Billboards rendering partially in 2D at particular zoom level

[Dphalos]

What happened?

While in 2D mode, some billboards' billboard fragment depths lose to terrain fragment depths between two frustums. You can observe it in a really specific position of camera, terrain and billboard. It is easier to produce with a device you can do smoother zoom (touch-pad etc.)

2D_frustums_bug.mp4

Reproduction steps

1. Add a TerrainProvider
2. Add Billboards
3. Switch to 2D mode
4. Zoom out slowly until you produce it.

Sandcastle example

https://sandcastle.cesium.com/#c=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

Environment

Browser: Chrome 123.0.6312.123 (Official Build) (64-bit)
CesiumJS Version: 1.116
Operating System: Windows 11

[ggetz]

Thanks for the detailed report @Dphalos!