average.hpp

 
#ifndef UFO_VISION_COLOR_AVERAGE_HPP
#define UFO_VISION_COLOR_AVERAGE_HPP
 
// UFO
#include <ufo/vision/color/arithmetic.hpp>
#include <ufo/vision/color/concepts.hpp>
#include <ufo/vision/color/convert.hpp>
#include <ufo/vision/color/type_traits.hpp>
#include <ufo/vision/color/weight.hpp>
 
// STL
#include <algorithm>
#include <concepts>
#include <functional>
#include <iterator>
#include <ranges>
 
namespace ufo
{
template <Color C>
[[nodiscard]] constexpr C average(C a, C const& b)
{
    if constexpr (ColorWithWeight<C>) {
        return a + b;
    } else {
        return removeWeight(addWeight(a) + addWeight(b));
    }
}
 
template <std::ranges::input_range R>
  requires Color<std::ranges::range_value_t<R>>
[[nodiscard]] constexpr std::ranges::range_value_t<R> average(R&& r)
{
    using C = std::ranges::range_value_t<R>;
    using D = typename color_traits<C>::template rebind<float, color_traits<C>::flags |
                                                                   ColorFlags::Weight>;
 
    if constexpr (std::same_as<C, D>) {
        return std::ranges::fold_left(r, D{}, std::plus{});
    } else if constexpr (!ColorWithWeight<C> && FloatingPointColor<C>) {
        auto sum = std::ranges::fold_left(
            r | std::views::transform([](C c) { return addWeight(c); }), D{}, std::plus{});
        return removeWeight(sum);
    } else {
        // Normalise to weighted float, sum, then convert back to target type
        auto sum = std::ranges::fold_left(
            r | std::views::transform([](C c) { return convert<D>(c); }), D{}, std::plus{});
        return convert<C>(sum);
    }
}
 
template <std::input_iterator InputIt, std::sentinel_for<InputIt> Sentinel>
  requires Color<std::iter_value_t<InputIt>>
[[nodiscard]] constexpr std::iter_value_t<InputIt> average(InputIt first, Sentinel last)
{
    return average(std::ranges::subrange(std::move(first), std::move(last)));
}
 
template <Color C>
[[nodiscard]] constexpr C average(std::initializer_list<C> il)
{
    return average(std::ranges::subrange(il));
}
 
}  // namespace ufo
 
#endif  // UFO_VISION_COLOR_AVERAGE_HPP