Ue Uds Fog And Atmosphere

UDS fog and atmosphere

UDS owns three air-shading systems — height fog, volumetric fog, and the global volumetric material — plus a sky-coloring layer with two backends. This skill covers each and the interactions between them.

When to use this skill

• Tuning how thick fog gets with cloud coverage / weather / dust.
• Making fog look different per weather (cloudy, foggy, dusty).
• Enabling volumetric fog and dealing with its cost.
• Adding ground fog or 3D noise variation to the fog.
• Setting up underwater fog tinting/extinction.
• Picking between Sky Atmosphere and Simplified Color for sky shading.
• Tuning sunset/twilight color, Rayleigh scattering, or overcast luminance.
• Diagnosing a hard fog line, sky flickering black, or pixelated volumetric fog.

Fog Density

Category: Fog Density. Derives the height fog component's density, falloff, and start distance from inputs like Cloud Coverage, Fog, and Dust Amount.

Increasing Cloud Coverage / Fog / Dust automatically thickens distance fog. For different moods per weather, tune the per-state contributions in this category.

Fog Color

Category: Fog Color. The project setting Support Sky Atmosphere Affecting Height Fog is what determines whether these settings are actually used.

This dependency disappears entirely if Color Mode = Simplified Color — Simplified Color doesn't enable the sky atmosphere, so all Fog Color settings are live.

Path Tracer distance fog

Render Height Fog In Path Tracer Using Post Process (in Fog Color category, on by default). Lets the path tracer approximate distant height fog via post process — the path tracer otherwise lacks native height fog support. See ue-uds-cinematics-rendering.

Volumetric Fog

Unreal's volumetric fog renders advanced fog nearby the camera that receives/scatters light from local sources and supports variable color/extinction via volumetric materials. Enable from the Volumetric Fog category.

Performance and scalability

Volumetric Fog is expensive. Notes:

Global Volumetric Material

Also in Volumetric Fog category. Adds global controls of extinction and color.

Dust

Category: Dust. Imitates dust/smoke/particulates in the air.

If UDW is in the scene, UDW takes control of Dust Amount as part of weather state.

Sky Atmosphere

When Color Mode = Sky Atmosphere (default), main sky color comes from the Sky Atmosphere category.

Simplified Color

When Color Mode = Simplified Color, main sky color comes from the Simplified Color category. Cheaper at the material level than Sky Atmosphere, more directly tweakable.

The LUT textures are involved to author from scratch. For tweaks, prefer doing color transforms on the included textures.

Runtime / Blueprint control

Copy code
// Active properties — set directly, cache picks up:
UDS.Fog          = 0.4    // (use UDW instead if present)
UDS.CloudCoverage = 0.7
UDS.DustAmount   = 0.2

// Volumetric fog enable / extinction / distance — many are static:
UDS.bEnableVolumetricFog = true
UDS.CallStaticPropertiesVolumetricFog()   // apply

If a runtime change has no effect, look for the matching Static Properties - <Category> function and call it. Last-resort full refresh: Hard Reset Cache. See ue-uds-performance-mobile-troubleshooting.

Performance

Gotchas

• Hard line where fog/atmosphere suddenly starts — sky atmosphere position is wrong relative to the scene. Place UDS at ground level so the camera is never significantly below the UDS actor.
• Sky color flickers black when moving the camera — engine bug; camera dipped below the sky atmosphere "ground". Select the Sky Atmosphere component on UDS (in the top components list) and move it down below the lowest point the camera can reach.
• Volumetric fog pixelated / low quality — that's project scalability. Volumetric fog's scalability cvars are in the Shadow Quality group. UDS doesn't override them.
• Volumetric fog completely invisible — default Low/Medium engine scalability disables volumetric fog entirely. Check scalability settings.
• Fog Color changes have no effect — Support Sky Atmosphere Affecting Height Fog project setting is on, so fog colors come from the sky atmosphere. Either disable the project setting or switch Color Mode to Simplified Color.
• Dust Amount ignored on UDS — UDW is in the scene; UDW's weather state owns it.
• Ground Fog feature has no effect — project setting to generate mesh distance fields is off. Enable it.

References & source material

Docs (Ultra Dynamic Sky 9.5):

• Fog Density
• Fog Color
• Volumetric Fog (incl. Global Volumetric Material)
• Dust
• Sky Atmosphere
• Simplified Color
• Common Issues — General Rendering

Related skills: ue-uds-setup-and-modes, ue-uds-clouds, ue-uds-modifiers-configs-state (water level), ue-uds-cinematics-rendering, ue-udw-particles-lightning-wind-sounds (UDW Dust flows into UDS Dust Amount), ue-udw-material-and-screen-effects (Weather Mask masking applies to Global Volumetric Material).