[Epic] Ray-traced global illumination

sky_line commented

2026-09-27 05:44:58 +00:00

Owner

Goal: dynamic diffuse global illumination (bounce light) on RT-capable GPUs.

Approach options (pick after a spike)

Probe-based (DDGI-style) - recommended first. Camera-following cascaded irradiance-probe grid; each frame a budgeted subset of probes traces N rays against the TLAS, shades hits with sun/sky/local lights (+ previous-frame probe irradiance for multi-bounce), stores irradiance + distance moments (Chebyshev visibility). Lit pass samples probes for indirect diffuse. Stable, low noise, no heavy per-pixel denoising, scales well to large SL scenes, amortizable.
Screen-space ReSTIR GI. Higher fidelity, much heavier denoising dependence; revisit after TAA + denoiser mature.

Interplay

SL already has reflection probes (our VK probe path handles specular); GI replaces/augments the diffuse ambient term. Needs a clear blend with probe ambient and SL's environment ambient to avoid double counting.
Hit shading needs a material/texture lookup at hit points (albedo from the RT material table - the alpha-test code already samples textures).

Children

Spike: probe grid prototype (static cascade, sun only) + debug visualisation.
Probe update pass (budgeted rays, hit shading incl. local lights, multi-bounce).
Lit-pass sampling + blend with probe ambient.
Cascades + camera scrolling + teleport invalidation.
Settings/quality tiers + GPU timers.

Size: L. Depends on: RT foundation (done), benefits from temporal epic. Risk: light leaking through thin SL walls (mitigate with Chebyshev visibility + probe relocation), cost in dense sims.

Acceptance: enclosed spaces

A sealed room goes dark. A fully enclosed box/room with no openings and no lights inside renders black (apart from its own local lights and emissive surfaces, #91 tier 1). Indoor sky ambient comes only from GI rays that escape to the sky.
GI replaces the ambient floor, it doesn't add to it. With GI on, SL's flat environment ambient is not added on top. A minimum ambient setting (default 0 with GI on) keeps sealed builds navigable for people who want a floor.
Reflections are occluded too. Specular must not leak the sky into a sealed room: probe0 (the always-selected sky baseline) and other outside probes get occlusion from the GI visibility data, or interior probes fully take over inside an enclosure.
Thin walls and small rooms. SL walls are often 1-10 cm and a small sealed box can be smaller than the probe spacing (every surrounding probe outside, all rejected by Chebyshev visibility). Must handle it: finer near-camera cascade, probe relocation out of walls/geometry, and/or per-pixel short-range rays for the near field (option 2's screen-space ReSTIR GI as the near-field term).
Test cases: 10 m sealed room; 2 m sealed box (smaller than the probe spacing); 1 cm-thick walls; the same room with a door (light enters only through the opening); a sealed room with one lamp. Each checked for diffuse and specular leaks, with GPU timers.

**Goal:** dynamic diffuse global illumination (bounce light) on RT-capable GPUs. ### Approach options (pick after a spike) 1. **Probe-based (DDGI-style) - recommended first.** Camera-following cascaded irradiance-probe grid; each frame a budgeted subset of probes traces N rays against the TLAS, shades hits with sun/sky/local lights (+ previous-frame probe irradiance for multi-bounce), stores irradiance + distance moments (Chebyshev visibility). Lit pass samples probes for indirect diffuse. Stable, low noise, no heavy per-pixel denoising, scales well to large SL scenes, amortizable. 2. **Screen-space ReSTIR GI.** Higher fidelity, much heavier denoising dependence; revisit after TAA + denoiser mature. ### Interplay - SL already has reflection probes (our VK probe path handles specular); GI replaces/augments the *diffuse* ambient term. Needs a clear blend with probe ambient and SL's environment ambient to avoid double counting. - Hit shading needs a material/texture lookup at hit points (albedo from the RT material table - the alpha-test code already samples textures). ### Children 1. Spike: probe grid prototype (static cascade, sun only) + debug visualisation. 2. Probe update pass (budgeted rays, hit shading incl. local lights, multi-bounce). 3. Lit-pass sampling + blend with probe ambient. 4. Cascades + camera scrolling + teleport invalidation. 5. Settings/quality tiers + GPU timers. **Size:** L. **Depends on:** RT foundation (done), benefits from temporal epic. **Risk:** light leaking through thin SL walls (mitigate with Chebyshev visibility + probe relocation), cost in dense sims. ### Acceptance: enclosed spaces - **A sealed room goes dark.** A fully enclosed box/room with no openings and no lights inside renders black (apart from its own local lights and emissive surfaces, #91 tier 1). Indoor sky ambient comes only from GI rays that escape to the sky. - **GI replaces the ambient floor, it doesn't add to it.** With GI on, SL's flat environment ambient is not added on top. A **minimum ambient** setting (default 0 with GI on) keeps sealed builds navigable for people who want a floor. - **Reflections are occluded too.** Specular must not leak the sky into a sealed room: probe0 (the always-selected sky baseline) and other outside probes get occlusion from the GI visibility data, or interior probes fully take over inside an enclosure. - **Thin walls and small rooms.** SL walls are often 1-10 cm and a small sealed box can be smaller than the probe spacing (every surrounding probe outside, all rejected by Chebyshev visibility). Must handle it: finer near-camera cascade, probe relocation out of walls/geometry, and/or per-pixel short-range rays for the near field (option 2's screen-space ReSTIR GI as the near-field term). - **Test cases:** 10 m sealed room; 2 m sealed box (smaller than the probe spacing); 1 cm-thick walls; the same room with a door (light enters only through the opening); a sealed room with one lamp. Each checked for diffuse and specular leaks, with GPU timers.

sky_line added this to the Rendering: temporal + RT effects milestone

2026-09-27 05:44:58 +00:00

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2026-09-27 05:44:58 +00:00

sky_line referenced this issue

2026-09-27 06:34:26 +00:00

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

sky_line commented

2026-09-27 06:34:26 +00:00

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Scope note: GI hit shading must include emissive radiance (PBR emissive + legacy fullbright/glow mapping) so emissive surfaces contribute soft bounce light. Sharp emissive area lighting is tracked separately in #91.

sky_line added this to the Slipstream project

2026-10-06 15:04:15 +00:00

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 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 commented

2026-10-19 14:16:33 +00:00

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Child ticket: #869 ReSTIR DI (shadowed direct lighting from all local lights / projectors / emissive). Also supplies hit lighting for GI rays (world light grid + RIS) instead of looping all lights at hit points.

sky_line referenced this issue

2026-10-19 14:36:54 +00:00

Investigate: DLSS Ray Reconstruction / FSR ray regeneration as an optional neural denoise + upscale path #870

sky_line referenced this issue

2026-10-19 15:28:48 +00:00

PBR materials tinted blue: dark / black materials render as saturated blue (e.g. black clothing shows navy) #872

sky_line referenced this issue

2026-10-19 15:33:27 +00:00

PBR materials tinted blue: dark / black materials render as saturated blue (e.g. black clothing shows navy) #872

sky_line referenced this issue from a commit

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

#87 GI-1: ray-traced one-bounce GI replacing the probes' diffuse ambient (RenderVKGI, default 0)