RaTeX

简体中文 | English

KaTeX-compatible math rendering engine in pure Rust — no JavaScript, no WebView, no DOM.

One Rust core, one display list, every platform renders natively.

\frac{-b \pm \sqrt{b^2-4ac}}{2a}   →   iOS · Android · Flutter · React Native · Web · PNG · SVG · PDF

→ Live Demo — type LaTeX and compare RaTeX vs KaTeX side-by-side · → Support table — RaTeX vs KaTeX across all test formulas · → Web benchmark — head-to-head perf in the browser

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Why RaTeX?

Every major cross-platform math renderer today runs LaTeX through a browser or JavaScript engine — a hidden WebView eating 50–150 MB RAM, startup latency before the first formula, no offline guarantee. KaTeX is excellent on the web, but on every other surface — iOS, Android, Flutter, server-side, embedded — you're either hosting a WebView or shelling out to headless Chrome.

RaTeX is the same KaTeX-compatible math engine compiled to a portable Rust core, so the same renderer runs natively everywhere — and produces byte-identical output across every target.

	KaTeX	MathJax	RaTeX
Runtime	JS (V8)	JS (V8)	Pure Rust
Surfaces it runs on	Web only*	Web only*	iOS · Android · Flutter · RN · Web · server · SVG · PDF
Mobile	WebView wrapper	WebView wrapper	Native
Server-side rendering	headless Chrome	mathjax-node	Single binary, no JS runtime
Output substrate	DOM (<span> tree)	DOM / SVG	Display list → Canvas / PNG / SVG / PDF
Memory	GC / heap	GC / heap	Predictable, no GC
Offline	Depends	Depends	Yes
Syntax coverage	100%	~100%	~99%

_{* Embeddable in non-web targets only by hosting a WebView or headless browser, which most native and server contexts can't tolerate.}

On the web specifically, KaTeX has a decade of V8 JIT optimization behind it and remains the obvious choice for web-only projects. RaTeX's contribution isn't beating it on its home turf — it's being the only KaTeX-compatible engine that runs natively on every other surface, with pixel-identical output across all of them.

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What it renders

Math — ~99% of KaTeX syntax: fractions, radicals, integrals, matrices, environments, stretchy delimiters, and more.

Chemistry — full mhchem support via \ce and \pu:

\ce{H2SO4 + 2NaOH -> Na2SO4 + 2H2O}
\ce{Fe^{2+} + 2e- -> Fe}
\pu{1.5e-3 mol//L}

Physics units — \pu for value + unit expressions following IUPAC conventions.

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Platform targets

Platform	How	Status
iOS	XCFramework + Swift / CoreGraphics	Out of the box
Android	JNI + Kotlin + Canvas · AAR	Out of the box
Flutter	Dart FFI + CustomPainter	Out of the box
React Native	Native module + C ABI · iOS/Android views	Out of the box
Compose Multiplatform	Kotlin Multiplatform + Compose Canvas · Android / iOS / JVM Desktop	Via RaTeX-CMP
Web	WASM → Canvas 2D · <ratex-formula> Web Component	Out of the box
Server / CI	tiny-skia → PNG rasterizer	Out of the box
SVG	ratex-svg → self-contained vector SVG	Out of the box
PDF	ratex-pdf → vector PDF with embedded KaTeX fonts	Out of the box

Screenshots

From the demo apps in demo/screenshots/.

iOS	Android
Flutter (iOS)	React Native (iOS)
Compose Multiplatform

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Architecture

flowchart LR
    A["LaTeX string\n(math · \\ce · \\pu)"]
    subgraph core["Rust core"]
        B[ratex-lexer]
        C[ratex-parser\nmhchem \\ce / \\pu]
        D[ratex-layout]
        E[DisplayList]
    end
    F[ratex-ffi\niOS · Android · Flutter · RN]
    G[ratex-wasm\nWeb / Canvas 2D]
    H[ratex-render\nPNG · tiny-skia]
    I[ratex-svg\nSVG]
    J[ratex-pdf\nPDF]
    A --> B --> C --> D --> E
    E --> F
    E --> G
    E --> H
    E --> I
    E --> J

Loading

Crate	Role
ratex-types	Shared types: DisplayItem, DisplayList, Color, MathStyle
ratex-font	KaTeX-compatible font metrics and symbol tables
ratex-lexer	LaTeX → token stream
ratex-parser	Token stream → ParseNode AST; includes mhchem \ce / \pu
ratex-layout	AST → LayoutBox tree → DisplayList
ratex-ffi	C ABI: exposes the full pipeline for native platforms
ratex-wasm	WASM: pipeline → DisplayList JSON for the browser
ratex-render	Server-side: DisplayList → PNG (tiny-skia)
ratex-svg	SVG export: DisplayList → SVG string
ratex-pdf	PDF export: DisplayList → PDF bytes (pdf-writer, embedded CID fonts)

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Quick start

Requirements: Rust 1.70+ (rustup)

git clone https://github.com/erweixin/RaTeX.git
cd RaTeX
cargo build --release

Render to PNG

echo '\frac{1}{2} + \sqrt{x}' | cargo run --release -p ratex-render -- --color '#1E88E5'

echo '\ce{H2SO4 + 2NaOH -> Na2SO4 + 2H2O}' | cargo run --release -p ratex-render

Render to SVG

# Default: glyphs as <text> elements (correct display requires KaTeX webfonts)
echo '\frac{1}{2} + \sqrt{x}' | cargo run --release -p ratex-svg --features cli -- --color '#1E88E5'

# Standalone: embed glyph outlines as <path> — no external fonts needed
echo '\int_0^\infty e^{-x^2} dx = \frac{\sqrt{\pi}}{2}' | \
  cargo run --release -p ratex-svg --features "cli embed-fonts" -- \
  --output-dir ./out

The standalone feature (enabled by cli) reads KaTeX TTF files from --font-dir and embeds glyph outlines directly into the SVG, producing a fully self-contained file that renders correctly without any CSS or web fonts.

The embed-fonts feature (implicitly enables standalone) bundles the same TTFs via the ratex-katex-fonts crate, so no --font-dir is needed and builds from crates.io stay self-contained. To refresh bundled fonts after upgrading KaTeX, run scripts/sync-katex-ttf-to-font-crate.sh.

Render to PDF

# `cli` implies `embed-fonts`: KaTeX TTFs are bundled via ratex-katex-fonts (--font-dir is ignored)
echo '\frac{1}{2} + \sqrt{x}' | cargo run --release -p ratex-pdf --features cli -- --output-dir ./out

# Equivalent font loading (explicit embed-fonts)
echo '\ce{H2SO4 + 2NaOH -> Na2SO4 + 2H2O}' | \
  cargo run --release -p ratex-pdf --features "cli embed-fonts" -- --output-dir ./out

The ratex-pdf crate writes one .pdf per non-empty line from stdin. Options include --output-dir (default output_pdf), --font-size, --dpr, and --inline (text style instead of display). The render-pdf binary always loads fonts from ratex-katex-fonts, so --font-dir does not change embedding. For library use without embed-fonts, set PdfOptions.font_dir to your KaTeX TTF directory instead.

Browser (WASM)

npm install ratex-wasm

<link rel="stylesheet" href="node_modules/ratex-wasm/fonts.css" />
<script type="module" src="node_modules/ratex-wasm/dist/ratex-formula.js"></script>

<ratex-formula latex="\frac{-b \pm \sqrt{b^2-4ac}}{2a}" font-size="48" color="#1E88E5"></ratex-formula>
<ratex-formula latex="\ce{CO2 + H2O <=> H2CO3}" font-size="32"></ratex-formula>

See platforms/web/README.md for the full setup.

Platform glue layers

Platform	Docs
iOS	platforms/ios/README.md
Android	platforms/android/README.md
Flutter	platforms/flutter/README.md
React Native	platforms/react-native/README.md
Compose Multiplatform	RaTeX-CMP
Web	platforms/web/README.md

Run tests

cargo test --all

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Equation numbering and \tag

RaTeX aims for KaTeX-compatible rendering. Automatic equation numbering is not implemented:

• No auto-numbering for equation, align, gather, alignat, etc. (their non-starred forms render the same as the starred forms).
• To display a number/label, use explicit \tag{...} or \tag*{...} at the end of a row (amsmath semantics).
• \notag / \nonumber are treated as no-ops when auto-numbering is not present.

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Acknowledgements

RaTeX owes a great debt to KaTeX — its parser architecture, symbol tables, font metrics, and layout semantics are the foundation of this engine. Chemistry notation (\ce, \pu) is powered by a Rust port of the mhchem state machine.

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Contributing

See CONTRIBUTING.md. To report a security issue, see SECURITY.md.

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License

MIT — Copyright (c) erweixin.