vault backup: 2024-10-12 17:19:45

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Material/ShowAsInputPin/ShowAsInputPin.md

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+# ShowAsInputPin
+
+- **功能描述：** 使得UMaterialExpression里的一些基础类型属性变成材质节点上的引脚。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Material
+- **元数据类型：** bool
+- **限制类型：** UMaterialExpression里的属性
+- **常用程度：** ★★★
+
+使得UMaterialExpression里的一些基础类型属性变成材质节点上的引脚。
+
+- 所谓基础类型，指的是float，FVector这种常用的类型。
+- 默认这些基础类型属性是不显示为引脚的。
+- ShowAsInputPin 值有两个选项，Primary可以直接显示出来，Advanced需要展开箭头后显示。
+
+## 测试代码：
+
+```cpp
+
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PinTest)
+	float MyFloat;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PinTest, meta = (ShowAsInputPin = "Primary"))
+	float MyFloat_Primary;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = PinTest, meta = (ShowAsInputPin = "Advanced"))
+	float MyFloat_Advanced;
+```
+
+## 测试结果：
+
+可见MyFloat没有显示在节点上。
+
+MyFloat_Primary显示在节点上。
+
+MyFloat_Advanced需要展开箭头后才显示出来。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+遍历UMaterialExpression里的属性，根据含有ShowAsInputPin 的类型来生成引脚。
+
+```cpp
+TArray<FProperty*> UMaterialExpression::GetPropertyInputs() const
+{
+	TArray<FProperty*> PropertyInputs;
+
+	static FName OverridingInputPropertyMetaData(TEXT("OverridingInputProperty"));
+	static FName ShowAsInputPinMetaData(TEXT("ShowAsInputPin"));
+	for (TFieldIterator<FProperty> InputIt(GetClass(), EFieldIteratorFlags::IncludeSuper, EFieldIteratorFlags::ExcludeDeprecated); InputIt; ++InputIt)
+	{
+		bool bCreateInput = false;
+		FProperty* Property = *InputIt;
+		// Don't create an expression input if the property is already associated with one explicitly declared
+		bool bOverridingInputProperty = Property->HasMetaData(OverridingInputPropertyMetaData);
+		// It needs to have the 'EditAnywhere' specifier
+		const bool bEditAnywhere = Property->HasAnyPropertyFlags(CPF_Edit);
+		// It needs to be marked with a valid pin category meta data
+		const FString ShowAsInputPin = Property->GetMetaData(ShowAsInputPinMetaData);
+		const bool bShowAsInputPin = ShowAsInputPin == TEXT("Primary") || ShowAsInputPin == TEXT("Advanced");
+
+		if (!bOverridingInputProperty && bEditAnywhere && bShowAsInputPin)
+		{
+			// Check if the property type fits within the allowed widget types
+			FFieldClass* PropertyClass = Property->GetClass();
+			if (PropertyClass == FFloatProperty::StaticClass()
+				|| PropertyClass == FDoubleProperty::StaticClass()
+				|| PropertyClass == FIntProperty::StaticClass()
+				|| PropertyClass == FUInt32Property::StaticClass()
+				|| PropertyClass == FByteProperty::StaticClass()
+				|| PropertyClass == FBoolProperty::StaticClass()
+				)
+			{
+				bCreateInput = true;
+			}
+			else if (PropertyClass == FStructProperty::StaticClass())
+			{
+				FStructProperty* StructProperty = CastField<FStructProperty>(Property);
+				UScriptStruct* Struct = StructProperty->Struct;
+				if (Struct == TBaseStructure<FLinearColor>::Get()
+					|| Struct == TBaseStructure<FVector4>::Get()
+					|| Struct == TVariantStructure<FVector4d>::Get()
+					|| Struct == TBaseStructure<FVector>::Get()
+					|| Struct == TVariantStructure<FVector3f>::Get()
+					|| Struct == TBaseStructure<FVector2D>::Get()
+					)
+				{
+					bCreateInput = true;
+				}
+			}
+		}
+		if (bCreateInput)
+		{
+			PropertyInputs.Add(Property);
+		}
+	}
+
+	return PropertyInputs;
+}
+```