/emscripten-library-generator

A library generator for the emscripten compiler

Primary LanguageJavaScriptMIT LicenseMIT

Emscripten Library Generator

This packages normal JavaScript libraries into emscripten's strange, undocumented library format which can be passed to the emscripten compiler with the --js-library flag. It can also be used to automatically populate the emscripten setting EXPORTED_FUNCTIONS using the --unresolved flag. It works by computing dependency and initialization information for global symbols and automatically prefixing all resolved global symbols with an underscore to match emscripten's output. Top-level statements other than variable or function declarations are not supported (put initialization into a JavaScript function that is called as the first statement inside main() in C++).

Library Generation

Terminal commands:

npm install -g emscripten-library-generator
emscripten-library-generator input1.js input2.js ... > library.js

Example input:

var handles = {};
function Foo(data) {
  this.data = data;
}
function Foo_new(ptr, data) {
  handles[ptr] = new Foo(data);
}
function Foo_delete(ptr) {
  delete handles[ptr];
}

Example output:

mergeInto(LibraryManager.library, {
    handles: {},
    Foo: function (data) {
        this.data = data;
    },
    Foo_new__deps: [
        'handles',
        'Foo'
    ],
    Foo_new: function (ptr, data) {
        _handles[ptr] = new _Foo(data);
    },
    Foo_delete__deps: ['handles'],
    Foo_delete: function (ptr) {
        delete _handles[ptr];
    }
});

Usage from C++:

struct Foo;

extern "C" {
  void Foo_new(Foo *foo, int data);
  void Foo_delete(Foo *foo);
}

struct Foo {
  Foo(int data) : _data(data) {
    Foo_new(this, data);
  }
  ~Foo() {
    Foo_delete(this);
  }
  
private:
  int _data;
};

Unresolved Symbols

Finds all unresolved symbols that start with an underscore, which are assumed to be extern "C" functions in C++. If these symbol names are not specified, the emscripten compiler may omit those functions as dead code and JavaScript won't be able to access them.

Terminal commands (notice the --unresolved flag):

npm install -g emscripten-library-generator
emscripten-library-generator --unresolved input1.js input2.js ... > unresolved.json

Example input:

var timeout = 0;
function wait(value, delay) {
  if (timeout) {
    clearTimeout(timeout);
    _interrupted(value);
  }
  timeout = setTimeout(function() {
    _success(value);
    timeout = 0;
  }, delay);
}

Example output:

["_interrupted","_success"]

Usage from C++:

extern "C" {
  void wait(int value, int delay);

  void interrupted(int value) {
    printf("interrupted: %d\n", value);
  }

  void success(int value) {
    printf("success: %d\n", value);
  }
}