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 real-world fixtures — the contract (an IHK contract form), the summary (a student summary: bullets, wrapped pictures, one table), the thesis (a 48-page thesis with charts, metafile figures and a German TOC) and the Math Guide (LibreOffice's own 63-page Math Guide: a title page, a three-page index, per-section masters, ~35 figure frames and 400 formulas) — still report. The thesis matches LibreOffice's 49 pages and so does the Math Guide at 63 — most of what is left is the engine rules below, not layout:

• A page-anchored frame's coordinates are its page's, but a frame in a header keeps the ones its zone gives it. Both are drawn out of flow; the body one (anchorPage, image.ts) sits behind the text at --page-cycle × (page − 1) + its svg:y.
• The index is its own pagination. A generated TOC is a block atom, so pagination has no inner position to put a spacer at; the node view breaks it between entries itself (tableOfContents.ts) and asks for one recompute when that changes its height.
• A hoisted text box loses the vertical offset it was anchored by. A frame's own offsets are drawn now (docs/architecture/frames.md), and a lifted box takes its anchor paragraph's spacing (docs/architecture/frames.md), but a text box anchored inside a paragraph is a block node here, so the importer lifts it out and it simply follows that paragraph. On the thesis' figure page that leaves its caption 4.7mm high — LibreOffice places the box by its own 19.52cm, we place it after the picture. Attempted and reverted: a top margin of the offset minus the previous block's measured height overshot by 4.5mm (231.2 against 227.7, from 223.0) and improved nothing in the corpus. The anchor paragraph's box is not the right basis — the frame it holds is a float, so its height is the text's alone.
• A page's last line is where the footer band ends. The body margin a file's header or footer reconstructs is the page margin plus the zone's declared height; the zone's own gap to the body sits inside that height (probed — styleResolver.ts). Getting that wrong costs a line on every page, which is worth more than any single block's spacing.
• Chromium floors every painted border to one pixel, so a table's rows come out ~0.25mm too tall each unless the excess is taken off the cell padding (docs/architecture/tables.md).
• Page geometry is document-wide. Headers and footers are per section (each is editable in place), but margins, orientation and format are not: they come from the master page governing the most body blocks (import/odt.ts), so a title page with its own margins is laid out with the body's. The Math Guide's title sits 9.8mm low and 3.3mm left for exactly that reason.
• 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. Attempted and reverted: line-height: 0 on the block with the content's line-height restored by an inline decoration does drop the strut, and measured right on a purpose-built fixture (a 24pt run over 10pt text came to 62.1pt against LibreOffice's 61.8, from 69.0). It cost the contract 22 issues all the same. Two things the strut was quietly holding up: a line of no runs at all — two breaks in a row — collapses to nothing, and the reserved paragraph mark is an ::after on the block, so the same rule takes the last line's height away with it. An empty widget span at the block's end gets that line back but not to the same value. Whatever replaces the strut has to carry both.
• Metafiles are placeholders, and a re-export keeps the placeholder. EMF/WMF/SVM have no JS decoder, so such a frame keeps its box and its label but not its picture (imageFormats.ts) — and what is exported is that placeholder. Charts are drawn now (import/chart.ts), but as a picture: a re-export carries the drawing, not a chart object, since the editor has none.
• A list level's own hanging indent is not read, only the 0.635cm both exports write (LIST_HANGING_CM). A left-set label wider than that overflows into the text, where Word moves the text to the next list tab — reading w:lvl/w:pPr/w:ind w:hanging would settle it. Deliberate for now: in flow, a wide marker pushed the text and cost the thesis fixture a page. (The level's left indent is read at every depth, and a right-set label — markerAlign, which is what the built-in Roman numberings use — grows into the margin, so the case that actually collided is gone.) What a probe of the ODF side turned up, before anything is built on it: LibreOffice honours a nested level's fo:text-indent linearly (−0.300 → label at 2.243cm, −1.000 → 1.543, −1.200 → 1.344, against fo:margin-left="2.540cm") — except at −1.270, the value odf-kit writes for level 2, where it draws its own flat 0.635cm hanging (1.909cm) instead. So reading the attribute back naively moves the markers of our own exports. Whatever rule that is has to be understood before the value is trusted.
• Lines take one word more or fewer than LibreOffice, which is most of the thesis' remaining lineBreak reports. Two causes, both measured on that fixture:
  • LibreOffice compresses inter-word spaces to fit a line, CSS justification only expands. Of 349 full-width justified lines, 91 are narrower in LibreOffice than their natural width here — up to 0.83px per space at 12pt (p99 0.68px). Attempted and reverted: word-spacing: -0.05em on justified blocks. It does fix the break decision (the thesis' page 6 paragraph goes 7 lines → LibreOffice's 6), but the corpus got worse — lineBreak 45 → 43 while lineEnd went 2 → 16, because the tighter spacing also shortens every paragraph's unjustified last line by 1–3mm.
  • Sub-0.1mm engine rounding, which accumulates: matching word widths (11.86mm for haben, on both sides) had drifted 0.45mm apart by the 150th mm of the line. LibreOffice quantizes each glyph advance where Chromium keeps it fractional, and nothing in CSS exposes that.

Findings that did not survive measurement

Kept here so they are not re-derived. Each was checked against soffice on a purpose-built one-page fixture.

• A trailing space on a right-aligned line. LibreOffice counts it exactly as we do (its last glyph lands at 189.0mm, ours at 188.9mm). Hanging it — which is what Word does — moved us 1.0mm away from the reference, so it was reverted.
• Breaking after a slash, and inside a run of dots. Neither engine does either: Sensor/Messinstrument and a 50-dot leader stay one word in both. What LibreOffice really does that we did not is break a word wider than its line; that is fixed (overflow-wrap: break-word).
• A block ending in a hard break. Real — the next paragraph sat 4.7mm too low — but the cause was not the trailing-break <br>: under pre-wrap that adds no line. It was the always-reserved paragraph mark, which is inline content past the break and so opened a line of its own. Fixed in editor.css.

Known ceilings

• A stop's leader is drawn, but the harness can't see it. The fill is CSS generated content, so Range.getClientRects() reads the gap as empty while LibreOffice's PDF has the dots in its text. The contract's Zwischen ...... line reports a lineBreak for that reason alone — compare it by eye, not by this harness. An index leader is real text on both sides, so it is compared: as one token, since how many dots fill the gap is the fill's business (norm). A TOC whose file declares no leader still gets ours.
• 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).