82 lines
3.8 KiB
Markdown
82 lines
3.8 KiB
Markdown
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# LatentInfo
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- **功能描述：** 和Latent配合，指明哪个函数参数是LatentInfo参数。
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- **使用位置：** UFUNCTION
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- **元数据类型：** string="abc"
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- **关联项：** [Latent](Latent.md)
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- **常用程度：** ★★★
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Latent的函数需要FLatentActionInfo才能工作。FLatentActionInfo里记录着这个延迟操作的ID以及下一步要执行的函数名称等。在蓝图的虚拟机运行环境下，一个Latent函数执行的时候，蓝图VM会收集当前的函数上下文信息（典型的比如下Latent函数连接的下一个节点），然后继续赋值到Latent函数的FLatentActionInfo参数上，再配合FPendingLatentAction注册到FLatentActionManager里面去。等时间到达或者触发条件达成后，FLatentActionManager会触发CallbackTarget->ProcessEvent(ExecutionFunction, &(LinkInfo.LinkID))，从而继续执行下去。
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如果没有用LatentInfo来指定函数参数，则因为断了LatentInfo的赋值操作，因此就无法正常工作，蓝图效果图见Latent页面。
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LatentInfo值就像WorldContext一样，会被蓝图VM系统自动的填充值。填充值的操作是在EmitLatentInfoTerm里执行的。把LatentInfoStruct的值填充到LatentInfo的函数参数里去。LatentInfo的参数位置并不重要。LatentInfo指定的函数参数Pin会被隐藏。
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```cpp
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void EmitFunctionCall(FKismetCompilerContext& CompilerContext, FKismetFunctionContext& FunctionContext, FBlueprintCompiledStatement& Statement, UEdGraphNode* SourceNode)
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{
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if (bIsUbergraph && FuncParamProperty->GetName() == FunctionToCall->GetMetaData(FBlueprintMetadata::MD_LatentInfo))
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{
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EmitLatentInfoTerm(Term, FuncParamProperty, Statement.TargetLabel);
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}
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}
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void EmitLatentInfoTerm(FBPTerminal* Term, FProperty* LatentInfoProperty, FBlueprintCompiledStatement* TargetLabel)
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{
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// Special case of the struct property emitter. Needs to emit a linkage property for fixup
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FStructProperty* StructProperty = CastFieldChecked<FStructProperty>(LatentInfoProperty);
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check(StructProperty->Struct == LatentInfoStruct);
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int32 StructSize = LatentInfoStruct->GetStructureSize();
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uint8* StructData = (uint8*)FMemory_Alloca(StructSize);
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StructProperty->InitializeValue(StructData);
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// Assume that any errors on the import of the name string have been caught in the function call generation
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StructProperty->ImportText_Direct(*Term->Name, StructData, NULL, 0, GLog);
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Writer << EX_StructConst;
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Writer << LatentInfoStruct;
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Writer << StructSize;
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checkSlow(Schema);
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for (FProperty* Prop = LatentInfoStruct->PropertyLink; Prop; Prop = Prop->PropertyLinkNext)
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{
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if (TargetLabel && Prop->GetBoolMetaData(FBlueprintMetadata::MD_NeedsLatentFixup))
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{
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// Emit the literal and queue a fixup to correct it once the address is known
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Writer << EX_SkipOffsetConst;
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CodeSkipSizeType PatchUpNeededAtOffset = Writer.EmitPlaceholderSkip();
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JumpTargetFixupMap.Add(PatchUpNeededAtOffset, FCodeSkipInfo(FCodeSkipInfo::Fixup, TargetLabel));
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}
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else if (Prop->GetBoolMetaData(FBlueprintMetadata::MD_LatentCallbackTarget))
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{
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FBPTerminal CallbackTargetTerm;
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CallbackTargetTerm.bIsLiteral = true;
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CallbackTargetTerm.Type.PinSubCategory = UEdGraphSchema_K2::PN_Self;
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EmitTermExpr(&CallbackTargetTerm, Prop);
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}
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else
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{
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// Create a new term for each property, and serialize it out
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FBPTerminal NewTerm;
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if(Schema->ConvertPropertyToPinType(Prop, NewTerm.Type))
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{
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NewTerm.bIsLiteral = true;
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Prop->ExportText_InContainer(0, NewTerm.Name, StructData, StructData, NULL, PPF_None);
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EmitTermExpr(&NewTerm, Prop);
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}
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else
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{
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// Do nothing for unsupported/unhandled property types. This will leave the value unchanged from its constructed default.
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Writer << EX_Nothing;
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}
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}
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}
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Writer << EX_EndStructConst;
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}
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```
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LatentInfo信息的收集是在FKCHandler_CallFunction::CreateFunctionCallStatement里
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