新增功能：终端颜色表示

src/tui/screen/color.cppm

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+/**
+ * @file        tui/screen/color.cppm
+ * @brief       适用于终端的颜色表示
+ * @author      KeqingMoe
+ * @date        2024-12-9
+ * @copyright   Copyright (c) 2024 KeqingMoe
+ * @license     MIT License
+ */
+
+export module kqm.tui.screen:color;
+import kqm.tui.plat;
+
+import std;
+
+template <std::floating_point Float, typename T>
+    requires requires(Float f, T x) { std::pow(x, f); }
+constexpr auto gamma_correct_interp(Float gamma, Float t, T a, T b) noexcept -> T
+{
+    auto af = std::pow(a, gamma);
+    auto bf = std::pow(b, gamma);
+    auto f  = std::lerp(af, bf, t);
+    return static_cast<T>(std::pow(f, 1 / gamma));
+}
+
+template <char ch>
+concept DecDigit = ch >= '0' && ch <= '9';
+
+template <char ch>
+concept FromAToF = (ch >= 'A' && ch <= 'F') || (ch >= 'a' && ch <= 'f');
+
+template <char ch>
+concept HexDigit = DecDigit<ch> || FromAToF<ch>;
+
+template <char ch1, char ch2, char... chs>
+constexpr auto HexLiteral = requires {
+    requires(ch1 == '0');
+    requires(ch2 == 'x' || ch2 == 'X');
+    requires(sizeof...(chs) > 0);
+    requires(HexDigit<chs> && ...);
+};
+
+export namespace kqm::tui
+{
+
+inline namespace screen
+{
+
+/**
+ * @brief 表示忽略平台相关的颜色处理的标签
+ */
+struct ignore_plat_t
+{
+    explicit constexpr ignore_plat_t() noexcept = default;
+} ignore_plat;
+
+struct color
+{
+public:
+    /**
+     * @brief 默认构造函数，产生透明的颜色（或表示终端默认颜色）
+     */
+    constexpr color() noexcept : color{palette1::transparent} {}
+
+    /**
+     * @brief 同默认构造函数
+     */
+    constexpr color(palette1 index) noexcept : colors{index} {}
+
+    /**
+     * @brief 从 16 种预设颜色构造
+     */
+    constexpr color(palette16 index) noexcept : colors{index} {}
+
+    /**
+     * @brief 从 256 种预设颜色构造
+     */
+    constexpr color(palette256 index) noexcept
+    {
+        if (plat::color_depth >= 8uz) colors = index;
+        else colors = get_nearest_palette16(index);
+    }
+
+    /**
+     * @brief 从 256 种预设颜色构造，强制使用原本的颜色（不转换到最近的受支持颜色）
+     */
+    constexpr color(ignore_plat_t, palette256 index) noexcept : colors{index} {}
+
+    /**
+     * @brief 从 RGB 真彩色构造
+     */
+    constexpr color(rgb_t rgb) noexcept : color{rgb.red, rgb.green, rgb.blue} {}
+
+    /**
+     * @brief 从 RGB 真彩色构造，强制使用原本的颜色（不转换到最近的受支持颜色）
+     */
+    constexpr color(ignore_plat_t, rgb_t rgb) noexcept : colors{rgb} {}
+
+    /**
+     * @brief 从 RGBA 构造
+     */
+    constexpr color(u8 red, u8 green, u8 blue, u8 alpha = 255) noexcept : alpha{alpha}
+    {
+        if (auto rgb = rgb_t{red, green, blue}; plat::color_depth >= 24uz) colors = rgb;
+        else if (auto p256 = get_nearest_palette256(rgb); plat::color_depth >= 8uz) colors = p256;
+        else colors = get_nearest_palette16(p256);
+    }
+
+    /**
+     * @brief 从 RGBA 真彩色构造，强制使用原本的颜色（不转换到最近的受支持颜色）
+     */
+    constexpr color(ignore_plat_t, u8 red, u8 green, u8 blue, u8 alpha = 255) noexcept
+        : colors{rgb_t{red,green,blue}}, alpha{alpha}
+    {
+    }
+
+    /**
+     * @brief 打印颜色的 ANSI 控制序列到输出迭代器
+     * 
+     * @tparam Out 
+     * @param out 
+     * @param is_bg 
+     * @return Out 
+     */
+    template <std::output_iterator<char> Out>
+    auto print_to(Out out, bool is_bg) -> Out
+    {
+        struct visitor
+        {
+            Out out;
+            bool is_bg;
+            char bg_ch;
+            constexpr auto operator()(palette1) -> Out
+            {
+                return std::format_to(out, "\e[{}9m", bg_ch);
+            }
+            constexpr auto operator()(palette16 x) -> Out
+            {
+                auto idx  = std::to_underlying(x);
+                auto code = is_bg ? palette16_bg_code[idx] : palette16_fg_code[idx];
+                return std::format_to(out, "\e[{}m", code);
+            }
+            constexpr auto operator()(palette256 x) -> Out
+            {
+                return std::format_to(out, "\e[{}8;5;{}m", bg_ch, std::to_underlying(x));
+            }
+            constexpr auto operator()(rgb_t rgb) -> Out
+            {
+                return std::format_to(out, "\e[{}8;2;{};{};{}m", bg_ch, rgb.red, rgb.green, rgb.blue);
+            }
+        } vis{out, is_bg, is_bg ? '4' : '3'};
+        return std::visit(vis, colors);
+    }
+
+    /**
+     * @brief 获得颜色对应的 ANSI 控制序列
+     * 
+     * @param is_bg 
+     * @return std::string 
+     */
+    auto print(bool is_bg) -> std::string
+    {
+        auto ret = std::string{};
+        print_to(std::back_inserter(ret), is_bg);
+        return ret;
+    }
+
+    /**
+     * @brief 打印前景色的 ANSI 控制序列到输出迭代器
+     * 
+     * @tparam Out 
+     * @param out 
+     * @return Out 
+     */
+    template <std::output_iterator<char> Out>
+    auto fg_to(Out out) -> Out
+    {
+        return print_to(out, false);
+    }
+
+    /**
+     * @brief 获得前景色的 ANSI 控制序列
+     * 
+     * @return std::string 
+     */
+    auto fg() -> std::string
+    {
+        auto ret = std::string{};
+        fg_to(std::back_inserter(ret));
+        return ret;
+    }
+
+    /**
+     * @brief 打印背景色的 ANSI 控制序列到输出迭代器
+     * 
+     * @tparam Out 
+     * @param out 
+     * @return Out 
+     */
+    template <std::output_iterator<char> Out>
+    auto bg_to(Out out) -> Out
+    {
+        return print_to(out, true);
+    }
+
+    /**
+     * @brief 获得背景色的 ANSI 控制序列
+     * 
+     * @return std::string 
+     */
+    auto bg() -> std::string
+    {
+        auto ret = std::string{};
+        bg_to(std::back_inserter(ret));
+        return ret;
+    }
+
+    /**
+     * @brief 颜色正规化
+     * 
+     * @return rgb_t 
+     */
+    constexpr auto normalize() const noexcept -> rgb_t
+    {
+        constexpr auto vis = [](auto&& x) static {
+            return colors::normalize(x);
+        };
+        return std::visit(vis, colors);
+    }
+
+    /**
+     * @brief 判断颜色是否为完全不透明
+     * 
+     * @return true 
+     * @return false 
+     */
+    constexpr auto is_opaque() const noexcept -> bool
+    {
+        return alpha == 255;
+    };
+
+    /**
+     * @brief 从 RGBA 构造颜色
+     * 
+     * @param red 
+     * @param green 
+     * @param blue 
+     * @param alpha 
+     * @return color 
+     */
+    static constexpr auto rgba(u8 red, u8 green, u8 blue, u8 alpha) noexcept -> color
+    {
+        return color{red, green, blue, alpha};
+    }
+
+    /**
+     * @brief 从 RGB 构造颜色
+     * 
+     * @param red 
+     * @param green 
+     * @param blue 
+     * @return color 
+     */
+    static constexpr auto rgb(u8 red, u8 green, u8 blue) noexcept -> color
+    {
+        return color{red, green, blue};
+    }
+
+    /**
+     * @brief 从 HSVA 构造颜色
+     * 
+     * @param h 
+     * @param s 
+     * @param v 
+     * @param alpha 
+     * @return color 
+     */
+    static constexpr auto hsva(u8 h, u8 s, u8 v, u8 alpha) noexcept -> color
+    {
+        auto region    = h / 43;
+        auto remainder = h % 43 * 6;
+        auto p0        = v * (255 - s) >> 8;
+        auto q0        = v * (255 - (s * remainder >> 8)) >> 8;
+        auto t0        = v * (255 - (s * (255 - remainder) >> 8)) >> 8;
+        auto [p, q, t] = std::tuple<u8, u8, u8>{p0, q0, t0};
+        switch (region) {
+        case 0:
+            return color{v, t, p, alpha};
+        case 1:
+            return color{q, v, p, alpha};
+        case 2:
+            return color{p, v, t, alpha};
+        case 3:
+            return color{p, q, v, alpha};
+        case 4:
+            return color{t, p, v, alpha};
+        case 5:
+            return color{v, p, q, alpha};
+        default:
+            std::unreachable();
+        }
+    }
+
+    /**
+     * @brief 从 HSV 构造颜色
+     * 
+     * @param h 
+     * @param s 
+     * @param v 
+     * @return color 
+     */
+    static constexpr auto hsv(u8 h, u8 s, u8 v) noexcept -> color
+    {
+        return hsva(h, s, v, 255);
+    }
+
+    /**
+     * @brief 插值两种颜色
+     * 
+     * @tparam Float 
+     * @param a 
+     * @param b 
+     * @param t 
+     * @return color 
+     */
+    template <std::floating_point Float>
+    static constexpr auto interpolate(color a, color b, Float t) noexcept -> color
+    {
+        constexpr auto vis = [](auto&& x) static {
+            return colors::normalize(x);
+        };
+
+        auto [r1, g1, b1] = std::visit(vis, a.colors);
+        auto [r2, g2, b2] = std::visit(vis, a.colors);
+
+        constexpr auto gamma = Float{2.2};
+        return rgb(gamma_correct_interp(gamma, t, r1, r2),
+                   gamma_correct_interp(gamma, t, g1, g2),
+                   gamma_correct_interp(gamma, t, b1, b2));
+    }
+
+    /**
+     * @brief 混合两种颜色
+     * 
+     * @param a 
+     * @param b 
+     * @return color 
+     */
+    static constexpr auto blend(color a, color b) noexcept -> color
+    {
+        auto ret  = interpolate(a, b, b.alpha / 256.0);
+        ret.alpha = a.alpha + b.alpha - a.alpha * b.alpha / 256;
+        return ret;
+    }
+
+    /**
+     * @brief 判断两种颜色是否相等
+     * 
+     * @param lhs 
+     * @param rhs 
+     * @return true 
+     * @return false 
+     */
+    friend auto operator==(color lhs, color rhs) noexcept -> bool
+    {
+        constexpr auto vis = [](auto&& x) static {
+            return colors::normalize(x);
+        };
+        auto lhs_rgb = std::visit(vis, lhs.colors);
+        auto rhs_rgb = std::visit(vis, rhs.colors);
+        return lhs_rgb == rhs_rgb;
+    }
+
+    std::variant<palette1, palette16, palette256, rgb_t> colors;
+    u8 alpha{255};
+};
+
+inline namespace literals
+{
+
+/**
+ * @brief RGB 颜色字面量
+ */
+template <char... chs>
+    requires requires {
+        requires HexLiteral<chs...>;
+        requires(sizeof...(chs) == 5uz || sizeof...(chs) == 8uz);
+    }
+constexpr auto operator""_rgb() noexcept -> color
+{
+    auto s = std::array{chs...};
+
+    auto rgb = std::uintmax_t{};
+    std::from_chars(s.begin() + 2uz, s.end(), rgb, 16);
+
+    auto r = u8{}, g = u8{}, b = u8{};
+
+    r = rgb >> 16;
+    g = rgb >> 8;
+    b = rgb;
+
+    return color::rgb(r, g, b);
+}
+
+/**
+ * @brief RGBA 颜色字面量
+ */
+template <char... chs>
+    requires requires {
+        requires HexLiteral<chs...>;
+        requires(sizeof...(chs) == 6uz || sizeof...(chs) == 10uz);
+    }
+constexpr auto operator""_rgba() noexcept -> color
+{
+    auto s = std::array{chs...};
+
+    auto rgba = std::uintmax_t{};
+    std::from_chars(s.begin() + 2uz, s.end(), rgba, 16);
+
+    auto r = u8{}, g = u8{}, b = u8{}, a = u8{};
+
+    r = rgba >> 24;
+    g = rgba >> 16;
+    b = rgba >> 8;
+    a = rgba;
+
+    return color::rgba(r, g, b, a);
+}
+
+}
+
+}
+
+}