AnalyticalGraphicsInc/cesium — pull request #576 by chris-cooper (2013-03-20 00:02:00+00:00)
Title: optimize imagery layer alpha=0

I think this is what Kevin had in mind and it seems to be basically working. I've kept it simple for a first pass so it just supports an alpha value (not a function).

As per this thread: https://groups.google.com/d/topic/cesium-dev/eZ-_QfHPRk0/discussion