Symbol & CJK Glyph Width

Terminals place every character on a fixed cell grid, but fonts don’t always agree with the grid about how wide a glyph should be. Korean and Japanese coding fonts (D2Coding, for example) design symbols like circled numbers (①…⑳), circled letters (Ⓐⓐ), ※, ★ and arrows at full width — twice the width of a normal character — while the Unicode width rules that terminals and apps follow allocate them one cell.

Damson has three mechanisms that deal with this. They sound similar but work at different layers, and only one of them can affect app layout.

Double-width icons

Settings ▸ Appearance ▸ Double-width icons — default on

Non-Mono Nerd Font variants (“JetBrainsMono Nerd Font” as opposed to ”…Nerd Font Mono”) design their icons larger than one cell. With this setting on, Damson renders those icons at natural size on a two-cell canvas, centered on their one-cell slot — the ink simply overflows into the neighboring cells visually.

This is rendering only. The grid still allocates one cell, so cursor math, column alignment and TUI layout are untouched. The only trade-off is that a big icon may visually overlap text immediately next to it. Turn it off to shrink oversized icons into their cell instead.

Powerline separators are always fitted edge-to-edge regardless of this setting, so segmented prompts never show seams.

Full-width symbol designs (automatic)

Some symbols are classified East Asian Width: Ambiguous by Unicode — circled numbers and letters, ※, ★, arrows, geometric shapes. Terminals allocate them one cell (that’s what wcwidth says, and what apps assume), but CJK fonts often draw them as full-width glyphs whose ink is ~1.7 cells wide.

Damson handles these automatically, with no setting:

• If the cell to the right is blank, the glyph renders at its designed natural size, anchored at its own cell’s left edge — ① item shows a full-size circled one.
• If the right cell is occupied (①②③ in a run), that instance is uniformly shrunk to fit its cell, so glyphs never overlap.

Either way the grid stays one cell, so nothing can misalign. Fonts whose symbol designs already fit one cell (most Latin coding fonts) are unaffected.

Ambiguous-width symbols as double width

Settings ▸ Appearance ▸ Ambiguous-width symbols as double width — default off

If you read a lot of Korean or Japanese text, shrunk circled numbers in consecutive runs may bother you. This setting — the same trade-off iTerm2 and WezTerm expose — allocates those symbols two real grid cells, so they render at their designed size everywhere, runs included.

Because this changes the layout contract, it can disagree with apps:

• Apps compute display width themselves (via wcwidth or string-width), and they count ambiguous symbols as one column.
• With the setting on, a table row whose content includes ① renders one cell wider than the app calculated — the right border of that row drifts and the vertical line zigzags.
• Line editing can look off too: type ① at a prompt and the shell believes the cursor advanced one column while the screen shows two.

Box-drawing characters (─ │ ┌ ┐) and prose punctuation are deliberately excluded, so TUI frames themselves never change width — only content containing those symbols shifts.

Recommendations

• Leave it off if you live in TUIs that draw tables (the automatic natural-size handling above is a good middle ground).
• Turn it on if you mostly read Korean/Japanese documents and logs and want 전각 symbols at their designed size.
• In Vim you can match the app to the terminal with set ambiwidth=double; Emacs has similar tables. Node-based TUIs generally can’t be configured, so prefer off when working with them.

Toggling applies to newly written output; existing rows re-render as apps redraw.

Fallback fonts and who draws what

Which face paints a glyph is independent of how many cells it gets. Damson resolves glyphs in a fixed order:

1. Your font — everything it covers.
2. Pinned CJK fallback (D2CodingLigature Nerd Font Mono when installed) — Hangul, CJK and symbols your font lacks, deterministic across machines.
3. Apple Color Emoji — emoji only.
4. System fallback — whatever CoreText recommends, shrunk to fit if needed.

So a font without circled-number glyphs still shows them (via tier 2), and if that fallback designs them full-width they follow all the rules above. Without any fallback you would see tofu (□), not a narrow glyph.