Black scene when heading south with custom heightmap terrain-provider

[tuif]

Hello,

We use a custom terrain-provider with 65x65 heightmap data, which works perfect under 1.54 and previous. With new 1.55/1.56, the scene become black when heading south. It occurs on macOS、Android Webivew and iOS WKWebview, all platforms we could test.

Cesium 1.56 heading north

Cesium 1.56 heading south

Here is a minimal sandcastle example that reproduce. Please wait a few seconds for auto-rotating starting.
https://cesiumjs.org/Cesium/Apps/Sandcastle/index.html#c=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

Browser:
Safari Version 12.0.3 (14606.4.5)
Chrome Version 73.0.3683.86

Operating System:
MacOS Mojave 10.14.3<!--

Mobile:
Android Webview 70.0.3538.110
iOS WKWebview 11.x~12.x

[lilleyse]

@tuif this is a 1.56 regression that we have a fix open for here: #7701.

[tuif]

#7701 relates to changes in 1.56 comparing 1.55. The back scene aforementioned appear in 1.55.
Is it truly the problem?

[lilleyse]

@tuif yeah you're right, this is also a problem with 1.55. I couldn't bisect to an exact spot but I think this broke somewhere in #7061. @kring do you have any ideas?

[tuif]

It seems it only occurs when sky is visible. If adjusting pitch toward the ground more where the sky is invisible, everything is fine.
Is it possible that I missed something in my custom terrain-provider?

Here is the sandcastle:
https://cesiumjs.org/Cesium/Apps/Sandcastle/index.html#c=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

[tuif]

just tried 1.56.1, the same issue.

[kring]

Thanks for the Sandcastle repro @tuif, huge help!

I have a fix here, but I need to consider whether it's totally the right solution before PRing it:
https://github.com/AnalyticalGraphicsInc/cesium/compare/mercator-culling

The problem is that this terrain uses the Web Mercator tiling scheme which has a single tile at the root, and OrientedBoundingBox.fromRectangle produces a rubbish bounding box for a whole-world rectangle. HeightmapTessellator guards against this (https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Core/HeightmapTessellator.js#L410), but in the new terrain engine that bounding box isn't used and the OBB is computed separately instead. So we were getting a bad OBB and the single root tile was getting culled.

[tuif]

Wow, so quick response. Hope it could be fixed in the next release!

[hpinkos]

@kring will you be able to have a fix for this before the next release?

[tuif]

Thank you all. Look forward to the next release.