color.h

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/*
    MIT License

    Copyright (c) 2026, Alexey Dynda

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE.
*/
#pragma once

#include <stdint.h>

namespace lcdgfx
{

struct Color
{
    uint32_t rgb;

    static constexpr Color from_rgb(uint8_t r, uint8_t g, uint8_t b)
    {
        return Color{ (uint32_t)((uint32_t)r << 16) | (uint32_t)((uint32_t)g << 8) | (uint32_t)b };
    }

    static constexpr Color from_rgb888(uint32_t v)
    {
        return Color{ v & 0x00FFFFFFu };
    }

    static constexpr Color from_rgb565(uint16_t v)
    {
        // 5-bit r/b expanded to 8 by replicating high bits into low.
        return from_rgb(
            (uint8_t)(((v >> 11) & 0x1F) * 255u / 31u),
            (uint8_t)(((v >>  5) & 0x3F) * 255u / 63u),
            (uint8_t)(( v        & 0x1F) * 255u / 31u));
    }

    static constexpr Color from_rgb332(uint8_t v)
    {
        return from_rgb(
            (uint8_t)(((v >> 5) & 0x07) * 255u / 7u),
            (uint8_t)(((v >> 2) & 0x07) * 255u / 7u),
            (uint8_t)(( v       & 0x03) * 255u / 3u));
    }

    static constexpr Color from_gray4(uint8_t v)
    {
        return from_rgb(
            (uint8_t)(((v & 0x0F) * 255u) / 15u),
            (uint8_t)(((v & 0x0F) * 255u) / 15u),
            (uint8_t)(((v & 0x0F) * 255u) / 15u));
    }

    static constexpr Color from_mono(uint8_t v)
    {
        return v ? from_rgb(0xFF, 0xFF, 0xFF) : from_rgb(0, 0, 0);
    }

    constexpr uint8_t r() const { return (uint8_t)((rgb >> 16) & 0xFFu); }
    constexpr uint8_t g() const { return (uint8_t)((rgb >> 8) & 0xFFu); }
    constexpr uint8_t b() const { return (uint8_t)(rgb & 0xFFu); }

    constexpr uint32_t to_rgb888() const { return rgb & 0x00FFFFFFu; }

    constexpr uint16_t to_rgb565() const
    {
        return (uint16_t)(((rgb >> 8)  & 0xF800u) |
                          ((rgb >> 5)  & 0x07E0u) |
                          ((rgb >> 3)  & 0x001Fu));
    }

    constexpr uint8_t to_rgb332() const
    {
        return (uint8_t)(((rgb >> 16) & 0xE0u) |
                         ((rgb >>  11) & 0x1Cu) |
                         ((rgb >>  6)  & 0x03u));
    }

    constexpr uint8_t to_gray4() const
    {
        // Integer approximation of 0.299*R + 0.587*G + 0.114*B, then >>4.
        // 77*R + 150*G + 29*B fits in 16 bits and matches the standard
        // ITU-R BT.601 weighting to within one LSB.
        return (uint8_t)((((uint32_t)r() * 77u +
                           (uint32_t)g() * 150u +
                           (uint32_t)b() * 29u) >> 8) >> 4);
    }

    constexpr uint8_t to_mono() const
    {
        return (((uint32_t)r() * 77u +
                 (uint32_t)g() * 150u +
                 (uint32_t)b() * 29u) >= (128u * 256u)) ? 1u : 0u;
    }

    template <unsigned Bpp>
    constexpr uint32_t to_native() const;

    constexpr bool operator==(const Color &other) const { return to_rgb888() == other.to_rgb888(); }
    constexpr bool operator!=(const Color &other) const { return !(*this == other); }
};

template <> constexpr uint32_t Color::to_native<1>()  const { return to_mono(); }
template <> constexpr uint32_t Color::to_native<4>()  const { return to_gray4(); }
template <> constexpr uint32_t Color::to_native<8>()  const { return to_rgb332(); }
template <> constexpr uint32_t Color::to_native<16>() const { return to_rgb565(); }
template <> constexpr uint32_t Color::to_native<24>() const { return to_rgb888(); }

} // namespace lcdgfx