【UE4 C++】四叉树实现及可视化

前言

主要参考
- Quadtree - wikipedia
- quadtree-js dynamic example
- 碰撞檢測的優化-四叉樹(Quadtree)
- UE4自带 TQuadTree
  - GenericQuadTree.h 和 WaterQuadTree.h
  - 源码见附录。写到最后，才发现引擎有这部分源码了，不过没有树的更新。
实现版本 4.26.2
存在问题
- 不使用完全清除四叉树的方法而直接动态更新，会有bug：这边是运行久了，对象丢失，对象无法复原状态和响应。
- 如果有大佬，看了代码知道为什么，希望指导一下，非常感谢
本文原创

概念

四叉树是一种树形数据结构，其每个节点至多有四个子节点，表示将当前空间划分为四个子空间，如此递归下去，直到达到一定深度或者满足某种要求后停止划分。
所有的四叉树法有共同之特点:
- 可分解成为各自的区块
- 每个区块都有节点容量。当节点达到最大容量时，节点分裂
- 树状数据结构依造四叉树法加以区分
应用
- 二维数据查找
- 图像压缩
- 光线求交
- 地形渲染
- 二维的碰撞检测等

实现

效果

代码

树节点

//@ https://www.cnblogs.com/shiroe/p/15526194.html
// 四叉树的节点
class QuadTreeNode:public TSharedFromThis<QuadTreeNode> {

public:
	FVector center; // 中心点
	FVector extend; // 扩展尺寸
	bool isLeaf;    //是否是叶子节点
	int32 depth = 0;
	int32 maxCount = 4;

	TArray<ABattery*>objs; 
	static UObject* worldObject;
	bool bInRange;
	
	TSharedPtr<QuadTreeNode> root;
	TArray<TSharedPtr<QuadTreeNode>> child_node;
public:
	QuadTreeNode(FVector _center, FVector _extend, int32 _depth, TSharedPtr<QuadTreeNode> _root=nullptr)
		: center(_center), extend(_extend), depth(_depth) {
		root = _root;
		isLeaf = true;
		child_node.Init(nullptr, 4);
		bInRange = false;
	}
	~QuadTreeNode() {
		root = nullptr;
		objs.Empty();
		child_node.Empty();
	}

	bool IsNotUsed() {
		return isLeaf && objs.Num() <= 0;
	}

	//方形与圆形求交
	bool InterSection(FVector _OCenter, float _radian) {
		FVector v = _OCenter - center; //取相对原点
		float x = UKismetMathLibrary::Min(v.X, extend.X); 
		x = UKismetMathLibrary::Max(x, -extend.X);

		float y = UKismetMathLibrary::Min(v.Y, extend.Y);
		y = UKismetMathLibrary::Max(y, -extend.Y);
		return (x - v.X) * (x - v.X) + (y - v.Y) * (y - v.Y) <= _radian * _radian; //注意此时圆心的相对坐标
	}

	//点是否在本区域内
	bool InterSection(FVector _point) {	
		return (_point.X >= center.X - extend.X &&
			_point.X <= center.X + extend.X &&
			_point.Y >= center.Y - extend.Y &&
			_point.Y <= center.Y + extend.Y);
	}

	//点是否在指定区域内
	bool InterSection(FVector _pMin, FVector _pMax, FVector _point) {		
		return (_point.X >= _pMin.X &&
			_point.X <= _pMax.X &&
			_point.Y >= _pMin.Y &&
			_point.Y <= _pMax.Y);
	}
	
	//插入对象
	void InsertObj(ABattery* obj) {
		objs.Add(obj);
		if (isLeaf && objs.Num() <= maxCount) //直接插入			
		{				
			return;
		}	

		float dx[4] = { 1, -1, -1, 1 };
		float dy[4] = { 1, 1, -1, -1 };
		//超过上限个数，创建子节点;或者不再是叶子节点
		isLeaf = false;
		for (auto& item : objs) {
			for (int i = 0; i < 4; i++) {//四个象限
				FVector p = center + FVector(extend.X * dx[i], extend.Y * dy[i], 0);
				FVector pMin = p.ComponentMin(center);
				FVector pMax = p.ComponentMax(center);
				if (InterSection(pMin, pMax, item->GetActorLocation())) {
					if (!child_node[i].IsValid())
					{
						root = root.IsValid() ? root : this->AsShared();
						child_node[i] = MakeShareable(new QuadTreeNode(pMin/2+pMax/2, extend / 2, depth + 1, root));
					}
					child_node[i]->InsertObj(item);
					//break; //确保只在一个象限内
				}
			}			
		}
		objs.Empty(); //确保非叶子节点不存
	}

	// 绘制区域边界
	void DrawBound(float time = 0.02f, float thickness = 2.0f) {	
		if (worldObject)
		{
			FLinearColor drawColor = bInRange ? FLinearColor::Green : FLinearColor::Red;
			FVector drawCenter = center + (bInRange ? FVector(0, 0, 8) : FVector(0, 0, 5));
			UKismetSystemLibrary::DrawDebugBox(worldObject, drawCenter, extend+FVector(0,0,1), drawColor, FRotator::ZeroRotator, time, thickness);
		}
		
	}

	// 判断电池是否在扫描器的范围类
	void TraceObjectInRange(AActor* traceActor, float _radian) {
		FVector _OCenter = traceActor->GetActorLocation();
		if (InterSection(_OCenter, _radian)) {
			bInRange = true;
			if (isLeaf) {
				for (ABattery* obj : objs)
				{					
					_OCenter.Z = obj->GetActorLocation().Z;
					bool bCanActive = FVector::Distance(_OCenter, obj->GetActorLocation()) <= _radian;
					obj->ActiveState(bCanActive, traceActor);
				}
			}
			else {
				for (auto& node : child_node)
				{
					if (node.IsValid()) {
						node->TraceObjectInRange(traceActor, _radian);
					}
				}
			}
		}
		else {
			TraceObjectOutRange(_OCenter, _radian);
		}
	}
	

	void TraceObjectOutRange(FVector _OCenter, float _radian) {
		bInRange = false;
		for (ABattery* obj : objs){
			{				
				obj->ActiveState(false, nullptr);
			}
		}
		for (auto& node: child_node)
		{

			if (node.IsValid()) {
				node->TraceObjectOutRange(_OCenter, _radian);
			}			
		}
	}

	// 更新状态
	void UpdateState() {
		DrawBound(1 / UKismetSystemLibrary::GetFrameCount()); //根据帧数绘制

		if (!isLeaf) {	//如果不是叶子节点，则递归到子树下去，如果子树为空，则回收该节点
			for (auto& node : child_node){
				if (node.IsValid())
				{
					node->UpdateState();
					if (node->IsNotUsed())
					{
						node.Reset();
						node = nullptr;	
					}					
				}
			}

			int32 count = 4;
			for (auto& node : child_node) {
				if (!node.IsValid())
					count--;
			}
			if (count == 0) {
				isLeaf = true;
			}else
				return;
		}
		
		if (isLeaf && objs.Num()>0){ //如果叶子节点，更新物体是否在区域内；不在区域则移出，并重新插入
			int32 i = 0;
			while (i<objs.Num())
			{
				if (!InterSection(objs[i]->GetActorLocation())) {	
					ABattery* battery = objs[i];
					objs.Swap(i, objs.Num() - 1);
					objs.Pop();
					root->InsertObj(battery);
					continue;
				}
				i++;
			}
		}
	}
};

树、管理器

头文件

//@ https://www.cnblogs.com/shiroe/p/15526194.html
UCLASS()
class PRIME_API AQuadTree : public AActor  //该类可以当成树
{
	GENERATED_BODY()
	
public:	
	AQuadTree();
protected:
	virtual void BeginPlay() override;
public:	
	virtual void Tick(float DeltaTime) override;
	void SpawnActors();
	void ActorsAddVelocity();

public:
	UPROPERTY(EditAnywhere)
		int32 cubeCount=20;
	UPROPERTY(EditAnywhere)
		int32 width=500;
	UPROPERTY(EditAnywhere)
		int32 height=500;
	UPROPERTY(EditAnywhere)
		float playRate=0.05;
	UPROPERTY(EditAnywhere)
		TSubclassOf<ABattery> BatteryClass;
	UPROPERTY(EditAnywhere)
		AActor* traceActor;
	UPROPERTY(EditAnywhere)
		float affectRadianRange=50;
	UPROPERTY()
		TArray<ABattery*> objs;

	TSharedPtr<QuadTreeNode> root;
	FTimerHandle timer;
	FTimerHandle timer2;
};

cpp

//@ https://www.cnblogs.com/shiroe/p/15526194.html
AQuadTree::AQuadTree()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

}

UObject* QuadTreeNode::worldObject=nullptr;

void AQuadTree::BeginPlay()
{
	Super::BeginPlay();
	QuadTreeNode::worldObject = GetWorld();
	root = MakeShareable(new QuadTreeNode(FVector::ZeroVector, FVector(height, width, 0), 0));
	GetWorld()->GetTimerManager().SetTimer(timer, this, &AQuadTree::SpawnActors, playRate, true);
	GetWorld()->GetTimerManager().SetTimer(timer2, this, &AQuadTree::ActorsAddVelocity, 2, true);
}

void AQuadTree::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);
	if (root.IsValid())
	{			
		root->UpdateState(); //更新状态
		root->TraceObjectInRange(traceActor, affectRadianRange); //判断是否在扫描器的范围内	
	}
}

// 定时生成物体
void AQuadTree::SpawnActors()
{
	if (cubeCount < 0) {
		GetWorld()->GetTimerManager().ClearTimer(timer);
		return;
	}
	cubeCount--;
	FVector pos = FVector(UKismetMathLibrary::RandomIntegerInRange(-height+10, height-10),
		UKismetMathLibrary::RandomIntegerInRange(-width+10, width-10), 11);
	FTransform trans = FTransform(FRotator(0, UKismetMathLibrary::RandomFloatInRange(0, 360), 0), pos, FVector(0.2));
	ABattery* actor= GetWorld()->SpawnActor<ABattery>(BatteryClass, trans);
	if (IsValid(actor))
	{
		objs.Add(actor);
		root->InsertObj(actor);	
	}
}

// 定时给物体一个速度
void AQuadTree::ActorsAddVelocity()
{
	for (ABattery* actor :objs)
	{
		actor->GetStaticMeshComponent()->SetPhysicsLinearVelocity(UKismetMathLibrary::RandomUnitVector() * 50);
	}
}

电池物体类 Battery

头文件

//@ https://www.cnblogs.com/shiroe/p/15526194.html
UCLASS()
class PRIME_API ABattery : public AStaticMeshActor
{
	GENERATED_BODY()
public:	
	ABattery();
protected:
	virtual void BeginPlay() override;
public:	
	virtual void Tick(float DeltaTime) override;
	void ActiveState(bool _bActive, AActor* _targetActor);

public:
	UPROPERTY(EditAnywhere)
		UMaterial* m_normal;
	UPROPERTY(EditAnywhere)
		UMaterial* m_active;
	UPROPERTY()
		AActor* targetActor;
	bool bActive = false;
};

cpp

//@ https://www.cnblogs.com/shiroe/p/15526194.html
#include "Battery.h"
#include "Kismet/KismetMathLibrary.h"
#include "DrawDebugHelpers.h"
#include "Kismet/KismetSystemLibrary.h"

ABattery::ABattery()
{
	PrimaryActorTick.bCanEverTick = true;
	GetStaticMeshComponent()->SetMobility(EComponentMobility::Movable);
	GetStaticMeshComponent()->SetConstraintMode(EDOFMode::XYPlane);
	GetStaticMeshComponent()->SetSimulatePhysics(true);	
}

void ABattery::BeginPlay()
{
	Super::BeginPlay();	
}

void ABattery::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);
	if (bActive && targetActor)
	{
		float drawTime = 1 / UKismetSystemLibrary::GetFrameCount();
		DrawDebugLine(GetWorld(), GetActorLocation(), targetActor->GetActorLocation(), FColor(0,148,220,255), false, drawTime, 1, 4.0f);
	}
}

void ABattery::ActiveState(bool _bActive, AActor* _targetActor){
	if (bActive == _bActive)
		return;
	bActive = _bActive;
	targetActor = _targetActor;
	GetStaticMeshComponent()->SetMaterial(0, bActive ? m_active : m_normal);
}

其他
- LevelSequece 设置扫描器的空中移动路径
- 电池物体类 Battery 创建蓝图派生类，用来设置资源

附录

\Engine\Source\Runtime\Engine\Public\GenericQuadTree.h

点击查看代码

// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"

ENGINE_API DECLARE_LOG_CATEGORY_EXTERN(LogQuadTree, Log, Warning);

template <typename ElementType, int32 NodeCapacity = 4>
class TQuadTree
{
	typedef TQuadTree<ElementType, NodeCapacity> TreeType;
public:

  /** DO NOT USE. This constructor is for internal usage only for hot-reload purposes. */
  TQuadTree();

  TQuadTree(const FBox2D& InBox, float InMinimumQuadSize = 100.f);

  /** Gets the TreeBox so systems can test insertions before trying to do so with invalid regions */
  const FBox2D& GetTreeBox() const { return TreeBox; }

  /** Inserts an object of type ElementType with an associated 2D box of size Box (log n). Pass in a DebugContext so when an issue occurs the log can report what requested this insert. */
  void Insert(const ElementType& Element, const FBox2D& Box, const TCHAR* DebugContext = nullptr);

  /** Given a 2D box, returns an array of elements within the box. There will not be any duplicates in the list. */
	template<typename ElementAllocatorType>
	void GetElements(const FBox2D& Box, TArray<ElementType, ElementAllocatorType>& ElementsOut) const;

	/** Removes an object of type ElementType with an associated 2D box of size Box (log n). Does not cleanup tree*/
	bool Remove(const ElementType& Instance, const FBox2D& Box);

	/** Does a deep copy of the tree by going through and re-creating the internal data. Cheaper than re-insertion as it should be linear instead of nlogn */
	void Duplicate(TreeType& OutDuplicate) const;

	/** Removes all elements of the tree */
	void Empty();
	
	void Serialize(FArchive& Ar);

	TreeType& operator=(const TreeType& Other);

	~TQuadTree();

private:
	enum QuadNames
	{
		TopLeft = 0,
		TopRight = 1,
		BottomLeft = 2,
		BottomRight = 3
	};

	/** Node used to hold the element and its corresponding 2D box*/
	struct FNode
	{
		FBox2D Box;
		ElementType Element;

		FNode() {};

		FNode(const ElementType& InElement, const FBox2D& InBox)
			: Box(InBox)
			, Element(InElement)
		{}

		friend FArchive& operator<<(FArchive& Ar, typename TQuadTree<ElementType, NodeCapacity>::FNode& Node)
		{
			return Ar << Node.Box << Node.Element;
		}
	};

	/** Given a 2D box, return the subtrees that are touched. Returns 0 for leaves. */
	int32 GetQuads(const FBox2D& Box, TreeType* Quads[4]) const;

	/** Split the tree into 4 sub-trees */
	void Split();

	/** Given a list of nodes, return which ones actually intersect the box */
	template<typename ElementAllocatorType>
	void GetIntersectingElements(const FBox2D& Box, TArray<ElementType, ElementAllocatorType>& ElementsOut) const;

	/** Given a list of nodes, remove the node that contains the given element */
	bool RemoveNodeForElement(const ElementType& Element);

	/** Internal recursive implementation of @see Insert */
	void InsertElementRecursive(const ElementType& Element, const FBox2D& Box, const TCHAR* DebugContext);

private:

	/**
	 * Contains the actual elements this tree is responsible for. Nodes are used to keep track of each element's AABB as well.
	 * For a non-internal leaf, this is the list of nodes that are fully contained within this tree.
	 * For an internal tree, this contains the nodes that overlap multiple subtrees.
	 */
	TArray<FNode> Nodes;

	/** The sub-trees of this tree */
	TreeType* SubTrees[4];

	/** AABB of the tree */
	FBox2D TreeBox;

	/** Center position of the tree */
	FVector2D Position;

	/** The smallest size of a quad allowed in the tree */
	float MinimumQuadSize;

	/** Whether this is a leaf or an internal sub-tree */
	bool bInternal;
};

template <typename ElementType, int32 NodeCapacity /*= 4*/>
typename TQuadTree<ElementType, NodeCapacity>::TreeType& TQuadTree<ElementType, NodeCapacity>::operator=(const TreeType& Other)
{
	Other.Duplicate(*this);
	return *this;
}

template <typename ElementType, int32 NodeCapacity /*= 4*/>
void TQuadTree<ElementType, NodeCapacity>::Serialize(FArchive& Ar)
{
	Ar << Nodes;

	bool SubTreeFlags[4] = { SubTrees[0] != nullptr, SubTrees[1] != nullptr, SubTrees[2] != nullptr, SubTrees[3] != nullptr };
	Ar << SubTreeFlags[0] << SubTreeFlags[1] << SubTreeFlags[2] << SubTreeFlags[3];

	for (int32 Idx = 0; Idx < 4; ++Idx)
	{
		if (SubTreeFlags[Idx])
		{
			if (Ar.IsLoading())
			{
				SubTrees[Idx] = new TreeType(FBox2D(), MinimumQuadSize);
			}

			SubTrees[Idx]->Serialize(Ar);
		}
	}

	Ar << TreeBox;
	Ar << Position;
	Ar << bInternal;
}

template <typename ElementType, int32 NodeCapacity>
TQuadTree<ElementType, NodeCapacity>::TQuadTree(const FBox2D& Box, float InMinimumQuadSize)
	: TreeBox(Box)
	, Position(Box.GetCenter())
	, MinimumQuadSize(InMinimumQuadSize)
	, bInternal(false)
{
	SubTrees[0] = SubTrees[1] = SubTrees[2] = SubTrees[3] = nullptr;
}

template <typename ElementType, int32 NodeCapacity>
TQuadTree<ElementType, NodeCapacity>::TQuadTree()
{
	EnsureRetrievingVTablePtrDuringCtor(TEXT("TQuadTree()"));
}

template <typename ElementType, int32 NodeCapacity>
TQuadTree<ElementType, NodeCapacity>::~TQuadTree()
{
	for (TreeType* SubTree : SubTrees)
	{
		delete SubTree;
		SubTree = nullptr;
	}
}

template <typename ElementType, int32 NodeCapacity>
void TQuadTree<ElementType, NodeCapacity>::Split()
{
	check(bInternal == false);

	const FVector2D Extent = TreeBox.GetExtent();
	const FVector2D XExtent = FVector2D(Extent.X, 0.f);
	const FVector2D YExtent = FVector2D(0.f, Extent.Y);

	/************************************************************************
	 *  ___________max
	 * |     |     |
	 * |     |     |
	 * |-----c------
	 * |     |     |
	 * min___|_____|
	 *
	 * We create new quads by adding xExtent and yExtent
	 ************************************************************************/

	const FVector2D C = Position;
	const FVector2D TM = C + YExtent;
	const FVector2D ML = C - XExtent;
	const FVector2D MR = C + XExtent;
	const FVector2D BM = C - YExtent;
	const FVector2D BL = TreeBox.Min;
	const FVector2D TR = TreeBox.Max;

	SubTrees[TopLeft] = new TreeType(FBox2D(ML, TM), MinimumQuadSize);
	SubTrees[TopRight] = new TreeType(FBox2D(C, TR), MinimumQuadSize);
	SubTrees[BottomLeft] = new TreeType(FBox2D(BL, C), MinimumQuadSize);
	SubTrees[BottomRight] = new TreeType(FBox2D(BM, MR), MinimumQuadSize);

	//mark as no longer a leaf
	bInternal = true;

	// Place existing nodes and place them into the new subtrees that contain them
	// If a node overlaps multiple subtrees, we retain the reference to it here in this quad
	TArray<FNode> OverlappingNodes;
	for (const FNode& Node : Nodes)
	{
		TreeType* Quads[4];
		const int32 NumQuads = GetQuads(Node.Box, Quads);
		check(NumQuads > 0);

		if (NumQuads == 1)
		{
			Quads[0]->Nodes.Add(Node);
		}
		else
		{
			OverlappingNodes.Add(Node);
		}
	}

	// Hang onto the nodes that don't fit cleanly into a single subtree
	Nodes = OverlappingNodes;
}

template <typename ElementType, int32 NodeCapacity>
void TQuadTree<ElementType, NodeCapacity>::Insert(const ElementType& Element, const FBox2D& Box, const TCHAR* DebugContext)
{
	if (!Box.Intersect(TreeBox))
	{
		// Elements shouldn't be added outside the bounds of the top-level quad
		UE_LOG(LogQuadTree, Warning, TEXT("[%s] Adding element (%s) that is outside the bounds of the quadtree root (%s). Consider resizing."), DebugContext ? DebugContext : TEXT("Unknown Source"), *Box.ToString(), *TreeBox.ToString());
	}

	InsertElementRecursive(Element, Box, DebugContext);
}

template <typename ElementType, int32 NodeCapacity>
void TQuadTree<ElementType, NodeCapacity>::InsertElementRecursive(const ElementType& Element, const FBox2D& Box, const TCHAR* DebugContext)
{
	TreeType* Quads[4];
	const int32 NumQuads = GetQuads(Box, Quads);
	if (NumQuads == 0)
	{
		// This should only happen for leaves
		check(!bInternal);

		// It's possible that all elements in the leaf are bigger than the leaf or that more elements than NodeCapacity exist outside the top level quad
		// In either case, we can get into an endless spiral of splitting
		const bool bCanSplitTree = TreeBox.GetSize().SizeSquared() > FMath::Square(MinimumQuadSize);
		if (!bCanSplitTree || Nodes.Num() < NodeCapacity)
		{
			Nodes.Add(FNode(Element, Box));

			if (!bCanSplitTree)
			{
				UE_LOG(LogQuadTree, Verbose, TEXT("[%s] Minimum size %f reached for quadtree at %s. Filling beyond capacity %d to %d"), DebugContext ? DebugContext : TEXT("Unknown Source"), MinimumQuadSize, *Position.ToString(), NodeCapacity, Nodes.Num());
			}
		}
		else
		{
			// This quad is at capacity, so split and try again
			Split();
			InsertElementRecursive(Element, Box, DebugContext);
		}
	}
	else if (NumQuads == 1)
	{
		check(bInternal);

		// Fully contained in a single subtree, so insert it there
		Quads[0]->InsertElementRecursive(Element, Box, DebugContext);
	}
	else
	{
		// Overlaps multiple subtrees, store here
		check(bInternal);
		Nodes.Add(FNode(Element, Box));
	}
}

template <typename ElementType, int32 NodeCapacity>
bool TQuadTree<ElementType, NodeCapacity>::RemoveNodeForElement(const ElementType& Element)
{
	int32 ElementIdx = INDEX_NONE;
	for (int32 NodeIdx = 0, NumNodes = Nodes.Num(); NodeIdx < NumNodes; ++NodeIdx)
	{
		if (Nodes[NodeIdx].Element == Element)
		{
			ElementIdx = NodeIdx;
			break;
		}
	}

	if (ElementIdx != INDEX_NONE)
	{
		Nodes.RemoveAtSwap(ElementIdx, 1, false);
		return true;
	}

	return false;
}

template <typename ElementType, int32 NodeCapacity>
bool TQuadTree<ElementType, NodeCapacity>::Remove(const ElementType& Element, const FBox2D& Box)
{
	bool bElementRemoved = false;

	TreeType* Quads[4];
	const int32 NumQuads = GetQuads(Box, Quads);

	// Remove from nodes referenced by this quad
	bElementRemoved = RemoveNodeForElement(Element);

	// Try to remove from subtrees if necessary
	for (int32 QuadIndex = 0; QuadIndex < NumQuads && !bElementRemoved; QuadIndex++)
	{
		bElementRemoved = Quads[QuadIndex]->Remove(Element, Box);
	}

	return bElementRemoved;
}

template <typename ElementType, int32 NodeCapacity>
template <typename ElementAllocatorType>
void TQuadTree<ElementType, NodeCapacity>::GetElements(const FBox2D& Box, TArray<ElementType, ElementAllocatorType>& ElementsOut) const
{
	TreeType* Quads[4];
	const int32 NumQuads = GetQuads(Box, Quads);

	// Always include any nodes contained in this quad
	GetIntersectingElements(Box, ElementsOut);

	// As well as all relevant subtrees
	for (int32 QuadIndex = 0; QuadIndex < NumQuads; QuadIndex++)
	{
		Quads[QuadIndex]->GetElements(Box, ElementsOut);
	}
}

template <typename ElementType, int32 NodeCapacity>
template <typename ElementAllocatorType>
void TQuadTree<ElementType, NodeCapacity>::GetIntersectingElements(const FBox2D& Box, TArray<ElementType, ElementAllocatorType>& ElementsOut) const
{
	ElementsOut.Reserve(ElementsOut.Num() + Nodes.Num());
	for (const FNode& Node : Nodes)
	{
		if (Box.Intersect(Node.Box))
		{
			//Debug performance will be at least 1 order slower
			checkSlow(!ElementsOut.Contains(Node.Element));
			ElementsOut.Add(Node.Element);
		}
	};
}

template <typename ElementType, int32 NodeCapacity>
int32 TQuadTree<ElementType, NodeCapacity>::GetQuads(const FBox2D& Box, TreeType* Quads[4]) const
{
	int32 QuadCount = 0;
	if (bInternal)
	{
		bool bNegX = Box.Min.X <= Position.X;
		bool bNegY = Box.Min.Y <= Position.Y;

		bool bPosX = Box.Max.X >= Position.X;
		bool bPosY = Box.Max.Y >= Position.Y;

		if (bNegX && bNegY)
		{
			Quads[QuadCount++] = SubTrees[BottomLeft];
		}

		if (bPosX && bNegY)
		{
			Quads[QuadCount++] = SubTrees[BottomRight];
		}

		if (bNegX && bPosY)
		{
			Quads[QuadCount++] = SubTrees[TopLeft];
		}

		if (bPosX && bPosY)
		{
			Quads[QuadCount++] = SubTrees[TopRight];
		}
	}

	return QuadCount;
}

template <typename ElementType, int32 NodeCapacity>
void TQuadTree<ElementType, NodeCapacity>::Duplicate(TreeType& OutDuplicate) const
{
	for (int32 TreeIdx = 0; TreeIdx < 4; ++TreeIdx)
	{
		if (TreeType* SubTree = SubTrees[TreeIdx])
		{
			OutDuplicate.SubTrees[TreeIdx] = new TreeType(FBox2D(0, 0), MinimumQuadSize);
			SubTree->Duplicate(*OutDuplicate.SubTrees[TreeIdx]);	//duplicate sub trees
		}

	}

	OutDuplicate.Nodes = Nodes;
	OutDuplicate.TreeBox = TreeBox;
	OutDuplicate.Position = Position;
	OutDuplicate.MinimumQuadSize = MinimumQuadSize;
	OutDuplicate.bInternal = bInternal;
}

template <typename ElementType, int32 NodeCapacity>
void TQuadTree<ElementType, NodeCapacity>::Empty()
{
	for (int32 TreeIdx = 0; TreeIdx < 4; ++TreeIdx)
	{
		if (TreeType* SubTree = SubTrees[TreeIdx])
		{
			delete SubTree;
			SubTrees[TreeIdx] = nullptr;
		}

	}

	Nodes.Empty();
	bInternal = false;
}

posted @ 2021-11-08 21:10 砥才人阅读(2966) 评论(0) 编辑收藏举报

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