Volumetric clouds are jagged along mesh edges when Fog Height Falloff is 0

Volumetric clouds are composited against opaque mesh silhouettes at a reduced resolution. A blocky and jagged edge appears along the silhouette. The fog brightness of the clouds also changes abruptly across the edge. This happens when Exponential Height Fog has Fog Height Falloff set to 0 (or a very small value) and a low Fog Density.

This is a regression in 5.8.0. It does not reproduce in 5.7.4. Setting r.VolumetricCloud.ApplyFogLate 0 avoids the issue and restores the 5.7 behaviour. The default of this CVar was changed from 0 to 1 in 5.8 (CL 46585016).

1. Create a new project and add a new Level using the "Basic" template

(the template already contains ExponentialHeightFog, SkyAtmosphere and VolumetricCloud).

1. Select the ExponentialHeightFog actor and set:

• Fog Height Falloff = 0.0
• Fog Density = 0.0001

1. Place a Cube (or any opaque static mesh) in the level.
2. Move the viewport camera so that the edge of the Cube overlaps the volumetric

clouds in the sky.

Observe the silhouette of the Cube where it overlaps the clouds.

RESULT:
The cloud pixels along the Cube's silhouette are resolved at a visibly reduced resolution. A blocky / jagged (aliased) staircase edge appears along the silhouette, and the fog brightness of the clouds changes abruptly between neighbouring pixels across the edge.

EXPECTED:
The clouds composite smoothly against the Cube's silhouette at full resolution, as in 5.7.4 and earlier.