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几种空间分割算法研究之bsp
BSP:
二叉分割树，是一种分割场景的方法，下面代码是BSP树一种实现可运行：
运行例子中，将定义的16个空间面，分割为一个深度是3的BSP树，上图显示的是运行结果：
#include "stdafx.h"
#include <map>
#include <vector>
#include <iostream>
using namespace std;
//定义空间的点结构
struct point
{
float x,y,z;
point():x(0.0f),y(0.0f),z(0.0f){};
point(float a,float b,float c):x(a),y(b),z(c){}
void operator += (int n)
{
x += n;
y += n;
z += n;
}
void operator = (point& p)
{
memcpy(this,(void*)&p,sizeof(*this));
}
};
//定义空间的面结构
struct face
{
point P[3];
void operator +=(int n)
{
P[0] += n;
P[1] += n;
P[2] += n;
}
};
//定义包围盒结构
struct BBox
{
point Min;
point Max;
BBox():Min(),Max(){}
};
enum EAxis
{//沿的轴枚举
Axis_X,
Axis_Y,
Axis_Z,
};
//树节点的定义
struct TreeNode
{
TreeNode():box(),nDepth(0),pLChild(NULL),pRChild(NULL),Axis(Axis_X),Split(0.0f){vFaceId.reserve(16);}
int nDepth;
TreeNode* pLChild;
TreeNode* pRChild;
std::vector<int> vFaceId;
int Axis;
BBox box;
float Split;
};
//存储空间的面
std::map<int,face> m_mFace;
//通过面ID获取面的地址
face* GetFaceByID(int nID)
{
std::map<int,face>::iterator itr = m_mFace.find(nID);
if (itr != m_mFace.end() )
{
return &(m_mFace[nID]);
}
return NULL;
}
//BSP类的定义实现
class BspTree
{
public:
BspTree():m_pRoot(NULL){};
~BspTree()
{
if (m_pRoot)
{
DeleteNode(m_pRoot);
}
}
//初始化树根
void InitTreeRoot(TreeNode *pNode);
//释放整个树的资源
void DeleteNode(TreeNode * pNode);
//生成AABB包围盒
void BuildAABB(TreeNode * pNode);
//切分整个空间
void SplitSpace(TreeNode* pRoot,int nAxis,int ndepth);
//切分面
void SplitFace( int nFaceId, float fSplit, int nAxis, int* pLeftNum, int* pRightNum, int* pBothNum );
//遍历整个树
void ErgodicTree(TreeNode * pNode);
protected:
private:
TreeNode *m_pRoot;
};
void BspTree::InitTreeRoot(TreeNode *pNode)
{
if (pNode == NULL)
return;
m_pRoot = pNode;
}
void BspTree::DeleteNode(TreeNode * pNode)
{
if (pNode == NULL)
return;
DeleteNode(pNode->pLChild);
DeleteNode(pNode->pRChild);
delete pNode;
}
//遍历整个树
void BspTree::ErgodicTree(TreeNode * pNode)
{
if (pNode == NULL)
return;
ErgodicTree(pNode->pLChild);
cout<<"节点深度: "<<pNode->nDepth<<"含有多少个面: "<<pNode->vFaceId.size();
switch (pNode->Axis)
{
case Axis_X:
{
cout<<" 沿X轴分割"<<"分割点是: x ="<<pNode->Split<<endl;
break;
}
case Axis_Y:
{
cout<<" 沿Y轴分割"<<"分割点是: y ="<<pNode->Split<<endl;
break;
}
case Axis_Z:
{
cout<<" 沿Z轴分割"<<"分割点是: z ="<<pNode->Split<<endl;
break;
}
}
ErgodicTree(pNode->pRChild);
}
void BspTree::BuildAABB(TreeNode * pNode)
{
if(!pNode)
return;
point Min(1000000,1000000,1000000);
point Max(-1000000,-1000000,-1000000);
for(int n = 0; n < pNode->vFaceId.size(); ++n)
{
face *pFa = GetFaceByID(n);
if (pFa == NULL)
continue;
for(int m = 0; m < 3; ++m)
{
if (pFa->P[m].x > Max.x)
Max.x = pFa->P[m].x;
if (pFa->P[m].y > Max.y)
Max.y = pFa->P[m].y;
if (pFa->P[m].z > Max.z)
Max.z = pFa->P[m].z;
if (pFa->P[m].x < Min.x)
Min.x = pFa->P[m].x;
if (pFa->P[m].y < Min.y)
Min.y = pFa->P[m].y;
if (pFa->P[m].z < Min.z)
Min.z = pFa->P[m].z;
}
}
pNode->box.Max = Max;
pNode->box.Min = Min;
}
int CompareFloat(float a,float b,float fOff)
{
if (abs(a - b) < fOff)
return 0;
if ( a > b)
return 1;
else
return -1;
}
void BspTree::SplitFace( int nFaceId, float fSplit, int nAxis, int* pLeftNum, int* pRightNum, int* pBothNum )
{
face* pFace = GetFaceByID(nFaceId);
int nLeftCount = 0;
int nRightCount = 0;
int nBothCount = 0;
float t[3];
switch( nAxis )
{
case Axis_X:
t[0] = pFace->P[0].x;
t[1] = pFace->P[1].x;
t[2] = pFace->P[2].x;
break;
case Axis_Y:
t[0] = pFace->P[0].y;
t[1] = pFace->P[1].y;
t[2] = pFace->P[2].y;
break;
case Axis_Z:
t[0] = pFace->P[0].z;
t[1] = pFace->P[1].z;
t[2] = pFace->P[2].z;
break;
}
for( int i = 0; i < 3; i++ )
{
int c = CompareFloat( t[i], fSplit ,0.001f);
if( c < 0 ) // 左边
nLeftCount++;
else if( c > 0 ) // 右边
nRightCount++;
else // 正中间
nBothCount++;
}
*pLeftNum = nLeftCount;
*pRightNum = nRightCount;
*pBothNum = nBothCount;
}
void BspTree::SplitSpace(TreeNode* pRoot,int nAxis,int ndepth)
{
if(!pRoot)
return;
pRoot->nDepth = ndepth;
pRoot->Axis = nAxis;
if (pRoot->vFaceId.size() < 3 || ndepth > 2)
{
pRoot->pLChild = NULL;
pRoot->pRChild = NULL;
return;
}
pRoot->pLChild = new TreeNode;
pRoot->pRChild = new TreeNode;
pRoot->pLChild->box.Max = pRoot->box.Max;
pRoot->pLChild->box.Min = pRoot->box.Min;
pRoot->pRChild->box.Max = pRoot->box.Max;
pRoot->pRChild->box.Min = pRoot->box.Min;
nAxis = (int)Axis_X;
float XLength = pRoot->box.Max.x - pRoot->box.Min.x;
float YLength = pRoot->box.Max.y - pRoot->box.Min.y;
float ZLength = pRoot->box.Max.z - pRoot->box.Min.z;
if (YLength > XLength)
{
nAxis = Axis_Y;
XLength = YLength;
}
if (ZLength > XLength)
{
nAxis = Axis_Z;
}
float fslit = 0.0f;
switch (nAxis)
{
case Axis_X:
{
fslit = (pRoot->box.Max.x + pRoot->box.Min.x)/2.0;
pRoot->pLChild->box.Max.x = fslit;
pRoot->pRChild->box.Min.x = fslit;
}break;
case Axis_Y:
{
fslit = (pRoot->box.Max.y + pRoot->box.Min.y)/2.0;
pRoot->pLChild->box.Max.y = fslit;
pRoot->pRChild->box.Min.y = fslit;
}break;
case Axis_Z:
{
fslit = (pRoot->box.Max.z + pRoot->box.Min.z)/2.0;
pRoot->pLChild->box.Max.z = fslit;
pRoot->pRChild->box.Min.z = fslit;
}break;
}
pRoot->Split = fslit;
int nSize = pRoot->vFaceId.size();
int nLeftCount,nRightCount,nBothCount;
for (int n = 0; n < nSize; ++n)
{
SplitFace(pRoot->vFaceId.at(n),fslit,nAxis,&nLeftCount,&nRightCount,&nBothCount);
// 如果左边有
if( nLeftCount > 0 || nBothCount > 0 )
pRoot->pLChild->vFaceId.push_back( pRoot->vFaceId.at(n) );
if( nRightCount > 0 || nBothCount > 0 )
pRoot->pRChild->vFaceId.push_back( pRoot->vFaceId.at(n) );
}
pRoot->vFaceId.clear();
// 递归
SplitSpace( pRoot->pLChild, nAxis , ndepth+1);
SplitSpace( pRoot->pRChild, nAxis , ndepth+1);
}
int _tmain(int argc, _TCHAR* argv[])
{
BspTree bspTree;
TreeNode *pRoot = new TreeNode;
face fa;
fa.P[0].x = -10;fa.P[0].y = -10;fa.P[0].z = -10;
fa.P[1].x = 2;fa.P[1].y = 2;fa.P[1].z = 2;
fa.P[2].x = 5;fa.P[2].y = 5;fa.P[2].z = 5;
for (int n = 0; n < 16; ++n)
{
if (n % 5 == 0)
fa += 2*(-n);
else
fa += 2*n;
m_mFace[n] = fa;
pRoot->vFaceId.push_back(n);
}
bspTree.InitTreeRoot(pRoot);
bspTree.BuildAABB(pRoot);
bspTree.SplitSpace(pRoot,0,0);
bspTree.ErgodicTree(pRoot);
getchar();
return 0;}