Bindings Synchronization Agent Skill

Cross-Platform Language Bindings Synchronization

When making changes to public Filament C++ APIs, AI agents must ensure the changes are mirrored in the Java and JavaScript/TypeScript binding layers.

1. Trigger Conditions

You must check and update the language bindings if your changes touch any public headers under filament/include/filament/, specifically:

• New/Modified/Deleted Methods on core classes (e.g., View, Engine, Camera, LightManager, RenderableManager).
• Options Structs (e.g., AmbientOcclusionOptions, BloomOptions, FogOptions).

> [!IMPORTANT]

> If you modify options structs defined in filament/include/filament/Options.h, you must run the beamsplitter tool. The tool parses Options.h and automatically updates Java bindings, JavaScript/TypeScript bindings, and C++ JSON serialization files.

>

> Run it via:

> `bash

> cd tools/beamsplitter && go run .

> `

• Enums & Constants (e.g., BlendMode, QualityLevel, AntiAliasing under filament/include/filament/ or nested inside classes).

2. Java & Android JNI Synchronization

All JNI JNI-exported functions use automatic symbol resolution (dynamic mapping), meaning they are mapped by signature rather than a static registration table.

File Mappings

• Java Class: android/filament-android/src/main/java/com/google/android/filament/<ClassName>.java
• JNI C++ Wrapper: android/filament-android/src/main/cpp/<ClassName>.cpp

Guidelines

• API Consistency: Keep method visibility public (unless the API is strictly internal to the Java package). Follow Java naming conventions (camelCase).
• Getter/Setter Completeness: If you add a Setter (e.g., setFoo), always add the corresponding Getter (e.g., isFoo or getFoo).
• JNI Signature:
• Native declarations in Java must be private static native.
• The corresponding C++ function in JNI must be decorated with extern "C" JNIEXPORT <ReturnType> JNICALL Java_com_google_android_filament_<ClassName>_<NativeMethodName>.
• Return values from native C++ booleans should be cast to jboolean using (jboolean) or static_cast<jboolean>().

3. JavaScript & TypeScript Synchronization

Filament uses Emscripten's Embind to export C++ APIs to JS.

File Mappings

• Embind Source: web/filament-js/jsbindings.cpp
• Enums Embind Source: web/filament-js/jsenums.cpp
• TypeScript Definition: web/filament-js/filament.d.ts
• JS Extension Wrappers: web/filament-js/extensions.js

Guidelines

• Embind Registration:
• Register member functions in jsbindings.cpp within the corresponding class_<ClassName>("<JSClassName>") block using .function("methodName", &ClassName::methodName).
• TypeScript Declarations:
• Always update filament.d.ts to match any changes. Every bound C++ method should have a corresponding declaration inside export class <ClassName> to avoid IDE type errors.
• Complex Option Structs:
• If you modify or add fields to an options struct (like BloomOptions), make sure to:
• Register the new fields in jsbindings.cpp using .field("fieldName", &ClassName::Options::fieldName).
• Update the TypeScript interface in filament.d.ts to include the new properties.
• Check if extensions.js contains a prototype-overrides wrapper for merging the options (e.g., Filament.View.prototype.setBloomOptions). Update the default options object if needed.

4. Verification Check

Before concluding a task:

• Double-check JNI signature signatures against the Java class.
• Verify that type bindings and return types match up.
• Verify that TS definitions in filament.d.ts are 100% synchronized.