FaceNeighborAACubeTreeStrategy.h

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#ifndef GfxTL__FACENEIGHBORAACUBETREESTRATEGY_HEADER__
#define GfxTL__FACENEIGHBORAACUBETREESTRATEGY_HEADER__
 
namespace GfxTL
{
 
    // requires that InheritedStrategyT supports StrategyBase::CellParent() and CellType::Center()
    template< class InheritedStrategyT >
    struct FaceNeighborAACubeTreeStrategy
    {
        typedef typename InheritedStrategyT::value_type value_type;
 
        class CellData
            : public InheritedStrategyT::CellData
        {};
 
        template< class BaseT >
        class StrategyBase
            : public InheritedStrategyT::template StrategyBase< BaseT >
        {
public:
            typedef typename InheritedStrategyT::template StrategyBase< BaseT > BaseType;
            typedef typename BaseType::CellType CellType;
            enum { Dim = CellType::Dim };
 
            // returns the face neighbor along axis in direction (0 = left, 1 = right)
            // returns in level the level of the neighbor relative to the input cell (upwards)
            // returns NULL if the cell is on the boundary
            // This function does not return all face neighbors in the given direction
            // in the case that the neighbors live on a deeper level than the input cell.
            // In such a case the face neighbor on the same level as the input cell is
            // return. All face neighbors on that side are children of the returned cell.
            const CellType* CellFaceNeighbor(const CellType& cell,
                                             unsigned int axis, unsigned int dir, size_t* level) const
            {
                const CellType* parent = BaseType::CellParent(cell);
                if (!parent)
                {
                    return NULL;    // root cell does not have any face neighbors
                }
                unsigned int childRelation = CellChildRelation(cell, *parent);
                // check if face neighbor is another child of parent
                // this is the case if dir is opposite to the childRelation
                if (((childRelation >> (Dim - 1 - axis)) & 1) ^ (dir & 1)) // cell on opposite side?
                {
                    unsigned int faceNeighborRelation
                        = childRelation ^ (1 << (Dim - 1 - axis)); // flip the respective bit
                    if (BaseType::ExistChild(*parent, faceNeighborRelation))
                    {
                        *level = 0;
                        return &(*parent)[faceNeighborRelation];
                    }
                    *level = 1;
                    return parent; // degenerate case -> cell does not have an actual face neighbor
                }
                // otherwise the face neighbor is a neighbor of the parent
                size_t l;
                const CellType* n = CellFaceNeighbor(*parent, axis, dir, &l);
                if (!n)
                {
                    return NULL;
                }
                if (l > 0) // if the face neighbor of the parent does not live on the same level as the parent
                    // we are unable to find any deeper face neighbor
                {
                    *level = l + 1;
                    return n;
                }
                // otherwise try to find the child of n that is our face neighbor
                // our face neighbor is the child that has the opposite side than us on axis
                unsigned int faceNeighborRelation
                    = childRelation ^ (1 << (Dim - 1 - axis)); // flip the respective bit
                if (BaseType::ExistChild(*n, faceNeighborRelation))
                {
                    *level = 0;
                    return &(*n)[faceNeighborRelation];
                }
                *level = 1;
                return n;
            }
 
            // non-const version
            CellType* CellFaceNeighbor(CellType& cell,
                                       unsigned int axis, unsigned int dir, size_t* level)
            {
                return const_cast< CellType* >(CellFaceNeighbor(cell, axis, dir, level));
            }
 
            unsigned int CellChildRelation(const CellType& cell, const CellType& parent) const
            {
                unsigned int childRelation = 0;
                for (unsigned int i = 0; i < Dim; ++i)
                {
                    if (cell.Center()[i] > parent.Center()[i])
                    {
                        childRelation |= 1 << (Dim - 1 - i);
                    }
                }
                return childRelation;
            }
        };
    };
 
};
 
#endif