Fix #1749 by adding an OIT flag.

[emackey]

Turns out OIT can be easily turned on and off at runtime, for example picking temporarily disables it.

[pjcozzi]

Thanks @emackey. Can you update README.md, add a test, and rename to orderIndependentTranslucency so it is consistent with fxaaOrderIndependentTranslucency, fxaa, and friends?

[bagnell]

OIT uses a few textures and framebuffers. You may want to create/destroy it to create/release those resources.

[pjcozzi]

If this requires anything but completely trivial code, let's do what I suggested in #1749 since there is no value in being able to do this at runtime other than for a tech demo that we already have.

[pjcozzi]

Regardless, this should get pass through the constructors too.

[emackey]

This is moved to the constructors to save resources. Setting to true does not guarantee OIT of course, there are other factors at play, some of them per-frame. Do we need a property to expose whether or not OIT was used on a given frame?

Also, our SceneSpec does not test any of the construction options. It uses an external helper function to construct test scenes with test-suite construction options.

By README.md, did you mean CHANGES.md?

[pjcozzi]

Ah, yes, CHANGES.md.

Do we need a property to expose whether or not OIT was used on a given frame?

Wouldn't worry about it for now.

Tests like these would be OK:

https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Specs/Widgets/CesiumWidget/CesiumWidgetSpec.js#L154

https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Specs/Widgets/Viewer/ViewerSpec.js#L285

We could also add a rendering test with a spy to ensure it disables OIT (assuming the system supports OIT) but it is borderline overkill.

Also, I want to make a few tweaks to cleanup the logic but I won't be able to get to it until next week after FOSS4G.

[emackey]

Tests added, other comments addressed. @pjcozzi just tell me what cleanup is needed and I'll clean it up, or open a separate PR after FOSS4G, but please don't let another branch go stale.

[pjcozzi]

This still needs a readonly like scene3DOnly. I also don't know why the check for options.orderIndependentTranslucency is so complicated, undefined will result in false, right? Or use defaultValue.

Bare with me on the review as I am on travel working around the clock for us.

[emackey]

Great suggestions, thanks. Code is cleaner as a result.

[pjcozzi]

Thanks!