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[HDRP] Improve path traced subsurface scattering for transmissive surfaces #5485

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Merged
merged 3 commits into from
Sep 1, 2021
Merged

[HDRP] Improve path traced subsurface scattering for transmissive surfaces #5485

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30c7d09
Improve subsurface scatering for transmissive surfaces
pmavridis Aug 31, 2021
091e896
Add changelog + fix throughput multiplication
pmavridis Aug 31, 2021
ea82cdc
Merge branch 'hd/bugfix' into HDRP/pt_sss_doubleside
sebastienlagarde Sep 1, 2021
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1 change: 1 addition & 0 deletions com.unity.render-pipelines.high-definition/CHANGELOG.md
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Expand Up @@ -381,6 +381,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
- Fixed issue with depth slope scale depth bias when a material uses depth offset.
- Fixed shadow sampling artifact when using the spot light shadow option 'custom spot angle'
- Fixed issue with fading in SSR applying fade factor twice, resulting in darkening of the image in the transition areas.
- Fixed path traced subsurface scattering for transmissive surfaces (case 1329403)

### Changed
- Changed Window/Render Pipeline/HD Render Pipeline Wizard to Window/Rendering/HDRP Wizard
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10 changes: 10 additions & 0 deletions ...pipelines.high-definition/Runtime/RenderPipeline/PathTracing/Shaders/PathTracingBSDF.hlsl
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Expand Up @@ -607,6 +607,16 @@ bool RandomWalk(float3 position, float3 normal, float3 diffuseColor, float3 mean
result.exitNormal = intersection.value;
}

// if the material is transmissive, pick a side for the normal randomly to properly handle thin surfaces (case 1329403)
#ifdef _MATERIAL_FEATURE_TRANSMISSION
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I will accept the PR for the fix, but let's have in mind that _MATERIAL_FEATURE_TRANSMISSION isn't a standard name for "transmission". This is define only per Material and Material don't have obligation to reuse this name (on raster side). We may need to revisit how we handle transmission from a general point of view later.

// 108 is the next available dimension after the screen space sub-pixel sampling
if (GetSample(pixelCoord, _RaytracingSampleIndex, 108) < 0.5)
{
result.exitNormal = -result.exitNormal;
}
result.throughput *= 2.0;
#endif

return true;
}

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