RT reflections without SSR as the maximum-quality reflection path #976

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opened 2026-10-23 16:43:50 +00:00 by sky_line · 0 comments

sky_line commented

2026-10-23 16:43:50 +00:00

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Final design target for maximum quality: ray-traced reflections as the complete reflection path, with screen-space reflections (SSR) off.

Today RT reflections are hybrid (RenderVKRTReflections 1): SSR is primary and RT fills in only where SSR has no confident answer, replacing the probe share. With SSR off, RT already covers every smooth pixel, but that mode was never designed or tuned as the top-quality path.

Why

SSR reflects only what's on screen and re-reads the previous frame, so every frame adds another bounce. In mirror-like enclosures (a box of gold walls) any small error loops between the walls and spreads, and there's no proper multi-bounce control. In the gold-cube test, SSR + RT together showed a faint glow that neither had alone.
Pure RT gives correct off-screen and occluded reflections, avatars included, with one consistent lighting model under GI.

Scope (to investigate)

A quality mode where RT handles all reflections with SSR off, with a clear user-facing preset (the old "reserved" RenderVKRTReflections 2 slot is a candidate).
Roughness range: today RT only traces surfaces smoother than RenderVKRTReflectionsRough. Glossy and rough reflections need a sampled-lobe trace plus a denoiser, or DLSS Ray Reconstruction.
Multi-bounce: optional bounded secondary reflection bounces (a mirror seen in a mirror) instead of SSR's frame feedback.
Ray budget and cost at 1080p / 4K and under DLSS, plus a fallback when RT is unavailable.
The open RT reflection work this depends on: hit shading quality, alpha / blend handling, the hit occlusion and haze rules under GI (#87 x #859), and probe removal under GI (#968).

Done when

With SSR off, RT reflections are the best-looking reflection path on the 5090 reference machine, with no light leaks in sealed rooms, stable (no flicker), and a measured cost per tier.

Final design target for maximum quality: **ray-traced reflections as the complete reflection path, with screen-space reflections (SSR) off.** Today RT reflections are hybrid (`RenderVKRTReflections 1`): SSR is primary and RT fills in only where SSR has no confident answer, replacing the probe share. With SSR off, RT already covers every smooth pixel, but that mode was never designed or tuned as the top-quality path. ## Why - SSR reflects only what's on screen and re-reads the previous frame, so every frame adds another bounce. In mirror-like enclosures (a box of gold walls) any small error loops between the walls and spreads, and there's no proper multi-bounce control. In the gold-cube test, SSR + RT together showed a faint glow that neither had alone. - Pure RT gives correct off-screen and occluded reflections, avatars included, with one consistent lighting model under GI. ## Scope (to investigate) - A quality mode where RT handles all reflections with SSR off, with a clear user-facing preset (the old "reserved" `RenderVKRTReflections 2` slot is a candidate). - Roughness range: today RT only traces surfaces smoother than `RenderVKRTReflectionsRough`. Glossy and rough reflections need a sampled-lobe trace plus a denoiser, or DLSS Ray Reconstruction. - Multi-bounce: optional bounded secondary reflection bounces (a mirror seen in a mirror) instead of SSR's frame feedback. - Ray budget and cost at 1080p / 4K and under DLSS, plus a fallback when RT is unavailable. - The open RT reflection work this depends on: hit shading quality, alpha / blend handling, the hit occlusion and haze rules under GI (#87 x #859), and probe removal under GI (#968). ## Done when With SSR off, RT reflections are the best-looking reflection path on the 5090 reference machine, with no light leaks in sealed rooms, stable (no flicker), and a measured cost per tier.

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2026-10-23 16:43:50 +00:00

sky_line added this to the Slipstream project

2026-10-23 16:43:50 +00:00

sky_line self-assigned this

2026-10-26 02:58:24 +00:00