Volumetric fog: denser fog over bodies of water, and rolling fog driven by weather and the windlight #963

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opened 2026-10-23 05:35:54 +00:00 by sky_line · 0 comments

sky_line commented

2026-10-23 05:35:54 +00:00

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Wanted

1. Fog gains volume over water

The volumetric fog's density rises over bodies of water (region water, and water prims if they are identifiable), the way mist forms over lakes, rivers and the sea:

a height-limited layer above the surface (densest at the water, thinning over a few metres; the thickness a setting / derived from conditions);
stronger when the air is cooler than the water (dusk, night, early morning by the windlight's sun angle) and in calm wind; thinner and torn in strong wind;
fades out over land within a short distance of the shore, so it reads as water-borne mist, not a flat global term.

2. Rolling fog

Fog that moves: banks that drift, roll over terrain and pool in low ground, instead of a static uniform density.

Wind-driven: the density field (3D noise / low-frequency banks) advects with the weather wind (direction, speed, gusts) -- the same motion input as precipitation in the fog (see the #954 follow-up that moves precipitation visibility into the volumetric fog).
Weather-driven: rain and snow raise humidity-driven fog; clearing weather lifts it; storms tear it into patches.
Windlight-driven: the region / parcel sky (EEP haze, density, humidity-like parameters, sun angle) sets the base fog amount and colour, so a misty windlight gets rolling mist without user settings; dawn / dusk favour low fog.
Terrain-aware: denser in valleys and low ground (height relative to local terrain), so fog pools and rolls down slopes.
Never indoors: zero under cover (the weather roof / cover map), like the precipitation density.

Constraints

Lives in the existing froxel volumetric fog (one density pipeline: base + water mist + rolling banks + precipitation), lit by its existing lighting / shadows; temporally stable (no screen-space noise).
Respects the weather VRAM tier and graphics quality; a cheap path or off on the small tier; GPU cost in the existing fog timers.
Deterministic from shared inputs (synced time, region / parcel seed, wind) where it should look the same for everyone in a place.
Settings with sensible defaults; a user can turn water mist and rolling fog off independently.

Test

Calm dusk by a lake: a low mist layer over the water, thinning toward the shore; strong wind: torn / gone.
Misty windlight: rolling banks that drift with the wind and pool in a valley.
Rain then clearing: fog builds then lifts.
Indoors / under a roof: no fog density added.
GPU timers before / after; small tier.

## Wanted ### 1. Fog gains volume over water The volumetric fog's density rises over bodies of water (region water, and water prims if they are identifiable), the way mist forms over lakes, rivers and the sea: - a height-limited layer above the surface (densest at the water, thinning over a few metres; the thickness a setting / derived from conditions); - stronger when the air is cooler than the water (dusk, night, early morning by the windlight's sun angle) and in calm wind; thinner and torn in strong wind; - fades out over land within a short distance of the shore, so it reads as water-borne mist, not a flat global term. ### 2. Rolling fog Fog that moves: banks that drift, roll over terrain and pool in low ground, instead of a static uniform density. - **Wind-driven:** the density field (3D noise / low-frequency banks) advects with the weather wind (direction, speed, gusts) -- the same motion input as precipitation in the fog (see the #954 follow-up that moves precipitation visibility into the volumetric fog). - **Weather-driven:** rain and snow raise humidity-driven fog; clearing weather lifts it; storms tear it into patches. - **Windlight-driven:** the region / parcel sky (EEP haze, density, humidity-like parameters, sun angle) sets the base fog amount and colour, so a misty windlight gets rolling mist without user settings; dawn / dusk favour low fog. - **Terrain-aware:** denser in valleys and low ground (height relative to local terrain), so fog pools and rolls down slopes. - Never indoors: zero under cover (the weather roof / cover map), like the precipitation density. ### Constraints - Lives in the existing froxel volumetric fog (one density pipeline: base + water mist + rolling banks + precipitation), lit by its existing lighting / shadows; temporally stable (no screen-space noise). - Respects the weather VRAM tier and graphics quality; a cheap path or off on the small tier; GPU cost in the existing fog timers. - Deterministic from shared inputs (synced time, region / parcel seed, wind) where it should look the same for everyone in a place. - Settings with sensible defaults; a user can turn water mist and rolling fog off independently. ## Test - Calm dusk by a lake: a low mist layer over the water, thinning toward the shore; strong wind: torn / gone. - Misty windlight: rolling banks that drift with the wind and pool in a valley. - Rain then clearing: fog builds then lifts. - Indoors / under a roof: no fog density added. - GPU timers before / after; small tier.

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2026-10-23 05:35:54 +00:00

sky_line added this to the Slipstream project

2026-10-23 05:35:54 +00:00

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