RaTeX — Flutter Integration Guide

Native Flutter rendering of LaTeX math formulas via Dart FFI and CustomPainter. No WebView, no JavaScript.

How it works

LaTeX string
    ↓ RaTeXFfi.parseAndLayout()   [Dart FFI → libratex_ffi]
JSON DisplayList
    ↓ DisplayList.fromJson()       [Dart JSON decode]
DisplayList
    ↓ RaTeXPainter.paint()         [flutter/canvas]
CustomPaint Widget

Out of the box

  1. Add dependency — In pubspec.yaml: ratex_flutter: ^0.0.3, then run flutter pub get. No native build required — the published package includes prebuilt Android .so and iOS XCFramework.
  2. Use — Use RaTeXWidget: 
    RaTeXWidget(
  latex: r'\frac{-b \pm \sqrt{b^2-4ac}}{2a}',
  fontSize: 28,
  onError: (e) => debugPrint('RaTeX: $e'),
)

Installation

Add to your pubspec.yaml:

dependencies:
  ratex_flutter: ^0.0.3

Then run flutter pub get. No native build required — the published package includes prebuilt Android .so and iOS RaTeX.xcframework.

From local path (development)

If you use the package from the RaTeX repo:

dependencies:
  ratex_flutter:
    path: /path/to/RaTeX/platforms/flutter

You must build the native libraries first:

Platform Command
iOS bash platforms/ios/build-ios.sh (produces RaTeX.xcframework)
Android bash platforms/android/build-android.sh (produces .so files)

Prerequisites for building from source: Flutter 3.10+, Dart 3.0+, Rust 1.75+.

Usage

import 'package:ratex_flutter/ratex_flutter.dart';

class MathPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) => Scaffold(
    body: Center(
      child: RaTeXWidget(
        latex: r'\frac{-b \pm \sqrt{b^2-4ac}}{2a}',
        fontSize: 28,
        onError: (e) => debugPrint('RaTeX: $e'),
      ),
    ),
  );
}

Low-level CustomPainter

import 'package:ratex_flutter/ratex_flutter.dart';

final dl      = RaTeXEngine.instance.parseAndLayout(r'\sum_{n=1}^\infty \frac{1}{n^2}');
final painter = RaTeXPainter(displayList: dl, fontSize: 24);

// In a CustomPaint widget:
CustomPaint(painter: painter, size: Size(painter.widthPx, painter.totalHeightPx))

Inline formula (mixed text + LaTeX)

Flutter's RichText + WidgetSpan is the recommended approach for mixing plain text with inline formulas. Use PlaceholderAlignment.middle for vertical centering:

import 'package:flutter/material.dart';
import 'package:ratex_flutter/ratex_flutter.dart';

/// Parses [text] with `$...$` inline math markers and returns a [RichText]
/// that intermixes plain [TextSpan]s with [WidgetSpan]s.
Widget buildInlineMath(String text, {double mathFontSize = 18, TextStyle? textStyle}) {
  final style = textStyle ??
      const TextStyle(fontSize: 16, height: 1.8, color: Colors.black87);

  final parts = text.split(r'$');
  final spans = <InlineSpan>[];

  for (int i = 0; i < parts.length; i++) {
    if (parts[i].isEmpty) continue;
    if (i.isEven) {
      // Plain text
      spans.add(TextSpan(text: parts[i], style: style));
    } else {
      // Inline math
      spans.add(WidgetSpan(
        alignment: PlaceholderAlignment.middle,
        baseline: TextBaseline.alphabetic,
        child: RaTeXWidget(
          latex: parts[i],
          fontSize: mathFontSize,
          onError: (e) => debugPrint('RaTeX inline error: $e'),
          loading: const SizedBox.shrink(),
        ),
      ));
    }
  }

  return RichText(text: TextSpan(children: spans));
}

// Usage:
buildInlineMath(
  r'质能等价关系 $E = mc^2$，其中光速 $c \approx 3\times10^8\ \text{m/s}$。',
)

Use $...$ as delimiters inside the string. The $ character is split on, so odd-indexed parts are LaTeX, even-indexed are plain text.

Async (large formulas)

import 'package:flutter/foundation.dart';

final dl = await compute(
  (latex) => RaTeXEngine.instance.parseAndLayout(latex),
  r'\prod_{n=1}^\infty \left(1 - \frac{1}{n^2}\right)',
);

Coordinate system

Same as iOS/Android: all coordinates are in em units, multiplied by fontSize (logical pixels) to get screen coordinates. Y increases downward from the top of the bounding box. The baseline is at Y = height × fontSize.

File map

File Purpose
pubspec.yaml Flutter plugin manifest
ios/ iOS plugin (podspec + RaTeXPlugin.swift); links RaTeX.xcframework
android/ Android plugin (RaTeXPlugin.kt); uses in-package jniLibs for libratex_ffi.so
lib/ratex_flutter.dart Public API: RaTeXEngine, RaTeXWidget
lib/src/display_list.dart Dart JSON types (DisplayList, DisplayItem, …)
lib/src/ratex_ffi.dart Dart FFI bindings to libratex_ffi
lib/src/ratex_painter.dart CustomPainter drawing loop

Publishing to pub.dev (maintainers)

To publish an out-of-the-box package that works without building native code:

  1. Android — Build and copy JNI libs into the package:

    # From repo root
./platforms/android/build-android.sh
cp -R platforms/android/src/main/jniLibs/* platforms/flutter/android/src/main/jniLibs/

  2. iOS — Ensure RaTeX.xcframework is inside the package (not a symlink):

    # From repo root
./platforms/ios/build-ios.sh
# If platforms/flutter/ios/RaTeX.xcframework is a symlink, replace with real copy:
rm -rf platforms/flutter/ios/RaTeX.xcframework
cp -R platforms/ios/RaTeX.xcframework platforms/flutter/ios/

  3. Validate and publish:

    cd platforms/flutter
dart pub publish --dry-run
dart pub publish

    CI: Pushing a version tag (e.g. v0.0.4) runs release-flutter.yml: it builds Android and iOS native libs, injects them into this package, and runs dart pub publish. Ensure the tag matches the version in pubspec.yaml. Repository secret required: PUB_DEV_TOKEN (create at https://pub.dev/settings/tokens).

Libraries

ratex
ratex_flutter