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

#include "PostProcess/PostProcessDownsample.h"
#include "PostProcess/PostProcessEyeAdaptation.h"
#include "PixelShaderUtils.h"

namespace
{
const int32 GDownsampleTileSizeX = 8;
const int32 GDownsampleTileSizeY = 8;

BEGIN_SHADER_PARAMETER_STRUCT(FDownsampleParameters, )
	SHADER_PARAMETER_STRUCT_REF(FViewUniformShaderParameters, ViewUniformBuffer)
	SHADER_PARAMETER_STRUCT(FScreenPassTextureViewportParameters, Input)
	SHADER_PARAMETER_STRUCT(FScreenPassTextureViewportParameters, Output)
	SHADER_PARAMETER_RDG_TEXTURE(Texture2D, InputTexture)
	SHADER_PARAMETER_SAMPLER(SamplerState, InputSampler)
END_SHADER_PARAMETER_STRUCT()

FDownsampleParameters GetDownsampleParameters(const FViewInfo& View, FScreenPassTexture Output, FScreenPassTexture Input, EDownsampleQuality DownsampleMethod)
{
	check(Output.IsValid());
	check(Input.IsValid());

	const FScreenPassTextureViewportParameters InputParameters = GetScreenPassTextureViewportParameters(FScreenPassTextureViewport(Input));
	const FScreenPassTextureViewportParameters OutputParameters = GetScreenPassTextureViewportParameters(FScreenPassTextureViewport(Output));

	FDownsampleParameters Parameters;
	Parameters.ViewUniformBuffer = View.ViewUniformBuffer;
	Parameters.Input = InputParameters;
	Parameters.Output = OutputParameters;
	Parameters.InputTexture = Input.Texture;
	Parameters.InputSampler = TStaticSamplerState<SF_Bilinear, AM_Clamp, AM_Clamp, AM_Clamp>::GetRHI();
	return Parameters;
}

class FDownsampleQualityDimension : SHADER_PERMUTATION_ENUM_CLASS("DOWNSAMPLE_QUALITY", EDownsampleQuality);
using FDownsamplePermutationDomain = TShaderPermutationDomain<FDownsampleQualityDimension>;

class FDownsamplePS : public FGlobalShader
{
public:
	DECLARE_GLOBAL_SHADER(FDownsamplePS);
	SHADER_USE_PARAMETER_STRUCT(FDownsamplePS, FGlobalShader);

	using FPermutationDomain = FDownsamplePermutationDomain;

	BEGIN_SHADER_PARAMETER_STRUCT(FParameters, )
		SHADER_PARAMETER_STRUCT_INCLUDE(FDownsampleParameters, Common)
		RENDER_TARGET_BINDING_SLOTS()
	END_SHADER_PARAMETER_STRUCT()

	static bool ShouldCompilePermutation(const FGlobalShaderPermutationParameters& Parameters)
	{
		return true;
	}
};

IMPLEMENT_GLOBAL_SHADER(FDownsamplePS, "/Engine/Private/PostProcessDownsample.usf", "MainPS", SF_Pixel);

class FDownsampleCS : public FGlobalShader
{
public:
	DECLARE_GLOBAL_SHADER(FDownsampleCS);
	SHADER_USE_PARAMETER_STRUCT(FDownsampleCS, FGlobalShader);

	using FPermutationDomain = FDownsamplePermutationDomain;

	BEGIN_SHADER_PARAMETER_STRUCT(FParameters, )
		SHADER_PARAMETER_STRUCT_INCLUDE(FDownsampleParameters, Common)
		SHADER_PARAMETER(FScreenTransform, DispatchThreadIdToInputUV)
		SHADER_PARAMETER_RDG_TEXTURE_UAV(RWTexture2D<float4>, OutComputeTexture)
	END_SHADER_PARAMETER_STRUCT()

	static bool ShouldCompilePermutation(const FGlobalShaderPermutationParameters& Parameters)
	{
		return IsFeatureLevelSupported(Parameters.Platform, ERHIFeatureLevel::SM5);
	}

	static void ModifyCompilationEnvironment(const FGlobalShaderPermutationParameters& Parameters, FShaderCompilerEnvironment& OutEnvironment)
	{
		FGlobalShader::ModifyCompilationEnvironment(Parameters,OutEnvironment);
		OutEnvironment.SetDefine(TEXT("THREADGROUP_SIZEX"), GDownsampleTileSizeX);
		OutEnvironment.SetDefine(TEXT("THREADGROUP_SIZEY"), GDownsampleTileSizeY);
	}
};

IMPLEMENT_GLOBAL_SHADER(FDownsampleCS, "/Engine/Private/PostProcessDownsample.usf", "MainCS", SF_Compute);
} //! namespace

FScreenPassTexture AddDownsamplePass(
	FRDGBuilder& GraphBuilder,
	const FViewInfo& View,
	const FDownsamplePassInputs& Inputs)
{
	check(Inputs.SceneColor.IsValid());

	bool bIsComputePass = View.bUseComputePasses;

	if ((Inputs.Flags & EDownsampleFlags::ForceRaster) == EDownsampleFlags::ForceRaster)
	{
		bIsComputePass = false;
	}

	FScreenPassRenderTarget Output;

	// Construct the output texture to be half resolution (rounded up to even) with an optional format override.
	{
		FRDGTextureDesc Desc = Inputs.SceneColor.Texture->Desc;
		Desc.Reset();
		Desc.Extent = FIntPoint::DivideAndRoundUp(Desc.Extent, 2);
		Desc.Extent.X = FMath::Max(1, Desc.Extent.X);
		Desc.Extent.Y = FMath::Max(1, Desc.Extent.Y);
		Desc.Flags &= ~(TexCreate_RenderTargetable | TexCreate_UAV | TexCreate_Presentable);
		Desc.Flags |= bIsComputePass ? TexCreate_UAV : TexCreate_RenderTargetable;
		Desc.Flags |= GFastVRamConfig.Downsample;
		Desc.ClearValue = FClearValueBinding(FLinearColor(0, 0, 0, 0));

		if (Inputs.FormatOverride != PF_Unknown)
		{
			Desc.Format = Inputs.FormatOverride;
		}

		if (Inputs.UserSuppliedOutput && Translate(Inputs.UserSuppliedOutput->GetDesc()) == Desc)
		{
			Output.Texture = GraphBuilder.RegisterExternalTexture(Inputs.UserSuppliedOutput, Inputs.Name);
		}
		else
		{
			Output.Texture = GraphBuilder.CreateTexture(Desc, Inputs.Name);
		}
		Output.ViewRect = FIntRect::DivideAndRoundUp(Inputs.SceneColor.ViewRect, 2);
		Output.LoadAction = ERenderTargetLoadAction::ENoAction;
	}

	if (bIsComputePass)
	{
		AddDownsampleComputePass(GraphBuilder, View, Inputs.SceneColor, Output, Inputs.Quality, bIsComputePass ? ERDGPassFlags::Compute : ERDGPassFlags::Raster);
	}
	else
	{
		FDownsamplePermutationDomain PermutationVector;
		PermutationVector.Set<FDownsampleQualityDimension>(Inputs.Quality);

		FDownsamplePS::FParameters* PassParameters = GraphBuilder.AllocParameters<FDownsamplePS::FParameters>();
		PassParameters->Common = GetDownsampleParameters(View, Output, Inputs.SceneColor, Inputs.Quality);
		PassParameters->RenderTargets[0] = Output.GetRenderTargetBinding();

		TShaderMapRef<FDownsamplePS> PixelShader(View.ShaderMap, PermutationVector);
		FPixelShaderUtils::AddFullscreenPass(
			GraphBuilder,
			View.ShaderMap,
			RDG_EVENT_NAME("Downsample(%s Quality=%s PS) %dx%d -> %dx%d",
				Output.Texture->Name,
				Inputs.Quality == EDownsampleQuality::High ? TEXT("High") : TEXT("Bilinear"),
				Inputs.SceneColor.ViewRect.Width(), Inputs.SceneColor.ViewRect.Height(),
				Output.ViewRect.Width(), Output.ViewRect.Height()),
			PixelShader,
			PassParameters,
			Output.ViewRect);
	}

	return MoveTemp(Output);
}

void AddDownsampleComputePass(FRDGBuilder& GraphBuilder, const FViewInfo& View, FScreenPassTexture Input, FScreenPassTexture Output, EDownsampleQuality Quality, ERDGPassFlags PassFlags)
{
	check(PassFlags == ERDGPassFlags::Compute || PassFlags == ERDGPassFlags::AsyncCompute);

	FDownsampleCS::FParameters* PassParameters = GraphBuilder.AllocParameters<FDownsampleCS::FParameters>();
	PassParameters->Common = GetDownsampleParameters(View, Output, Input, Quality);
	PassParameters->DispatchThreadIdToInputUV = ((FScreenTransform::Identity + 0.5f) / Output.ViewRect.Size()) * FScreenTransform::ChangeTextureBasisFromTo(FScreenPassTextureViewport(Input), FScreenTransform::ETextureBasis::ViewportUV, FScreenTransform::ETextureBasis::TextureUV);
	PassParameters->OutComputeTexture = GraphBuilder.CreateUAV(Output.Texture);

	FDownsamplePermutationDomain PermutationVector;
	PermutationVector.Set<FDownsampleQualityDimension>(Quality);

	TShaderMapRef<FDownsampleCS> ComputeShader(View.ShaderMap, PermutationVector);
	FComputeShaderUtils::AddPass(
		GraphBuilder,
		RDG_EVENT_NAME("Downsample(%s Quality=%s CS) %dx%d -> %dx%d",
			Output.Texture->Name,
			Quality == EDownsampleQuality::High ? TEXT("High") : TEXT("Bilinear"),
			Input.ViewRect.Width(), Input.ViewRect.Height(),
			Output.ViewRect.Width(), Output.ViewRect.Height()),
		PassFlags,
		ComputeShader,
		PassParameters,
		FComputeShaderUtils::GetGroupCount(Output.ViewRect.Size(), FIntPoint(GDownsampleTileSizeX, GDownsampleTileSizeY)));
}

void FSceneDownsampleChain::Init(
	FRDGBuilder& GraphBuilder,
	const FViewInfo& View,
	const FEyeAdaptationParameters& EyeAdaptationParameters,
	FScreenPassTexture HalfResolutionSceneColor,
	EDownsampleQuality DownsampleQuality,
	bool bLogLumaInAlpha)
{
	check(HalfResolutionSceneColor.IsValid());

	RDG_EVENT_SCOPE(GraphBuilder, "SceneDownsample");

	static const TCHAR* PassNames[StageCount] =
	{
		nullptr,
		TEXT("Scene(1/4)"),
		TEXT("Scene(1/8)"),
		TEXT("Scene(1/16)"),
		TEXT("Scene(1/32)"),
		TEXT("Scene(1/64)")
	};
	static_assert(UE_ARRAY_COUNT(PassNames) == StageCount, "PassNames size must equal StageCount");

	// The first stage is the input.
	Textures[0] = HalfResolutionSceneColor;

	for (uint32 StageIndex = 1; StageIndex < StageCount; StageIndex++)
	{
		const uint32 PreviousStageIndex = StageIndex - 1;

		FDownsamplePassInputs PassInputs;
		PassInputs.Name = PassNames[StageIndex];
		PassInputs.SceneColor = Textures[PreviousStageIndex];
		PassInputs.Quality = DownsampleQuality;

		Textures[StageIndex] = AddDownsamplePass(GraphBuilder, View, PassInputs);

		if (bLogLumaInAlpha)
		{
			bLogLumaInAlpha = false;

			Textures[StageIndex] = AddBasicEyeAdaptationSetupPass(GraphBuilder, View, EyeAdaptationParameters, Textures[StageIndex]);
		}
	}

	bInitialized = true;
}