@docen/layout

Pure TypeScript layout engine for docen — zero DOM, zero rendering libraries. The inner ring (text/, block/) measures and breaks text and lays out paragraphs/tables; the outer ring builds on it (flow/ — docx page boxing — is in; fixed/ for pptx shape text and grid/ for xlsx come with their editors).

Consumed by @docen/docx's projection (DocumentOptions → LayoutDoc) and painted by @docen/core's canvas stage.

Design

• Input is a LayoutDoc projection, all-px, style-cascades already resolved. Adapters (docx from Tiptap/ProseMirror, pptx from its shape tree, xlsx from its grid) convert their document units and resolve their style chains exactly once; the engine never sees a styleId, a twip, or a Tiptap node. Only layout semantics keep their OOXML shape (line rules, grid pitch, snap flags) — those are the rules this engine exists to implement.
• FontMetrics is the measuring seam. The engine works from per-code-unit advances supplied by a FontMetrics provider (browserFontMetrics measures through canvas 2d today; headless and server providers slot into the same interface). Misses fall back with a warning — Word's behavior.
• One packer for text, hard breaks, and inline pictures — the unified breaker the DOM route never had. UAX #14 line breaking (linebreak.js) with CJK kinsoku, trailing-space hanging, first-line indent, float-zone width reduction, and per-line OOXML line-height semantics (exact / atLeast / multiple × docGrid pitch, CJK ceil snap).
• Determinism is a contract. Same input → same output every pass — the property the paginator's convergence depends on.

Known boundaries: no GSUB shaping (ligature substitution — advances run slightly wide, conservative for breaking); rowspan cell content counts fully on its start row.

Usage

import { TextMeasurer, browserFontMetrics, layoutBlock } from "@docen/layout";

const measurer = new TextMeasurer(browserFontMetrics);
const laid = layoutBlock(paragraph, 612, { linePitchPx: 25 }, measurer);
// laid.lines — y, height, positioned items, split points

License

• MIT © Demo Macro