Weather: vehicles don't carve snow; dark blotches and a stippled pattern on snow #906

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opened 2026-10-21 01:25:33 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-21 01:25:33 +00:00

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A user drove a vehicle (a ground car, avatar seated) through snowy streets in Beta 1.4.0 and sent a video. Seen in the video:

1. The vehicle doesn't carve tracks

The car drives through fresh snow but leaves no compacted wheel tracks or ruts behind it.
At rest, the wheels sink into the snow: the snow surface is drawn through the wheels and lower body, with no hollow under the car.
Faint pale curved lines appear on the ground in places, which may be rims without a trench, or older tracks; needs checking.
Expected: a moving vehicle (physical object, or a linkset with a seated avatar) presses tracks the way other moving objects do. Its wheels or lowest parts should compact the snow, with a parked vehicle sitting in a hollow, not sunk into the surface.

2. The snow looks wrong

Dark blotches: on some surfaces (sidewalks, raised kerbs, the street edge next to buildings) the snow shows large dark or black camouflage-like patches. Some have hard, jagged staircase edges, like grid cells. They are near-black, not the grey of the ground showing through.
Stippled pattern: across open snow there is a regular pattern of small dark dots in rows (looks like a repeating noise or normal texture), which reads as dirty or pebbled snow rather than smooth snow.
Bright streaks: long bright bands on the ground near the vehicle.

To investigate

Why a vehicle is not picked up as a snow mover: check how movers are chosen (physics flag, velocity, linkset root vs child prims, seated avatar, size limits, the moving-object stamp list), and whether the press uses the object's lowest surface.
What the dark blotches are: snow coverage noise thresholds on certain surfaces, the snow mesh missing over raised prims, shadowing of the snow mesh, or bad lighting (NaN or zero normals) on snow at coarse grid cells. The jagged edges point at the grid cell size.
What the dotted pattern is: the snow detail normal or noise at a scale that aliases at street level.

## Report A user drove a vehicle (a ground car, avatar seated) through snowy streets in Beta 1.4.0 and sent a video. Seen in the video: ### 1. The vehicle doesn't carve tracks - The car drives through fresh snow but leaves no compacted wheel tracks or ruts behind it. - At rest, the wheels sink into the snow: the snow surface is drawn through the wheels and lower body, with no hollow under the car. - Faint pale curved lines appear on the ground in places, which may be rims without a trench, or older tracks; needs checking. - Expected: a moving vehicle (physical object, or a linkset with a seated avatar) presses tracks the way other moving objects do. Its wheels or lowest parts should compact the snow, with a parked vehicle sitting in a hollow, not sunk into the surface. ### 2. The snow looks wrong - **Dark blotches:** on some surfaces (sidewalks, raised kerbs, the street edge next to buildings) the snow shows large dark or black camouflage-like patches. Some have hard, jagged staircase edges, like grid cells. They are near-black, not the grey of the ground showing through. - **Stippled pattern:** across open snow there is a regular pattern of small dark dots in rows (looks like a repeating noise or normal texture), which reads as dirty or pebbled snow rather than smooth snow. - **Bright streaks:** long bright bands on the ground near the vehicle. ## To investigate - Why a vehicle is not picked up as a snow mover: check how movers are chosen (physics flag, velocity, linkset root vs child prims, seated avatar, size limits, the moving-object stamp list), and whether the press uses the object's lowest surface. - What the dark blotches are: snow coverage noise thresholds on certain surfaces, the snow mesh missing over raised prims, shadowing of the snow mesh, or bad lighting (NaN or zero normals) on snow at coarse grid cells. The jagged edges point at the grid cell size. - What the dotted pattern is: the snow detail normal or noise at a scale that aliases at street level.

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2026-10-21 01:25:33 +00:00

sky_line added this to the Slipstream project

2026-10-21 01:25:33 +00:00

sky_line commented

2026-10-21 01:33:33 +00:00

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Update from the reporter: shadows were off in the video. Turning shadows on made the snow look better, so the dark blotches and stipple are likely a bug in the shadows-off path (snow shading reading a stale or placeholder shadow input when shadows are disabled). The vehicle-tracks part is unaffected.

Update from the reporter: shadows were **off** in the video. Turning shadows on made the snow look better, so the dark blotches and stipple are likely a bug in the shadows-off path (snow shading reading a stale or placeholder shadow input when shadows are disabled). The vehicle-tracks part is unaffected.

sky_line referenced this issue from a commit

2026-10-21 02:45:33 +00:00

#906: vehicle tracks without temporal history; snow coating follows depth; no bare lee shadows; smooth relief

sky_line referenced this issue from a commit

2026-10-21 02:45:33 +00:00

#906: at-rest mover presses take only the first half of the stamp cap (moving boxes always find a slot)

sky_line referenced this issue from a commit

2026-10-23 15:49:37 +00:00

#970: snow and wetness in ray-traced reflections (weather at RT hits + lying-snow height-field march)

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