color.hpp

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#pragma once
 
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <iomanip>
#include <sstream>
#include <stdexcept>
#include <string>
 
class Color {
private:
  float _r; 
  float _g; 
  float _b; 
  float _a; 
 
  static constexpr float _clamp01(float v) {
    return v < 0.0f ? 0.0f : (v > 1.0f ? 1.0f : v);
  }
 
public:
  Color(void) : _r(0.0f), _g(0.0f), _b(0.0f), _a(1.0f) {}
 
  Color(float r, float g, float b)
      : _r(_clamp01(r)), _g(_clamp01(g)), _b(_clamp01(b)), _a(1.0f) {}
 
  Color(float r, float g, float b, float a)
      : _r(_clamp01(r)), _g(_clamp01(g)), _b(_clamp01(b)), _a(_clamp01(a)) {}
 
  float r(void) const { return _r; }
  float g(void) const { return _g; }
  float b(void) const { return _b; }
  float a(void) const { return _a; }
 
  void setR(float v) { _r = _clamp01(v); }
  void setG(float v) { _g = _clamp01(v); }
  void setB(float v) { _b = _clamp01(v); }
  void setA(float v) { _a = _clamp01(v); }
 
  Color withAlpha(float alpha) const { return Color(_r, _g, _b, alpha); }
 
  Color lerp(const Color &to, float t) const {
    float u = _clamp01(t);
    return Color(_r + (to._r - _r) * u, _g + (to._g - _g) * u,
                 _b + (to._b - _b) * u, _a + (to._a - _a) * u);
  }
 
  Color premultiplied() const { return Color(_r * _a, _g * _a, _b * _a, _a); }
 
  Color over(const Color &bg) const {
    float outA = _a + bg._a * (1.0f - _a);
    if (outA <= 0.0f)
      return Color(0, 0, 0, 0);
    float outR = (_r * _a + bg._r * bg._a * (1.0f - _a)) / outA;
    float outG = (_g * _a + bg._g * bg._a * (1.0f - _a)) / outA;
    float outB = (_b * _a + bg._b * bg._a * (1.0f - _a)) / outA;
    return Color(outR, outG, outB, outA);
  }
 
  struct RGBA8 {
    uint8_t r;
    uint8_t g;
    uint8_t b;
    uint8_t a;
  };
 
  RGBA8 toRGBA8() const {
    auto to8 = [](float v) -> uint8_t {
      float cl = v <= 0.0f ? 0.0f : (v >= 1.0f ? 1.0f : v);
      return static_cast<uint8_t>(std::round(cl * 255.0f));
    };
    return RGBA8{to8(_r), to8(_g), to8(_b), to8(_a)};
  }
 
  static Color fromRGBA8(uint8_t r, uint8_t g, uint8_t b, uint8_t a = 255) {
    auto toF = [](uint8_t v) -> float {
      return static_cast<float>(v) / 255.0f;
    };
    return Color(toF(r), toF(g), toF(b), toF(a));
  }
 
  std::string toHex(bool includeAlphaIfOpaque = false) const {
    auto p = toRGBA8();
    std::ostringstream oss;
    oss << '#' << std::uppercase << std::hex << std::setfill('0')
        << std::setw(2) << static_cast<int>(p.r) << std::setw(2)
        << static_cast<int>(p.g) << std::setw(2) << static_cast<int>(p.b);
    if (includeAlphaIfOpaque || p.a != 255) {
      oss << std::setw(2) << static_cast<int>(p.a);
    }
    return oss.str();
  }
 
  static Color fromHex(const std::string &hex) {
    auto isHex = [](char c) {
      return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') ||
             (c >= 'A' && c <= 'F');
    };
 
    std::string s = hex;
    if (!s.empty() && s[0] == '#')
      s.erase(0, 1);
    if (s.size() != 3 && s.size() != 4 && s.size() != 6 && s.size() != 8)
      throw std::invalid_argument("Invalid hex color length");
    for (char c : s) {
      if (!isHex(c))
        throw std::invalid_argument("Invalid hex color character");
    }
 
    auto hexToByte = [](const std::string &hh) -> uint8_t {
      return static_cast<uint8_t>(std::stoul(hh, nullptr, 16));
    };
 
    if (s.size() == 3 || s.size() == 4) {
      // short form: expand nibbles: #RGB -> #RRGGBB
      uint8_t r = hexToByte(std::string{s[0], s[0]});
      uint8_t g = hexToByte(std::string{s[1], s[1]});
      uint8_t b = hexToByte(std::string{s[2], s[2]});
      uint8_t a = 0xFF;
      if (s.size() == 4)
        a = hexToByte(std::string{s[3], s[3]});
      return fromRGBA8(r, g, b, a);
    }
 
    // long form
    uint8_t r = hexToByte(s.substr(0, 2));
    uint8_t g = hexToByte(s.substr(2, 2));
    uint8_t b = hexToByte(s.substr(4, 2));
    uint8_t a = 0xFF;
    if (s.size() == 8)
      a = hexToByte(s.substr(6, 2));
    return fromRGBA8(r, g, b, a);
  }
 
  bool operator==(const Color &other) const {
    return _r == other._r && _g == other._g && _b == other._b && _a == other._a;
  }
  bool operator!=(const Color &other) const { return !(*this == other); }
 
  Color operator+(const Color &o) const {
    return Color(_clamp01(_r + o._r), _clamp01(_g + o._g), _clamp01(_b + o._b),
                 _clamp01(_a + o._a));
  }
 
  Color operator-(const Color &o) const {
    return Color(_clamp01(_r - o._r), _clamp01(_g - o._g), _clamp01(_b - o._b),
                 _clamp01(_a - o._a));
  }
 
  Color operator*(float s) const {
    return Color(_clamp01(_r * s), _clamp01(_g * s), _clamp01(_b * s), _a);
  }
 
  static Color Black() { return Color(0.0f, 0.0f, 0.0f, 1.0f); }
  static Color White() { return Color(1.0f, 1.0f, 1.0f, 1.0f); }
  static Color Red() { return Color(1.0f, 0.0f, 0.0f, 1.0f); }
  static Color Green() { return Color(0.0f, 1.0f, 0.0f, 1.0f); }
  static Color Blue() { return Color(0.0f, 0.0f, 1.0f, 1.0f); }
  static Color Transparent() { return Color(0.0f, 0.0f, 0.0f, 0.0f); }
};