虚幻4渲染笔记【第二卷：不用虚幻4Shader管线使用自己的shader】

先直接上效果：

这个球的颜色是通过自己的shader实现的：

下面就来一步一步实现使用自己的shader吧。

首先我们先创建一个插件。插件其实相当于一个独立的模块，我不想再项目里做，当然再游戏模块里做也是没问题的。我们先把整个流程搞清楚了再去改引擎。

首先创建个插件，名字取为ShadertestPlugin

然后打开工程里的这个插件，在插件目录下加一个Shaders文件夹

然后再在Shaders文件夹里加Private文件夹

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然后再在private里面夹里新建一个文本文档，然后把后缀名改位.usf

在这个MyShader.usf里键入如下代码：

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

float4 SimpleColor;

void MainVS(
 in float4 InPosition : ATTRIBUTE0,
 out float4 OutPosition : SV_POSITION
 )
{
 // screenspace position from vb
    OutPosition = InPosition;
}

void MainPS(
    out float4 OutColor : SV_Target0
    )
{
    OutColor = SimpleColor;
}

我声明了一个MyColor的颜色，这个变量后面会和c++绑定，到时候就可以让它跟cpu交互了。然后声明了一个顶点着色器和像素着色i器。

完成了这个之后，再在插件的source文件夹下加两个文件

新建两个文本文档然后把后缀改位.h和.cpp就可以了。做完这些之后记得右键Uproject文件重写generate一下工程

然后重新加载vs项目就可以啦。

然后在把ShadertestPlugin.uplugin文件改一下，如下图。把加载顺序改成在引擎前加载。PostConfigInit。shader必须要在引擎加载完成前加载完才行。

做完这个后，再在MyShader.h中打入如下代码：

然后再在MyShader.cpp中打入如下代码：

// Copyright 1998-2018 Epic Games, Inc. All Rights Reserved.

#include "MyShaderTest.h"

#include "Classes/Engine/TextureRenderTarget2D.h"
#include "Classes/Engine/World.h"
#include "Public/GlobalShader.h"
#include "Public/PipelineStateCache.h"
#include "Public/RHIStaticStates.h"
#include "Public/SceneUtils.h"
#include "Public/SceneInterface.h"
#include "Public/ShaderParameterUtils.h"
#include "Public/Logging/MessageLog.h"
#include "Public/Internationalization/Internationalization.h"
#include "Public/StaticBoundShaderState.h"

#define LOCTEXT_NAMESPACE "TestShader"

UTestShaderBlueprintLibrary::UTestShaderBlueprintLibrary(const FObjectInitializer& ObjectInitializer)
	: Super(ObjectInitializer)
{

}

class FMyShaderTest : public FGlobalShader
{
public:

	FMyShaderTest(){}

	FMyShaderTest(const ShaderMetaType::CompiledShaderInitializerType& Initializer)
		: FGlobalShader(Initializer)
	{
		SimpleColorVal.Bind(Initializer.ParameterMap, TEXT("SimpleColor"));
	}

	static bool ShouldCache(EShaderPlatform Platform)
	{
		return true;
	}

	static bool ShouldCompilePermutation(const FGlobalShaderPermutationParameters& Parameters)
	{
		//return IsFeatureLevelSupported(Parameters.Platform, ERHIFeatureLevel::SM4);
		return true;
	}

	static void ModifyCompilationEnvironment(const FGlobalShaderPermutationParameters& Parameters, FShaderCompilerEnvironment& OutEnvironment)
	{
		FGlobalShader::ModifyCompilationEnvironment(Parameters, OutEnvironment);
		OutEnvironment.SetDefine(TEXT("TEST_MICRO"), 1);
	}

	void SetParameters(
		FRHICommandListImmediate& RHICmdList,
		const FLinearColor &MyColor
		)
	{
		SetShaderValue(RHICmdList, GetPixelShader(), SimpleColorVal, MyColor);
	}

	virtual bool Serialize(FArchive& Ar) override
	{
		bool bShaderHasOutdatedParameters = FGlobalShader::Serialize(Ar);
		Ar << SimpleColorVal;
		return bShaderHasOutdatedParameters;
	}

private:

	FShaderParameter SimpleColorVal;

};

class FShaderTestVS : public FMyShaderTest
{
	DECLARE_SHADER_TYPE(FShaderTestVS, Global);

public:
	FShaderTestVS(){}

	FShaderTestVS(const ShaderMetaType::CompiledShaderInitializerType& Initializer)
		: FMyShaderTest(Initializer)
	{

	}
};


class FShaderTestPS : public FMyShaderTest
{
	DECLARE_SHADER_TYPE(FShaderTestPS, Global);

public:
	FShaderTestPS() {}

	FShaderTestPS(const ShaderMetaType::CompiledShaderInitializerType& Initializer)
		: FMyShaderTest(Initializer)
	{

	}
};


IMPLEMENT_SHADER_TYPE(, FShaderTestVS, TEXT("/Plugin/ShadertestPlugin/Private/MyShader.usf"), TEXT("MainVS"), SF_Vertex)
IMPLEMENT_SHADER_TYPE(, FShaderTestPS, TEXT("/Plugin/ShadertestPlugin/Private/MyShader.usf"), TEXT("MainPS"), SF_Pixel)

static void DrawTestShaderRenderTarget_RenderThread(
	FRHICommandListImmediate& RHICmdList, 
	FTextureRenderTargetResource* OutputRenderTargetResource,
	ERHIFeatureLevel::Type FeatureLevel,
	FName TextureRenderTargetName,
	FLinearColor MyColor
)
{
	check(IsInRenderingThread());

#if WANTS_DRAW_MESH_EVENTS
	FString EventName;
	TextureRenderTargetName.ToString(EventName);
	SCOPED_DRAW_EVENTF(RHICmdList, SceneCapture, TEXT("ShaderTest %s"), *EventName);
#else
	SCOPED_DRAW_EVENT(RHICmdList, DrawUVDisplacementToRenderTarget_RenderThread);
#endif

	//设置渲染目标
	SetRenderTarget(
		RHICmdList,
		OutputRenderTargetResource->GetRenderTargetTexture(),
		FTextureRHIRef(),
		ESimpleRenderTargetMode::EUninitializedColorAndDepth,
		FExclusiveDepthStencil::DepthNop_StencilNop
	);

	//设置视口
	//FIntPoint DrawTargetResolution(OutputRenderTargetResource->GetSizeX(), OutputRenderTargetResource->GetSizeY());
	//RHICmdList.SetViewport(0, 0, 0.0f, DrawTargetResolution.X, DrawTargetResolution.Y, 1.0f);

	TShaderMap<FGlobalShaderType>* GlobalShaderMap = GetGlobalShaderMap(FeatureLevel);
	TShaderMapRef<FShaderTestVS> VertexShader(GlobalShaderMap);
	TShaderMapRef<FShaderTestPS> PixelShader(GlobalShaderMap);

	// Set the graphic 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 = GetVertexDeclarationFVector4();
	GraphicsPSOInit.BoundShaderState.VertexShaderRHI = GETSAFERHISHADER_VERTEX(*VertexShader);
	GraphicsPSOInit.BoundShaderState.PixelShaderRHI = GETSAFERHISHADER_PIXEL(*PixelShader);
	SetGraphicsPipelineState(RHICmdList, GraphicsPSOInit);

	//RHICmdList.SetViewport(0, 0, 0.0f, DrawTargetResolution.X, DrawTargetResolution.Y, 1.0f);
	PixelShader->SetParameters(RHICmdList, MyColor);

	// Draw grid.
	//uint32 PrimitiveCount = 2;
	//RHICmdList.DrawPrimitive(PT_TriangleList, 0, PrimitiveCount, 1);
	FVector4 Vertices[4];
	Vertices[0].Set(-1.0f, 1.0f, 0, 1.0f);
	Vertices[1].Set(1.0f, 1.0f, 0, 1.0f);
	Vertices[2].Set(-1.0f, -1.0f, 0, 1.0f);
	Vertices[3].Set(1.0f, -1.0f, 0, 1.0f);
	static const uint16 Indices[6] =
	{
		0, 1, 2,
		2, 1, 3
	};
	//DrawPrimitiveUP(RHICmdList, PT_TriangleStrip, 2, Vertices, sizeof(Vertices[0]));
	DrawIndexedPrimitiveUP(
		RHICmdList,
		PT_TriangleList,
		0,
		ARRAY_COUNT(Vertices),
		2,
		Indices,
		sizeof(Indices[0]),
		Vertices,
		sizeof(Vertices[0])
	);

	// Resolve render target.
	RHICmdList.CopyToResolveTarget(
		OutputRenderTargetResource->GetRenderTargetTexture(),
		OutputRenderTargetResource->TextureRHI,
		false, FResolveParams());
}

void UTestShaderBlueprintLibrary::DrawTestShaderRenderTarget(
	UTextureRenderTarget2D* OutputRenderTarget, 
	AActor* Ac,
	FLinearColor MyColor
)
{
	check(IsInGameThread());

	if (!OutputRenderTarget)
	{
		return;
	}
	
	FTextureRenderTargetResource* TextureRenderTargetResource = OutputRenderTarget->GameThread_GetRenderTargetResource();
	UWorld* World = Ac->GetWorld();
	ERHIFeatureLevel::Type FeatureLevel = World->Scene->GetFeatureLevel();
	FName TextureRenderTargetName = OutputRenderTarget->GetFName();
	ENQUEUE_RENDER_COMMAND(CaptureCommand)(
		[TextureRenderTargetResource, FeatureLevel, MyColor, TextureRenderTargetName](FRHICommandListImmediate& RHICmdList)
		{
			DrawTestShaderRenderTarget_RenderThread(RHICmdList,TextureRenderTargetResource, FeatureLevel, TextureRenderTargetName, MyColor);
		}
	);

}

#undef LOCTEXT_NAMESPACE

稍后我会一行行解释这些代码的意思。

然后我们要修改下c#文件

完成这些后再generate一下工程，然后就可以打开项目了。

我们新建如下资源

打开BP_Shader_Test蓝图做如下设置

新建一个颜色变量，然后再beginplay函数先清空一下我们的那张ShaderTestRT渲染目标，然后把我们这个shadertestrt渲染目标给我们的DrawTestShaderRenderTarget函数。还需要注意设置input，这样actor才能接收到我们的input事件。

做完这些之后再建一个材质，把RT拖到材质里（这里只是想让我们的shader效果被看到，我们的shader已经可以运作了）

这个操作其实已经是多pass了！！！

然后把BP_Shader_Test拖到场景里，你按下1 2 3 就能看到如下效果了：

下一节我会讲述代码原理。