Depth fail epsilon

[lilleyse]

Cesium has a mechanism to draw primitives that fails the depth test with a depthFailAppearance, but if a primitive is coplanar with other geometry there may be flickering between the appearance and the depthFailAppearance. This is a screenshot of a polygon on a point cloud.

It would be useful to have a depth fail epsilon where the depthFailAppearance is only used if the rendered geometry fails the depth test past by some epsilon value in meters. This would help stop the flickering when viewing the primitive face on but still use the depthFailAppearance correctly when viewing it from the other side where the geometry is obscured.

There was also some discussion about this for point clouds in #6714 (comment)