WebGLBuffer object and OpenGL buffer handle interop between JavaScript and C++

Question

I want to use spector.js metadata API to simplify debugging of a WebGL application compiled from C++ using emscripten. Spector.js API expects JavaScript WebGLBuffer objects created via WebGL API. The question is how to get them from the C++ side which operates with raw OpenGL handles. I see two options:

Provide gl buffer handles to js via emscripten C++<->JS API and create WebGL objects from them somehow
Create WebGLBufers on the js side and provide handles to C++ via C++<->JS API

Problem with the first option is that I can't find a way to create a WebGLBuffer from a raw OpenGL buffer handle. Problem with the second option is that I don't see any way to get a raw gl buffer handle from the js WebGLBuffer object to forward it to the C++ code.

Maybe there are also other options?

score 2 · Accepted Answer · 2020-03-04 15:52:00Z

2

Augment the emscripten library. The WebGLObjects are tracked right here

https://github.com/emscripten-core/emscripten/blob/46df50cfd170521d91a31e0a74f2dfdeb4522968/src/library_webgl.js#L112

For example

  javascriptWebGLBuffer = $GL.buffers[openGLBufferId];

  openglBufferId = $GL.buffers.indexOf(javascriptWebGLBuffer);

also see _glGenObject and its usage on how to generate a new WebGLBuffer for both JavaScript and C++

You can plugin spector in that file.

You can use --js-library path-to-file to use your modified library to use it

edited Mar 4, 2020 at 15:52

answered Mar 3, 2020 at 16:06

user128511

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4 Comments

Alexander Over a year ago

Thank you for the reply! I'll report asap when I've tried it.

Alexander Over a year ago

Okay, I see how to inject spector there. But I don't really understand how to get access to $GL from the js library I add.

user128511 Over a year ago

Without liooking into it deeper add a line window.gl = $GL in the library somewhere would be one solution

Alexander Over a year ago

So modification of the emscripten js library is the way to do it. Not perfect, but it does the trick .Thank you.

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