UnrealEngine/Engine/Shaders/Private/MegaLights/MegaLightsVisibleLightHash.usf

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

#include "../Common.ush"
#include "MegaLights.ush"

RWStructuredBuffer<uint> RWVisibleLightHash;
RWStructuredBuffer<uint> RWVisibleLightMaskHash;

#ifdef VisibleLightHashCS

Texture2D<uint> LightSamples;
Texture2D<uint> LightSampleRays;

uint2 VisibleLightHashViewMinInTiles;
uint2 VisibleLightHashViewSizeInTiles;

/**
 * Prepare visible light list for light guiding in the next frame
 */
[numthreads(THREADGROUP_SIZE, THREADGROUP_SIZE, 1)]
void VisibleLightHashCS(
	uint3 GroupId : SV_GroupID,
	uint3 GroupThreadId : SV_GroupThreadID,
	uint3 DispatchThreadId : SV_DispatchThreadID)
{	
	uint VisibleLightHash[VISIBLE_LIGHT_HASH_SIZE];
	uint VisibleLightMaskHash[VISIBLE_LIGHT_HASH_SIZE];
	for (uint IndexInHash = 0; IndexInHash < VISIBLE_LIGHT_HASH_SIZE; ++IndexInHash)
	{
		VisibleLightHash[IndexInHash] = 0;
		VisibleLightMaskHash[IndexInHash] = 0;
	}

	const uint2 VisibleLightHashTileSize = (uint(THREADGROUP_SIZE) >> DownsampleFactorMultShift) * uint2(NUM_SAMPLES_PER_PIXEL_2D_X, NUM_SAMPLES_PER_PIXEL_2D_Y);
	const uint2 TileCoord = VisibleLightHashViewMinInTiles + GroupId.xy;
	const uint2 TileSampleCoord = TileCoord * VisibleLightHashTileSize;
	const uint2 TileSampleCoordMax = (TileCoord + 1) * VisibleLightHashTileSize;
	const uint NumSamplesPerThreadX = DivideAndRoundUp(VisibleLightHashTileSize.x, THREADGROUP_SIZE);
	const uint NumSamplesPerThreadY = DivideAndRoundUp(VisibleLightHashTileSize.y, THREADGROUP_SIZE);

	for (uint SampleOffsetY = 0; SampleOffsetY < NumSamplesPerThreadY; ++SampleOffsetY)
	{
		for (uint SampleOffsetX = 0; SampleOffsetX < NumSamplesPerThreadX; ++SampleOffsetX)
		{
			uint2 SampleCoord = TileSampleCoord + GroupThreadId.xy * uint2(NumSamplesPerThreadX, NumSamplesPerThreadY) + uint2(SampleOffsetX, SampleOffsetY);
			if (all(SampleCoord < TileSampleCoordMax))
			{
				FLightSample LightSample = UnpackLightSample(LightSamples[SampleCoord]);
				if (LightSample.bVisible)
				{
					uint Hash = PCGHash(LightSample.LocalLightIndex);

					// Mark light
					{
						uint WrappedLocalLightIndex = Hash % (4 * 32);
						uint DWORDIndex = WrappedLocalLightIndex / 32;
						uint BitMask = 1u << (WrappedLocalLightIndex % 32);
						VisibleLightHash[DWORDIndex] |= BitMask;

						WrappedLocalLightIndex = (Hash >> 8) % (4 * 32);
						DWORDIndex = WrappedLocalLightIndex / 32;
						BitMask = 1u << (WrappedLocalLightIndex % 32);
						VisibleLightHash[DWORDIndex] |= BitMask;
					}

					// Mark light mask
					{
						FLightSampleRay LightSampleRay = UnpackLightSampleRay(LightSampleRays[SampleCoord]);

						uint2 RandomCoord;
						RandomCoord.x = LightSampleRay.UV.x > 0.5f ? 1 : 0;
						RandomCoord.y = LightSampleRay.UV.y > 0.5f ? 1 : 0;

						uint WrappedLocalLightIndex = (Hash >> 16) % 32;
						uint DWORDIndex = WrappedLocalLightIndex / 8;
						uint BitMask = 1u << (4 * (WrappedLocalLightIndex % 8) + RandomCoord.x + 2 * RandomCoord.y);
						VisibleLightMaskHash[DWORDIndex] |= BitMask;
					}
				}
			}
		}
	}

	for (uint IndexInHash = 0; IndexInHash < VISIBLE_LIGHT_HASH_SIZE; ++IndexInHash)
	{
		VisibleLightHash[IndexInHash] = WaveActiveBitOr(VisibleLightHash[IndexInHash]);
		VisibleLightMaskHash[IndexInHash] = WaveActiveBitOr(VisibleLightMaskHash[IndexInHash]);
	}

	uint LaneIndex = WavePrefixCountBits(true);
	if (LaneIndex < VISIBLE_LIGHT_HASH_SIZE)
	{
		const uint HashBufferBase = VISIBLE_LIGHT_HASH_SIZE * (TileCoord.y * VisibleLightHashViewSizeInTiles.x + TileCoord.x);
		InterlockedOr(RWVisibleLightHash[HashBufferBase + LaneIndex], VisibleLightHash[LaneIndex]);
		InterlockedOr(RWVisibleLightMaskHash[HashBufferBase + LaneIndex], VisibleLightMaskHash[LaneIndex]);
	}
}

#endif // VisibleLightHashCS

#ifdef VolumeVisibleLightHashCS

Texture3D<uint> LightSamples;

uint3 VolumeVisibleLightHashTileSize;
uint3 VolumeVisibleLightHashViewSizeInTiles;

/**
 * Prepare visible light list for light guiding in the next frame
 */
[numthreads(THREADGROUP_SIZE, THREADGROUP_SIZE, THREADGROUP_SIZE)]
void VolumeVisibleLightHashCS(
	uint3 GroupId : SV_GroupID,
	uint3 GroupThreadId : SV_GroupThreadID,
	uint3 DispatchThreadId : SV_DispatchThreadID)
{	
	uint VisibleLightHash[VISIBLE_LIGHT_HASH_SIZE];
	for (uint IndexInHash = 0; IndexInHash < VISIBLE_LIGHT_HASH_SIZE; ++IndexInHash)
	{
		VisibleLightHash[IndexInHash] = 0;
	}

	const uint3 NumSamplesPerTile = VolumeVisibleLightHashTileSize * uint3(NUM_SAMPLES_PER_VOXEL_3D_X, NUM_SAMPLES_PER_VOXEL_3D_Y, NUM_SAMPLES_PER_VOXEL_3D_Z);

	const uint3 TileCoord = DispatchThreadId.xyz;
	const uint3 TileSampleCoord = TileCoord * NumSamplesPerTile;
	const uint3 TileSampleCoordMax = (TileCoord + 1) * NumSamplesPerTile;
	const uint NumSamplesPerThreadX = NumSamplesPerTile.x;
	const uint NumSamplesPerThreadY = NumSamplesPerTile.y;
	const uint NumSamplesPerThreadZ = NumSamplesPerTile.z;

	for (uint SampleOffsetZ = 0; SampleOffsetZ < NumSamplesPerThreadZ; ++SampleOffsetZ)
	{
		for (uint SampleOffsetY = 0; SampleOffsetY < NumSamplesPerThreadY; ++SampleOffsetY)
		{
			for (uint SampleOffsetX = 0; SampleOffsetX < NumSamplesPerThreadX; ++SampleOffsetX)
			{
				uint3 SampleCoord = TileSampleCoord + uint3(SampleOffsetX, SampleOffsetY, SampleOffsetZ);
				if (all(SampleCoord < TileSampleCoordMax))
				{
					FLightSample LightSample = UnpackLightSample(LightSamples[SampleCoord]);
					if (LightSample.bVisible)
					{
						uint Hash = PCGHash(LightSample.LocalLightIndex);

						// Mark light
						{
							uint WrappedLocalLightIndex = Hash % (4 * 32);
							uint DWORDIndex = WrappedLocalLightIndex / 32;
							uint BitMask = 1u << (WrappedLocalLightIndex % 32);
							VisibleLightHash[DWORDIndex] |= BitMask;

							WrappedLocalLightIndex = (Hash >> 8) % (4 * 32);
							DWORDIndex = WrappedLocalLightIndex / 32;
							BitMask = 1u << (WrappedLocalLightIndex % 32);
							VisibleLightHash[DWORDIndex] |= BitMask;
						}
					}
				}
			}
		}
	}

	const uint HashBufferBase = VISIBLE_LIGHT_HASH_SIZE * ((TileCoord.z * VolumeVisibleLightHashViewSizeInTiles.y + TileCoord.y) * VolumeVisibleLightHashViewSizeInTiles.x + TileCoord.x);

	for (uint IndexInHash = 0; IndexInHash < VISIBLE_LIGHT_HASH_SIZE; ++IndexInHash)
	{
		InterlockedOr(RWVisibleLightHash[HashBufferBase + IndexInHash], VisibleLightHash[IndexInHash]);
	}
}

#endif // VolumeVisibleLightHashCS