UE4 FShaderParameter FShaderParameterMap

ShaderParameters.h

/** A shader parameter's register binding. e.g. float1/2/3/4, can be an array, UAV */
class FShaderParameter
{
	DECLARE_EXPORTED_TYPE_LAYOUT(FShaderParameter, RENDERCORE_API, NonVirtual);
public:
	FShaderParameter()
	:	BufferIndex(0)
	,	BaseIndex(0)
	,	NumBytes(0)
	{}

	RENDERCORE_API void Bind(const FShaderParameterMap& ParameterMap,const TCHAR* ParameterName, EShaderParameterFlags Flags = SPF_Optional);
	friend RENDERCORE_API FArchive& operator<<(FArchive& Ar,FShaderParameter& P);
	bool IsBound() const { return NumBytes > 0; }
	
	inline bool IsInitialized() const 
	{ 
		return true;
	}

	uint32 GetBufferIndex() const { return BufferIndex; }
	uint32 GetBaseIndex() const { return BaseIndex; }
	uint32 GetNumBytes() const { return NumBytes; }

private:
	LAYOUT_FIELD(uint16, BufferIndex);
	LAYOUT_FIELD(uint16, BaseIndex);
	// 0 if the parameter wasn't bound
	LAYOUT_FIELD(uint16, NumBytes);
};

ShaderParameters.cpp

void FShaderParameter::Bind(const FShaderParameterMap& ParameterMap,const TCHAR* ParameterName,EShaderParameterFlags Flags)
{
	if (!ParameterMap.FindParameterAllocation(ParameterName,BufferIndex,BaseIndex,NumBytes) && Flags == SPF_Mandatory)
	{
		if (!UE_LOG_ACTIVE(LogShaders, Log))
		{
			UE_LOG(LogShaders, Fatal,TEXT("Failure to bind non-optional shader parameter %s!  The parameter is either not present in the shader, or the shader compiler optimized it out."),ParameterName);
		}
		else
		{
			// We use a non-Slate message box to avoid problem where we haven't compiled the shaders for Slate.
			FPlatformMisc::MessageBoxExt( EAppMsgType::Ok, *FText::Format(
				NSLOCTEXT("UnrealEd", "Error_FailedToBindShaderParameter", "Failure to bind non-optional shader parameter {0}! The parameter is either not present in the shader, or the shader compiler optimized it out. This will be an assert with LogShaders suppressed!"),
				FText::FromString(ParameterName)).ToString(), TEXT("Warning"));
		}
	}
}

FArchive& operator<<(FArchive& Ar,FShaderParameter& P)
{
	uint16& PBufferIndex = P.BufferIndex;
	return Ar << P.BaseIndex << P.NumBytes << PBufferIndex;
}

bool FShaderParameterMap::FindParameterAllocation(const TCHAR* ParameterName,uint16& OutBufferIndex,uint16& OutBaseIndex,uint16& OutSize) const
{
	const FParameterAllocation* Allocation = ParameterMap.Find(ParameterName);
	if(Allocation)
	{
		OutBufferIndex = Allocation->BufferIndex;
		OutBaseIndex = Allocation->BaseIndex;
		OutSize = Allocation->Size;

		if (Allocation->bBound)
		{
			// Can detect copy-paste errors in binding parameters.  Need to fix all the false positives before enabling.
			//UE_LOG(LogShaders, Warning, TEXT("Parameter %s was bound multiple times. Code error?"), ParameterName);
		}

		Allocation->bBound = true;
		return true;
	}
	else
	{
		return false;
	}
}