reduce.hpp

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namespace boost { namespace mpl {
///////////////////////////////////////////////////////
/// \brief Represents the virtual cross-product of the types generated from VecOfVecs.
/// \ingroup CrossVector
/// INPUT: 
///   VecOfVecs - a vector of vector types. For example [ [A1,A2,A3], [B1,B2], [C1,C2,C3,C4] ]
///       Each element must be a non-empty mpl vector
///   TypeGen - a metafunction that generates a type from a vector of types, each of which can be
///       selected from the corresponding vector in VecOfVecs. For example, [A1, B2, C4]
///       
/// Represents the virtual cross-product of the types generated from VecOfVecs.
/// For example, [ TypeGen[A1,B1,C1], TypeGen[A2,B1,C1], TypeGen[A3,B1,C1],
///                TypeGen[A1,B2,C1], TypeGen[A2,B2,C1], TypeGen[A3,B2,C1],
///                TypeGen[A1,B1,C2], TypeGen[A2,B1,C2], TypeGen[A3,B1,C2], ... ]
/// 
/// Models an immutable MPL Random Access Sequence
/// Traversal, random-access, etc, is defined, but mutable operations, 
///  such as push_back and pop_front are not supported
///////////////////////////////////////////////////////

template <typename VecOfVecs, typename TypeGen>
struct cross_vector {};

/// \brief Iterator of cross_vector
/// \ingroup CrossVectorIterator
template <typename VecOfVecs, typename TypeGen, std::size_t K>
struct cross_iterator {
    typedef mpl::random_access_iterator_tag category;
};

///////////////////////////////////////////////////////
/// Implementation of the iterator functions of cross vector
///////////////////////////////////////////////////////

/// \brief Dereferences a cross-vector iterator
/// \ingroup CrossVectorIterator
/// Creates a vector of the sizes of each type vector in VecOfVecs, then uses it as a basis
/// to represent the iterator's position K as a vector of indices. Extracts the corresponding type of 
/// each input vector and passes the element types to the type generation function, which returns the dereferenced type
template <typename VecOfVecs, typename TypeGen, std::size_t K>
struct deref<cross_iterator<VecOfVecs,TypeGen,K> > {
private:
    typedef typename detail::select_subvector_c<VecOfVecs, K>::type DerefTypes;
public:
    typedef typename TypeGen::template apply<DerefTypes>::type type;
};

/// \brief Increments a cross-vector iterator.
/// \ingroup CrossVectorIterator
template <typename VecOfVecs, typename TypeGen, std::size_t K>
struct next<cross_iterator<VecOfVecs,TypeGen,K> > {
    typedef cross_iterator<VecOfVecs,TypeGen,K+1> type;
};

/// \brief Decrements a cross-vector iterator.
/// \ingroup CrossVectorIterator
template <typename VecOfVecs, typename TypeGen, std::size_t K>
struct prior<cross_iterator<VecOfVecs,TypeGen,K> > {
    typedef cross_iterator<VecOfVecs,TypeGen,K-1> type;
};

/// \brief Advances a cross-vector iterator.
/// \ingroup CrossVectorIterator
template <typename VecOfVecs, typename TypeGen, std::size_t K, typename Distance>
struct advance<cross_iterator<VecOfVecs,TypeGen,K>, Distance > {
    typedef cross_iterator<VecOfVecs,TypeGen,K+Distance::value> type;
};

/// \brief Computes the distance between two cross-vector iterator-s.
/// \ingroup CrossVectorIterator
// (shortened the names of the template arguments - otherwise doxygen cannot parse this...)
template <typename VecOfVecs, typename TypeGen, std::size_t K1, std::size_t K2>
struct distance<cross_iterator<VecOfVecs,TypeGen,K1>, cross_iterator<VecOfVecs,TypeGen,K2> > {
    typedef size_t<K2-K1> type;
};

///////////////////////////////////////////////////////
/// Implementation of cross vector
///////////////////////////////////////////////////////
/// \brief Computes the size of a cross vector as the product of the sizes of all vectors in VecOfVecs
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen>
struct size<cross_vector<VecOfVecs,TypeGen> > {
    typedef typename fold<VecOfVecs, size_t<1>, times<_1, size<_2> > >::type type;
    static const std::size_t value=type::value;
};

/// \brief Determines whether a cross vector is empty
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen>
struct empty<cross_vector<VecOfVecs,TypeGen> > {
    typedef typename empty<VecOfVecs>::type type;
};

/// \brief Returns the K-th element of a cross vector
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen, typename K>
struct at<cross_vector<VecOfVecs,TypeGen>, K> {
private:
    typedef cross_iterator<VecOfVecs,TypeGen,K::value> KthIterator;
public:
    typedef typename deref<KthIterator>::type type;
};

/// \brief Returns an iterator to the first element of a cross vector
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen>
struct begin<cross_vector<VecOfVecs,TypeGen> > {
    typedef cross_iterator<VecOfVecs,TypeGen,0> type;
};

/// \brief Returns an iterator to the last element of a cross vector
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen>
struct end<cross_vector<VecOfVecs,TypeGen> > {
private:
    typedef cross_vector<VecOfVecs,TypeGen> this_t;
public:
    typedef cross_iterator<VecOfVecs,TypeGen,size<this_t>::value> type;
};

/// \brief Returns the first element of a cross vector
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen>
struct front<cross_vector<VecOfVecs,TypeGen> > {
private:
    typedef cross_vector<VecOfVecs,TypeGen> this_t;
public:
    typedef typename deref<typename begin<this_t>::type>::type type;
};

/// \brief Returns the last element of a cross vector
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen>
struct back<cross_vector<VecOfVecs,TypeGen> > {
private:
    typedef cross_vector<VecOfVecs,TypeGen> this_t;
    typedef typename size<this_t>::type            size;
    typedef typename minus<size, size_t<1> >::type last_index;
public:
    typedef typename at<this_t, last_index>::type type;
};

/// \brief Transforms the elements of a cross vector
/// \ingroup CrossVector
template <typename VecOfVecs, typename TypeGen, typename OPP>
struct transform<cross_vector<VecOfVecs,TypeGen>, OPP > {
    typedef typename lambda<OPP>::type Op;
    struct adapter {
        template <typename Elements> 
        struct apply {
            typedef typename TypeGen::template apply<Elements>::type orig_t;
            typedef typename Op::template apply<orig_t>::type type;
        };
    };
    typedef cross_vector<VecOfVecs, adapter > type; 
};

} } // boost::mpl

namespace boost { namespace gil {

template <typename Types, typename T> struct type_to_index;
template <typename V> struct view_is_basic;
struct rgb_t;
struct lab_t;
struct hsb_t;
struct cmyk_t;
struct rgba_t;
struct error_t;


namespace detail {
    ////////////////////////////////////////////////////////
    ////
    ////   Generic reduce operation
    ////
    ////////////////////////////////////////////////////////
    template <typename Op, typename T>
    struct reduce {
        typedef T type;
    };

    ////////////////////////////////////////////////////////
    ////
    ////   Unary reduce_view operation. Splits into basic and non-basic views.
    ////   Algorithm-specific reduce should specialize for basic views
    ////
    ////////////////////////////////////////////////////////

    template <typename Op, typename View, bool IsBasic>
    struct reduce_view_basic {
        typedef View type;
    };

    template <typename Op, typename Loc>
    struct reduce<Op, image_view<Loc> > 
        : public reduce_view_basic<Op,image_view<Loc>,view_is_basic<image_view<Loc> >::value> {};
 
    ////////////////////////////////////////////////////////
    ////
    ////   Unary reduce_image operation. Splits into basic and non-basic images.
    ////   Algorithm-specific reduce should specialize for basic images
    ////
    ////////////////////////////////////////////////////////

    template <typename Op, typename Img, bool IsBasic>
    struct reduce_image_basic {
        typedef Img type;
    };

    template <typename Op, typename V, typename Alloc>
    struct reduce<Op, image<V,Alloc> > : public reduce_image_basic<Op,image<V,Alloc>,image_is_basic<image<V,Alloc> >::value > {};

    ////////////////////////////////////////////////////////
    ////
    ////   Binary reduce_view operation. Splits into basic and non-basic views.
    ////   Algorithm-specific reduce should specialize for basic views
    ////
    ////////////////////////////////////////////////////////

    template <typename Op, typename V1, typename V2, bool AreBasic>
    struct reduce_views_basic {
        typedef std::pair<const V1*, const V2*> type;
    };

    template <typename Op, typename L1, typename L2>
    struct reduce<Op, std::pair<const image_view<L1>*, const image_view<L2>*> > 
        : public reduce_views_basic<Op,image_view<L1>,image_view<L2>,
                 mpl::and_<view_is_basic<image_view<L1> >, view_is_basic<image_view<L2> > >::value >
    {};


    ////////////////////////////////////////////////////////
    ////
    ////   Color space unary reduce operation. Reduce a color space to a base with the same number of channels
    ////
    ////////////////////////////////////////////////////////

    template <typename Cs>
    struct reduce_color_space {
        typedef Cs type;
    };

    template <> struct reduce_color_space<lab_t> { typedef rgb_t type; };
    template <> struct reduce_color_space<hsb_t> { typedef rgb_t type; };
    template <> struct reduce_color_space<cmyk_t> { typedef rgba_t type; };

    /*
    ////////////////////////////////////////////////////////
    ////
    ////   Color space binary reduce operation. Given a source and destination color spaces, 
    ////   returns a reduced source and destination color spaces that have the same mapping of channels
    ////
    ////   Precondition: The two color spaces must be compatible (i.e. must have the same set of channels)
    ////////////////////////////////////////////////////////

    template <typename Vec, int Basis, int VecSize> 
    struct type_vec_to_integer_impl {
        typedef typename mpl::back<Vec>::type     last;
        typedef typename mpl::pop_back<Vec>::type rest;
        static const int value = type_vec_to_integer_impl<rest, Basis, VecSize-1>::value * Basis + last::value;