diff --git a/03-UnrealEngine/Rendering/RenderingPipeline/Materials/材质中PassSwitch节点实现方式.md b/03-UnrealEngine/Rendering/RenderingPipeline/Materials/材质中PassSwitch节点实现方式.md
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+---
+title: Untitled
+date: 2024-09-23 19:47:03
+excerpt: 
+tags: 
+rating: ⭐
+---
+# ShadowPassSwitch
+## Cpp
+MaterialExpressionShadowReplace.h
+
+MaterialExpressions.cpp
+```c++
+int32 UMaterialExpressionShadowReplace::Compile(class FMaterialCompiler* Compiler, int32 OutputIndex)
+{
+	if (!Default.GetTracedInput().Expression)
+	{
+		return Compiler->Errorf(TEXT("Missing input Default"));
+	}
+	else if (!Shadow.GetTracedInput().Expression)
+	{
+		return Compiler->Errorf(TEXT("Missing input Shadow"));
+	}
+	else
+	{
+		const int32 Arg1 = Default.Compile(Compiler);
+		const int32 Arg2 = Shadow.Compile(Compiler);
+		return Compiler->ShadowReplace(Arg1, Arg2);
+	}
+}
+```
+
+MaterialCompiler.h => **HLSLMaterialTranslator.cpp**
+```c++
+int32 FHLSLMaterialTranslator::ShadowReplace(int32 Default, int32 Shadow)  
+{  
+    return GenericSwitch(TEXT("GetShadowReplaceState()"), Shadow, Default);  
+}
+```
+
+```c++
+int32 FHLSLMaterialTranslator::GenericSwitch(const TCHAR* SwitchExpressionText, int32 IfTrue, int32 IfFalse)
+{
+	if (IfTrue == INDEX_NONE || IfFalse == INDEX_NONE)
+	{
+		return INDEX_NONE;
+	}
+
+	// exactly the same inputs on both sides - no need to generate anything extra
+	if (IfTrue == IfFalse)
+	{
+		return IfTrue;
+	}
+
+	FMaterialUniformExpression* IfTrueExpression = GetParameterUniformExpression(IfTrue);
+	FMaterialUniformExpression* IfFalseExpression = GetParameterUniformExpression(IfFalse);
+	if (IfTrueExpression &&
+		IfFalseExpression &&
+		IfTrueExpression->IsConstant() &&
+		IfFalseExpression->IsConstant())
+	{
+		FMaterialRenderContext DummyContext(nullptr, *Material, nullptr);
+		FLinearColor IfTrueValue;
+		FLinearColor IfFalseValue;
+		IfTrueExpression->GetNumberValue(DummyContext, IfTrueValue);
+		IfFalseExpression->GetNumberValue(DummyContext, IfFalseValue);
+		if (IfTrueValue == IfFalseValue)
+		{
+			// If both inputs are wired to == constant values, avoid adding the runtime switch
+			// This will avoid breaking various offline checks for constant values
+			return IfTrue;
+		}
+	}
+
+	// Both branches of '?:' need to be the same type
+	const EMaterialValueType ResultType = GetArithmeticResultType(IfTrue, IfFalse);
+	const FString IfTrueCode = CoerceParameter(IfTrue, ResultType);
+	const FString IfFalseCode = CoerceParameter(IfFalse, ResultType);
+	
+	if (IsLWCType(ResultType))
+	{
+		AddLWCFuncUsage(ELWCFunctionKind::Other);
+		return AddCodeChunk(ResultType, TEXT("LWCSelect(%s, %s, %s)"), SwitchExpressionText, *IfTrueCode, *IfFalseCode);
+	}
+	else
+	{
+		return AddCodeChunk(ResultType, TEXT("(%s ? (%s) : (%s))"), SwitchExpressionText, *IfTrueCode, *IfFalseCode);
+	}
+}
+```
+
+>可以看得出最终会编译成(%s ? (%s) : (%s))，也就是 GetShadowReplaceState() ? True的Shader ： False时的Shader。
+
+## Shader
+### Common.ush
+```c++
+// NOTE: The raytraced implementation of the ShadowPassSwitch node is kept in RayTracingShaderUtils.ush as it needs to access per ray information.  
+#if RAYHITGROUPSHADER == 0  
+// Experimental way to allow adjusting the OpacityMask for shadow map rendering of masked materials.  
+// This is exposed via the ShadowPassSwitch material node. This can also be accessed with a Custom  
+// material node. If this turns out to be very useful we can expose as MaterialFunction  
+// and potentially expose other queries as well (e.g. SkeletalMesh, HitProxy, ).  
+// @return 0:no, 1:yes  
+bool GetShadowReplaceState()  
+{  
+#if SHADOW_DEPTH_SHADER  
+    return true;  
+#else  
+    return false;  
+#endif  
+}  
+  
+float IsShadowDepthShader()  
+{  
+    return GetShadowReplaceState() ? 1.0f : 0.0f;  
+}  
+  
+#endif // RAYHITGROUPSHADER == 0
+```
+
+可以看得出主要通过**SHADOW_DEPTH_SHADER**宏进行判断，而渲染阴影的Shader ShadowDepthVertexShader.usf&ShadowDepthPixelShader.usf都定义该宏为1。
+
+### NaniteRasterizer.usf
+```c++
+// This must be defined before including Common.ush (see GetShadowReplaceState)  
+#define SHADOW_DEPTH_SHADER DEPTH_ONLY
+```
+在NaniteCullRaster.cpp中DEPTH_ONLY设置为1。
+
+### RayTracingShaderUtils.ush
+光追相关
+```c++
+#ifndef RAYHITGROUPSHADER  
+#error "This header should only be included in raytracing contexts"  
+#endif  
+  
+#ifndef PATH_TRACING // Path Tracing has a similar implemental with a slightly different set of flags  
+  
+#include "RayTracingCommon.ush"  
+  
+static int CurrentPayloadInputFlags = 0;  
+  
+bool GetShadowReplaceState()  
+{  
+    return (CurrentPayloadInputFlags & RAY_TRACING_PAYLOAD_INPUT_FLAG_SHADOW_RAY) != 0;  
+}  
+  
+float IsShadowDepthShader()  
+{  
+    return GetShadowReplaceState() ? 1.0f : 0.0f;  
+}  
+  
+#endif
+```
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