UE4 四叉树 QuadTree

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

TQuadTree

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;
};

Usage

#include "GenericQuadTree.h"//Setup the Quad tree
float UVsQuadTreeMinSize = 0.001f;
TQuadTree<uint32, 100> QuadTree(BaseMeshUVBound,UVsQuadTreeMinSize);
//Insert data
for (FTriangleElement& TriangleElement : Triangles)
{QuadTree.Insert(TriangleElement.TriangleIndex, TriangleElement.UVsBound, DebugContext);
}
//Find a match triangle for every target vertices
TArray<uint32> QuadTreeTriangleResults;
//Reserve 10% to speed up the query
QuadTreeTriangleResults.Reserve(Triangles.Num() / 10); for (uint32 TargetVertexIndex = 0; TargetVertexIndex < (uint32)TargetVertices.Num(); ++TargetVertexIndex)
{//Reset the last data without flushing the memmery allocationQuadTreeTriangleResults.Reset();FVector2D Extent(DistanceThreshold, DistanceThreshold);FBox2D CurBox(TargetUV - Extent, TargetUV + Extent);while (QuadTreeTriangleResults.Num() <= 0){QuadTree.GetElements(CurBox, QuadTreeTriangleResults);Extent *= 2;CurBox = FBox2D(TargetUV - Extent, TargetUV + Extent);}
}

应用

UE4聚合图测试

参考

UE4 LOD Screen Size

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UE4 四叉树 QuadTree

UE4 四叉树 QuadTree

TQuadTree

Usage

应用

参考

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