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RenderDependencyGraph学习笔记（三）——在插件中使用PixelShader

RenderDependencyGraph学习笔记（三）——在插件中使用PixelShader

2020年11月10日 1.4k 字 大概 7 分钟
  1. 1. 前言
  2. 2. 设置Shader虚拟目录
  3. 3. 参考案例
  4. 4. 使用DrawFullscreenPixelShader绘制
  5. 5. CommonRenderResources
  6. 6. RenderTarget的传入与绑定
  7. 7. 资源清理
  8. 8. RDGPixelDraw
    1. 8.1. 自定义顶点格式部分

前言

在插件中使用RDG调用ComputeShader的方法，我花了没几天就搞定了。但PixelShader相对来说就麻烦了，怎么搞都没有绘制到RT上。最后还是通过改写DrawFullscreenPixelShader的代码搞定了。

另外说一下PixelShader的调用和传统的GlobalShader调用很相似。

设置Shader虚拟目录

这个之前忘记说了，所以这里补充一下，具体操作为在插件的模块启动函数中添加以下代码：：

void FBRPluginsModule::StartupModule()
{
    FString PluginShaderDir = FPaths::Combine(IPluginManager::Get().FindPlugin(TEXT("BRPlugins"))->GetBaseDir(), TEXT("Shaders"));
    AddShaderSourceDirectoryMapping(TEXT("/BRPlugins"), PluginShaderDir);
}

之后就可以使用这个虚拟目录来定义Shader：

IMPLEMENT_GLOBAL_SHADER(FSimpleRDGComputeShader, "/BRPlugins/Private/SimpleComputeShader.usf", "MainCS", SF_Compute);

参考案例

这里我没什么管理可以推荐的，感觉都不是很好。但你可以搜索ERDGPassFlags::Raster就可以找到RDG调用PixelShader的代码。

使用DrawFullscreenPixelShader绘制

在RDG中已经封装了一个绘制函数DrawFullscreenPixelShader()，可以拿来做测试。使用的方法也比较简单，直接在GraphBuilder.AddPass的Lambda中调用DrawFullscreenPixelShader即可。但

其使用的顶点格式是公共资源(CommonRenderResources.h)中的GFilterVertexDeclaration.VertexDeclarationRHI、GScreenRectangleVertexBuffer.VertexBufferRHI、GScreenRectangleIndexBuffer.IndexBufferRHI。

void FScreenRectangleVertexBuffer::InitRHI()
{
    TResourceArray<FFilterVertex, VERTEXBUFFER_ALIGNMENT> Vertices;
    Vertices.SetNumUninitialized(6);

    Vertices[0].Position = FVector4(1, 1, 0, 1);
    Vertices[0].UV = FVector2D(1, 1);

    Vertices[1].Position = FVector4(0, 1, 0, 1);
    Vertices[1].UV = FVector2D(0, 1);

    Vertices[2].Position = FVector4(1, 0, 0, 1);
    Vertices[2].UV = FVector2D(1, 0);

    Vertices[3].Position = FVector4(0, 0, 0, 1);
    Vertices[3].UV = FVector2D(0, 0);

    //The final two vertices are used for the triangle optimization (a single triangle spans the entire viewport )
    Vertices[4].Position = FVector4(-1, 1, 0, 1);
    Vertices[4].UV = FVector2D(-1, 1);

    Vertices[5].Position = FVector4(1, -1, 0, 1);
    Vertices[5].UV = FVector2D(1, -1);

    // Create vertex buffer. Fill buffer with initial data upon creation
    FRHIResourceCreateInfo CreateInfo(&Vertices);
    VertexBufferRHI = RHICreateVertexBuffer(Vertices.GetResourceDataSize(), BUF_Static, CreateInfo);
}

DrawFullscreenPixelShader()使用的VertexShader是FScreenVertexShaderVS，usf为FullscreenVertexShader.usf。代码如下：

#include "../Common.ush"

void MainVS(
    float2 InPosition : ATTRIBUTE0,
    float2 InUV       : ATTRIBUTE1, // TODO: kill
    out float4 Position : SV_POSITION)
{
    Position = float4(InPosition.x * 2.0 - 1.0, 1.0 - 2.0 * InPosition.y, 0, 1);
}

这里可以看得出一个问题，那就是PixelShader无法获得UV坐标。所以DrawFullscreenPixelShader()能做事情很有限。因此本人写的例子是自定义了顶点格式。

CommonRenderResources

Ue4的已经帮我们设置好了几个基础的VertexDeclaration，位于RenderCore\Public\CommonRenderResources.h。

GEmptyVertexDeclaration.VertexDeclarationRHI，在Shader中的Input为：

in uint InstanceId : SV_InstanceID,
in uint VertexId : SV_VertexID,

GFilterVertexDeclaration.VertexDeclarationRHI，在Shader中的Input为：

in float4 InPosition : ATTRIBUTE0,
in float2 InUV : ATTRIBUTE1,

对应的顶点缓存与索引缓存为TGlobalResource GScreenRectangleVertexBuffer与TGlobalResource GScreenRectangleIndexBuffer;

如果你想在调用PixelShader时使用FScreenRectangleVertexBuffer，就需要转换UV坐标了，(-1,1)=>(0,1)，因为FScreenRectangleVertexBuffer的UV定义范围为(-1,1)。

RenderTarget的传入与绑定

传入的RenderTarget皆可以用Texture2D类型声明。例如：

BEGIN_SHADER_PARAMETER_STRUCT(FParameters, )
    SHADER_PARAMETER_STRUCT_REF(FSimpleUniformStructParameters, SimpleUniformStruct)
    SHADER_PARAMETER_TEXTURE(Texture2D, TextureVal)
    SHADER_PARAMETER_SAMPLER(SamplerState, TextureSampler)
    SHADER_PARAMETER(FVector4, SimpleColor)
    RENDER_TARGET_BINDING_SLOTS()
END_SHADER_PARAMETER_STRUCT()

绑定需要在上面的声明宏中加入RENDER_TARGET_BINDING_SLOTS()，之后设置变量时绑定：

FSimpleRDGPixelShader::FParameters *Parameters = GraphBuilder.AllocParameters<FSimpleRDGPixelShader::FParameters>();
Parameters->RenderTargets[0] = FRenderTargetBinding(RDGRenderTarget, ERenderTargetLoadAction::ENoAction);

还可以绑定DepthStencil

Parameters->RenderTargets.DepthStencil = FDepthStencilBinding(OutDepthTexture,ERenderTargetLoadAction::ELoad,ERenderTargetLoadAction::ELoad,FExclusiveDepthStencil::DepthNop_StencilWrite);

在USF中对应Out为：

out float4 OutColor : SV_Target0, 
out float  OutDepth : SV_Depth

如果有多个RenderTarget绑定，会如SV_Target0、SV_Target1、SV_Target2一般递增。

资源清理

本人案例中因为只有一个Pass，所以就没有用这两个函数。

ValidateShaderParameters(PixelShader, Parameters);
ClearUnusedGraphResources(PixelShader, Parameters);

RDGPixelDraw

直接上代码了。

void RDGDraw(FRHICommandListImmediate &RHIImmCmdList, FTexture2DRHIRef RenderTargetRHI, FSimpleShaderParameter InParameter, const FLinearColor InColor, FTexture2DRHIRef InTexture)
{
    check(IsInRenderingThread());

    //Create PooledRenderTarget
    FPooledRenderTargetDesc RenderTargetDesc = FPooledRenderTargetDesc::Create2DDesc(RenderTargetRHI->GetSizeXY(),RenderTargetRHI->GetFormat(), FClearValueBinding::Black, TexCreate_None, TexCreate_RenderTargetable | TexCreate_ShaderResource | TexCreate_UAV, false);
    TRefCountPtr<IPooledRenderTarget> PooledRenderTarget;

    //RDG Begin
    FRDGBuilder GraphBuilder(RHIImmCmdList);
    FRDGTextureRef RDGRenderTarget = GraphBuilder.CreateTexture(RenderTargetDesc, TEXT("RDGRenderTarget"));

    //Setup Parameters
    FSimpleUniformStructParameters StructParameters;
    StructParameters.Color1 = InParameter.Color1;
    StructParameters.Color2 = InParameter.Color2;
    StructParameters.Color3 = InParameter.Color3;
    StructParameters.Color4 = InParameter.Color4;
    StructParameters.ColorIndex = InParameter.ColorIndex;

    FSimpleRDGPixelShader::FParameters *Parameters = GraphBuilder.AllocParameters<FSimpleRDGPixelShader::FParameters>();
    Parameters->TextureVal = InTexture;
    Parameters->TextureSampler = TStaticSamplerState<SF_Trilinear, AM_Clamp, AM_Clamp, AM_Clamp>::GetRHI();
    Parameters->SimpleColor = InColor;
    Parameters->SimpleUniformStruct = TUniformBufferRef<FSimpleUniformStructParameters>::CreateUniformBufferImmediate(StructParameters, UniformBuffer_SingleFrame);
    Parameters->RenderTargets[0] = FRenderTargetBinding(RDGRenderTarget, ERenderTargetLoadAction::ENoAction);

    const ERHIFeatureLevel::Type FeatureLevel = GMaxRHIFeatureLevel; //ERHIFeatureLevel::SM5
    FGlobalShaderMap *GlobalShaderMap = GetGlobalShaderMap(FeatureLevel);
    TShaderMapRef<FSimpleRDGVertexShader> VertexShader(GlobalShaderMap);
    TShaderMapRef<FSimpleRDGPixelShader> PixelShader(GlobalShaderMap);

    //ValidateShaderParameters(PixelShader, Parameters);
    //ClearUnusedGraphResources(PixelShader, Parameters);

    GraphBuilder.AddPass(
        RDG_EVENT_NAME("RDGDraw"),
        Parameters,
        ERDGPassFlags::Raster,
        [Parameters, VertexShader, PixelShader, GlobalShaderMap](FRHICommandList &RHICmdList) {
            FRHITexture2D *RT = Parameters->RenderTargets[0].GetTexture()->GetRHI()->GetTexture2D();
            RHICmdList.SetViewport(0, 0, 0.0f, RT->GetSizeX(), RT->GetSizeY(), 1.0f);

            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 = GTextureVertexDeclaration.VertexDeclarationRHI;

            GraphicsPSOInit.BoundShaderState.VertexShaderRHI = VertexShader.GetVertexShader();
            GraphicsPSOInit.BoundShaderState.PixelShaderRHI = PixelShader.GetPixelShader();
            SetGraphicsPipelineState(RHICmdList, GraphicsPSOInit);
            RHICmdList.SetStencilRef(0);
            SetShaderParameters(RHICmdList, PixelShader, PixelShader.GetPixelShader(), *Parameters);

            RHICmdList.SetStreamSource(0, GRectangleVertexBuffer.VertexBufferRHI, 0);
            RHICmdList.DrawIndexedPrimitive(
                GRectangleIndexBuffer.IndexBufferRHI,
                /*BaseVertexIndex=*/0,
                /*MinIndex=*/0,
                /*NumVertices=*/4,
                /*StartIndex=*/0,
                /*NumPrimitives=*/2,
                /*NumInstances=*/1);
        });

    GraphBuilder.QueueTextureExtraction(RDGRenderTarget, &PooledRenderTarget);
    GraphBuilder.Execute();

    //Copy Result To RenderTarget Asset
    RHIImmCmdList.CopyTexture(PooledRenderTarget->GetRenderTargetItem().ShaderResourceTexture, RenderTargetRHI->GetTexture2D(), FRHICopyTextureInfo());
}

调用方法和之前的ComputeShader部分相同，这里就不赘述了。具体的可以参考我的插件。

自定义顶点格式部分

struct FTextureVertex
    {
        FVector4 Position;
        FVector2D UV;
    };

    class FRectangleVertexBuffer : public FVertexBuffer
    {
    public:
        /** Initialize the RHI for this rendering resource */
        void InitRHI() override
        {
            TResourceArray<FTextureVertex, VERTEXBUFFER_ALIGNMENT> Vertices;
            Vertices.SetNumUninitialized(6);

            Vertices[0].Position = FVector4(1, 1, 0, 1);
            Vertices[0].UV = FVector2D(1, 1);

            Vertices[1].Position = FVector4(-1, 1, 0, 1);
            Vertices[1].UV = FVector2D(0, 1);

            Vertices[2].Position = FVector4(1, -1, 0, 1);
            Vertices[2].UV = FVector2D(1, 0);

            Vertices[3].Position = FVector4(-1, -1, 0, 1);
            Vertices[3].UV = FVector2D(0, 0);

            //The final two vertices are used for the triangle optimization (a single triangle spans the entire viewport )
            Vertices[4].Position = FVector4(-1, 1, 0, 1);
            Vertices[4].UV = FVector2D(-1, 1);

            Vertices[5].Position = FVector4(1, -1, 0, 1);
            Vertices[5].UV = FVector2D(1, -1);

            // Create vertex buffer. Fill buffer with initial data upon creation
            FRHIResourceCreateInfo CreateInfo(&Vertices);
            VertexBufferRHI = RHICreateVertexBuffer(Vertices.GetResourceDataSize(), BUF_Static, CreateInfo);
        }
    };

    class FRectangleIndexBuffer : public FIndexBuffer
    {
    public:
        /** Initialize the RHI for this rendering resource */
        void InitRHI() override
        {
            // Indices 0 - 5 are used for rendering a quad. Indices 6 - 8 are used for triangle optimization.
            const uint16 Indices[] = {0, 1, 2, 2, 1, 3, 0, 4, 5};

            TResourceArray<uint16, INDEXBUFFER_ALIGNMENT> IndexBuffer;
            uint32 NumIndices = UE_ARRAY_COUNT(Indices);
            IndexBuffer.AddUninitialized(NumIndices);
            FMemory::Memcpy(IndexBuffer.GetData(), Indices, NumIndices * sizeof(uint16));

            // Create index buffer. Fill buffer with initial data upon creation
            FRHIResourceCreateInfo CreateInfo(&IndexBuffer);
            IndexBufferRHI = RHICreateIndexBuffer(sizeof(uint16), IndexBuffer.GetResourceDataSize(), BUF_Static, CreateInfo);
        }
    };

    class FTextureVertexDeclaration : public FRenderResource
    {
    public:
        FVertexDeclarationRHIRef VertexDeclarationRHI;
        virtual void InitRHI() override
        {
            FVertexDeclarationElementList Elements;
            uint32 Stride = sizeof(FTextureVertex);
            Elements.Add(FVertexElement(0, STRUCT_OFFSET(FTextureVertex, Position), VET_Float2, 0, Stride));
            Elements.Add(FVertexElement(0, STRUCT_OFFSET(FTextureVertex, UV), VET_Float2, 1, Stride));
            VertexDeclarationRHI = RHICreateVertexDeclaration(Elements);
        }
        virtual void ReleaseRHI() override
        {
            VertexDeclarationRHI.SafeRelease();
        }
    };

    /*
     *  Vertex Resource Declaration
     */
    extern TGlobalResource<FTextureVertexDeclaration> GTextureVertexDeclaration;
    extern TGlobalResource<FRectangleVertexBuffer> GRectangleVertexBuffer;
    extern TGlobalResource<FRectangleIndexBuffer> GRectangleIndexBuffer;

TGlobalResource<FTextureVertexDeclaration> GTextureVertexDeclaration;
TGlobalResource<FRectangleVertexBuffer> GRectangleVertexBuffer;
TGlobalResource<FRectangleIndexBuffer> GRectangleIndexBuffer;
UnrealEngine
本文作者：BlueRose
本文链接：http://www.blueroses.top/2020/11/10/renderdependencygraph-xue-xi-bi-ji-san-zai-cha-jian-zhong-shi-yong-pixelshader/
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