edentext/tests/render-parity

Render parity

Opens the same document in LibreOffice and in the editor, then compares the resulting text layout. Everything else in tests/ compares documents at the model level (JSON → export → import); this leg is the only one that checks what a page actually looks like.

npm run test:parity:fixtures   # (re)generate the baseline .docx corpus
npm run test:parity            # whole corpus
npm run test:parity -- path/to/file.docx --json report.json

Exit code 1 when any document differs. --json also dumps both sides' lines (y, x, x2 in mm, per page) — that dump is what you diagnose from.

How it compares

	reference	editor
render	soffice --convert-to pdf	Playwright Chromium, real app, real file input
read	pdftotext -bbox-layout (word boxes, pt)	Range.getClientRects() (word boxes, px)

Both sides are normalized to mm from the top-left of each page, grouped into lines, and compared as: page count → line count → line text → line position. Comparison is whitespace-insensitive, because the spell-check decorations split text nodes mid-word and the two engines needn't agree on word boundaries — only on what sits on a line.

Reported differences are pageCount, lineCount, lineBreak (same line, different words) and position (same words, off by more than POS_TOL_MM). Comparison of a page stops at the first line-level divergence, since everything after it is noise.

Prerequisites

apt-get install -y --no-install-recommends libreoffice-writer poppler-utils
npm install --no-save playwright-core && npx playwright-core install chromium
cp src/assets/fonts/*.ttf /usr/local/share/fonts/ && fc-cache -f

The font step is not optional. LibreOffice renders with system fonts; without the repo's own TTFs installed it substitutes DejaVu for Liberation Serif and every line breaks differently for a reason that is not a bug. With them, both engines resolve Times New Roman → Liberation Serif, Arial → Liberation Sans, Calibri → Carlito, Cambria → Caladea — the same files the editor bundles.

The runner starts npm run dev on port 5199 itself if nothing answers there.

Fixtures

make-fixtures.mjs authors the baseline corpus with the docx lib directly, not through src/lib/export/docx.ts — otherwise the corpus would test our exporter against itself. Real-world .docx/.odt files dropped into fixtures/ are picked up too. The directory is gitignored: run the generator once, and keep whatever real-world files you test against local.

Differences that are not editor bugs

• Justified text. LibreOffice compresses inter-word spaces (measured: 0.864mm against a natural 1.058mm) to pull one more word onto a line. CSS justification only stretches, and Chromium exposes no minimum-word-spacing control, so a justified line may end one word short. 02-blocks reports this permanently.
• Omitted properties of built-in styles. For a style it recognizes by name, LibreOffice fills what the file leaves out from its own defaults (a Heading with no spacing gets 0.42cm before). Word uses only what the file declares, and so do we — so fixtures must declare heading spacing and font explicitly, or the reference disagrees with Word rather than with us.

Prerequisites, part two: Calibri Light

Word's default theme heading font. LibreOffice's substitution table knows Calibri but not Calibri Light, so without an alias it falls to fontconfig's generic — DejaVu Serif, a serif heading nothing else renders. Word substitutes plain Calibri, and so does the editor (global.css), so give LibreOffice the same answer:

<!-- /etc/fonts/conf.d/30-calibri-light.conf, then fc-cache -f -->
<match target="pattern">
  <test name="family"><string>Calibri Light</string></test>
  <edit name="family" mode="prepend" binding="strong"><string>Carlito</string></edit>
</match>

Open findings

What the three real-world fixtures — the contract (an IHK contract form), the summary (a student summary: bullets, wrapped pictures, one table) and the thesis (a 48-page thesis with charts, metafile figures and a German TOC) — still report:

• A frame's vertical anchor offset is ignored. A wp:anchor carries a y offset from its paragraph; the editor floats it at the anchor itself, so a top-and-bottom wrapped figure sits where its caption paragraph is instead of where Word puts it (the thesis' page 15, 131mm out). The horizontal offset round-trips (wrapOffset); the vertical one has no CSS equivalent while the frame stays in flow.
• One header/footer set for the whole document. Word gives every section its own, including its own first page; the contract's second section repeats the letterhead on page 10 and the body starts 25mm lower there than here.
• Dot leaders. LibreOffice fills a TOC entry to its page number with dots; the editor's index lays the number out with flex and leaves the gap empty.
• A block ending in a hard break renders one line too many. ProseMirror appends a trailing-break <br> so the empty last line stays caret-reachable, but under white-space: pre-wrap that line already exists. Hiding the hack node fixes the height and costs the caret that line, so it is hidden only after an inline atom, where there is no such line (editor.css). Reproduces natively with Shift+Enter, no import needed.
• Chromium does not break after a slash, LibreOffice does — "Sensor/Messinstrument" stays one word in a narrow table cell and wraps a line later.
• Line height follows the paragraph, not the line. The block's CSS strut applies to every line; a word processor takes each line's own runs and the paragraph mark only on the last. The mark's font rides the block (blockFontSize.ts), and a paragraph whose runs all agree takes theirs — which covers everything the corpus has. A paragraph of mixed sizes still struts at the block's.
• Charts and metafiles are placeholders. No renderer exists for either, so an undrawable frame keeps its box and its label but not its picture (imageFormats.ts). Exporting writes the placeholder back out — the original is gone from the moment it is imported.
• Tabs that wrap lose their advance. Six consecutive tabs at a line end stay on that line in Chromium and the continuation starts at the margin; LibreOffice carries the tab positions onto it (91mm apart in the contract).
• A run of dots is one unbreakable word to Chromium, while LibreOffice breaks inside it — a dotted fill-in line wraps at a different place.
• A list marker sits where the browser puts it, not at the hanging indent. The level's w:ind w:hanging reaches the text (which lands at Word's 1.27cm) but not the bullet: CSS gives ::marker no position, and Chromium sets it flush against the text, ~4mm right of where Word and LibreOffice draw it. Only a ::before marker could place it, which listMarker.ts and every ordered format ride on.
• A trailing space counts toward a right-aligned line under white-space: pre-wrap, pushing the text ~1.2mm left of where LibreOffice puts it.
• Lines whose natural width lands within ~0.2mm of the right margin may take one word more or fewer than LibreOffice. Sub-0.1mm engine rounding, not a layout rule.

What tab stops (tabStops.ts) deliberately left out, none of it exercised by a fixture:

• Leader characters (w:tab w:leader, style:leader-text) are dropped — the dotted run before a TOC page number. odf-kit can't emit them either.
• The default tab interval is fixed at 1.25cm, so a file's own w:defaultTabStop / style:tab-stop-distance is ignored. It is the CSS tab-size, which the measuring pass leaves to handle every tab past the last custom stop.
• Header/footer zones get no stops: an inactive zone is static HTML from generateHTML, which no ProseMirror plugin reaches.

Known ceilings

• Lines are grouped by vertical band, so multi-column text on one page merges columns into single lines. Columns fixtures need per-block grouping first.
• Only where text sits is compared — not what it looks like. A dropped colour, highlight, fill, border or image changes nothing this harness can see, so a green run does not mean the page matches. Word's highlighter pen went unread through several rounds of green reports. Check that by eye: pdftoppm -r 96 -png the LibreOffice PDF beside a Playwright screenshot of the same page. Two traps there — the app's toolbar and ruler cover the top ~85px of a page in the viewport, and LibreOffice caches font matching per user profile, so a reused profile keeps substituting the font it resolved before 30-calibri-light.conf existed.
• LibreOffice is the reference, not Word. They agree on the layout rules exercised here, but not on everything (e.g. Word's own line-height rounding).