《Electric Dreams》项目中提供了一些自定义节点和子图（文件位置:“/Content/PCG/Assets/PCGCustomNodes”），这些节点和子图在《Electric Dreams》被广泛使用，对于理解《Electric Dreams》非常重要，而且它们可以直接移植到新的项目中使用。所以写个博客分析一下

前导文章

《虚幻引擎程序化资源生成框架PCG 之 UPCGBlueprintElement源码笔记（一）》
《虚幻引擎程序化资源生成框架PCG 之 UPCGBlueprintElement源码笔记（二）数据流》

Passthrough节点

作用

数据流的开关

Execute with Context

用Enabled控制是否将从Input输入进来的从Output输出，当Enabled为false的时候，输出的PCGDataCollection中的Tagged Data数组将会是一个空数组。

PointNormalToColor节点

作用

将Point法线存入Color属性

Point Loop Body

先看一下它的Point Loop Body

Point Loop Body的逻辑就是将每一个Point的Up Vector存储在Color属性中，然后把修改过的Point输出。

Execute with Context

注释见上图，在PointLoopBody后面有一个Initialize from Data节点，代码如下：

void UPCGSpatialData::InitializeFromData(const UPCGSpatialData* InSource, const UPCGMetadata* InMetadataParentOverride, bool bInheritMetadata, bool bInheritAttributes)
{if (InSource && TargetActor.IsExplicitlyNull()){TargetActor = InSource->TargetActor;}if (!Metadata){Metadata = NewObject<UPCGMetadata>(this);}if (!bInheritMetadata || InMetadataParentOverride || InSource){const UPCGMetadata* ParentMetadata = bInheritMetadata ? (InMetadataParentOverride ? InMetadataParentOverride : (InSource ? InSource->Metadata : nullptr)) : nullptr;Metadata->Initialize(ParentMetadata, bInheritAttributes);}else{UE_LOG(LogPCG, Warning, TEXT("InitializeFromData has both no source and no metadata override"));}
}

Initialize from Data做了两件事：

• 将源Data中的TargetActor赋值给新PCGSpatialData的TargetActor
• 用源Data的metadata初始化新PCGSpatialData的metadata

PointFromPCGVolume节点

作用

使用Context中Source的Component或者Component的几何信息(Transform和Bound)构造1个PCGPoint。

Execute with Context

我们先看一下GetComponent和GetOriginalComponent

UPCGComponent* UPCGBlueprintHelpers::GetComponent(FPCGContext& Context)
{return Context.SourceComponent.Get();
}UPCGComponent* UPCGBlueprintHelpers::GetOriginalComponent(FPCGContext& Context)
{if (Context.SourceComponent.IsValid() &&Cast<APCGPartitionActor>(Context.SourceComponent->GetOwner()) &&Cast<APCGPartitionActor>(Context.SourceComponent->GetOwner())->GetOriginalComponent(Context.SourceComponent.Get())){return Cast<APCGPartitionActor>(Context.SourceComponent->GetOwner())->GetOriginalComponent(Context.SourceComponent.Get());}else{return Context.SourceComponent.Get();}
}

再看看它是如何获取GetActorLocalBoundsPCG的

UPCGBlueprintHelpers::GetActorLocalBoundsPCG

FBox UPCGBlueprintHelpers::GetActorLocalBoundsPCG(AActor* InActor, bool bIgnorePCGCreatedComponents)
{return PCGHelpers::GetActorLocalBounds(InActor, bIgnorePCGCreatedComponents);
}

PCGHelpers::GetActorLocalBounds

FBox GetActorLocalBounds(const AActor* InActor, bool bIgnorePCGCreatedComponents){// Specialized version of CalculateComponentsBoundingBoxInLocalScape that skips over PCG generated components// This is to ensure stable bounds and no timing issues (cleared ISMs, etc.)FBox Box(EForceInit::ForceInit);const bool bNonColliding = true;const bool bIncludeFromChildActors = true;if (InActor){const FTransform& ActorToWorld = InActor->GetTransform();const FTransform WorldToActor = ActorToWorld.Inverse();InActor->ForEachComponent<UPrimitiveComponent>(bIncludeFromChildActors, [bNonColliding, bIgnorePCGCreatedComponents, &WorldToActor, &Box](const UPrimitiveComponent* InPrimComp){if ((bNonColliding || InPrimComp->IsCollisionEnabled()) &&(!bIgnorePCGCreatedComponents || !InPrimComp->ComponentTags.Contains(DefaultPCGTag))){const FTransform ComponentToActor = InPrimComp->GetComponentTransform() * WorldToActor;Box += InPrimComp->CalcBounds(ComponentToActor).GetBox();}});}else{UE_LOG(LogPCG, Error, TEXT("Actor is invalid in GetActorLocalBounds"));}return Box;}

所谓LocalBounds就是把所属Actor的所有PrimitiveComponent叠加起来获得最大的FBox