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figcraft/crates/doc
BFlat f665765128 M4: text behaviour suite: metrics, line height, CJK (#134)
## What

**A text behaviour suite written from the public documentation, and fixes for every divergence it found.** Each documented rule (Auto / % / px line height and how the leading is split, letter spacing in % and px, paragraph spacing and indent, auto width / auto height / fixed / truncate with max lines, vertical trim, decorations from the font's metrics) is a table-driven case with the numbers the rule implies and a one-line derivation, read from the face actually used so it holds on any machine with a font. CJK line breaking follows UAX #14 and the CJK line-start / line-end rules; caret steps follow UAX #29 grapheme clusters. Where the documentation is silent the case says so and pins today's behaviour.

**Fixes (6 of the 13 text cases fail on the old layout; the break and caret rules are new functions)**
- **CJK line breaking**: lines break between ideographs, kana and Hangul and before or after a Latin word next to them (before: no break before an ideograph that follows Latin, none after `。`, full-width forms, CJK punctuation or Extension B ideographs), never inside a Latin word, with kinsoku: closing brackets and quotes, `、。,.!?`, small kana, the prolonged sound mark and iteration marks never start a line (the character before moves down with them), opening brackets never end one. The ideographic space hangs at the line's end like a space. One small break-class table in `crates/text/src/breaks.rs`, no new crate.
- **Fallback fonts no longer move the baseline**: a style's ascent, descent, line height and cap height come from its own font, not the fallback face that drew some of its characters, so a line with CJK or emoji keeps the height and baseline of a Latin line (with a fixed line height the mixed line's baseline used to shift by the CJK face's taller metrics; with Auto the line grew). Decorations likewise use the style's font and size, so an underline runs at one height and weight through mixed scripts (and isn't thinned by synthesised small caps).
- **Paragraph indent applies to left-aligned text only** (documented); right-to-left paragraphs keep it when right-aligned (their start). The Type settings field is disabled with a hint otherwise.
- **Carets by grapheme cluster**: Left / Right, Delete and Backspace step over a whole emoji ZWJ sequence, flag, skin-tone sequence or letter with combining marks (they moved one code point at a time, leaving the caret inside an emoji and deleting half of it). A cluster is also shaped with one font, so a joiner or variation selector no longer splits an emoji sequence across faces.
- **Words by script**: double-click and word moves (Alt on macOS, Ctrl on Windows and Linux) take one script's run in text without spaces (`日本語` | `の` | `テキスト`), Hangul words end at spaces, and a Latin word keeps its combining marks (before: a whole CJK sentence was one word, and `cafe` + combining acute split at the accent).

**Missing documented setting, added**
- **Vertical trim** (cap height to baseline): `leadingTrim: none | capHeight` (`CAP_HEIGHT` from REST JSON) through `node.set`, a Standard / cap-height segmented control in Type settings, `inspect_document` and Dev Mode properties, CSS `text-box: trim-both cap alphabetic` in generated code. The box runs from the first line's cap height to the last baseline (auto height shrinks, auto layout parents follow); truncation counts the trimmed bottom; exports reach past the box so descenders below the last baseline aren't clipped. Canvas, PNG, SVG and PDF all draw from the same layout.

New strings go through `tr(...)` with `en.toml` / `es.toml` entries; the new segmented control reuses the Type settings one (accessible toggle names). Each edit is one undo step. `unicode-segmentation` (already in `Cargo.lock` through egui and winit) became a direct dependency of `figcraft-text`.

## Verified
- **Desktop app** over the control channel (own target dir, separate `APPDATA`, stopped by PID): a 200 px auto-height box of Japanese wraps with no line starting with `、。」` and `「` never ending a line (`…テスト` / `を折り返す、テスト` / `です。「括弧」は行` / `末に来ません。漢` / `字とかなとカタカ` / `ナ。`, the last `ナ` carried down with `。`); a Latin / CJK / Latin paragraph at 36 px line height is 108 px with evenly spaced baselines; the same text with vertical trim is 89.45 px (cap height 17.45 + 2 × 36), its box running from the cap height to the last baseline, and the Type settings control turns it off (108 px) and undo brings it back in one step; one Right arrow from after `a` in `a👨‍👩‍👧b` lands after the whole family emoji and Shift+Right then selects `b`; a double click selects the katakana run テキスト.
- **MCP**: `figcraft-cli mcp` (headless) built the same three texts; `inspect_document` reports 108 px for the 36 px paragraph and 89.42 px with `leadingTrim: capHeight` for the trimmed one (cap height of the headless font), the PNG export wraps the Japanese by the same rules and keeps the trimmed text's descenders, and `inspect.code` emits `text-box: trim-both cap alphabetic`.
- **Web**: `cargo xtask wasm` passes (part of the gate).
- **Performance**: text layout of a 2,250-char Latin and a 2,000-char Japanese paragraph wrapped at 300 px (release, median of 7 × 30 runs) before and after on the same machine: Latin 0.70 → 0.42–0.50 ms, Japanese 0.46 → 0.37–0.47 ms (within noise or faster: line metrics are now computed once per style change instead of per glyph). All-ASCII text skips grapheme segmentation.
- `cargo +1.99.0 xtask ci` passes (fmt, clippy, tests, layers, assets, wasm), after merging #131 and #132.

## Tests
- `text` (`behaviour_tests`, 13 tests): line height Auto / % / px; leading split above and below every line (positive and negative); letter spacing % / px / negative; paragraph spacing and indent by alignment; resizing and truncation with max lines; vertical trim (heights, first baseline, glyph spacing kept, truncation); decorations from the font's metrics through mixed scripts; fallback fonts keep line height and baseline (Auto, px, %); 22 break-opportunity cases; CJK wrapping with kinsoku, Latin words in CJK and Korean; the ideographic space hanging; grapheme steps over ZWJ families, flags, combining marks, skin tones and emoji presentation; one face per cluster. Font-dependent cases skip on a machine without fonts.
- `engine` (`text_behaviour_tests`, 5): arrows, Shift+arrows, Delete and Backspace by cluster; double-click and word moves by script (and through `keymap::text_motion` for Ctrl and Alt); IME composition with CJK wrapping and growing the box before commit; vertical trim through `node.set` (box size, PNG ink at the top, export bounds below the box, SVG and PDF, CSS, inspect, undo, junk refused, REST spelling); paragraph indent only on left-aligned text.
- `format` REST import test covers `leadingTrim: CAP_HEIGHT`.

## Not in this PR
- Documented but not modelled yet: list spacing, hanging quotes and hanging lists, underline style / thickness / offset / skip ink.
- Documentation silent, behaviour pinned: Korean wraps by syllable (no word mode); Han compounds next to each other are one word (no dictionary segmentation); letter spacing is added after the last character too; a fallback font's taller glyphs may overflow the line rather than grow it.
- `.fig` import doesn't read vertical trim yet (the field wasn't checked against real files).
- Spell check (on hold, #113).
- Progress docs: target-app-parity area 10 85%/64% → 87%/68%, 7–13 h → 5–10 h with the suite listed under text editing depth; feature breadth and ready for real work unchanged at this rounding; full parity ~323–621 h → ~321–618 h (target-app-parity, ROADMAP); ui-parity text row.
2026-10-11 22:09:46 +07:00
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