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