split_heuristics.h

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/** @file
 *  @author Bram de Greve (bram@cocamware.com)
 *  @author Tom De Muer (tom@cocamware.com)
 *
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 *  The contents of this file are subject to the Common Public Attribution License 
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 *  the License. You may obtain a copy of the License at 
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 *  Mozilla Public License Version 1.1 but Sections 14 and 15 have been added to cover 
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 *  with Exhibit B.
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 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *  
 *  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"
 
#include <cstddef>
 
namespace lass
{
namespace spat
{
namespace impl
{
    template <typename ObjectTraits> 
    typename ObjectTraits::TValue aabbCenterForAxis(const typename ObjectTraits::TAabb& box, size_t axis)
    {
        return (ObjectTraits::coord(ObjectTraits::aabbMin(box), axis) + ObjectTraits::coord(ObjectTraits::aabbMax(box), axis)) / 2;
    };
 
    template <typename ObjectTraits>
    class LessAxis
    {
    public:
        LessAxis(size_t iAxis): axis_(iAxis) {}
        template <typename Input> bool operator()(const Input& a, const Input& b) const
        {
            return aabbCenterForAxis<ObjectTraits>(a.aabb, axis_) < aabbCenterForAxis<ObjectTraits>(b.aabb, axis_);
        }           
    private:
        size_t axis_;
    };
}
 
 
 
template <typename ObjectTraits>
struct SplitInfo
{
    typedef typename ObjectTraits::TAabb TAabb;
    typedef typename ObjectTraits::TValue TValue;
    typedef size_t TAxis;
 
    constexpr static TAxis dontSplit = size_t(-1);
 
    SplitInfo(const TAabb& aabb, TValue x, TAxis axis):
        aabb(aabb), x(x), axis(axis)
    {
    }
 
    static SplitInfo makeLeaf(const TAabb& aabb)
    {
        return SplitInfo(aabb, 0, dontSplit);
    }
 
    bool isLeaf() const { return axis == dontSplit; }
 
    TAabb aabb;
    TValue x;
    TAxis axis;
 
private:
};
 
 
 
namespace impl
{
    template <typename ObjectTraits>
    class Splitter
    {
    public:
        Splitter(const SplitInfo<ObjectTraits>& split): split_(split) {}
        template <typename Input> bool operator()(const Input& input) const
        {
            return aabbCenterForAxis<ObjectTraits>(input.aabb, split_.axis) <= split_.x;
        }           
    private:
        SplitInfo<ObjectTraits> split_;
    };
}
 
 
 
class DefaultSplitHeuristics
{
public:
    DefaultSplitHeuristics(size_t maxObjectsPerLeaf, size_t maxDepth): 
        maxObjectsPerLeaf_(maxObjectsPerLeaf),
        maxDepth_(maxDepth)
    {
    }
 
    size_t maxObjectsPerLeaf() const { return maxObjectsPerLeaf_; }
    size_t maxDepth() const { return maxDepth_; }
 
protected:
 
    void swap(DefaultSplitHeuristics& other)
    {
        std::swap(maxObjectsPerLeaf_, other.maxObjectsPerLeaf_);
        std::swap(maxDepth_, other.maxDepth_);
    }
 
    template <typename ObjectTraits, typename RandomIterator>
    SplitInfo<ObjectTraits> split(RandomIterator first, RandomIterator last)
    {
        typedef typename ObjectTraits::TAabb TAabb;
        typedef typename ObjectTraits::TPoint TPoint;
        typedef typename ObjectTraits::TValue TValue;
 
        LASS_ASSERT(maxObjectsPerLeaf_ > 0);
 
        TAabb aabb = ObjectTraits::aabbEmpty();
        for (RandomIterator i = first; i != last; ++i)
        {
            aabb = ObjectTraits::aabbJoin(aabb, i->aabb);
        }
 
        const size_t n = static_cast<size_t>(last - first);
        if (n <= maxObjectsPerLeaf_)
        {
            return SplitInfo<ObjectTraits>::makeLeaf(aabb);
        }
        
        const TPoint min = ObjectTraits::aabbMin(aabb);
        const TPoint max = ObjectTraits::aabbMax(aabb);
        size_t axis = 0;
        TValue maxDistance = ObjectTraits::coord(max, 0) - ObjectTraits::coord(min, 0);
        for (size_t 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 = impl::aabbCenterForAxis<ObjectTraits>(aabb, axis);
        return SplitInfo<ObjectTraits>(aabb, x, axis);
    }
 
private:
    size_t maxObjectsPerLeaf_;
    size_t maxDepth_;
};
 
 
 
class SAHSplitHeuristics
{
public:
    SAHSplitHeuristics(size_t maxObjectsPerLeaf, size_t maxDepth): 
        maxObjectsPerLeaf_(maxObjectsPerLeaf),
        maxDepth_(maxDepth)
    {
    }
 
    size_t maxObjectsPerLeaf() const { return maxObjectsPerLeaf_; }
    size_t maxDepth() const { return maxDepth_; }
 
protected:
 
    void swap(SAHSplitHeuristics& other)
    {
        std::swap(maxObjectsPerLeaf_, other.maxObjectsPerLeaf_);
        std::swap(maxDepth_, other.maxDepth_);
    }
 
    template <typename ObjectTraits, typename RandomIterator>
    SplitInfo<ObjectTraits> split(RandomIterator first, RandomIterator last)
    {
        typedef typename ObjectTraits::TAabb TAabb;
        typedef typename ObjectTraits::TValue TValue;
 
        const TValue costNode = 1; // must be non zero!
        const TValue costObject = 1000;
 
        LASS_ASSERT(maxObjectsPerLeaf_ > 0);
 
        const size_t n = static_cast<size_t>(last - first);
        if (n <= maxObjectsPerLeaf_)
        {
            TAabb aabb = ObjectTraits::aabbEmpty();
            for (RandomIterator i = first; i != last; ++i)
            {
                aabb = ObjectTraits::aabbJoin(aabb, i->aabb);
            }           
            return SplitInfo<ObjectTraits>::makeLeaf(aabb);
        }
 
        TValue bestCost = n * costObject;
        size_t bestAxis = SplitInfo<ObjectTraits>::dontSplit;
        TValue bestX = 0;
        std::vector<TValue> leftArea(n);
        TAabb totalBox = ObjectTraits::aabbEmpty();
        TValue totalArea = 0;
 
        for (size_t axis = 0; axis < ObjectTraits::dimension; ++axis)
        {
            std::sort(first, last, impl::LessAxis<ObjectTraits>(axis));
 
            TAabb box = ObjectTraits::aabbEmpty();
            for (size_t k = 0; k < n; ++k)
            {
                RandomIterator i = first + static_cast<std::ptrdiff_t>(k);
                box = ObjectTraits::aabbJoin(box, i->aabb);
                leftArea[k] = ObjectTraits::aabbSurfaceArea(box);
            }
 
            if (axis == 0)
            {
                totalBox = box;
                totalArea = ObjectTraits::aabbSurfaceArea(totalBox);
                if (totalArea == 0)
                {
                    return SplitInfo<ObjectTraits>::makeLeaf(totalBox);
                }
            }
 
            box = ObjectTraits::aabbEmpty();
            for (size_t k = n; k > 0; --k)
            {
                RandomIterator i = first + static_cast<std::ptrdiff_t>(k) - 1;
                const TValue rightArea = ObjectTraits::aabbSurfaceArea(box);
                const TValue cost = 2 * costNode + (leftArea[k - 1] * k + rightArea * (n - k)) * costObject / totalArea;
                if (cost < bestCost)
                {
                    bestCost = cost;
                    bestAxis = axis;
                    bestX = impl::aabbCenterForAxis<ObjectTraits>(i->aabb, axis);
                }
                box = ObjectTraits::aabbJoin(box, i->aabb);
            }
        }
        
        return SplitInfo<ObjectTraits>(totalBox, bestX, bestAxis);
    }
 
private:
 
    size_t maxObjectsPerLeaf_;
    size_t maxDepth_;
};
 
 
 
}
 
}
 
#endif
 
// EOF