Steffen Becker
9be1578b97
Both come from the document's language, read off Intl: the symbol's side and spacing, the short date's order and padding. Each minted data style names that language — without it LibreOffice prints its own locale's separators (probed: a German document's 1.234,00 € came out $1,234.00). A date is a serial day from LibreOffice's day 0, 1899-12-30. Word's formula dialog offers no date, so the DOCX leg uses the field's \@ picture. Also drops a document's name from three older comments.
107 lines
6.2 KiB
Markdown
107 lines
6.2 KiB
Markdown
# Formulas
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Insert/edit a mathematical formula (`editor/extensions/formula.ts`, `components/FormulaDialog.svelte`),
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round-tripping to an embedded ODF formula object and to Word's OMML.
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## One LaTeX string is the model
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The `formula` node stores **`latex`** and a `display` flag — nothing else. Everything is derived:
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```
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latex ──parse──▶ AST ──▶ MathML (screen + .odt)
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└──▶ OMML (.docx)
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OMML ──parse──▶ AST ──▶ latex (.docx import)
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MathML──parse──▶ AST ──▶ latex (.odt import)
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```
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Foreign markup is parsed into the AST and re-serialized, never passed through. That is why the
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node view may set `innerHTML` — the MathML it renders is always our own output, so a foreign
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`annotation-xml` can't smuggle in HTML. It also means an imported formula is always editable;
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there is no read-only state to fall back to.
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The price: a construct outside the AST degrades. Unknown OMML/MathML elements recurse into
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their `m:e`/child rows, so content survives even where structure doesn't — the same trade
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LibreOffice makes routing OMML through StarMath.
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`src/lib/math/`: `latex.ts` (AST types, parser, serializer, symbol table), `mathml.ts`,
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`omml.ts`. AST kinds: `row`, `txt` (`i`/`n`/`o`/`f` = identifier/number/operator/upright name),
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`frac`, `script`, `sqrt`, `fence`, `nary`, `acc`, `matrix`, `space`.
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## The LaTeX subset
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`\frac`, `_`/`^`, `\sqrt[n]{}`, `\left…\right`, the n-ary operators with limits, the accents,
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`matrix`/`pmatrix`/`bmatrix`/`Bmatrix`/`vmatrix`/`cases`, the upright function names, `\text{}`
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/`\mathrm{}`, greek + the common operators and relations, `{}` grouping, `&` / `\\`, and the
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spacing macros. **Not** supported, deliberately: `align` environments, `\substack`, user macros,
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color. An unknown macro degrades to `\text{name}` rather than vanishing.
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Two invariants the tests pin (`tests/unit/math.test.ts`, `tests/unit/docx-formula.test.ts`):
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- `astToLatex(parseLatex(x)) === x` for every stored source. Without it, opening an imported
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formula in the dialog and pressing Apply would silently rewrite it.
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- A literal `^` or `_` in an imported run's **text** is escaped on the way out (Word documents
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contain typed-in code like `corr.^2`), or re-parsing would read it as a script marker.
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- Whitespace inside an OMML run is dropped (`omml.ts` `tokenize`): math layout ignores it, and
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keeping it breaks the invariant above.
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## STIX Two Math is required, not decoration
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MathML is typeset by the browser natively — no KaTeX/MathJax. But Chromium needs a font with
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an **OpenType MATH table**: measured in this container with only the bundled Liberation/Carlito
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faces installed, `∑` and `ϕ` render as *nothing* and `(` `)` stay glyph-height beside a
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fraction. `src/assets/fonts/STIXTwoMath-Regular.woff2` (OFL, the Fontsource latin subset —
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the MATH table and the operators survive it) is bundled and wired in `global.css`;
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`editor.css` puts it first in the `math` font stack. Word uses Cambria Math for the same job.
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## ODF
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Export (`export/odt.ts`, sentinel `MTH` U+E012, pass `applyFormulas` right after `applyImages`):
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a `<draw:frame text:anchor-type="as-char" draw:style-name="MthFr">` holding
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`<draw:object xlink:href="./Formula{n}"/>`, plus `Formula{n}/content.xml` — an ODF formula
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sub-document whose root *is* the MathML — and two manifest entries (`Formula{n}/` as
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`application/vnd.oasis.opendocument.formula`, its `content.xml` as `text/xml`).
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- **No `svg:width`/`svg:height` on the frame, on purpose.** With a size LibreOffice scales the
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object to fill it (a frame measured at the dialog's preview font size magnified the formula
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~1.5×); without one it typesets at the natural size, matched to the body text. Verified by
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rendering through `soffice`.
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- `MthFr` carries `style:vertical-pos="middle" style:vertical-rel="text"`, what LibreOffice
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writes for its own formula frames. `bottom`/`baseline` was tried and drops the formula below
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the line.
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- The LaTeX rides in `<annotation encoding="application/x-tex">` so our own files re-import
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exactly. **LibreOffice strips it** and substitutes a StarMath annotation, so the fallback
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path (parse its MathML back to LaTeX) is the one that actually runs after a LO re-save — and
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it reproduces the source exactly (`tests/lo-roundtrip.test.ts`).
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- **`display` is read off the paragraph, not the object** (`import/odt.ts` `aloneInParagraph`):
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ODF has no inline/display flag, and LibreOffice writes `display="block"` on every formula it
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re-saves, so trusting the attribute turned every inline formula into a displayed one.
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## DOCX
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Export (`export/docx.ts`, sentinel `MTH`, post-pack pass `applyFormulasDocx` beside
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`applyTextBoxesDocx`): the run holding the sentinel is replaced by `<m:oMath>`, or by
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`<m:oMathPara>` when `display` — which is what centers it on its own line. The namespace is
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declared inline on the `m:` element, like the `wps`/`a` namespaces in the text-box XML.
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Import: `m:oMath`/`m:oMathPara` sit **beside** the `w:r` runs in their own namespace, so
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`convertInline` picks them up before its `namespaceURI !== W` guard — that guard is why every
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formula in a Word document was silently dropped before this feature. `m:oMathPara` →
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`display: true`. Word stores no size for a formula, and neither do we.
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## A pasted formula is a picture, not a formula
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Real documents mix both: one will carry OMML formulas *and* equations its author pasted
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as raster images. Those import as `image` nodes and offer the image toolbar's wrap options on
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click — in Word and LibreOffice too. Nothing short of OCR changes that, so a click that offers
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wrap options instead of the formula dialog is the document's doing, not a broken import.
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## Testing note
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`npm run test:lo`'s formula leg needs the **`libreoffice-math`** package — LibreOffice is
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modular and Writer alone cannot hold a formula object, so without it every formula is dropped
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on load without a word (measured: converting a formula-bearing `.docx` with a Writer-only
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install yields an `.odt` with zero formulas). The leg then fails on "both objects survive", which
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looks like a broken export but is the missing component. Check `dpkg -l | grep
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libreoffice-math` before believing that failure. A desktop LibreOffice ships Math; only
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stripped-down server/container installs don't.
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