pixel_density.hpp

// Copyright Take Vos 2024.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "pixels_per_inch.hpp"
#include "dips.hpp"
#include "pixels.hpp"
#include "font_size.hpp"
#include "../utility/utility.hpp"
#include "../macros.hpp"
 
namespace hi { inline namespace v1 {
 
struct pixel_density {
    pixels_per_inch_f ppi;
    device_type type;
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<Pixels, std::common_type_t<float, T>>
    operator*(pixel_density const& lhs, au::Quantity<Dips, T> const& rhs) noexcept
    {
        return pixels(lhs.density_scale() * rhs.in(dips));
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<Pixels, std::common_type_t<float, T>>
    operator*(au::Quantity<Dips, T> const& lhs, pixel_density const& rhs) noexcept
    {
        return rhs * lhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<Pixels, std::common_type_t<float, T>>
    operator*(pixel_density const& lhs, au::Quantity<au::Inches, T> const& rhs) noexcept
    {
        return lhs.ppi * rhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<Pixels, std::common_type_t<float, T>>
    operator*(au::Quantity<au::Inches, T> const& lhs, pixel_density const& rhs) noexcept
    {
        return rhs * lhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<Pixels, std::common_type_t<float, T>>
    operator*(pixel_density const& lhs, au::Quantity<Pixels, T> const& rhs) noexcept
    {
        return rhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<Pixels, std::common_type_t<float, T>>
    operator*(au::Quantity<Pixels, T> const& lhs, pixel_density const& rhs) noexcept
    {
        return lhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(pixel_density const& lhs, au::Quantity<DipsPerEm, T> const& rhs) noexcept
    {
        return pixels_per_em(lhs.density_scale() * rhs.in(dips_per_em));
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(au::Quantity<DipsPerEm, T> const& lhs, pixel_density const& rhs) noexcept
    {
        return rhs * lhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(pixel_density const& lhs, au::Quantity<PointsPerEm, T> const& rhs) noexcept
    {
        return lhs.ppi * rhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(au::Quantity<PointsPerEm, T> const& lhs, pixel_density const& rhs) noexcept
    {
        return rhs * lhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(pixel_density const& lhs, au::Quantity<PixelsPerEm, T> const& rhs) noexcept
    {
        return rhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(au::Quantity<PixelsPerEm, T> const& lhs, pixel_density const& rhs) noexcept
    {
        return lhs;
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(pixel_density const& lhs, font_size_quantity<T> const& rhs) noexcept
    {
        if (auto const* dips_per_em_ptr = std::get_if<au::Quantity<DipsPerEm, T>>(&rhs)) {
            return *dips_per_em_ptr * lhs;
        } else if (auto const* pixels_per_em_ptr = std::get_if<au::Quantity<PixelsPerEm, T>>(&rhs)) {
            return *pixels_per_em_ptr * lhs;
        } else if (auto const* points_per_em_ptr = std::get_if<au::Quantity<PointsPerEm, T>>(&rhs)) {
            return *points_per_em_ptr * lhs;
        } else {
            hi_no_default();
        }
    }
 
    template<typename T>
    [[nodiscard]] constexpr friend au::Quantity<PixelsPerEm, std::common_type_t<float, T>>
    operator*(font_size_quantity<T> const& lhs, pixel_density const& rhs) noexcept
    {
        return rhs * lhs;
    }
 
private:
    [[nodiscard]] constexpr float density_scale() const noexcept
    {
        constexpr auto scale_table = std::array{
            0.5f,
            0.5f,
            0.5f,
 
            0.75f, // 120 dpi
 
            1.0f, // 160 dpi
            1.0f,
 
            1.5f, // 240 dpi
            1.5f,
 
            2.0f, // 320 dpi
            2.0f,
            2.0f,
            2.0f,
 
            3.0f, // 480 dpi
            3.0f,
            3.0f,
            3.0f,
            4.0f, // 640 dpi
        };
 
        // The base density is based on the device type which determines
        // the viewing distance. We strip off the last three bits as there
        // are multiple devices that need unique values but have the same
        // base density.
        auto const base_density = std::to_underlying(type) & 0xf8;
 
        // casting to unsigned int is faster than size_t.
        auto const index = static_cast<unsigned int>(ppi.in(pixels_per_inch)) * 4 / base_density;
 
        // Using a table here is faster than the compiler will generate with
        // a switch statement. The bound check here will result in a conditional
        // move instead of a conditional jump.
        if (index < scale_table.size()) {
            return scale_table[index];
        } else {
            return scale_table.back();
        }
    }
};
 
}} // namespace hi::v1