Question

我发现了一个现象，CGAL AABB树的构造函数对于std::vector非常慢。

这是一个最小的测试代码：

Point a(1.0, 0.0, 0.0);
Point b(0.0, 1.0, 0.0);
Point c(0.0, 0.0, 1.0);
std::vector<Triangle> triangles;    
for (size_t I=0;I<245000;I++)
{
    triangles.push_back(Triangle(a,b,c));
}
// constructs AABB tree
MyTree tree(triangles.begin(),triangles.end());

245000原始，未构建，运行速度慢得多。我找到了来源：

template<typename Tr>
template<typename ConstPrimitiveIterator, typename ... T>
void AABB_tree<Tr>::insert(ConstPrimitiveIterator first,
                         ConstPrimitiveIterator beyond,
                         T ... t)
{
set_shared_data(t...);      
    while(first != beyond)
    {
        m_primitives.push_back(Primitive(first,t...));
        ++first;            
    }
m_need_build = true;
}

我怀疑vector push_back函数会重新分配内存，但我不确定是什么原因，所以我尝试了这段代码：

template<typename Tr>
template<typename ConstPrimitiveIterator, typename ... T>
void AABB_tree<Tr>::insert(ConstPrimitiveIterator first,
                         ConstPrimitiveIterator beyond,
                         T ... t)
{
set_shared_data(t...);
m_primitives.assign(beyond-first,first);//pre allcate promitives
size_t Index = 0;
    while(first != beyond)
    {           
        m_primitives[Index] = Primitive(first,t...);
        ++first;
        ++Index;
    }
m_need_build = true;
}

问题解决了！我需要更多的建议，我认为这需要更新到CGAL源？

================== 14-9-18更新=============== 我做了一个简单的测试：

#include <iostream>
#include <list>
#include "boost/timer/timer.hpp"
#include <CGAL/Simple_cartesian.h>
#include <CGAL/AABB_tree.h>
#include <CGAL/AABB_traits.h>
#include <CGAL/AABB_triangle_primitive.h>
#include <CGAL/Polyhedron_3.h>
typedef CGAL::Simple_cartesian<double> K;
typedef K::FT FT;
typedef K::Ray_3 Ray;
typedef K::Line_3 Line;
typedef K::Point_3 Point;
typedef K::Triangle_3 Triangle;
typedef std::vector<Triangle>::iterator Iterator;
typedef CGAL::AABB_triangle_primitive<K, Iterator> Primitive;
typedef CGAL::AABB_traits<K, Primitive> AABB_triangle_traits;
typedef CGAL::AABB_tree<AABB_triangle_traits> Tree;
int main()
{
    Point a(1.0, 0.0, 0.0);
    Point b(0.0, 1.0, 0.0);
    Point c(0.0, 0.0, 1.0);
    std::vector<Triangle> triangles;    
    for (size_t I=0;I<245000;I++)
    {
        triangles.push_back(Triangle(a,b,c));
    }
    #define TIMER_SECOND boost::timer::nanosecond_type(1000000000LL)

    auto first = triangles.begin();
    auto beyond = triangles.end();
    boost::timer::cpu_timer CountTimer;
    //Test 1    
    std::vector<Primitive> TestV1;
    CountTimer.start();
    while(first != beyond)
    {
        TestV1.push_back(Primitive(first));
        ++first;            
    }
    std::cout << "Test1 Time:" << CountTimer.elapsed().wall << std::endl;
    //Test 2
    first = triangles.begin();
    beyond = triangles.end();
    std::vector<Primitive> TestV2;
    CountTimer.start();
    TestV2.reserve(std::distance(first,beyond));
    while(first != beyond)
    {
        TestV2.push_back(Primitive(first));
        ++first;            
    }
    std::cout << "Test2 Time:" << CountTimer.elapsed().wall << std::endl;

    system("pause");
    return EXIT_SUCCESS;
}

在发布模式下：

测试1时间：3426459
测试2时间：926136

在调试模式下：

测试1时间：503719044580

测试2时间：224280791

对于std :: vector，AABB Tree Constructor函数非常慢

0 个答案: