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HSVからRGBへの変換をGLSLで実装する

前提

HSVからRGBへの変換 - Wikipediaに基づいて、HSV色空間からRGB色空間への変換を実装する。変換の対象となるH, S, Vの定義は以下の通りとし、変換後のR, G, Bは0.0 - 1.0の範囲とする。

  • H (Hue) : 色相
    • 0.0 - 360.0のfloat
  • S (Saturation) : 彩度
    • 0.0 - 1.0のfloat
  • V (Value) : 明度
    • 0.0 - 1.0のfloat

実装

円柱モデルと円錐モデルでわずかに異なる。
下記のコードでは円錐モデルを採用しているためfloat c = sとなっているが、円柱モデルにする場合はこれをfloat c = v * sとすれば良い。

vec3 hsvToRgb(float h, float s, float v) {
    // h: 0.0 - 360.0, s: 0.0 - 1.0, v: 0.0 - 1.0
    float c = s; // float c = v * s;
    float h2 = h / 60.0;
    float x = c * (1.0 - abs(mod(h2, 2.0) - 1.0));
    vec3 rgb = (v - c) * vec3(1.0, 1.0, 1.0);

    if (0.0 <= h2 && h2 < 1.0) {
        rgb += vec3(c, x, 0.0);
    } else if (1.0 <= h2 && h2 < 2.0) {
        rgb += vec3(x, c, 0.0);
    } else if (2.0 <= h2 && h2 < 3.0) {
        rgb += vec3(0.0, c, x);
    } else if (3.0 <= h2 && h2 < 4.0) {
        rgb += vec3(0.0, x, c);
    } else if (4.0 <= h2 && h2 < 5.0) {
        rgb += vec3(x, 0.0, c);
    } else if (5.0 <= h2 && h2 < 6.0) {
        rgb += vec3(c, 0.0, x);
    }

    return rgb;
}

以上

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