Workaround Safari 9 WebGL bug

[pjcozzi]

Not for 1.13 today.

Discussion: https://twitter.com/pjcozzi/status/638390320619761664

If we need to workaround this, replace all uses of WebGLRenderingContext with the actual constant, e.g.,

WebGLRenderingContext.LESS

becomes

0x0201 // WebGLRenderingContext.LESS

@lilleyse let's discuss.

[pjcozzi]

Should be fixed in https://bugs.webkit.org/show_bug.cgi?id=148449 but doesn't work yet in WebKit r189243 (02 September 2015).

[mramato]

Still broken in r189485 (September 8th). If iOS 9 does get released tomorrow, I'm assuming Cesium will be broken.

[mramato]

iOS 9 will be released on September 16

[pjcozzi]

@lilleyse can you do this soon? Unfortunately, we're going to need this workaround. I think the best approach is to introduce a new static class like ContextLimits with _all _ the constants from the spec (perhaps called ContextConstants or WebGLConstants).

[mramato]

@pjcozzi should we make an announcement on the mailing list ahead of time? No need to be too negative on Safari, but just mention that it will break existing Cesium apps and people shouldn't upgrade iOS or Safari if they need Cesium until we release a workaround (or Apple releases a fix).

[lilleyse]

Yes I can start working on this today.

[lilleyse]

There are many areas that already hard code constants, like https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Renderer/BufferUsage.js#L11-L14

Should I modify all of these to use the new constants class as well?

[pjcozzi]

Should I modify all of these to use the new constants class as well?

Yes, those are very old...before I even knew of WebGLRenderingContext.

@pjcozzi should we make an announcement on the mailing list ahead of time?

Yes, go ahead.