[UE4]Shader Development Notes

Keywords: UE4, Shader Development Notes

Environment Setup

Steps

Set LoadingPhase as PostConfigInit, default is Default.
e.g. TestProj.uproject:

 {
     "FileVersion": 3,
     "EngineAssociation": "4.25",
     "Category": "",
     "Description": "",
     "Modules": [
         {
             "Name": "TestProj",
             "Type": "Runtime",
             "LoadingPhase": "PostConfigInit"
         }
     ]
 }

Otherwise there’s error on building:

 Shader type was loaded after engine init, use ELoadingPhase::PostConfigInit on your module to cause it to load earlier.

Turn on r.ShaderDevelopmentMode in \Engine\Config\ConsoleVariables.ini.
ConsoleVariables.ini:

 [Startup]
 ; Uncomment to get detailed logs on shader compiles and the opportunity to retry on errors
 r.ShaderDevelopmentMode=1

Otherwise there’s error on building:

 Failed to compile global shader XXXX. Enable `r.ShaderDevelopmentMode` in ConsoleVariables.ini for retries.

Add RenderCore, Renderer in your .Build.cs. Maybe RHI is also need to be added.

 PublicDependencyModuleNames.AddRange(new string[] { "RenderCore", "Renderer", "RHI" });

Now you can setup your shader source in your game source, and these shader would be compiled on editor starting.
MyActor.cpp (quoted from Engine\Source\Runtime\Renderer\Private\PostProcess\PostProcessVisualizeBuffer.cpp):

 namespace
 {
     class FVisualizeBufferPS : public FGlobalShader
     {
     public:
         DECLARE_GLOBAL_SHADER(FVisualizeBufferPS);
         SHADER_USE_PARAMETER_STRUCT(FVisualizeBufferPS, FGlobalShader);

         BEGIN_SHADER_PARAMETER_STRUCT(FParameters, )
             SHADER_PARAMETER_STRUCT(FScreenPassTextureViewportParameters, Output)
             SHADER_PARAMETER_RDG_TEXTURE(Texture2D, InputTexture)
             SHADER_PARAMETER_SAMPLER(SamplerState, InputSampler)
             SHADER_PARAMETER(FLinearColor, SelectionColor)
             RENDER_TARGET_BINDING_SLOTS()
         END_SHADER_PARAMETER_STRUCT()

         static bool ShouldCompilePermutation(const FGlobalShaderPermutationParameters& Parameters)
         {
             return IsFeatureLevelSupported(Parameters.Platform, ERHIFeatureLevel::ES3_1);
         }
     };

     IMPLEMENT_GLOBAL_SHADER(FVisualizeBufferPS, "/Engine/Private/PostProcessVisualizeBuffer.usf", "MainPS", SF_Pixel);

     FScreenPassTexture AddVisualizeBufferPass(FRDGBuilder& GraphBuilder, const FViewInfo& View, const FVisualizeBufferInputs& Inputs)
     {
         ...
         FVisualizeBufferPS::FParameters* PassParameters = GraphBuilder.AllocParameters<FVisualizeBufferPS::FParameters>();
         PassParameters->Output = GetScreenPassTextureViewportParameters(OutputViewport);
         PassParameters->RenderTargets[0] = Output.GetRenderTargetBinding();
         PassParameters->InputTexture = Tile.Input.Texture;
         PassParameters->InputSampler = BilinearClampSampler;
         PassParameters->SelectionColor = SelectionColor;

         TShaderMapRef<FVisualizeBufferPS> PixelShader(View.ShaderMap);
         ...
     }

     void Test_RenderThread(FRHICommandListImmediate& RHICmdList)
     {
         ...
         TShaderMapRef<FDownsamplePS> PixelShader(ShaderMap, PermutationVector);
         ...
     }
 }

 AMyActor::TestFun()
 {
     ENQUEUE_RENDER_COMMAND(FDownsampleTestCommand)(
     [](FRHICommandListImmediate& RHICmdList)
     {
         Test_RenderThread(RHICmdList);
     });
 }

If want to specify the Shader Type (Global, Material, MeshMaterial, Niagara etc.), use IMPLEMENT_SHADER_TYPE instead of IMPLEMENT_GLOBAL_SHADER, see the example of PostProcessMaterial.cpp in engine.
quoted from Engine\Source\Runtime\Renderer\Private\PostProcess\PostProcessMaterial.cpp:
```
 IMPLEMENT_SHADER_TYPE(,FPostProcessMaterialVS, TEXT("/Engine/Private/PostProcessMaterialShaders.usf"), TEXT("MainVS"), SF_Vertex);
 IMPLEMENT_SHADER_TYPE(,FPostProcessMaterialPS, TEXT("/Engine/Private/PostProcessMaterialShaders.usf"), TEXT("MainPS"), SF_Pixel);
```

Blogs & Documents

Official

Shader Development
Adding Global Shaders to Unreal Engine

Shading Model

Extend the UE4 Shading Model
https://qiita.com/dgtanaka/items/41f96ef2090820035609

Reference

Examples

A tutorial project that shows how to implement HLSL Pixel and Compute shaders in UE4
https://github.com/Temaran/UE4ShaderPluginDemo

A compute shader plugin that is capable of sorting positional data in parallel directly on the GPU.
https://github.com/ValentinKraft/UE4_SortingComputeShader

Compiling

Compiling Shaders Manually
http://mpolaczyk.pl/compiling-shaders-manually/

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