merman 0.7.0-alpha.1 
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Flutter and Dart FFI bindings for merman headless Mermaid rendering.
merman Flutter/Dart FFI #
Flutter package for the canonical merman-ffi C ABI. The public package name is merman.
Merman renders Mermaid diagrams without a browser. It can parse Mermaid source, return semantic JSON, compute layout JSON, and render SVG through a headless Rust engine. See the project README, FFI protocol, and diagram coverage status for the main library contract.
The package exposes a small Dart API for SVG, semantic JSON, and layout JSON. On Flutter targets,
the plugin also carries the native merman-ffi library, so application code normally opens the
engine with Merman.open() and does not pass a dynamic library path.
Supported Flutter Platforms #
- Android: bundled
libmerman_ffi.soslices underandroid/src/main/jniLibs. - iOS: bundled
MermanFFI.xcframework, linked as a dynamic framework so Dart FFI can useDynamicLibrary.process()without shipping the much larger Rust static archive. - macOS: bundled
Libraries/libmerman_ffi.dylib, linked by CocoaPods. - Windows: bundled
merman_ffi.dll, installed into the Flutter app bundle by CMake. - Linux: bundled
linux/lib/<arch>/libmerman_ffi.so, installed into the Flutter app bundle by CMake.
API #
import 'package:merman/merman.dart';
final merman = Merman.open();
final source = 'flowchart TD\nA[Hello] --> B[World]';
final version = merman.packageVersion;
final svg = merman.renderSvg(
source,
optionsJson: '{"svg":{"pipeline":"readable"}}',
);
final semantic = merman.parseJson(source);
final layout = merman.layoutJson(source);
try {
merman.renderSvg(source, optionsJson: '{');
} on MermanException catch (error) {
print('${error.codeName}: ${error.message}');
}
optionsJson follows the shared schema in
docs/bindings/OPTIONS_JSON.md.
Rendering SVG In Flutter #
Merman.renderSvg returns SVG text; this package does not prescribe a Flutter widget. For highest
visual fidelity, render the SVG in a browser-capable surface such as webview_flutter:
final svg = Merman.open().renderSvg(source);
final controller = WebViewController()
..setJavaScriptMode(JavaScriptMode.unrestricted)
..loadHtmlString('''
<!doctype html>
<html>
<body style="margin:0;background:white">
$svg
</body>
</html>
''');
Mermaid-like SVG can include <style>, <marker>, and <foreignObject>. Those elements are valid
parts of the output: styles preserve theme behavior, markers draw arrowheads, and foreign objects
carry HTML labels. Native Flutter SVG widgets and some rasterizers may ignore or partially support
those elements, so diagrams can lose arrowheads, labels, or styling outside a WebView.
Do not blindly strip those tags in application code. Instead, select an explicit SVG pipeline for the target renderer:
final browserSvg = merman.renderSvg(source); // default parity output
final readableSvg = merman.renderSvg(
source,
optionsJson: '{"svg":{"pipeline":"readable"}}',
);
final resvgSafeSvg = merman.renderSvg(
source,
optionsJson: '{"svg":{"pipeline":"resvg-safe"}}',
);
Use the default parity output for WebView/browser display, readable when a renderer needs text
fallbacks for labels, and resvg-safe for stricter SVG consumers or raster/PDF export paths.
Local Dart Smoke #
Raw dart run does not execute Flutter's platform packaging step, so the smoke example accepts an
explicit native library path for local development:
cargo build -p merman-ffi
cd platforms/flutter
dart pub get
dart run example/smoke.dart ../../target/debug/libmerman_ffi.dylib
Use ../../target/debug/libmerman_ffi.so on Linux and ../../target/debug/merman_ffi.dll on
Windows. In Flutter applications, use Merman.open() without a path.
Building Native Artifacts For The Flutter Package #
Android slices are built from the shared Android script and copied into the Flutter package:
python3 platforms/android/build-android.py --targets aarch64-linux-android x86_64-linux-android
mkdir -p platforms/flutter/android/src/main/jniLibs
cp -R platforms/android/src/main/jniLibs/* platforms/flutter/android/src/main/jniLibs/
iOS uses a Flutter-specific dynamic framework XCFramework:
bash platforms/flutter/build-ios.sh
Desktop artifacts are built with:
bash platforms/flutter/build-desktop.sh --host
For release packaging, use --all on macOS with cargo-zigbuild and zig installed. This creates
the macOS universal dylib plus Linux x86_64/aarch64 and Windows x86_64 artifacts.
Packaging Smoke #
To verify Android plugin packaging through a temporary Flutter app:
python3 platforms/flutter/tool/android-smoke.py
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Flutter and Dart FFI bindings for merman headless Mermaid rendering.
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