Volumetric clouds light up when CesiumSunSky is set to night

Cesium for Unreal
1

Hi, I seem to be encountering some kind of bug into my own project, and I have just seen that the same error occurs in your sample projects.

When the sunsky is set at a time at night, I expect the scene to become pitch black. But somehow the clouds stay visible, the sky is black but the landscape is still light up. It completely looks unrealistic. Anyone else experiencing this?

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Beside the problems, I really appreciate this software. Thanks for the awesome work guys :slight_smile: )

2

Hi @JustJasper,

Thanks for reporting this! I confirmed that I can see the same thing, though am not sure why it’s happening. CesiumSunSky is pretty much the same as Unreal’s SunSky; it’s simply been tweaked to sync up with the CesiumGeoreference. But I can confirm that Unreal’s SunSky darkens the volumetric clouds, whereas Cesium’s does not, so that’s not ideal.

I’ve opened an issue for this on Github. We’ll update that issue when we get the chance to investigate :face_with_monocle:

3

Thank you! It seems like it might be a regular UE5 bug instead of Cesium specific? Anyway, thanks for letting me know that it is not a bug only I am experiencing :slight_smile:

4

Hi there, has there been any resolution to this?

5

For UE 5.3 and 5.4.

Try the following:

  1. Click on the CesiumSunSky BP
  2. Under its components section, click on SkyAtmosphere
  3. Set TransmittanceMinLightElevationAngle from 90.0 to -90.0 (-90.0 is the default UE sets to that component)

Or for the C++ savy (with Cesium’s source):

  • In CesiumSunSky.cpp inside the constructor, line 105-ish
    SkyAtmosphere->TransmittanceMinLightElevationAngle = 90.0f;
    Set it to -90.0 instead.
6

More information about why we set it to 90 instead of -90 can be found here:

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