Lighting issues with glTF rendering

[mramato]

Check out the Milk Truck and Draco Compressed Model options in our 3D Models demo:

https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/?src=3D%20Models.html

The Milk Truck seems overly dark no matter what time of day it is, this is the brightest I could get it, but maybe this is correct?

Meanwhile, the Draco compressed version of the same model is super washed out:

I also just noticed the "fuzzy" Cesium logo on the hood.

Why do these two models look so different?

@lilleyse or @likangning93 any thoughts here?

[lilleyse]

The first is glTF 1, so we can't really do much about the lighting except to upgrade our sample models to glTF 2, and the second is glTF 2 / PBR and IBL seems too strong.

[mramato]

I actually just wrote up #7802 before you made this comment. We need to put our best foot forward and to me that means glTF 2.0.

[lilleyse]

Opened #7803 for making the lighting look better.

[mramato]

This has 2 more specific issues to deal with the problem described above.