus().cargo test(33 tests across lib + integration suites) passes.cargo clippy --all-targetsshows no new warnings from this change.