Opaque billboards impacted by globe translucency

Opaque billboards in front of the globe are always rendered as translucent when globe translucency is enabled and either frontFaceAlpha is < 1 or frontFaceAlphaByDistance is used. This even happens when the far alpha value is 1.0 and the far range is exceeded, at which point the globe should be opaque.

See the following example:

Sandcastle Example

Browser: Chrome 89.0.4389.90
Operating System: macOS Big Sur 11.1

There are a few unexpected things happening here:

• The blue icon is always translucent, except when translucency is disabled. Given it's in front of the globe, I would expect it to always be opaque.
• The red icon is always displayed, even when translucency is disabled. Given it's beneath the surface of the globe, I would only expect to see it when the globe is translucent. The icon is hidden by an opaque globe if I enable World Terrain, but does not appear to behave the same with the default terrain provider. This was also unexpected.

Start with the linked Sandcastle Example and reproduce the behavior in Chrome using the reported globe translucency, frontFaceAlpha, frontFaceAlphaByDistance, and terrain settings. Compare the visibility and opacity of the blue and red billboards with translucency enabled and disabled; done means opaque billboards remain opaque and below-surface billboards are hidden by an opaque globe.