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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Object.create(canvas.getContext())
Date: Wed, 15 Nov 2017 02:32:10 +0100
Organization: PointedEars Software (PES)
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Jan Bruns wrote:

> Thomas 'PointedEars' Lahn:
>> […] this is particulary true of host objects as this one.  If subclassing
>> does not work either (or cannot be assumed to be available), create a
>> wrapper object.
> 
> That's what I wanted to avoid.
> 
> Open GL, GL ES, and webgl are all APIs that hide obejct oriented
> programming aspects by some state mechanism. For example, to change some
> object's property often means to first set the object reference to some
> "current object" state using some API method, to finally change the
> property of that "current object" using some other API method.
> 
> This is beacause initial OpenGL was focused on plain C usage, I guess.

WebGL is an *object-oriented* API based on OpenGL ES 2.0, so I do not see 
your point.
 
> Wrapping all the webgl methods explicitly just to get some functionality
> that the prototype chain and the API's host code could do doesn't sound
> very attractive either, so I'll decide to put the burden to distungish
> native API calls from helper API calls on some higher level helper API.

Your choice.  I see that subclassing does not work in this case.

But it appears to be rather easy to create such a wrapper, at least in 
Chromium 57:

  var my = (function () {
    var canvas = document.createElement("canvas");
    var context = canvas.getContext("webgl");
    var proto = Object.getPrototypeOf(context);

    function WebGLWrapper (context)
    {
      this.context = context;
    }

    /* Wrap built-in methods */
    Object.assign(WebGLWrapper.prototype, (function () {
      var wrappedMethods = Object.create(null);

      // Object.keys(proto).forEach(function (key) {
      Object.keys(proto).forEach((key) => {
        try
        {
          if (typeof proto[key] == "function")
          {
            wrappedMethods[key] = (function (freeKey) {
              return function (...args) {
                // this.context[freeKey].apply(this.context, arguments);
                return this.context[freeKey](...args);
              };
            }(key));
          }
        }
        catch (e) {}
      });

      return wrappedMethods;
    }()));

    Object.assign(WebGLWrapper.prototype, {
      /* custom methods */
    });

    return {
      /** @memberOf my */
      WebGLWrapper: WebGLWrapper
    };
  }());

  // gl = new my.WebGLWrapper(gl);

Barely tested.
 
>> If available, you can use “Proxy” (ECMAScript 2015+) or
>> “__noSuchMethod__” (Mozilla JavaScript 43+ only, obsolete) to implement
>> seamless access.
> 
> Didn't know about that, but currently looks like much of browser
> specifics

WebGL is browser-specific.  “Proxy” is not, in general.  However, Internet 
Explorer supports WebGL, but its JScript version does not implement either 
“Proxy” or “__noSuchMethod__”, which might be a showstopper for that 
approach.

> that don't have anything to do with webgl.

Yes, it is a general approach.  Your point being?

-- 
PointedEars
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