//
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// Copyright 2014 Bill Gallafent
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//
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// Distributed under the Boost Software License, Version 1.0
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// See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt
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//
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#ifndef BOOST_GIL_PREMULTIPLY_HPP
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#define BOOST_GIL_PREMULTIPLY_HPP
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#include <boost/gil/rgba.hpp>
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#include <boost/gil/detail/mp11.hpp>
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#include <boost/core/ignore_unused.hpp>
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#include <type_traits>
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namespace boost { namespace gil {
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template <typename SrcP, typename DstP>
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struct channel_premultiply
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{
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channel_premultiply(SrcP const & src, DstP & dst)
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: src_(src), dst_(dst)
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{}
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template <typename Channel>
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void operator()(Channel /* channel */) const
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{
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// TODO: Explain why 'channel' input paramater is not used, or used as tag only.
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// @todo: need to do a "channel_convert" too, in case the channel types aren't the same?
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get_color(dst_, Channel()) = channel_multiply(get_color(src_,Channel()), alpha_or_max(src_));
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}
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SrcP const & src_;
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DstP & dst_;
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};
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namespace detail
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{
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template <typename SrcP, typename DstP>
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void assign_alpha_if(std::true_type, SrcP const &src, DstP &dst)
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{
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get_color(dst,alpha_t()) = alpha_or_max(src);
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}
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template <typename SrcP, typename DstP>
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void assign_alpha_if(std::false_type, SrcP const& src, DstP& dst)
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{
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// nothing to do
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boost::ignore_unused(src);
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boost::ignore_unused(dst);
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}
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}
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struct premultiply
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{
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template <typename SrcP, typename DstP>
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void operator()(const SrcP& src, DstP& dst) const
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{
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using src_colour_space_t = typename color_space_type<SrcP>::type;
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using dst_colour_space_t = typename color_space_type<DstP>::type;
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using src_colour_channels = mp11::mp_remove<src_colour_space_t, alpha_t>;
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using has_alpha_t = std::integral_constant<bool, mp11::mp_contains<dst_colour_space_t, alpha_t>::value>;
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mp11::mp_for_each<src_colour_channels>(channel_premultiply<SrcP, DstP>(src, dst));
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detail::assign_alpha_if(has_alpha_t(), src, dst);
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}
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};
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template <typename SrcConstRefP, // const reference to the source pixel
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typename DstP> // Destination pixel value (models PixelValueConcept)
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class premultiply_deref_fn
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{
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public:
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using const_t = premultiply_deref_fn<SrcConstRefP, DstP>;
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using value_type = DstP;
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using reference = value_type; // read-only dereferencing
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using const_reference = const value_type &;
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using argument_type = SrcConstRefP;
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using result_type = reference;
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static constexpr bool is_mutable = false;
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result_type operator()(argument_type srcP) const
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{
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result_type dstP;
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premultiply()(srcP,dstP);
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return dstP;
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}
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};
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template <typename SrcView, typename DstP>
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struct premultiplied_view_type
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{
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private:
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using src_pix_ref = typename SrcView::const_t::reference; // const reference to pixel in SrcView
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using deref_t = premultiply_deref_fn<src_pix_ref, DstP>; // the dereference adaptor that performs color conversion
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using add_ref_t = typename SrcView::template add_deref<deref_t>;
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public:
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using type = typename add_ref_t::type; // the color converted view type
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static type make(const SrcView& sv) { return add_ref_t::make(sv, deref_t()); }
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};
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template <typename DstP, typename View> inline
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typename premultiplied_view_type<View,DstP>::type premultiply_view(const View& src)
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{
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return premultiplied_view_type<View,DstP>::make(src);
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}
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}} // namespace boost::gil
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#endif
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