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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/RigVM/Visible/Visible.md

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+# Visible
+
+- **功能描述：** 指定FRigUnit下的该属性为常量引脚，无法连接变量。
+- **使用位置：** UPROPERTY
+- **引擎模块：** RigVMStruct
+- **元数据类型：** bool
+- **限制类型：** FRigUnit中属性
+- **关联项：** [Input](../Input/Input.md)
+- **常用程度：** ★★★
+
+指定FRigUnit下的该属性为常量引脚，无法连接变量。
+
+Visible和Input+Constant的效果是一致的。
+
+## 测试代码：
+
+```cpp
+USTRUCT(meta = (DisplayName = "MyRig"))
+struct INSIDER_API FRigUnit_MyRig : public FRigUnit
+{
+	GENERATED_BODY()
+
+	RIGVM_METHOD()
+		virtual void Execute() override;
+
+public:
+	UPROPERTY()
+	float MyFloat_Normal;
+
+	UPROPERTY(meta = (Input))
+	float MyFloat_Input;
+
+	UPROPERTY(meta = (Output))
+	float MyFloat_Output;
+
+	UPROPERTY(meta = (Input, Output))
+	float MyFloat_IO;
+
+	UPROPERTY(meta = (Hidden))
+	float MyFloat_Hidden;
+
+	UPROPERTY(meta = (Visible))
+	float MyFloat_Visible;
+
+	UPROPERTY(meta = (Input, Constant))
+	float MyFloat_Constant;
+};
+```
+
+## 测试效果：
+
+Visible和Input+Constant的效果是一致的，也是成为一个常量。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+```cpp
+UENUM(BlueprintType)
+enum class ERigVMPinDirection : uint8
+{
+	Input, // A const input value
+	Output, // A mutable output value
+	IO, // A mutable input and output value
+	Visible, // A const value that cannot be connected to
+	Hidden, // A mutable hidden value (used for interal state)
+	Invalid // The max value for this enum - used for guarding.
+};
+
+FRigVMPinInfo::FRigVMPinInfo(FProperty* InProperty, ERigVMPinDirection InDirection, int32 InParentIndex, const uint8* InDefaultValueMemory)
+{
+	bIsConstant = InProperty->HasMetaData(TEXT("Constant"));
+}
+
+void URigVMController::ConfigurePinFromProperty(FProperty* InProperty, URigVMPin* InOutPin, ERigVMPinDirection InPinDirection) const
+{
+		InOutPin->bIsConstant = InProperty->HasMetaData(TEXT("Constant"));
+}
+
+bool URigVMPin::CanBeBoundToVariable(const FRigVMExternalVariable& InExternalVariable, const FString& InSegmentPath) const
+{
+	if (bIsConstant)
+	{
+		return false;
+	}
+}
+```