[Epic] Ambient occlusion tiers: GTAO (screen-space, replaces SSAO) + ray-traced AO (RTAO)

sky_line commented

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

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Goal: best-available ambient occlusion per hardware tier, all writing the same AO target that the lit pass applies to ambient/probe light (not direct light):

RTAO on ray-tracing GPUs: true occlusion, including off-screen and hidden occluders.
GTAO (Ground-Truth AO, Jimenez et al. 2016) as the screen-space tier for GPUs without RT. It replaces the LL-parity 8-tap SSAO, which stays available for comparison.

Status (2026-10-10)

Done: the consumer side. clean_ao.comp writes the shared AO target (LL-parity SSAO, 8 taps plus LL's blur, with geometric-normal / contact-slope / strength options). The lit pass reads it; RenderVKAOStandard selects standard vs LL-parity application. It runs async next to the RT shadow mask (q_mask_ao).
In progress: GTAO as a live-switchable method (RenderVKAOMethod: 0 = SSAO, 1 = GTAO) for an in-world A/B against SSAO, with its own GPU timer marks.
Later: RTAO.

GTAO (part 1)

Per pixel: N rotated slices, a screen-space horizon search within a world-space radius, then the analytic cosine-weighted visibility integral around the projected normal.
Optional: thickness heuristic, multi-bounce approximation, half-res option.
Writes the same AO target, so the blur and the consumer are unchanged.
A/B in-world: creases, flat-surface self-occlusion (SSAO greys flat floors), halos at depth edges, avatar contact shadows; cost from the GPU timers.
Becomes the non-RT tier (#98 hardware tiers).

RTAO (part 2, later)

Trace: half-res, 1 cosine-weighted ray/pixel, short radius (0.5-2 m), first-hit termination. It runs inside the async RT shadow-mask dispatch as an extra channel (shared setup); alpha-mask occluders go through the candidate loop and opacity micromaps.
Denoise: temporal (history, reprojection with the existing motion vectors, reactive term for animated avatars) plus spatial; reuse the shadow SVGF stages, adapted to the AO signal. Then a bilateral upsample.
Settings: RenderVKAOMethod 2 = RT, default on RT-capable GPUs once tuned. Radius/strength shared.
Expected cost on a 5090 at 4K: ~0.4-0.8 ms trace + ~0.3 ms denoise, mostly overlapped on the async queue.
A/B against GTAO, which is the right baseline.

Relates: #21 SSAO, #85 denoiser epic, #98 hardware tiers.

**Goal:** best-available ambient occlusion per hardware tier, all writing the same AO target that the lit pass applies to ambient/probe light (not direct light): - **RTAO** on ray-tracing GPUs: true occlusion, including off-screen and hidden occluders. - **GTAO** (Ground-Truth AO, Jimenez et al. 2016) as the screen-space tier for GPUs without RT. It replaces the LL-parity 8-tap SSAO, which stays available for comparison. ### Status (2026-10-10) - **Done:** the consumer side. `clean_ao.comp` writes the shared AO target (LL-parity SSAO, 8 taps plus LL's blur, with geometric-normal / contact-slope / strength options). The lit pass reads it; `RenderVKAOStandard` selects standard vs LL-parity application. It runs async next to the RT shadow mask (`q_mask_ao`). - **In progress:** **GTAO** as a live-switchable method (`RenderVKAOMethod`: 0 = SSAO, 1 = GTAO) for an in-world A/B against SSAO, with its own GPU timer marks. - **Later:** **RTAO**. ### GTAO (part 1) - **Per pixel:** N rotated slices, a screen-space horizon search within a world-space radius, then the analytic cosine-weighted visibility integral around the projected normal. - **Optional:** thickness heuristic, multi-bounce approximation, half-res option. - Writes the same AO target, so the blur and the consumer are unchanged. - **A/B in-world:** creases, flat-surface self-occlusion (SSAO greys flat floors), halos at depth edges, avatar contact shadows; cost from the GPU timers. - Becomes the non-RT tier (#98 hardware tiers). ### RTAO (part 2, later) - **Trace:** half-res, 1 cosine-weighted ray/pixel, short radius (0.5-2 m), first-hit termination. It runs inside the async RT shadow-mask dispatch as an extra channel (shared setup); alpha-mask occluders go through the candidate loop and opacity micromaps. - **Denoise:** temporal (history, reprojection with the existing motion vectors, reactive term for animated avatars) plus spatial; reuse the shadow SVGF stages, adapted to the AO signal. Then a bilateral upsample. - **Settings:** `RenderVKAOMethod` 2 = RT, default on RT-capable GPUs once tuned. Radius/strength shared. - **Expected cost** on a 5090 at 4K: ~0.4-0.8 ms trace + ~0.3 ms denoise, mostly overlapped on the async queue. - **A/B against GTAO**, which is the right baseline. **Relates:** #21 SSAO, #85 denoiser epic, #98 hardware tiers.

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

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

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2026-09-27 05:44:59 +00:00

SSAO #21

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2026-09-27 23:46:27 +00:00

Vulkan: screen-space ambient occlusion (LL/Alchemy parity + standard mode)

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

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2026-10-10 05:06:35 +00:00

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2026-10-10 05:33:01 +00:00

[Epic] RT denoiser (shadows, AO, GI) #85

sky_line changed title from ~~[Epic] Ray-traced ambient occlusion (SSAO fallback)~~ to [Epic] Ambient occlusion tiers: GTAO (screen-space, replaces SSAO) + ray-traced AO (RTAO)

2026-10-10 11:24:19 +00:00

sky_line commented

2026-10-10 11:24:19 +00:00

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Started 2026-10-10 with part 1, GTAO as a live-switchable method for an A/B against the current SSAO. RTAO (part 2) comes later.

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2026-10-10 11:24:19 +00:00

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2026-10-10 22:19:25 +00:00

clean_ao.comp: GTAO modes (#86) -- full-res (3), half-res (4), depth/normal-aware upsample (5)

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2026-10-10 22:19:25 +00:00

VK AO: RenderVKAOMethod (0 SSAO / 1 GTAO, live) + GTAO settings + per-method GPU sub-marks (#86)

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2026-10-10 22:19:26 +00:00

Graphics prefs: AO method (SSAO/GTAO) and reflection probe compression; probe format default RGB9E5 (#86, #565)

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2026-10-11 16:37:24 +00:00

sky_line commented

2026-10-11 16:37:24 +00:00

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GTAO shipped in 1.3.0 Beta 2 (RenderVKAOMethod, SSAO or GTAO). The ray-traced AO part (RTAO) is not started, so this epic goes back to the backlog until that is picked up.

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2026-10-18 20:11:53 +00:00

#843: GTAO temporal noise -- hashed per-frame offset, no constant-step drift

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2026-10-18 20:23:50 +00:00

#843: GTAO temporal noise -- hashed per-frame offset, no constant-step drift

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2026-10-18 22:22:34 +00:00

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