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

/*=============================================================================
	PixelShaderUtils.cpp: Implementations of utilities for pixel shaders.
=============================================================================*/

#include "PixelShaderUtils.h"
#include "CommonRenderResources.h"
#include "RenderGraph.h"

IMPLEMENT_SHADER_TYPE(, FPixelShaderUtils::FRasterizeToRectsVS, TEXT("/Engine/Private/RenderGraphUtilities.usf"), TEXT("RasterizeToRectsVS"), SF_Vertex);

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

BEGIN_SHADER_PARAMETER_STRUCT(FRasterizeToRectsUpload, )
	RDG_BUFFER_ACCESS(RectMinMaxBuffer, ERHIAccess::CopyDest)
END_SHADER_PARAMETER_STRUCT()

// static
void FPixelShaderUtils::DrawFullscreenTriangle(FRHICommandList& RHICmdList, uint32 InstanceCount)
{
	RHICmdList.SetStreamSource(0, GScreenRectangleVertexBuffer.VertexBufferRHI, 0);

	RHICmdList.DrawIndexedPrimitive(
		GScreenRectangleIndexBuffer.IndexBufferRHI,
		/*BaseVertexIndex=*/ 0,
		/*MinIndex=*/ 0,
		/*NumVertices=*/ 3,
		/*StartIndex=*/ 6,
		/*NumPrimitives=*/ 1,
		/*NumInstances=*/ InstanceCount);
}

// static
void FPixelShaderUtils::DrawFullscreenQuad(FRHICommandList& RHICmdList, uint32 InstanceCount)
{
	RHICmdList.SetStreamSource(0, GScreenRectangleVertexBuffer.VertexBufferRHI, 0);

	RHICmdList.DrawIndexedPrimitive(
		GScreenRectangleIndexBuffer.IndexBufferRHI,
		/*BaseVertexIndex=*/ 0,
		/*MinIndex=*/ 0,
		/*NumVertices=*/ 4,
		/*StartIndex=*/ 0,
		/*NumPrimitives=*/ 2,
		/*NumInstances=*/ InstanceCount);
}

// static
void FPixelShaderUtils::InitFullscreenPipelineState(
	FRHICommandList& RHICmdList,
	const FGlobalShaderMap* GlobalShaderMap,
	const TShaderRef<FShader>& PixelShader,
	FGraphicsPipelineStateInitializer& GraphicsPSOInit)
{
	TShaderMapRef<FScreenVertexShaderVS> VertexShader(GlobalShaderMap);
		
	RHICmdList.ApplyCachedRenderTargets(GraphicsPSOInit);
	GraphicsPSOInit.BlendState = TStaticBlendState<>::GetRHI();
	GraphicsPSOInit.RasterizerState = TStaticRasterizerState<>::GetRHI();
	GraphicsPSOInit.DepthStencilState = TStaticDepthStencilState<false, CF_Always>::GetRHI();

	GraphicsPSOInit.BoundShaderState.VertexDeclarationRHI = GFilterVertexDeclaration.VertexDeclarationRHI;
	GraphicsPSOInit.BoundShaderState.VertexShaderRHI = VertexShader.GetVertexShader();
	GraphicsPSOInit.BoundShaderState.PixelShaderRHI = PixelShader.GetPixelShader();
	GraphicsPSOInit.PrimitiveType = PT_TriangleList;
}

void FPixelShaderUtils::UploadRectMinMaxBuffer(FRDGBuilder& GraphBuilder,
	const TArray<FUintVector4, SceneRenderingAllocator>& RectMinMaxArray,
	FRDGBufferRef RectMinMaxBuffer)
{
	FRasterizeToRectsUpload* PassParameters = GraphBuilder.AllocParameters<FRasterizeToRectsUpload>();
	PassParameters->RectMinMaxBuffer = RectMinMaxBuffer;

	const uint32 RectMinMaxToRenderSizeInBytes = RectMinMaxArray.GetTypeSize() * RectMinMaxArray.Num();
	const void* RectMinMaxToRenderDataPtr = RectMinMaxArray.GetData();

	GraphBuilder.AddPass(
		RDG_EVENT_NAME("UploadRectMinMaxBuffer"),
		PassParameters,
		ERDGPassFlags::Copy,
		[PassParameters, RectMinMaxToRenderSizeInBytes, RectMinMaxToRenderDataPtr](FRHICommandListImmediate& RHICmdList)
	{
		void* DestBVHQueryInfoPtr = RHILockBuffer(PassParameters->RectMinMaxBuffer->GetRHI(), 0, RectMinMaxToRenderSizeInBytes, RLM_WriteOnly);
		FPlatformMemory::Memcpy(DestBVHQueryInfoPtr, RectMinMaxToRenderDataPtr, RectMinMaxToRenderSizeInBytes);
		RHIUnlockBuffer(PassParameters->RectMinMaxBuffer->GetRHI());
	});
}