Can I register my own emscripten::val <-> C++ type converter?

[svenpilz]

Hi!

Is it possible to hook into embind, such that I can specify conversion from/to emscripten::val for C++ types? For example, I would like to map Eigen types to corresponding Three.js ones, for which value_object might not be sufficient, as I need the whole JS object at once to set up the type on the C++ side.

Or phrased differently. Can a value_object have a constructor taking emscripten::val and can I provide lambdas for value_object members, that take a reference to the underlying object as argument?

Like

value_object<Eigen::MatrixXd>{"Matrix"}
    .constructor([](const emscripten::val& value) {
        Eigen::MatrixXd object;
        object.resize(value["rows"].as<int>(), value["cols"].as<int>());

        // set up the rest ...

        return object; 
    })
    .field("rows", [](const Eigen::MatrixXd& self) { return self.rows(); })
    .field("elements", [](const Eigen::MatrixXd& self) { return  toTypedArray(self.data())});

Thanks and greetings from Berlin.

[sbc100]

@brendandahl ?

[brendandahl]

There's not an official/documented way to do this currently. You could set up your own conversion, but this may break in the future.

namespace emscripten {
namespace internal {


template <>
struct BindingType<your_type> {
    using ValBinding = BindingType<val>;
    using WireType = ValBinding::WireType;


    static WireType toWireType(const your_type& yourObj) {
        val obj = val::object();
        // ... copy data from yourObj
        return ValBinding::toWireType(obj);
    }


    static your_type fromWireType(WireType value) {
        val val = ValBinding::fromWireType(value);
        your_type mine;
        mine.set(val);
        return mine;
    }
};


template <typename T>
struct TypeID<T,
              typename std::enable_if_t<
                  std::is_same<typename Canonicalized<T>::type, your_type>::value>> {
    static constexpr TYPEID get() { return TypeID<val>::get(); }
};
}}