84 lines
3.0 KiB
Markdown
84 lines
3.0 KiB
Markdown
# RequiredInput
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- **功能描述：** 在UMaterialExpression中指定FExpressionInput属性是否要求输入，引脚显示白色或灰色。
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- **使用位置：** UPROPERTY
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- **引擎模块：** Material
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- **元数据类型：** bool
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- **限制类型：** UMaterialExpression::FExpressionInput
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- **关联项：** [OverridingInputProperty](OverridingInputProperty/OverridingInputProperty.md)
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在UMaterialExpression中指定FExpressionInput属性是否要求输入，引脚显示白色或灰色。
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一般都配合OverridingInputProperty使用。
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代码和效果参见OverridingInputProperty
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## 原理：
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```cpp
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bool UMaterialExpression::CanEditChange(const FProperty* InProperty) const
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{
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bool bIsEditable = Super::CanEditChange(InProperty);
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if (bIsEditable && InProperty != nullptr)
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{
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// Automatically set property as non-editable if it has OverridingInputProperty metadata
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// pointing to an FExpressionInput property which is hooked up as an input.
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//
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// e.g. in the below snippet, meta=(OverridingInputProperty = "A") indicates that ConstA will
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// be overridden by an FExpressionInput property named 'A' if one is connected, and will thereby
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// be set as non-editable.
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//
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// UPROPERTY(meta = (RequiredInput = "false", ToolTip = "Defaults to 'ConstA' if not specified"))
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// FExpressionInput A;
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//
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// UPROPERTY(EditAnywhere, Category = MaterialExpressionAdd, meta = (OverridingInputProperty = "A"))
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// float ConstA;
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//
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static FName OverridingInputPropertyMetaData(TEXT("OverridingInputProperty"));
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if (InProperty->HasMetaData(OverridingInputPropertyMetaData))
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{
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const FString& OverridingPropertyName = InProperty->GetMetaData(OverridingInputPropertyMetaData);
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FStructProperty* StructProp = FindFProperty<FStructProperty>(GetClass(), *OverridingPropertyName);
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if (ensure(StructProp != nullptr))
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{
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static FName RequiredInputMetaData(TEXT("RequiredInput"));
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// Must be a single FExpressionInput member, not an array, and must be tagged with metadata RequiredInput="false"
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if (ensure( StructProp->Struct->GetFName() == NAME_ExpressionInput &&
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StructProp->ArrayDim == 1 &&
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StructProp->HasMetaData(RequiredInputMetaData) &&
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!StructProp->GetBoolMetaData(RequiredInputMetaData)))
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{
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const FExpressionInput* Input = StructProp->ContainerPtrToValuePtr<FExpressionInput>(this);
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if (Input->Expression != nullptr && Input->GetTracedInput().Expression != nullptr)
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{
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bIsEditable = false;
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}
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}
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}
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}
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if (bIsEditable)
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{
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// If the property has EditCondition metadata, then whether it's editable depends on the other EditCondition property
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const FString EditConditionPropertyName = InProperty->GetMetaData(TEXT("EditCondition"));
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if (!EditConditionPropertyName.IsEmpty())
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{
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FBoolProperty* EditConditionProperty = FindFProperty<FBoolProperty>(GetClass(), *EditConditionPropertyName);
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{
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bIsEditable = *EditConditionProperty->ContainerPtrToValuePtr<bool>(this);
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}
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}
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}
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}
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return bIsEditable;
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}
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```
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