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UE4 engine customizes screenpass and MRT output

2022-07-28 08:22:00 【Elder martial brother Dai Dai】

Preface

In front of the blog (UE4 4.27) Plug in add GlobalShder We define a GlobalShader Right one RT After treatment , That blog is also customized VertexShader, PixelShader, Vertex Format , Vertex array and so on , In fact, this is only used as a case teaching , In fact, UE4 There is a pattern in the engine ( Multiple sheets ) Texture post-processing has built-in RenderPass, It is ScreenPass.UE4 By default, we define FScreenVS And supporting DrawRectangle function , We just need to write ourselves easily PixelShader, After processing .

ScreenPass and MRT At the same time, output grayscale image and brightness adjustment image

here MRT yes MultiRenderTarget.

grayscale

Here I choose floating point algorithm .

Brightness adjustment chart

Color = Scale * Color

establish MRT Of ScreenPass Key code

FScreenVS + Self defined PixelShaderPass, The other is FRHIRenderPassInfo Input of must be specified FRHITexture Array

Self defined PixelShaderPass---DrawShader.usf


#include "/Engine/Public/Platform.ush"

Texture2D InTexture;
SamplerState InTextureSampler;

float4 MyColor;
float MyColorScale;

void MainPS(
	in float2 UV : TEXCOORD0,
	out float4 OutColor1 : SV_Target0,
	out float4 OutColor2 : SV_Target1)
{
	float4 TextureColor = InTexture.Sample(InTextureSampler, UV);
	float Gray = 0.3 * TextureColor.r + 0.59 * TextureColor.g + 0.11 * TextureColor.b;
	OutColor1 = float4(Gray, Gray, Gray, 1.0);
    OutColor2 = MyColor * TextureColor * MyColorScale;
}

RenderPass Code

static void DrawTestShaderToRenderTexture_RenderThread(
	FRHICommandListImmediate& RHICmdList,
	FTexture* InTextureResource,
	FTextureRenderTargetResource* OutGrayRTReource,
	FTextureRenderTargetResource* OutScaleRTReource,
	ERHIFeatureLevel::Type FeatureLevel,
	const FLinearColor& Color,
	float ColorScale)
{
	check(IsInRenderingThread());

	FRHITexture2D* OutGrayRTT = OutGrayRTReource->GetRenderTargetTexture();
	FRHITexture2D* OutScaleRTT = OutScaleRTReource->GetRenderTargetTexture();
	if (nullptr == OutGrayRTT || nullptr == OutScaleRTT)
		return;

	if (OutGrayRTT->GetSizeX() != OutScaleRTT->GetSizeX() || OutGrayRTT->GetSizeY() != OutScaleRTT->GetSizeY())
		return;

	FRHITexture* RTS[] = { OutGrayRTT, OutScaleRTT };
	IRendererModule* RendererModule = &FModuleManager::GetModuleChecked<IRendererModule>("Renderer");

	RHICmdList.Transition(FRHITransitionInfo(OutGrayRTT, ERHIAccess::SRVMask, ERHIAccess::RTV));
	RHICmdList.Transition(FRHITransitionInfo(OutScaleRTT, ERHIAccess::SRVMask, ERHIAccess::RTV));
	
	FRHIRenderPassInfo RPInfo(2, RTS, ERenderTargetActions::DontLoad_Store);
	RHICmdList.BeginRenderPass(RPInfo, TEXT("Render Test Shader To Texture"));
	{

		// Get Shaders
		FGlobalShaderMap* GlobalShaderMap = GetGlobalShaderMap(FeatureLevel);
		TShaderMapRef<FScreenVS> VertexShader(GlobalShaderMap);
		TShaderMapRef<FDrawPS> PixelShader(GlobalShaderMap);

		// Setup Pipeline state
		FGraphicsPipelineStateInitializer GraphicsPSOInit;
		RHICmdList.ApplyCachedRenderTargets(GraphicsPSOInit);
		GraphicsPSOInit.DepthStencilState = TStaticDepthStencilState<false, CF_Always>::GetRHI();
		GraphicsPSOInit.BlendState = TStaticBlendState<>::GetRHI();
		GraphicsPSOInit.RasterizerState = TStaticRasterizerState<>::GetRHI();

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

		// Upate viewport
		FIntPoint ViewportSize(OutGrayRTT->GetSizeX(), OutGrayRTT->GetSizeY());
		RHICmdList.SetViewport(0, 0, 0.0f, ViewportSize.X, ViewportSize.Y, 1.0f);

		// update shader uniform parameters
		PixelShader->SetParam(RHICmdList, InTextureResource, Color, ColorScale);


		RendererModule->DrawRectangle(RHICmdList, 0, 0, ViewportSize.X, ViewportSize.Y, 0, 0, 1, 1, ViewportSize, FIntPoint(1, 1), VertexShader);
	}
	RHICmdList.EndRenderPass();

	RHICmdList.Transition(FRHITransitionInfo(OutGrayRTT, ERHIAccess::RTV, ERHIAccess::SRVMask));
	RHICmdList.Transition(FRHITransitionInfo(OutScaleRTT, ERHIAccess::RTV, ERHIAccess::SRVMask));
}