Depth Test Failure / Z-fighting

[TJKoury]

What happened?

In 1.123, intermittent depth test failure or z-fighting issue. Not present in <1.122, unsure if it was introduced in 1.122 or 1.123. Goes away if viewer.scene.globe.depthTestAgainstTerrain is set to true.

Reproduction steps

Open sandcastle, track GeoEye-1, see the primitives show through the globe.

Sandcastle example

https://sandcastle.cesium.com/?src=CZML.html&label=DataSources

Environment

Browser: Version 131.0.6778.85 (Official Build) (64-bit)
CesiumJS Version: 1.123.1
Operating System: Pop!_OS 22.04 LTS

[jjhembd]

@TJKoury thanks for the report!
I wasn't able to reproduce the bug on Windows.

Could this be OS-specific? Something about depth textures not supported, or lower depth buffer precision?

[TJKoury]

Maybe, however here it is on mobile using an iPhone 14 Pro Max. I have not tried it on Windows. Track one of the satellites and see if that makes a difference.

It definitely did not do this prior to 1.122, some of the recent shader / pipeline work would be my guess.

[jjhembd]

Thanks @TJKoury,
When I track GeoEye1, I can sort of reproduce: I get brief flashes (maybe 1 frame) of the other side showing through. It only happens near certain time stamps.
Just wanted to let you know I'm working on it. I'll still need to refine my test case a bit, before I can properly trace back where it broke.

[jjspace]

@jjhembd this was also reported in #12371, might be another good sample sandcastle to help track this down.

[Rubeanster]

Yeah I see the same issue since I upgraded from 1.114 to 1.124. Seems like while tracking an entity I get flickering from other polylines. I couldn't get it to happen while not tracking an entity but working with the camera is a bit harder in that case to orientate it so not certain on that one.

[jjhembd]

I traced the bug to a single line from #12188. We changed this:

    positionEC = czm_modelView * position;
    gl_Position = czm_projection * positionEC;

to this:

    positionEC = czm_modelView * position;
    gl_Position = czm_modelViewProjection * position;

Reverting this change fixes the bug on my machine.