WDScreenSpaceShadows

Bend Studio's wavefront screen-space contact shadows for O3DE / Atom. A compute pass ray-marches the scene depth buffer toward the sun to produce a screen-space shadow mask, which is optionally combined into the directional-light visibility so the sun is darkened in contact areas that cascaded shadow maps miss — with no lighting-shader edits.

Ports Bend Studio's Apache-2.0 reference implementation (Graham Aldridge / © 2023 Sony Interactive Entertainment). See THIRD_PARTY.md and External/BendSSS/LICENSE.

How it works

The feature processor injects a parent pass before Forward with three children:

1. WDSSSComputePass — runs Bend's wavefront march (one compute dispatch per entry in the CPU dispatch list) over the hardware depth (DepthMSAA, read as Texture2DMS sample 0), writing an R8_UNORM mask published as the WDSSSMask pipeline-global.
2. WDSSSDebugPass — fullscreen grayscale visualization of the mask (only when the debug view is on).
3. WDSSSApplyPass — mins the mask into Atom's FullscreenShadowBuffer in place, so the Forward lighting (which already reads m_fullscreenShadow) darkens the sun. Only runs when apply is on.

Controls

Console variables (all default off):

CVar	Meaning
r.wdSSSEnabled 1	Produce the mask (and enable the debug view / apply).
r.wdSSSDebugView 1	Show the mask as a grayscale overlay (1 = lit, 0 = shadowed).
r.wdSSSApply 1	Darken the sun with the mask (min into FullscreenShadowBuffer).

ImGui panel: "WD Screen Space Shadows" → SSS Panel — toggles, the sun direction, and the Bend tunables (surface thickness, bilinear threshold, shadow contrast, edge flags).

Entity Inspector component: add WD Screen Space Shadows (Add Component → Level/Game → Graphics/Lighting) to a Level entity (or any entity) for per-level, authored + persisted settings — the same enabled/apply toggles, sun direction, and tuning, shown as sliders/checkboxes with tooltips.

Current limitations / follow-ups

• Sun direction is config-driven. DirectionalLightFeatureProcessorInterface exposes no CPU-side direction getter, and Bend's dispatch builder needs the light's screen position on the CPU, so set the sun direction (ImGui / component) to match the scene's sun. Auto-follow (reading the sun entity / light buffer) is a follow-up.
• MSAA hardware depth. WDSSS reads DepthMSAA as Texture2DMS (sample 0), matching Atom's FullscreenShadow and keeping Bend's non-linear depth space. A non-MSAA pipeline needs a Texture2D supervariant (the o_msaa path), not wired yet (TODO).
• Apply mechanism. The apply pass does an in-place R8 UAV min on FullscreenShadowBuffer (created as a render target by the shadow chain). If the frame graph rejects UAV usage on it, the fallbacks are: (A) re-publish FullscreenShadowBuffer from the apply output, or (B) a shader-option-guarded multiply in DirectionalLightShadow.azsli. This is the one item to watch on first run in the live Editor.
• Shadow length (SAMPLE_COUNT/HARD_SHADOW_SAMPLES/FADE_OUT_SAMPLES) is a compile-time shader #define (it sizes a groupshared array); runtime tuning would be a supervariant.
• Early-out (Bend's UseEarlyOut, a sky/occluded-pixel cull) is removed in WDSSS: it uses wave intrinsics that need a Vulkan 1.1 SPIR-V target env Atom doesn't set. Re-enabling it (a perf win) would require -fspv-target-env=vulkan1.1 on the Vulkan build.

License

WDScreenSpaceShadows is licensed under the MIT License. Feel free to fork or use privately if needed, just make sure to properly attribute.