Snow is missing from ray-traced reflections (lying snow mesh and snow coating not in the RT path) #970

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opened 2026-10-23 09:14:53 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-23 09:14:53 +00:00

Owner

Part of #783 (weather). Owner report: snow does not appear in ray-traced reflections -- a snowy scene reflected in water, glass or metal shows the bare ground and surfaces.

Likely causes

Lying snow geometry: the snow mesh is drawn as its own mesh (G-buffer, depth pre-pass, sun cascades) but is not in the ray-tracing acceleration structure, so reflection rays never hit it.
Snow coating / wetness: applied in the G-buffer material path (weatherSurface), not in the RT reflection (and GI) hit shading, so surfaces hit by reflection rays show their unweathered material.

Wanted

Reflection (and GI) hits shade weather consistently with the main view: apply the snow coating (and wetness) at the hit from the weather maps at the hit's world position, using the same function as the G-buffer path.
Lying snow geometry visible to rays: either add the snow mesh to the TLAS as its own BLAS (rebuilt / updated when the mesh rebuilds or is patched; cost and VRAM bounded, small tier off), or a cheaper approximation (a ray-marched height-field intersection against the snow depth grid at reflection hits). Measure both and pick; document the cost.
Frame-structure rules (no AS / descriptor re-creation mid-recording; prestep), validation-clean, GPU cost in the existing timers.

Test

Snowy scene reflected in calm water / a mirror / smooth metal: the reflection shows the snow cover and lying snow.
Footprints and trenches appear in reflections shortly after they are made.
GPU timers before / after; small tier.

Part of #783 (weather). Owner report: snow does not appear in ray-traced reflections -- a snowy scene reflected in water, glass or metal shows the bare ground and surfaces. ## Likely causes 1. **Lying snow geometry**: the snow mesh is drawn as its own mesh (G-buffer, depth pre-pass, sun cascades) but is not in the ray-tracing acceleration structure, so reflection rays never hit it. 2. **Snow coating / wetness**: applied in the G-buffer material path (`weatherSurface`), not in the RT reflection (and GI) hit shading, so surfaces hit by reflection rays show their unweathered material. ## Wanted - Reflection (and GI) hits shade weather consistently with the main view: apply the snow coating (and wetness) at the hit from the weather maps at the hit's world position, using the same function as the G-buffer path. - Lying snow geometry visible to rays: either add the snow mesh to the TLAS as its own BLAS (rebuilt / updated when the mesh rebuilds or is patched; cost and VRAM bounded, small tier off), or a cheaper approximation (a ray-marched height-field intersection against the snow depth grid at reflection hits). Measure both and pick; document the cost. - Frame-structure rules (no AS / descriptor re-creation mid-recording; prestep), validation-clean, GPU cost in the existing timers. ## Test - Snowy scene reflected in calm water / a mirror / smooth metal: the reflection shows the snow cover and lying snow. - Footprints and trenches appear in reflections shortly after they are made. - GPU timers before / after; small tier.

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2026-10-23 09:14:53 +00:00

sky_line added this to the Slipstream project

2026-10-23 09:14:53 +00:00

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)

sky_line referenced this issue from a commit

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