UnrealEngine/Engine/Shaders/Private/Lumen/LumenScreenProbeTracingCommon.ush

// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "../MonteCarlo.ush"
#include "../BlueNoise.ush"

float2 GetProbeTexelCenter(uint2 ScreenTileCoord)
{
#define JITTER_RAY_DIRECTION 1
#if JITTER_RAY_DIRECTION
	#define BLUE_NOISE_LUT 1
	#if BLUE_NOISE_LUT
		return BlueNoiseVec2(ScreenTileCoord, ScreenProbeRayDirectionFrameIndex);
	#else
		uint2 RandomSeed = Rand3DPCG16(int3(ScreenTileCoord, 0)).xy;
		return Hammersley16(ScreenProbeRayDirectionFrameIndex % 8, 8, RandomSeed);
	#endif
#else
	return float2(0.5, 0.5);
#endif
}

RWTexture2D<uint> RWTraceHit;
RWTexture2D<float3> RWTraceRadiance;
Texture2D<uint> TraceHit;

bool IsTraceMoving(float3 ProbeWorldPosition, float ProbeSceneDepth, uint2 ScreenProbeAtlasCoord, float3 HitWorldPosition, float3 HitWorldVelocity)
{
	//@todo - for pixels that use the velocity texture in GetHistoryScreenPosition, velocities transformed to world space are too inaccurate to use for a dis-occlusion test
	// See DEBUG_VISUALIZE_PROBE_WORLD_SPEED
#define VELOCITY_IS_ACCURATE 0
#if VELOCITY_IS_ACCURATE
	float3 ProbeWorldVelocity = ScreenProbeWorldVelocity.Load(int3(ScreenProbeAtlasCoord, 0)).xyz;
	float VelocityDampening = lerp(1, .1f, saturate(ProbeSceneDepth / 10000.0f));
	float3 ProbeToHit = HitWorldPosition - ProbeWorldPosition;
	float3 PrevProbeToPrevHit = HitWorldPosition - HitWorldVelocity * VelocityDampening - (ProbeWorldPosition - ProbeWorldVelocity * VelocityDampening);
	float3 CosAngle = dot(ProbeToHit, PrevProbeToPrevHit) / max(length(ProbeToHit) * length(PrevProbeToPrevHit), .0001f);
	float CosProbeTraceVelocityAngleThreshold = cos(1.0f * (float)PI / 180.0f);
	return CosAngle < CosProbeTraceVelocityAngleThreshold;
#else
	float ProbeWorldSpeed = GetScreenProbeSpeed(ScreenProbeAtlasCoord);

	return abs(ProbeWorldSpeed - length(HitWorldVelocity)) / max(ProbeSceneDepth, 100.0f) > RelativeSpeedDifferenceToConsiderLightingMoving;
#endif
}

float EncodeProbeHitDistanceForFiltering(float HitDistance)
{
	// Encode one negative value to indicate invalid ray
	return sqrt(HitDistance / GetProbeMaxHitDistance()) * 254.0f / 255.0f + 1.0f / 255.0f;
}

float DecodeProbeHitDistanceForFiltering(float Encoded)
{
	float Linear = Encoded * Encoded * GetProbeMaxHitDistance();
	return (Linear - 1.0f / 255.0f) * 255.0f / 254.0f;
}

// Stores a packed ray info for each tracing shader lane storing the direction and mip level of the ray to trace
Texture2D<uint> StructuredImportanceSampledRayInfosForTracing;
uint MaxImportanceSamplingOctahedronResolution;
uint ScreenProbeBRDFOctahedronResolution;

#define INVALID_TRACING_COORD 0xFE

uint PackRayInfo(uint2 TexelCoord, uint Level)
{
	// Pack in 16 bits
	return (TexelCoord.x & 0x3F) | ((TexelCoord.y & 0x3F) << 6) | ((Level & 0xF) << 12);
}

void UnpackRayInfo(uint RayInfo, out uint2 TexelCoord, out uint Level)
{
	TexelCoord.x = RayInfo & 0x3F;
	TexelCoord.y = (RayInfo >> 6) & 0x3F;
	Level = (RayInfo >> 12) & 0xF;
}

void GetProbeTracingUV(
	uint2 TraceBufferCoord,
	uint2 TracingTexelCoord,
	float2 ProbeTexelCenter,
	float NumSupersamples,
	out float2 ProbeUV,
	out float ConeHalfAngle)
{
#if STRUCTURED_IMPORTANCE_SAMPLING
	uint RayInfo = StructuredImportanceSampledRayInfosForTracing[TraceBufferCoord];
	uint2 RayTexelCoord;
	uint RayLevel;
	UnpackRayInfo(RayInfo, RayTexelCoord, RayLevel);

	uint MipSize = MaxImportanceSamplingOctahedronResolution >> RayLevel;
	float InvSupersampledMipSize = 1.0f / (MipSize * NumSupersamples);
	ProbeUV = (RayTexelCoord * NumSupersamples + ProbeTexelCenter) * InvSupersampledMipSize;
	ConeHalfAngle = acosFast(1.0f - 1.0f * InvSupersampledMipSize * InvSupersampledMipSize);

#else
	ProbeUV = (TracingTexelCoord * NumSupersamples + ProbeTexelCenter) / float(ScreenProbeTracingOctahedronResolution * NumSupersamples);
	// Evenly distributing the sphere solid angle among all cones
	ConeHalfAngle = acosFast(1.0f - 1.0f / (float)(ScreenProbeTracingOctahedronResolution * ScreenProbeTracingOctahedronResolution * NumSupersamples * NumSupersamples));
#endif
}

uint2 GetTraceBufferCoord(uint2 ScreenProbeAtlasCoord, uint2 TraceTexelCoord)
{
	#define DEINTERLEAVED_TRACE_BUFFER_STORAGE 0
	#if DEINTERLEAVED_TRACE_BUFFER_STORAGE
		return TraceTexelCoord * ScreenProbeAtlasViewSize + ScreenProbeAtlasCoord;
	#else
		return ScreenProbeAtlasCoord * ScreenProbeTracingOctahedronResolution + TraceTexelCoord;
	#endif
}

bool ShouldTraceScreenProbeTexel(uint2 TraceBufferCoord, float ProbeSceneDepth)
{
	bool bShouldTrace = ProbeSceneDepth > 0.0f;
	return bShouldTrace;
}

void GetScreenProbeTexelRay(
	uint2 TraceBufferCoord,
	uint2 TraceTexelCoord,
	uint2 ScreenTileCoord,
	float3 TranslatedWorldPosition,
	inout float3 RayDirection,
	inout float TraceDistance,
	inout float ConeHalfAngle)
{
	float2 ProbeUV;
	GetProbeTracingUV(TraceBufferCoord, TraceTexelCoord, GetProbeTexelCenter(ScreenTileCoord), 1, ProbeUV, ConeHalfAngle);

	RayDirection = EquiAreaSphericalMapping(ProbeUV);
}

float3 GetScreenProbeNormalForBiasing(uint2 ScreenProbeAtlasCoord, float3 RayWorldDirection, out bool bBackfaceRay)
{
	bBackfaceRay = false;
	float3 SceneNormal = GetScreenProbeNormal(ScreenProbeAtlasCoord);

	if (GetScreenProbeIsTwoSidedFoliage(ScreenProbeAtlasCoord))
	{
		bBackfaceRay = dot(SceneNormal, RayWorldDirection) < 0.0f;

		if (bBackfaceRay)
		{
			SceneNormal *= -1;
		}
	}

	return SceneNormal;
}

float3 GetScreenProbeNormalForBiasing(uint2 ScreenProbeAtlasCoord, float3 RayWorldDirection)
{
	bool bBackfaceRay;
	return GetScreenProbeNormalForBiasing(ScreenProbeAtlasCoord, RayWorldDirection, bBackfaceRay);
}

void WriteTraceHit(uint2 TraceBufferCoord, float HitDistance, bool bHit, bool bFastMoving, bool bReachedRadianceCache)
{
	RWTraceHit[TraceBufferCoord] = EncodeProbeRayDistance(HitDistance, bHit, bFastMoving, bReachedRadianceCache);
}

FProbeRayDistance ReadTraceHit(uint2 TraceBufferCoord)
{
	return DecodeProbeRayDistance(TraceHit[TraceBufferCoord].x);
}

void ReadTraceTexel(uint DispatchThreadId, out uint ScreenProbeIndex, out uint2 TraceTexelCoord)
{
	DecodeScreenProbeTraceTexel(CompactedTraceTexelData[DispatchThreadId], ScreenProbeIndex, TraceTexelCoord);
}