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Filename : channel_numeric_operations.hpp
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//
// Copyright 2005-2007 Adobe Systems Incorporated
//
// Distributed under the Boost Software License, Version 1.0
// See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt
//
#ifndef BOOST_GIL_EXTENSION_NUMERIC_CHANNEL_NUMERIC_OPERATIONS_HPP
#define BOOST_GIL_EXTENSION_NUMERIC_CHANNEL_NUMERIC_OPERATIONS_HPP

#include <boost/gil/channel.hpp>

namespace boost { namespace gil {

// Function objects and utilities for channel-wise numeric operations.
//
// List of currently defined functors:
//    channel_plus_t (+)
//    channel_minus_t (-)
//    channel_multiplies_t (*)
//    channel_divides_t (/),
//    channel_plus_scalar_t (+s)
//    channel_minus_scalar_t (-s),
//    channel_multiplies_scalar_t (*s)
//    channel_divides_scalar_t (/s),
//    channel_halves_t (/=2)
//    channel_zeros_t (=0)
//    channel_assigns_t (=)

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of addition of two channel values.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel1, typename Channel2, typename ChannelResult>
struct channel_plus_t
{
    using ChannelRef1 = typename channel_traits<Channel1>::const_reference;
    using ChannelRef2 = typename channel_traits<Channel2>::const_reference;
    static_assert(std::is_convertible<ChannelRef1, ChannelResult>::value,
        "ChannelRef1 not convertible to ChannelResult");
    static_assert(std::is_convertible<ChannelRef2, ChannelResult>::value,
        "ChannelRef2 not convertible to ChannelResult");

    /// \param ch1 - first of the two addends (augend).
    /// \param ch2 - second of the two addends.
    auto operator()(ChannelRef1 ch1, ChannelRef2 ch2) const -> ChannelResult
    {
        return ChannelResult(ch1) + ChannelResult(ch2);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of subtraction of two channel values.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel1, typename Channel2, typename ChannelResult>
struct channel_minus_t
{
    using ChannelRef1 = typename channel_traits<Channel1>::const_reference;
    using ChannelRef2 = typename channel_traits<Channel2>::const_reference;
    static_assert(std::is_convertible<ChannelRef1, ChannelResult>::value,
        "ChannelRef1 not convertible to ChannelResult");
    static_assert(std::is_convertible<ChannelRef2, ChannelResult>::value,
        "ChannelRef2 not convertible to ChannelResult");

    /// \param ch1 - minuend operand of the subtraction.
    /// \param ch2 - subtrahend operand of the subtraction.
    auto operator()(ChannelRef1 ch1, ChannelRef2 ch2) const -> ChannelResult
    {
        return ChannelResult(ch1) - ChannelResult(ch2);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of multiplication of two channel values.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel1, typename Channel2, typename ChannelResult>
struct channel_multiplies_t
{
    using ChannelRef1 = typename channel_traits<Channel1>::const_reference;
    using ChannelRef2 = typename channel_traits<Channel2>::const_reference;
    static_assert(std::is_convertible<ChannelRef1, ChannelResult>::value,
        "ChannelRef1 not convertible to ChannelResult");
    static_assert(std::is_convertible<ChannelRef2, ChannelResult>::value,
        "ChannelRef2 not convertible to ChannelResult");

    /// \param ch1 - first of the two factors (multiplicand).
    /// \param ch2 - second of the two factors (multiplier).
    auto operator()(ChannelRef1 ch1, ChannelRef2 ch2) const -> ChannelResult
    {
        return ChannelResult(ch1) * ChannelResult(ch2);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of division of two channel values.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel1, typename Channel2, typename ChannelResult>
struct channel_divides_t
{
    using ChannelRef1 = typename channel_traits<Channel1>::const_reference;
    using ChannelRef2 = typename channel_traits<Channel2>::const_reference;
    static_assert(std::is_convertible<ChannelRef1, ChannelResult>::value,
        "ChannelRef1 not convertible to ChannelResult");
    static_assert(std::is_convertible<ChannelRef2, ChannelResult>::value,
        "ChannelRef2 not convertible to ChannelResult");

    /// \param ch1 - dividend operand of the two division operation.
    /// \param ch2 - divisor operand of the two division operation.
    auto operator()(ChannelRef1 ch1, ChannelRef2 ch2) const -> ChannelResult
    {
        return ChannelResult(ch1) / ChannelResult(ch2);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of adding scalar to channel value.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel, typename Scalar, typename ChannelResult>
struct channel_plus_scalar_t
{
    using ChannelRef = typename channel_traits<Channel>::const_reference;
    static_assert(std::is_convertible<ChannelRef, ChannelResult>::value,
        "ChannelRef not convertible to ChannelResult");
    static_assert(std::is_scalar<Scalar>::value, "Scalar not a scalar");
    static_assert(std::is_convertible<Scalar, ChannelResult>::value,
        "Scalar not convertible to ChannelResult");

    auto operator()(ChannelRef channel, Scalar const& scalar) const -> ChannelResult
    {
        return ChannelResult(channel) + ChannelResult(scalar);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of subtracting scalar from channel value.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel, typename Scalar, typename ChannelResult>
struct channel_minus_scalar_t
{
    using ChannelRef = typename channel_traits<Channel>::const_reference;
    static_assert(std::is_convertible<ChannelRef, ChannelResult>::value,
        "ChannelRef not convertible to ChannelResult");
    static_assert(std::is_scalar<Scalar>::value, "Scalar not a scalar");
    static_assert(std::is_convertible<Scalar, ChannelResult>::value,
        "Scalar not convertible to ChannelResult");

    /// \param channel - minuend operand of the subtraction.
    /// \param scalar - subtrahend operand of the subtraction.
    auto operator()(ChannelRef channel, Scalar const& scalar) const -> ChannelResult
    {
        // TODO: Convertion after subtraction vs conversion of operands in channel_minus_t?
        return ChannelResult(channel - scalar);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of channel value by a scalar.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel, typename Scalar, typename ChannelResult>
struct channel_multiplies_scalar_t
{
    using ChannelRef = typename channel_traits<Channel>::const_reference;
    static_assert(std::is_convertible<ChannelRef, ChannelResult>::value,
        "ChannelRef not convertible to ChannelResult");
    static_assert(std::is_scalar<Scalar>::value, "Scalar not a scalar");
    static_assert(std::is_convertible<Scalar, ChannelResult>::value,
        "Scalar not convertible to ChannelResult");

    /// \param channel - first of the two factors (multiplicand).
    /// \param scalar - second of the two factors (multiplier).
    auto operator()(ChannelRef channel, Scalar const& scalar) const -> ChannelResult
    {
        return ChannelResult(channel) * ChannelResult(scalar);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of dividing channel value by scalar.
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel, typename Scalar, typename ChannelResult>
struct channel_divides_scalar_t
{
    using ChannelRef = typename channel_traits<Channel>::const_reference;
    static_assert(std::is_convertible<ChannelRef, ChannelResult>::value,
        "ChannelRef not convertible to ChannelResult");
    static_assert(std::is_scalar<Scalar>::value, "Scalar not a scalar");
    static_assert(std::is_convertible<Scalar, ChannelResult>::value,
        "Scalar not convertible to ChannelResult");

    /// \param channel - dividend operand of the two division operation.
    /// \param scalar - divisor operand of the two division operation.
    auto operator()(ChannelRef channel, Scalar const& scalar) const -> ChannelResult
    {
        return ChannelResult(channel) / ChannelResult(scalar);
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Arithmetic operation of dividing channel value by 2
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel>
struct channel_halves_t
{
    using ChannelRef = typename channel_traits<Channel>::reference;

    auto operator()(ChannelRef channel) const -> ChannelRef
    {
        // TODO: Split into steps: extract with explicit conversion to double, divide and assign?
        //double const v = ch;
        //ch = static_cast<Channel>(v / 2.0);
        channel /= 2.0;
        return channel;
    }
};

/// \ingroup ChannelNumericOperations
/// \brief Operation of setting channel value to zero
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel>
struct channel_zeros_t
{
    using ChannelRef = typename channel_traits<Channel>::reference;

    auto operator()(ChannelRef channel) const -> ChannelRef
    {
        channel = Channel(0);
        return channel;
    }
};

/// \ingroup ChannelNumericOperations
/// structure for assigning one channel to another
/// \note This is a generic implementation; user should specialize it for better performance.
template <typename Channel1, typename Channel2>
struct channel_assigns_t
{
    using ChannelRef1 = typename channel_traits<Channel1>::const_reference;
    using ChannelRef2 = typename channel_traits<Channel2>::reference;
    static_assert(std::is_convertible<ChannelRef1, Channel2>::value,
        "ChannelRef1 not convertible to Channel2");

    /// \param ch1 - assignor side (input) of the assignment operation
    /// \param ch2 - assignee side (output) of the assignment operation
    auto operator()(ChannelRef1 ch1, ChannelRef2 ch2) const -> ChannelRef2
    {
        ch2 = Channel2(ch1);
        return ch2;
    }
};

}}  // namespace boost::gil

#endif