Elemental2 oddities

[Craig Mitchell]

I'm switching to use Elemental2, and it's fantastic.  All the bindings I'll ever need.  A big thank you to all that created it!

There are some strange things though.  Like when setting up a WebGLRenderingContext, we need to pass WebGLContextAttributes.

However, doing:

WebGLContextAttributes contextAttributes = new WebGLContextAttributes();

compiles fine, but at runtime throws:

TypeError: $wnd.WebGLContextAttributes is not a constructor

I figured out I can do this instead:

WebGLContextAttributes contextAttributes = Js.uncheckedCast(JsPropertyMap.of());

But why can't I just use its constructor?  Am I doing something wrong?

[Jens]

Because it is only a dictionary (= a plain JS object)

https://registry.khronos.org/webgl/specs/latest/1.0/#5.2

In JS you simply do:

var canvas = document.getElementById('canvas');
var context = canvas.getContext('webgl', { antialias: false, stencil: true }); // 2nd argument is WebGLContextAttributes
var attributes = context.getContextAttributes();

Looks like it is again defined badly in closure-compiler externs. The generated elemental2 implementation should have a similar structure than for example elemental2 AddEventListenerOption. It is an interface with a static create() method which does exactly what you do in your solution.

See:

https://github.com/google/closure-compiler/blob/dc7f38bb0528b011984ef33a448c7941cf7e0b88/externs/browser/webgl.js#L2918

I think it should be @interface or @record instead of @constructor.

-- J.

[Craig Mitchell]

Thanks again Jens.  Issue raised:  https://github.com/google/closure-compiler/issues/4250