split_heuristics.h

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/** @file
 *  @author Bram de Greve (bramz@users.sourceforge.net)
 *  @author Tom De Muer (tomdemuer@users.sourceforge.net)
 *
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 *  The Original Code is LASS - Library of Assembled Shared Sources.
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 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
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#ifndef LASS_GUARDIAN_OF_INCLUSION_SPAT_SPLIT_HEURISTICS_H
#define LASS_GUARDIAN_OF_INCLUSION_SPAT_SPLIT_HEURISTICS_H

#include "spat_common.h"

namespace lass
{
namespace spat
{

template <typename ObjectTraits>
struct SplitInfo
{
    typedef typename ObjectTraits::TAabb TAabb;
    typedef typename ObjectTraits::TValue TValue;
    typedef int TAxis;

    SplitInfo(const TAabb& aabb, TValue x, TAxis axis):
        aabb(aabb), x(x), axis(axis)
    {
    }

    TAabb aabb;
    TValue x;
    TAxis axis;
};

template <int numObjectsPerLeaf = 1>
struct DefaultSplitHeuristics
{
    LASS_META_ASSERT(numObjectsPerLeaf > 0, numObjectsPerLeaf_must_be_strict_positive);
    
    template <typename ObjectTraits, typename RandomIterator>
    static SplitInfo<ObjectTraits> split(RandomIterator first, RandomIterator last)
    {
        typedef typename ObjectTraits::TAabb TAabb;
        typedef typename ObjectTraits::TPoint TPoint;
        typedef typename ObjectTraits::TValue TValue;

        LASS_ASSERT(numObjectsPerLeaf > 0);

        TAabb aabb = ObjectTraits::aabbEmpty();
        for (RandomIterator i = first; i != last; ++i)
        {
            aabb = ObjectTraits::aabbJoin(aabb, i->aabb);
        }

        const int n = static_cast<int>(last - first);
        if (n <= numObjectsPerLeaf)
        {
            return SplitInfo<ObjectTraits>(aabb, 0, -1);
        }
        
        const TPoint min = ObjectTraits::aabbMin(aabb);
        const TPoint max = ObjectTraits::aabbMax(aabb);
        int axis = 0;
        TValue maxDistance = ObjectTraits::coord(max, 0) - ObjectTraits::coord(min, 0);
        for (int k = 1; k < ObjectTraits::dimension; ++k)
        {
            const TValue distance = ObjectTraits::coord(max, k) - ObjectTraits::coord(min, k);
            if (distance > maxDistance)
            {
                axis = k;
                maxDistance = distance;
            }
        }

        const TValue x = (ObjectTraits::coord(min, axis) + ObjectTraits::coord(max, axis)) / 2;
        return SplitInfo<ObjectTraits>(aabb, x, axis);
    }
};

namespace impl
{

template <typename ObjectTraits>
class Splitter
{
public:
    Splitter(const SplitInfo<ObjectTraits>& split): split_(split) {}
    template <typename Input> bool operator()(const Input& input) const
    {
        typedef ObjectTraits OT;
        const typename OT::TValue x = 
            (OT::coord(OT::aabbMin(input.aabb), split_.axis) + OT::coord(OT::aabbMax(input.aabb), split_.axis)) / 2;
        return x < split_.x;
    }           
private:
    SplitInfo<ObjectTraits> split_;
};

template <typename ObjectTraits>
class LessAxis
{
public:
    LessAxis(int iAxis): axis_(iAxis) {}
    template <typename Input> bool operator()(const Input& a, const Input& b) const
    {
        typedef ObjectTraits OT;
        const typename OT::TValue xa = 
            (OT::coord(OT::aabbMin(a.aabb), axis_) + OT::coord(OT::aabbMax(a.aabb), axis_)) / 2;
        const typename OT::TValue xb = 
            (OT::coord(OT::aabbMin(b.aabb), axis_) + OT::coord(OT::aabbMax(b.aabb), axis_)) / 2;
        return xa < xb;
    }           
private:
    int axis_;
};

}

}

}

#endif

// EOF