HSV

https://gyazo.com/288442075997720bcb7072d5c6c4ea0e

RGB to HSV

$ V = \max(R, G, B)

$ M = \min(R, G, B)

$ C = V - M

$ S = \left\{ \begin{aligned} & 0 && {\rm if} \ V = 0 \\ & \frac{C}{V} && {\rm otherwise} \end{aligned} \right.

$ H = \left\{ \begin{aligned} & 0 && {\rm if} \ C = 0 \\ & 60 \ {\rm deg} \cdot \left( \frac{G - B}{C} \ {\rm mod} \ 6 \right) && {\rm if} \ V = R \\ & 60 \ {\rm deg} \cdot \left( \frac{B - R}{C} + 2 \right) && {\rm if} \ V = G \\ & 60 \ {\rm deg} \cdot \left( \frac{R - G}{C} + 4 \right) && {\rm if} \ V = B \end{aligned} \right.

GLSL

code:glsl

vec3 rgb2hsv(vec3 rgb) {

float v = max(max(rgb.r, rgb.g), rgb.b);

float m = min(min(rgb.r, rgb.g), rgb.b);

float c = v - m;

float s = v == 0.0 ? 0.0 : c / v;

float h = c == 0.0 ? 0.0 :

v == rgb.r ? mod((rgb.g - rgb.b) / c, 6.0) :

v == rgb.g ? (rgb.b - rgb.r) / c + 2.0 :

(rgb.r - rgb.g) / c + 4.0;

return vec3(h / 6.0, s, v);

}

HSV to RGB

$ R_H = {\rm saturate}(|x \ {\rm mod} \ 6 - 3|-1)

$ G_H = {\rm saturate}(|(x + 4) \ {\rm mod} \ 6 - 3|-1)

$ B_H = {\rm saturate}(|(x + 2) \ {\rm mod} \ 6 - 3|-1)

https://gyazo.com/62d05a355499fb12522acbcb482fd404

$ RGB = V * {\rm lerp}(\{1, 1, 1\}, \{R_H, G_H, B_H\}, S)

GLSL

code:glsl

vec3 hsv2rgb(vec3 hsv) {

vec3 h = saturate(abs(mod(6.0 * hsv.x + vec3(0, 4, 2), 6.0) - 3.0) - 1.0);

return hsv.z * mix(vec3(1.0), h, hsv.y);

}

肝心の虹色部分

どうせこれ使いたいだけでしょ

code:glsl

vec3 rainbow(float t) {

return saturate(abs(mod(6.0 * t + vec3(0, 4, 2), 6.0) - 3.0) - 1.0);

}