Document grid: lines per page and characters per line (#391)

[vangel76]

What

Layout › Page Setup › Document Grid (w:docGrid, ECMA-376 §17.6.5).

• Model + DOCX: SectionProps::doc_grid (type default|lines|linesAndChars|snapToChars, line pitch, w:charSpace) and paragraph w:snapToGrid, read and written (w:docGrid written after w:bidi in sectPr; Word's no-grid <w:docGrid w:linePitch="360"/> survives a round trip).
• Layout:
  • Line grid: in paragraphs that snap (the default; w:snapToGrid w:val="0" turns it off), each line's height rounds up to whole line pitches with the text centred in them. Multiple spacing is a multiple of the snapped height; Exactly isn't snapped. Headers and footers don't snap.
  • Character grid: linesAndChars gives East Asian characters (CJK ideographs, kana, Hangul, CJK punctuation, full-width forms) whole cells of the character pitch, glyph centred. The pitch is the Normal font size plus charSpace/4096 pt. A larger character takes round(size / default size) cells. Latin text keeps its own widths. With snapToChars, all text snaps to whole cells.
  • Hostile values (pitch 0, negative, NaN, huge; extreme charSpace) are clamped to 1–1584 pt.
  • The grid is part of the paragraph-layout cache key.
• Command layout.documentGrid {"type"?, "linesPerPage"?, "charsPerLine"?, "linePitch"?, "charSpace"?}: section scope like the other page-setup commands, one undo step, returns lines per page and characters per line. New catalog row: Layout › Page Setup › Document Grid (403/435).
• UI: the Page Setup dialog has a Document Grid section (no grid / lines only / lines and characters / text snaps to characters, characters per line, lines per page). When the section has a grid, View › Gridlines draws it instead of the drawing grid. New strings are in all 9 catalogs (including et, sr and sr-latn).
• The Asian Typography paragraph options (kinsoku, word wrap…) and kinsoku in layout were already on main. This PR doesn't change them.
• Docs: layout-parity, file-format-parity, target-app-parity (East Asian 15% → 25%), gaps, ROADMAP progress log, parity checklist.

How tested

• crates/layout/src/tests_grid.rs:
  • Every line height is a whole multiple of the pitch, and the first page holds floor(text height / line height) lines.
  • snapToGrid off gives the natural heights.
  • CJK clusters sit at k × pitch, and Latin advances don't change. No assertion depends on font metrics, and the test works when CJK glyphs are missing.
• crates/docx/tests/roundtrip.rs: section grid (linesAndChars, 17.5 pt, negative charSpace), a default grid, and snapToGrid round-trip.
• crates/engine/src/tests.rs: layout.documentGrid sets 40 lines / 30 chars, is one undo step, clamps hostile values, rejects an unknown type, and undoes back to no grid.
• crates/doc unit test: pitch clamping and lines/chars per page.
• Ran: cargo test on doc, docx, layout, engine and ui-egui (lib); clippy -D warnings on those crates; cargo fmt; cargo xtask layers, wasm and parity.
• Checked headlessly with ui_shot: Japanese text on a 30×30 grid, with the gridlines and the dialog shown.

Not done

• Run-level w:snapToGrid isn't read.
• Paragraph spacing isn't counted in grid lines.
• Word's exact vertical placement of glyphs in a grid cell isn't matched. Text is centred, which is close.
• Word's slight right-margin adjustment so that exactly N characters fit isn't done.
• Grid in headers/footers, footnotes and text boxes: body only (footnotes laid out with the body may snap).
• The grid isn't written to RTF or ODT.

Fixes #391

🤖 Generated with Claude Code

[echelon]

Thanks for the contribution, @vangel76! This is now merged into main. If you haven't already, please come join us on Discord: https://discord.gg/artcraft