Point light shadows (ray traced + cube shadow-map fallback) #439

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opened 2026-10-05 14:43:55 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-05 14:43:55 +00:00

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Point lights (SL's ordinary local lights) cast no shadows today. Only the sun/moon (ray traced) and projectors (shadow-map atlas RenderVKProjShadow*, or ray traced RenderVKRTProjShadowMax) do. Point lights are by far the most common lights in SL, and our site already says "lights cast proper shadows".

Same shape as the projector work: one setting, Point light shadows: Off / Shadow maps / Ray traced. Ray traced is greyed out without ray-query support. Both modes share a per-frame cap on how many lights cast shadows.

Ray traced (primary path)

No projection is involved. A shadow ray goes from the receiver to the light's position, so a sphere is the easiest case for RT.

Plug into the existing RT shadow mask pass (clean_rt_shadow_mask.comp). It already traces up to 4 shadowed projectors per pixel into the per-slot uRawProj array, and the temporal and spatial denoisers already handle those slots. Point lights become more candidates for the same per-pixel slots, picked in cluster order.
Soft shadows: jitter the ray target over a small sphere (the light's "size"), and the existing penumbra estimate and denoiser blur it.
Light selection each frame: score = screen coverage × intensity × proximity. Take the top N (RenderVKRTPointShadowMax, default 8–16). Unselected lights stay unshadowed, as today.

Shadow maps (fallback for cards without ray tracing)

Cube maps in a cube-map array: 6 faces per light, sampled by direction, with hardware-seamless filtering and no face seams. Rejected alternatives:
- Dual-paraboloid (2 renders): it warps straight edges unless geometry is finely tessellated, and SL prims are large, coarse triangles.
- Tetrahedral (4 faces): saves a third of the renders but needs custom seam handling.
GPU-driven, per our rules:
- One compute cull for every face of every selected light. The light radius (≤ 20 m in SL) bounds the cull.
- One layered multi-draw-indirect for all faces (gl_Layer / multiview).
- No per-face CPU work.
Depth = linear distance to the light. Normal-offset and slope-scaled bias; PCF by jittering the lookup direction.
Caching, as the projector atlas does:
- A static layer is re-rendered only when something static in range changes.
- Dynamic casters (avatars, movers) are re-rendered on a budget (RenderVKPointShadowDynamicInterval) and composited over the static layer.
- A per-frame cap on face renders.
Resolution tiers by screen size: 512² near, 256² mid, 128² far. Memory per light (D32): 512² ≈ 6 MB, 256² ≈ 1.5 MB, 128² ≈ 0.4 MB. It falls under the VRAM pressure ladder like the other shadow rungs.

SL-specific hazards (must handle, both paths)

Lights inside their own object. A bulb inside a lampshade, or a light inside a sconce mesh: the light's own linkset fully occludes it, and the lamp goes dark. Exclude the light's own object/linkset from its shadow casters (instance mask or per-instance ID compare). Also start rays / near-clip at a small radius around the light.
Attached lights / facelights. These would shadow the wearer's own head and hair. Default: attached lights don't shadow their owner, or don't cast at all, behind a setting.
Content built around no shadows. Fill lights placed behind walls or under floors are "designed" leaks. With shadows on, those spots go dark. Expected, but worth a release note and an easy toggle.
Lights on spinning, moving or animated objects need the dynamic path or the moving-caster flag the RT mask already tracks.

Performance estimate (to verify with RenderVKGpuTimers)

Ray traced: cost scales with the screen pixels each light covers, not the light count.
- Half-res mask at 1440p is ~0.9 M pixels. One ray per covered pixel per light comes to roughly 0.3–0.6 ms for a light covering the whole screen on an RTX 4070/4080-class card. Alpha-tested foliage (any-hit) pushes toward the top of that range.
- Typical point lights cover 5–20% of the screen, so about 0.05–0.15 ms each.
- 8–16 shadowed lights: ~0.5–1.5 ms in a busy club; denoise adds little (the slots already exist).
Shadow maps:
- Per light, a full refresh is 6 faces of geometry within ≤ 20 m. That's ~0.1–0.3 ms on a mid-high card, spread over frames by caching.
- Steady state with a refresh budget: ~0.3–1 ms per frame, plus ~0.05–0.2 ms of filtering per light for the pixels it covers.
- Worst case is a crowded club with every light seeing moving avatars. The dynamic-refresh budget caps that (stale-by-a-few-frames shadows instead of FPS loss).

Point lights (SL's ordinary local lights) cast no shadows today. Only the sun/moon (ray traced) and projectors (shadow-map atlas `RenderVKProjShadow*`, or ray traced `RenderVKRTProjShadowMax`) do. Point lights are by far the most common lights in SL, and our site already says "lights cast proper shadows". Same shape as the projector work: one setting, **Point light shadows: Off / Shadow maps / Ray traced**. Ray traced is greyed out without ray-query support. Both modes share a per-frame cap on how many lights cast shadows. ## Ray traced (primary path) No projection is involved. A shadow ray goes from the receiver to the light's position, so a sphere is the *easiest* case for RT. - Plug into the existing RT shadow mask pass (`clean_rt_shadow_mask.comp`). It already traces up to 4 shadowed projectors per pixel into the per-slot `uRawProj` array, and the temporal and spatial denoisers already handle those slots. Point lights become more candidates for the same per-pixel slots, picked in cluster order. - Soft shadows: jitter the ray target over a small sphere (the light's "size"), and the existing penumbra estimate and denoiser blur it. - Light selection each frame: score = screen coverage × intensity × proximity. Take the top N (`RenderVKRTPointShadowMax`, default 8–16). Unselected lights stay unshadowed, as today. ## Shadow maps (fallback for cards without ray tracing) - **Cube maps** in a cube-map array: 6 faces per light, sampled by direction, with hardware-seamless filtering and no face seams. Rejected alternatives: - Dual-paraboloid (2 renders): it warps straight edges unless geometry is finely tessellated, and SL prims are large, coarse triangles. - Tetrahedral (4 faces): saves a third of the renders but needs custom seam handling. - GPU-driven, per our rules: - One compute cull for every face of every selected light. The light radius (≤ 20 m in SL) bounds the cull. - One layered multi-draw-indirect for all faces (`gl_Layer` / multiview). - No per-face CPU work. - Depth = linear distance to the light. Normal-offset and slope-scaled bias; PCF by jittering the lookup direction. - Caching, as the projector atlas does: - A static layer is re-rendered only when something static in range changes. - Dynamic casters (avatars, movers) are re-rendered on a budget (`RenderVKPointShadowDynamicInterval`) and composited over the static layer. - A per-frame cap on face renders. - Resolution tiers by screen size: 512² near, 256² mid, 128² far. Memory per light (D32): 512² ≈ 6 MB, 256² ≈ 1.5 MB, 128² ≈ 0.4 MB. It falls under the VRAM pressure ladder like the other shadow rungs. ## SL-specific hazards (must handle, both paths) - **Lights inside their own object.** A bulb inside a lampshade, or a light inside a sconce mesh: the light's own linkset fully occludes it, and the lamp goes dark. Exclude the light's own object/linkset from its shadow casters (instance mask or per-instance ID compare). Also start rays / near-clip at a small radius around the light. - **Attached lights / facelights.** These would shadow the wearer's own head and hair. Default: attached lights don't shadow their owner, or don't cast at all, behind a setting. - **Content built around no shadows.** Fill lights placed behind walls or under floors are "designed" leaks. With shadows on, those spots go dark. Expected, but worth a release note and an easy toggle. - Lights on spinning, moving or animated objects need the dynamic path or the moving-caster flag the RT mask already tracks. ## Performance estimate (to verify with RenderVKGpuTimers) - **Ray traced:** cost scales with the *screen pixels each light covers*, not the light count. - Half-res mask at 1440p is ~0.9 M pixels. One ray per covered pixel per light comes to roughly 0.3–0.6 ms for a light covering the whole screen on an RTX 4070/4080-class card. Alpha-tested foliage (any-hit) pushes toward the top of that range. - Typical point lights cover 5–20% of the screen, so about 0.05–0.15 ms each. - 8–16 shadowed lights: ~0.5–1.5 ms in a busy club; denoise adds little (the slots already exist). - **Shadow maps:** - Per light, a full refresh is 6 faces of geometry within ≤ 20 m. That's ~0.1–0.3 ms on a mid-high card, spread over frames by caching. - Steady state with a refresh budget: ~0.3–1 ms per frame, plus ~0.05–0.2 ms of filtering per light for the pixels it covers. - Worst case is a crowded club with every light seeing moving avatars. The dynamic-refresh budget caps that (stale-by-a-few-frames shadows instead of FPS loss).

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sky_line referenced this issue

2026-10-10 11:55:54 +00:00

[Epic] Emissive surfaces as light sources (RT emissive lighting) #91

sky_line commented

2026-10-10 11:55:54 +00:00

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Direction decided 2026-10-10: point-light shadows come from ReSTIR DI (#91)

Instead of a standalone "top N shadowed point lights" selector in the RT mask's 4 slots, point lights become candidates in the shared ReSTIR DI many-light sampler. The design is in #91. Every point light can cast a shadow, with cost roughly independent of light count (~1 visibility ray per pixel plus reuse passes), and the same system handles projectors and emissive surfaces.

Requirements specific to this ticket (carry into the ReSTIR build):

Own-fixture exclusion: SL creators put point lights inside bulbs, lamp shades and lanterns. Shadow rays must ignore the light's own object/linkset, and/or start a small distance out from the light. Otherwise most lit builds go dark or get hard lamp-shade cut-outs.
Soft shadows: jitter the sample point over the light's radius.
Setting: Point light shadows Off / Ray traced (ReSTIR). The shadow-map (cube-map) fallback for non-RT GPUs comes later, after #567 makes maps cheaper, and with a small light cap.

The light scoring, light buffer and denoiser hookup planned here are the first pieces of the ReSTIR infrastructure, not separate work.

## Direction decided 2026-10-10: point-light shadows come from ReSTIR DI (#91) Instead of a standalone "top N shadowed point lights" selector in the RT mask's 4 slots, point lights become candidates in the shared **ReSTIR DI** many-light sampler. The design is in #91. Every point light can cast a shadow, with cost roughly independent of light count (~1 visibility ray per pixel plus reuse passes), and the same system handles projectors and emissive surfaces. **Requirements specific to this ticket (carry into the ReSTIR build):** - **Own-fixture exclusion:** SL creators put point lights inside bulbs, lamp shades and lanterns. Shadow rays must ignore the light's own object/linkset, and/or start a small distance out from the light. Otherwise most lit builds go dark or get hard lamp-shade cut-outs. - **Soft shadows:** jitter the sample point over the light's radius. - **Setting:** Point light shadows Off / Ray traced (ReSTIR). The shadow-map (cube-map) fallback for non-RT GPUs comes later, after #567 makes maps cheaper, and with a small light cap. The light scoring, light buffer and denoiser hookup planned here are the first pieces of the ReSTIR infrastructure, not separate work.

sky_line referenced this issue

2026-10-19 14:16:32 +00:00

ReSTIR DI: shadowed direct lighting from every local light, projector and emissive surface (RT tier) #869

sky_line referenced this issue from a commit

2026-10-22 19:32:55 +00:00

CANDIDATES (RenderVKReSTIRDI 1; generic-core pass 15 only -- a ReSTIR frame forces the core kernel):

sky_line referenced this issue from a commit

2026-10-22 19:32:55 +00:00

#439: point-light shadow-map fallback -- selection + VRAM budget and the render-path plan (RenderVKPointShadowMaps, default 0)

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