Acoustics: approximate diffraction via first-bounce visibility (sound around corners and through doorways) #858

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opened 2026-10-19 01:56:41 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-19 01:56:41 +00:00

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Follow-up to #683 (RT room acoustics).

Today: occlusion is a single listener-to-source ray, so a source is either blocked (muffled) or clear. A sound through an open doorway or around a corner gets fully muffled, and its direction is the straight line through the wall.

Proposal: reuse the listener's room rays.

Indirect path check: at each room ray's first hit point, cast one shadow ray to each occluded source (next-event estimation, as in path tracing).
Opening found: if a source is visible from a first-bounce point, there is a one-bounce path (doorway, around a corner):
- reduce its muffling by the strength of the best indirect path (shorter detour = clearer);
- optionally pan its apparent direction towards that opening by moving the source position used for spatialisation.
Second bounce later: a second bounce can be added if one is not enough (corridors).

Notes:

Cost: room rays × occluded sources shadow rays. Cap the sources (nearest / loudest occluded N) and the rays per source; the room rays are already traced.
Smoothing: keep the existing smoothing; the path strength changes slowly as you walk.
Scope: this is the cheap geometric stand-in for proper edge diffraction / pathing (Steam-Audio-class echograms are #683 Phase 1).

Done when: a sound behind an open door or around a corner is clearly less muffled than one behind a solid wall, and pans towards the opening, at under ~0.05 ms extra GPU on an RTX 3060-class card.

Follow-up to #683 (RT room acoustics). **Today:** occlusion is a single listener-to-source ray, so a source is either blocked (muffled) or clear. A sound through an open doorway or around a corner gets fully muffled, and its direction is the straight line through the wall. **Proposal:** reuse the listener's room rays. - **Indirect path check:** at each room ray's first hit point, cast one shadow ray to each **occluded** source (next-event estimation, as in path tracing). - **Opening found:** if a source is visible from a first-bounce point, there is a one-bounce path (doorway, around a corner): - reduce its muffling by the strength of the best indirect path (shorter detour = clearer); - optionally pan its apparent direction towards that opening by moving the source position used for spatialisation. - **Second bounce later:** a second bounce can be added if one is not enough (corridors). **Notes:** - **Cost:** room rays × occluded sources shadow rays. Cap the sources (nearest / loudest occluded N) and the rays per source; the room rays are already traced. - **Smoothing:** keep the existing smoothing; the path strength changes slowly as you walk. - **Scope:** this is the cheap geometric stand-in for proper edge diffraction / pathing (Steam-Audio-class echograms are #683 Phase 1). **Done when:** a sound behind an open door or around a corner is clearly less muffled than one behind a solid wall, and pans towards the opening, at under ~0.05 ms extra GPU on an RTX 3060-class card.

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sky_line added this to the Slipstream project

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2026-10-19 01:56:46 +00:00

Explore: Steam Audio (ray-traced occlusion, reverb, pathing, HRTF) for in-world sounds #683

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