color.h

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#pragma once
 
#include <liboscar/graphics/rgba.h>
 
#include <format>
#include <optional>
#include <string>
#include <string_view>
 
namespace osc
{
    using Color = Rgba<float>;
 
    // returns the linearized version of a sRGB component value
    float to_linear_colorspace(float srgb_component_value);
 
    // returns the sRGB version of a linearized component value
    float to_srgb_colorspace(float linear_component_value);
 
    // returns the linear version of a (presumed to be) sRGB color
    Color to_linear_colorspace(const Color&);
 
    // returns a color that is the (presumed to be) linear color with the sRGB gamma curve applied
    Color to_srgb_colorspace(const Color&);
 
    // returns the color as a hexadecimal string in the format "#rrggbbaa", as
    // commonly-used in web applications, configuration files, etc.
    //
    // - HDR values are clamped to LDR (they can't fit in this format)
    // - examples:
    //   - red --> "#ff0000ff"
    //   - green --> "#00ff00ff"
    //   - blue --> "#0000ffff"
    //   - black --> "#000000ff"
    //   - clear --> "#00000000"
    //   - etc.
    std::string to_html_string_rgba(const Color&);
    std::optional<Color> try_parse_html_color_string(std::string_view);
 
    // returns a color that is the result of converting `color` to HSLA multiplying
    // its luminance (L) by `factor`, and converting it back to RGBA
    Color multiply_luminance(const Color& color, float factor);
}
 
template<>
struct std::formatter<osc::Color> final {
    template<class ParseCtx>
    constexpr auto parse(ParseCtx& ctx) { return inner_.parse(ctx); }
 
    template<class FmtCtx>
    auto format(const osc::Color color, FmtCtx& ctx) const
    {
        auto it = std::ranges::copy(std::string_view{"Color("}, ctx.out()).out;
        std::string_view delimiter;
        for (const auto& component : color) {
            it = std::ranges::copy(delimiter, it).out;
            ctx.advance_to(it);
            it = inner_.format(component, ctx);
            delimiter = ", ";
        }
        *it++ = ')';
        return it;
    }
private:
    std::formatter<osc::Color::value_type> inner_;
};