bindings.cc

// at end of list of items that call "JS_GL_METHOD"
  JS_GL_METHOD("drawBuffers", DrawBuffers);
  JS_GL_METHOD("extWEBGL_draw_buffers", EXTWEBGL_draw_buffers);

procs.cc

// add to bottom of list of items that use "eglGetProcAddress"
  glDrawBuffers=reinterpret_cast<PFNGLDRAWBUFFERSEXTPROC>(eglGetProcAddress("glDrawBuffersEXT"));

procs.h

// at end
  PFNGLDRAWBUFFERSEXTPROC glDrawBuffers;

webgl.cc

// at bottom add:
GL_METHOD(DrawBuffers) {
  GL_BOILERPLATE;

  v8::Local<v8::Array> buffersArray = v8::Local<v8::Array>::Cast(info[0]);
  GLuint numBuffers = buffersArray->Length();
  GLenum buffers[numBuffers];
  for (size_t i = 0; i < numBuffers; i++) {
    int bufferAttachment = buffersArray->Get(i)->Uint32Value();
    if (bufferAttachment < GL_COLOR_ATTACHMENT0_EXT || bufferAttachment > GL_COLOR_ATTACHMENT15_EXT) {
      Nan::ThrowError("Invalid color attachments");
    }
    buffers[i] = bufferAttachment;
  }

  (inst->glDrawBuffers)(numBuffers, buffers);
}

GL_METHOD(EXTWEBGL_draw_buffers) {
  GL_BOILERPLATE;

  v8::Local<v8::Object> result = Nan::New<v8::Object>();
//   Nan::SetMethod(result, "drawBuffersWEBGL", DrawBuffers);
  result->Set(Nan::New("COLOR_ATTACHMENT0_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT0_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT1_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT1_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT2_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT2_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT3_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT3_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT4_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT4_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT5_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT5_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT6_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT6_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT7_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT7_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT8_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT8_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT9_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT9_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT10_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT10_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT11_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT11_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT12_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT12_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT13_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT13_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT14_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT14_EXT));
  result->Set(Nan::New("COLOR_ATTACHMENT15_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_COLOR_ATTACHMENT15_EXT));

  result->Set(Nan::New("DRAW_BUFFER0_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER0_EXT));
  result->Set(Nan::New("DRAW_BUFFER1_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER1_EXT));
  result->Set(Nan::New("DRAW_BUFFER2_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER2_EXT));
  result->Set(Nan::New("DRAW_BUFFER3_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER3_EXT));
  result->Set(Nan::New("DRAW_BUFFER4_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER4_EXT));
  result->Set(Nan::New("DRAW_BUFFER5_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER5_EXT));
  result->Set(Nan::New("DRAW_BUFFER6_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER6_EXT));
  result->Set(Nan::New("DRAW_BUFFER7_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER7_EXT));
  result->Set(Nan::New("DRAW_BUFFER8_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER8_EXT));
  result->Set(Nan::New("DRAW_BUFFER9_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER9_EXT));
  result->Set(Nan::New("DRAW_BUFFER10_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER10_EXT));
  result->Set(Nan::New("DRAW_BUFFER11_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER11_EXT));
  result->Set(Nan::New("DRAW_BUFFER12_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER12_EXT));
  result->Set(Nan::New("DRAW_BUFFER13_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER13_EXT));
  result->Set(Nan::New("DRAW_BUFFER14_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER14_EXT));
  result->Set(Nan::New("DRAW_BUFFER15_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_DRAW_BUFFER15_EXT));

  result->Set(Nan::New("MAX_COLOR_ATTACHMENTS_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_MAX_COLOR_ATTACHMENTS_EXT));
  result->Set(Nan::New("MAX_DRAW_BUFFERS_WEBGL").ToLocalChecked(), Nan::New<v8::Number>(GL_MAX_DRAW_BUFFERS_EXT));

  info.GetReturnValue().Set(result);
}

webgl.js

// included for context, but already in webgl.js
var gl = nativeGL.WebGLRenderingContext.prototype

// extend getExtension with the following
gl.getExtension = function getExtension (name) {
  var str = name.toLowerCase()
  if (str in this._extensions) {
    return this._extensions[str]
  }
  var ext = null
  switch (str) {
    case 'webgl_draw_buffers':
      ext = this.extWEBGL_draw_buffers();
      ext.drawBuffersWEBGL = this.drawBuffers.bind(this)
      break
  }
  if (ext) {
    this._extensions[str] = ext
  }
  return ext
}