Extents Modifier 和 Bounds Modifier这两个节点看起来很像，都是修改Point的Bouding Box，查看一下源代码，简单看一下它们的区别

两个节点的代码对比

Bounds Modifier

源代码

switch (Mode)
	{
	case EPCGBoundsModifierMode::Intersect:
		ProcessPoints(Context, Inputs, Outputs, [&Bounds, bAffectSteepness, Steepness](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetLocalBounds(InPoint.GetLocalBounds().Overlap(Bounds));
			
			if (bAffectSteepness)
			{
				OutPoint.Steepness = FMath::Min(InPoint.Steepness, Steepness);
			}

			return true;
		});
		break;

	case EPCGBoundsModifierMode::Include:
		ProcessPoints(Context, Inputs, Outputs, [&Bounds, bAffectSteepness, Steepness](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetLocalBounds(InPoint.GetLocalBounds() + Bounds);

			if (bAffectSteepness)
			{
				OutPoint.Steepness = FMath::Max(InPoint.Steepness, Steepness);
			}

			return true;
		});
		break;

	case EPCGBoundsModifierMode::Translate:
		ProcessPoints(Context, Inputs, Outputs, [&BoundsMin, &BoundsMax, bAffectSteepness, Steepness](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.BoundsMin += BoundsMin;
			OutPoint.BoundsMax += BoundsMax;

			if (bAffectSteepness)
			{
				OutPoint.Steepness = FMath::Clamp(InPoint.Steepness + Steepness, 0.0f, 1.0f);
			}

			return true;
		});
		break;

	case EPCGBoundsModifierMode::Scale:
		ProcessPoints(Context, Inputs, Outputs, [&BoundsMin, &BoundsMax, bAffectSteepness, Steepness](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.BoundsMin *= BoundsMin;
			OutPoint.BoundsMax *= BoundsMax;

			if (bAffectSteepness)
			{
				OutPoint.Steepness = FMath::Clamp(InPoint.Steepness * Steepness, 0.0f, 1.0f);
			}

			return true;
		});
		break;

	case EPCGBoundsModifierMode::Set:
		ProcessPoints(Context, Inputs, Outputs, [&Bounds, bAffectSteepness, Steepness](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetLocalBounds(Bounds);

			if (bAffectSteepness)
			{
				OutPoint.Steepness = Steepness;
			}

			return true;
		});
		break;
	}

Bounds Modifier

源代码

switch (Mode)
	{
	case EPCGPointExtentsModifierMode::Minimum:
		ProcessPoints(Context, Inputs, Outputs, [Extents](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetExtents(FVector::Min(Extents, InPoint.GetExtents()));
			return true;
		});
		break;

	case EPCGPointExtentsModifierMode::Maximum:
		ProcessPoints(Context, Inputs, Outputs, [Extents](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetExtents(FVector::Max(Extents, InPoint.GetExtents()));
			return true;
		});
		break;

	case EPCGPointExtentsModifierMode::Add:
		ProcessPoints(Context, Inputs, Outputs, [Extents](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetExtents(Extents + InPoint.GetExtents());
			return true;
		});
		break;

	case EPCGPointExtentsModifierMode::Multiply:
		ProcessPoints(Context, Inputs, Outputs, [Extents](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetExtents(Extents * InPoint.GetExtents());
			return true;
		});
		break;

	case EPCGPointExtentsModifierMode::Set:
		ProcessPoints(Context, Inputs, Outputs, [Extents](const FPCGPoint& InPoint, FPCGPoint& OutPoint){
			OutPoint = InPoint;
			OutPoint.SetExtents(Extents);
			return true;
		});
		break;
	}

从代码上看，除了运算模式的区别，和它们的名字一样Bounds Modifier操作的目标是Point的Bounds而Extents Modifier 操作的目标是Point的Extents，并且Bounds Modifier可以选择性地影响Steepness，而Extents Modifier没有这个选项。所以问题的关键就是Bounds和Extents的区别。下面我们看一下PCGPoint的代码:

USTRUCT(BlueprintType)
struct PCG_API FPCGPoint
{
	GENERATED_BODY()
public:
	FPCGPoint() = default;
	FPCGPoint(const FTransform& InTransform, float InDensity, int32 InSeed);

	FBox GetLocalBounds() const;
	FBox GetLocalDensityBounds() const;
	void SetLocalBounds(const FBox& InBounds);
	FBoxSphereBounds GetDensityBounds() const;

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	FTransform Transform;

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	float Density = 1.0f;

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	FVector BoundsMin = -FVector::One();

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	FVector BoundsMax = FVector::One();

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	FVector4 Color = FVector4::One();

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties, meta = (ClampMin = "0", ClampMax = "1"))
	float Steepness = 0.5f;

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	int32 Seed = 0;

	UPROPERTY(BlueprintReadOnly, VisibleAnywhere, Category = "Properties|Metadata")
	int64 MetadataEntry = -1;

	FVector GetExtents() const { return (BoundsMax - BoundsMin) / 2.0; }
	void SetExtents(const FVector& InExtents)
	{
		const FVector Center = GetLocalCenter();
		BoundsMin = Center - InExtents;
		BoundsMax = Center + InExtents;
	}

	FVector GetScaledExtents() const { return GetExtents() * Transform.GetScale3D(); }

	FVector GetLocalCenter() const { return (BoundsMax + BoundsMin) / 2.0; }
	void SetLocalCenter(const FVector& InCenter)
	{
		const FVector Delta = InCenter - GetLocalCenter();
		BoundsMin += Delta;
		BoundsMax += Delta;
	}

	using PointCustomPropertyGetter = TFunction<bool(const FPCGPoint&, void*)>;
	using PointCustomPropertySetter = TFunction<bool(FPCGPoint&, const void*)>;

	static bool HasCustomPropertyGetterSetter(FName Name);
	static TUniquePtr<IPCGAttributeAccessor> CreateCustomPropertyAccessor(FName Name);
};

在Point中并没有Extents这个成员变量，而只有BoundsMin和BoundsMax这两个Vector3的成员变量

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	FVector BoundsMin = -FVector::One();

	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Properties)
	FVector BoundsMax = FVector::One();

Extents和Bounds之间的关系：

FVector GetExtents() const { return (BoundsMax - BoundsMin) / 2.0; }

	void SetExtents(const FVector& InExtents)
	{
		const FVector Center = GetLocalCenter();
		BoundsMin = Center - InExtents;
		BoundsMax = Center + InExtents;
	}

小结

Extents Modifier 和 Bounds Modifier的本质并没有区别