Set a callback function in val::object

[fidel espanto]

I'm quite new to emscripten, so please be patient with me :)

My goal is to create a wrapper class with an instance of a VideoDecoder object from WebCodecs API and pass some configurations inside it from C++.

 I'm trying to pass an object called 'init' on the global "VideoDecoder" object, which accepts a callback function on its members: output and error:

LVideoDecoderWebCodecs::LVideoDecoderWebCodecs()

{

    val VideoDecoder = val::global("VideoDecoder");

    if (!VideoDecoder.as<bool>()) {

        EM_ASM(

            console.error("WebCodecs API not available");

        );

    }

    val config = val::object();

    config.set("codec", val("vp8"));

    config.set("codedWidth", val(640));

    config.set("codedHeight", val(480));

    val init = val::object();

    init.set("output", [](val frame) {

        EM_ASM(

            console.log("Got frame: ", frame);

        );

    });

    init.set("error", [](val e) {

        EM_ASM(

            console.error("Error initializing decoder: ", e);

        );

    });

    val decoder = VideoDecoder.new_(init);

    decoder.call<void>("configure", config);

}

The module compiles successfully but when I run it on the browser it says,
wasmapi.js:4543 Uncaught BindingError: _emval_take_value has unknown type

It seems that I can't set a callback function on the init object.

Is there a solution to this? Or what can you suggest I handle this one.

[Brendan Dahl]

Lambdas don't currently work with val. You could do something like this:

struct Init {

void output(val frame) {

EM_ASM(

console.log("Got frame: ", frame);

);

}

void error(val e) {

EM_ASM(

console.error("Error initializing decoder: ", e);

);

}

};

EMSCRIPTEN_BINDINGS(xxx) {

class_<Init>("Init")

.function("output", &Init::output)

.function("error", &Init::error)

;

}

....

// This needs to be deleted at some pointed...

Init* init = new Init();

val decoder = VideoDecoder.new_(init);