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premultiply.hpp
//
// Copyright 2014 Bill Gallafent
//
// 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_PREMULTIPLY_HPP
#define BOOST_GIL_PREMULTIPLY_HPP
#include <boost/gil/rgba.hpp>
#include <boost/gil/detail/mp11.hpp>
#include <boost/core/ignore_unused.hpp>
#include <type_traits>
namespace boost { namespace gil {
template <typename SrcP, typename DstP>
struct channel_premultiply
{
channel_premultiply(SrcP const & src, DstP & dst)
: src_(src), dst_(dst)
{}
template <typename Channel>
void operator()(Channel /* channel */) const
{
// TODO: Explain why 'channel' input paramater is not used, or used as tag only.
// @todo: need to do a "channel_convert" too, in case the channel types aren't the same?
get_color(dst_, Channel()) = channel_multiply(get_color(src_,Channel()), alpha_or_max(src_));
}
SrcP const & src_;
DstP & dst_;
};
namespace detail
{
template <typename SrcP, typename DstP>
void assign_alpha_if(std::true_type, SrcP const &src, DstP &dst)
{
get_color(dst,alpha_t()) = alpha_or_max(src);
}
template <typename SrcP, typename DstP>
void assign_alpha_if(std::false_type, SrcP const& src, DstP& dst)
{
// nothing to do
boost::ignore_unused(src);
boost::ignore_unused(dst);
}
}
struct premultiply
{
template <typename SrcP, typename DstP>
void operator()(const SrcP& src, DstP& dst) const
{
using src_colour_space_t = typename color_space_type<SrcP>::type;
using dst_colour_space_t = typename color_space_type<DstP>::type;
using src_colour_channels = mp11::mp_remove<src_colour_space_t, alpha_t>;
using has_alpha_t = std::integral_constant<bool, mp11::mp_contains<dst_colour_space_t, alpha_t>::value>;
mp11::mp_for_each<src_colour_channels>(channel_premultiply<SrcP, DstP>(src, dst));
detail::assign_alpha_if(has_alpha_t(), src, dst);
}
};
template <typename SrcConstRefP, // const reference to the source pixel
typename DstP> // Destination pixel value (models PixelValueConcept)
class premultiply_deref_fn
{
public:
using const_t = premultiply_deref_fn<SrcConstRefP, DstP>;
using value_type = DstP;
using reference = value_type; // read-only dereferencing
using const_reference = const value_type &;
using argument_type = SrcConstRefP;
using result_type = reference;
static constexpr bool is_mutable = false;
result_type operator()(argument_type srcP) const
{
result_type dstP;
premultiply()(srcP,dstP);
return dstP;
}
};
template <typename SrcView, typename DstP>
struct premultiplied_view_type
{
private:
using src_pix_ref = typename SrcView::const_t::reference; // const reference to pixel in SrcView
using deref_t = premultiply_deref_fn<src_pix_ref, DstP>; // the dereference adaptor that performs color conversion
using add_ref_t = typename SrcView::template add_deref<deref_t>;
public:
using type = typename add_ref_t::type; // the color converted view type
static type make(SrcView const& sv) { return add_ref_t::make(sv, deref_t()); }
};
template <typename DstP, typename View>
inline auto premultiply_view(View const& src)
-> typename premultiplied_view_type<View,DstP>::type
{
return premultiplied_view_type<View,DstP>::make(src);
}
}} // namespace boost::gil
#endif
boost::gil::channel_multiply
auto channel_multiply(Channel a, Channel b) -> typename channel_traits< Channel >::value_type
A function multiplying two channels. result = a * b / max_value.
Definition: channel_algorithm.hpp:561
boost::gil::get_color
auto get_color(ColorBase &cb, Color=Color()) -> typename color_element_reference_type< ColorBase, Color >::type
Mutable accessor to the element associated with a given color name.
Definition: color_base_algorithm.hpp:190
boost
defined(BOOST_NO_CXX17_HDR_MEMORY_RESOURCE)
Definition: algorithm.hpp:36