RT mirrors: replace the planar hero-mirror render with ray-traced reflections on RT hardware #860

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opened 2026-10-19 02:35:38 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-19 02:35:38 +00:00

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Follow-up to #859 (hybrid RT reflections).

Goal

On RT-capable hardware, render surfaces flagged as mirrors (SL "hero probe" / mirror objects) with ray-traced reflections instead of the per-frame planar/hero re-render of the whole scene.

Why

The hero mirror re-renders the full scene from the mirrored viewpoint every frame: a large fixed cost, paid whether the mirror covers 2% or 100% of the screen.
RT cost scales with the mirror's on-screen pixels only; a small mirror across the room becomes nearly free.

Depends on

The #859 hybrid fallback is not sufficient: its cheap hit shading (no local/projector lights, no second bounce, half-res option, RT scene lacks particles/some alpha) is acceptable on glossy floors but obvious on a perfect mirror. This needs the later full-RT reflection mode (RenderVKRTReflections = 2) with proper hit lighting:

local + projector lights at the hit (clustered light lookup or ReSTIR-style sampling)
full material evaluation at the hit
at least one extra bounce, or probe fallback for secondary reflections
a plan for content missing from the TLAS (particles, alpha-blended faces, water, sky)

Scope

Keep honouring the mirror flag set by content creators; only the drawing method changes.
Mirror pixels: forced roughness 0, full resolution, no SSR-miss gating (trace every mirror pixel, or SSR first if quality-equivalent).
The planar/hero mirror path stays as the fallback for non-RT cards and when RT stands down under VRAM pressure.
Setting to choose planar vs RT mirrors on RT hardware, for A/B comparison.
GPU timers on both paths; A/B against the planar mirror at a fixed camera (small mirror far away, full-screen mirror up close).

Acceptance

Visual parity with the planar mirror (lit rooms, avatars, alpha, particles) or documented, accepted gaps.
Lower GPU time than the planar mirror in typical scenes.

Follow-up to #859 (hybrid RT reflections). ## Goal On RT-capable hardware, render surfaces flagged as mirrors (SL "hero probe" / mirror objects) with ray-traced reflections instead of the per-frame planar/hero re-render of the whole scene. ## Why - The hero mirror re-renders the full scene from the mirrored viewpoint every frame: a large fixed cost, paid whether the mirror covers 2% or 100% of the screen. - RT cost scales with the mirror's on-screen pixels only; a small mirror across the room becomes nearly free. ## Depends on The #859 hybrid fallback is **not** sufficient: its cheap hit shading (no local/projector lights, no second bounce, half-res option, RT scene lacks particles/some alpha) is acceptable on glossy floors but obvious on a perfect mirror. This needs the later full-RT reflection mode (`RenderVKRTReflections` = 2) with proper hit lighting: - local + projector lights at the hit (clustered light lookup or ReSTIR-style sampling) - full material evaluation at the hit - at least one extra bounce, or probe fallback for secondary reflections - a plan for content missing from the TLAS (particles, alpha-blended faces, water, sky) ## Scope - Keep honouring the mirror flag set by content creators; only the drawing method changes. - Mirror pixels: forced roughness 0, full resolution, no SSR-miss gating (trace every mirror pixel, or SSR first if quality-equivalent). - The planar/hero mirror path stays as the fallback for non-RT cards and when RT stands down under VRAM pressure. - Setting to choose planar vs RT mirrors on RT hardware, for A/B comparison. - GPU timers on both paths; A/B against the planar mirror at a fixed camera (small mirror far away, full-screen mirror up close). ## Acceptance - Visual parity with the planar mirror (lit rooms, avatars, alpha, particles) or documented, accepted gaps. - Lower GPU time than the planar mirror in typical scenes.

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2026-10-19 02:35:38 +00:00

sky_line added this to the Slipstream project

2026-10-19 02:35:38 +00:00

sky_line referenced this issue

2026-10-19 02:35:43 +00:00

Hybrid reflections: ray-traced fallback where SSR misses (off-screen / occluded content) #859

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